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The oxidative potential (OP) of ambient particulate matter (PM) is a metric commonly used to link the aerosol exposure to its adverse health effects. In this study, we report the first-ever real-ti...

Real-time, in situ molecular composition measurements of the organic fraction of fine particulate matter (PM2.5) remain challenging, hindering a full understanding of the climate impacts and health effects of PM2.5. In particular, the thermal decomposition and ionization-induced fragmentation affecting current techniques has limited a detailed investigation of secondary organic aerosol (SOA), which typically dominates OA. Here we deploy a novel extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF-MS) during winter 2017 in downtown Zurich, Switzerland, which overcomes these limitations, together with an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) and supporting instrumentation. Positive matrix factorization (PMF) implemented within the Multilinear Engine (ME-2) program was applied to the EESI-TOF-MS data to quantify the primary and secondary contributions to OA. An 11-factor solution was selected as the best representation of the data, including five primary and six secondary factors. Primary factors showed influence from cooking, cigarette smoke, biomass burning (two factors) and a special local unknown event occurred only during two nights. Secondary factors were affected by biomass burning (three factors, distinguished by temperature and/or wind direction), organonitrates, monoterpene oxidation, and undetermined regional processing, in particular the contributions of wood combustion. While the AMS attributed slightly over half the OA mass to SOA but did not identify its source, the EESI-TOF-MS showed that most (>70 %) of the SOA was derived from biomass burning. Together with significant contributions from less aged biomass burning factors identified by both AMS and EESI-TOF-MS, this firmly establishes biomass burning as the single most important contributor to OA mass at this site during winter. High correlation was obtained between EESI-TOF-MS and AMS PMF factors where specific analogues existed, as well as between total signal and POA–SOA apportionment. This suggests the EESI-TOF-MS apportionment in the current study can be approximately taken at face value, despite ion-by-ion differences in relative sensitivity. The apportionment of specific ions measured by the EESI-TOF-MS (e.g., levoglucosan, nitrocatechol, and selected organic acids) and utilization of a cluster analysis-based approach to identify key marker ions for the EESI-TOF-MS factors are investigated. The interpretability of the EESI-TOF-MS results and improved source separation relative to the AMS within this pilot campaign validate the EESI-TOF-MS as a promising approach to source apportionment and atmospheric composition research.

Smog chamber experiments were conducted to characterize the light absorption of brown carbon (BrC) from primary and photochemically aged coal combustion emissions. Light absorption was measured by the UV-visible spectrophotometric analysis of water and methanol extracts of filter samples. The single-scattering albedo at 450 nm was 0.73 ± 0.10 for primary emissions and 0.75 ± 0.13 for aged emissions. The light absorption coefficient at 365 nm of methanol extracts was higher than that of water extracts by a factor of 10 for primary emissions and a factor of 7 for aged emissions. This suggests that the majority of BrC is water-insoluble even after aging. The mass absorption efficiency of this BrC (MAE365) for primary OA (POA) was dependent on combustion conditions, with an average of 0.84 ± 0.54 m2 g-1, which was significantly higher than that for aged OA (0.24 ± 0.18 m2 g-1). Secondary OA (SOA) dominated aged OA and the decreased MAE365 after aging indicates that SOA is less light absorbing than POA and/or that BrC is bleached (oxidized) with aging. The estimated MAE365 of SOA (0.14 ± 0.08 m2 g-1) was much lower than that of POA. A comparison of MAE365 of residential coal combustion with other anthropogenic sources suggests that residential coal combustion emissions are among the strongest absorbing BrC organics.

Krakow is routinely affected by very high air pollution levels, especially during the winter months. Although a lot of effort has been done on characterization of ambient aerosols, there is a lack of online and long-term measurements of non-refractory aerosols. Our measurements at AGH University provide online long-term chemical composition of ambient submicron particulate matter (PM1) between January 2018 and April 2019. Here we report the chemical characterization of non-refractory submicron aerosols and source apportionment of the organic fraction by positive matrix factorization (PMF). In contrast to other long-term source apportionment studies, we let a small PMF window roll over the dataset instead of performing PMF over the full dataset or on separate seasons. In this way, the seasonal variation of the source profiles can be captured. The uncertainties of the PMF solutions are addressed by the bootstrap resampling strategy and the random a-value approach for constrained factors.We observe clear seasonal patterns in concentration and composition of PM1, with high concentrations during the winter months and lower concentrations during the summer months. Organics are the dominant species throughout the campaign. Five organic aerosol (OA) factors are resolved, of which three are of primary nature (hydrocarbon-like OA (HOA), biomass burning OA (BBOA) and coal combustion OA (CCOA)) and two are of secondary nature (more oxidized oxygenated OA (MO-OOA) and less oxidized oxygenated OA (LO-OOA)). While HOA contributes on average 8.6 % ± 2.3 % throughout the campaign, the solid fuel combustion related BBOA and CCOA show a clear seasonal trend with average contributions of 10.4 % ± 2.7 % and 14.1 %, ± 2.1 % respectively. The highest contributions are observed during wintertime as a result of residential heating. Throughout the campaign, the OOA can be separated into MO-OOA and LO-OOA with average contribution of 38.4 % ± 8.4 % and 28.5 % ± 11.2 %, respectively.

Aerosol particles negatively affect human health while also having climatic relevance due to, for example, their ability to act as cloud condensation nuclei. Ultrafine particles (diameter Dp < 100 nm) typically comprise the largest fraction of the total number concentration, however, their chemical characterization is difficult because of their low mass. Using an extractive electrospray time-of-flight mass spectrometer (EESI-TOF), we characterize the molecular composition of freshly nucleated particles from naphthalene and β-caryophyllene oxidation products at the CLOUD chamber at CERN. We perform a detailed intercomparison of the organic aerosol chemical composition measured by the EESI-TOF and an iodide adduct chemical ionization mass spectrometer equipped with a filter inlet for gases and aerosols (FIGAERO-I-CIMS). We also use an aerosol growth model based on the condensation of organic vapors to show that the chemical composition measured by the EESI-TOF is consistent with the expected condensed oxidation products. This agreement could be further improved by constraining the EESI-TOF compound-specific sensitivity or considering condensed-phase processes. Our results show that the EESI-TOF can obtain the chemical composition of particles as small as 20 nm in diameter with mass loadings as low as hundreds of ng m−3 in real time. This was until now difficult to achieve, as other online instruments are often limited by size cutoffs, ionization/thermal fragmentation and/or semi-continuous sampling. Using real-time simultaneous gas- and particle-phase data, we discuss the condensation of naphthalene oxidation products on a molecular level., Using real-time simultaneous gas- and particle-phase data, the condensation of naphthalene and β-caryophyllene oxidation products on a molecular level is discussed.

We have collected one year of aerosol chemical speciation monitor (ACSM) data in Magadino, a village located in the south of the Swiss Alpine region, which is one of the most polluted areas in Switzerland. We analysed the mass spectra of organic aerosol (OA) by positive matrix factorization (PMF) using Source Finder Professional (SoFi Pro) to retrieve the origins of OA. Therein, we deployed the rolling algorithm to account for the temporal changes of the source profiles, which is closer to the real world. As the first ever application of rolling PMF analysis for a rural cite, we resolved two primary OA factors (traffic-related hydrocarbon-like OA (HOA) and biomass burning OA (BBOA)), one local OA (LOA) factor, a less oxidized oxygenated OA (LO-OOA) factor, and a more oxidized oxygenated OA (MO-OOA) factor. HOA showed stable contributions to the total OA through the whole year ranging from 8.1–10.1 %, while the contribution of BBOA showed a clear seasonal variation with a range of 8.3–27.4 % (highest during winter, lowest during summer) and a yearly average of 17.1 %. The OOA was represented by two factors (LO-OOA and MO-OOA) throughout the year. OOA contributed 71.6 % of the OA mass, varying from 62.5 % (in winter) to 78 % (in spring and summer). The uncertainties (σ) for the modelled OA factors (i.e., rotational uncertainty and statistical variability of the sources) varied from ±4 % (LOA) to a maximum of ±40 % (LO-OOA). Considering the fact that BBOA and LO-OOA (showing influences of biomass burning in winter) had significant contributions to the total OA mass, we suggest a reduction and control of the residential heating as a mitigation strategy for better air quality and lower PM levels in this region. In Appendix A, we conducted a head-to-head comparison between the conventional seasonal PMF analysis and the rolling mechanism. It showed similar or slightly improved results in terms of mass concentrations, correlations with external tracers and factor profiles of the constrained POA factors. The rolling results show smaller scaled residuals and enhanced correlations between OOA factors and corresponding inorganic salts than those of the seasonal solutions, was most likely because the rolling PMF analysis can capture the temporal variations of the oxidation processes for OOA sources. Specifically, the time dependent factor profiles of MO-OOA and LO-OOA can well explain the temporal viabilities of two main ions for OOA factors, m/z 44 (CO2+) and m/z 43 (mostly C2H3O+). This rolling PMF analysis therefore provides a more realistic source apportionment (SA) solution, with time-dependent OA sources. The rolling results show also good agreement with offline Aerodyne aerosol mass spectrometer (AMS) SA results from filter samples, except for winter. This is likely because the online measurement is capable of capturing the fast oxidation processes of biomass burning sources. This study demonstrates the strengths of the rolling mechanism and provides a comprehensive criterion list for ACSM users to obtain reproducible SA results and is a role model for similar analyses of such world-wide available data.

National Capital Region (NCR) encompassing New Delhi is one of the most polluted urban metropolitan areas in the world. Real-time chemical characterization of fine particulate matter (PM1 and PM2.5) was carried out using three aerosol mass spectrometers, two aethalometers, and one single particle soot photometer (SP2) at two sites in Delhi (urban) and one site located ~40 km downwind of Delhi, during January–March 2018. The campaign mean PM2.5 (NR-PM2.5 + BC) concentrations at the two urban sites were 153.8 ± 109.4 μg.m−3 and 127.8 ± 83.2 μg.m−3, respectively, whereas PM1 (NR-PM1 + BC) was 72.3 ± 44.0 μg.m−3 at the downwind site. PM2.5 particles were composed mostly of organics (43–44)% followed by chloride (14–17)%, ammonium (9–11)%, nitrate (9%), sulfate (8–10)%, and black carbon (11–16)%, whereas PM1 particles were composed of 47% organics, 13% sulfate as well as ammonium, 11% nitrate as well as chloride, and 5% black carbon. Organic aerosol (OA) source apportionment was done using positive matrix factorization (PMF), solved using an advanced multi-linear engine (ME-2) model. Highly mass-resolved OA mass spectra at one urban and downwind site were factorized into three primary organic aerosol (POA) factors including one traffic-related and two solid-fuel combustion (SFC), and three oxidized OA (OOA) factors. Whereas unit mass resolution OA at the other urban site was factorized into two POA factors related to traffic and SFC, and one OOA factor. OOA constituted a majority of the total OA mass (45–55)% with maximum contribution during afternoon hours ~(70–80)%. Significant differences in the absolute OOA concentration between the two urban sites indicated the influence of local emissions on the oxidized OA formation. Similar PM chemical composition, diurnal and temporal variations at the three sites suggest similar type of sources affecting the particulate pollution in Delhi and adjoining cities, but variability in mass concentration suggest more local influence than regional.

Particulate chloride is an important component of fine particulate matter in marine air masses. Recent field studies also report elevated concentrations of gas-phase reactive chlorine species and particulate chloride related to anthropogenic activities. This work focuses on particulate chloride detection and quantification issues observed for some quadrupole aerosol chemical speciation monitors (Q-ACSMs) which are designed for the long-term measurement of ambient aerosol composition. The ACSM reports particle concentrations based on the difference between measurements of ambient air (sample mode) and particle-free ambient air (filter mode). For our long-term campaign in Krakow, Poland, the Q-ACSM reports apparent negative total chloride concentration for most of the campaign when analyzed with the default fragmentation table. This is the result of the difference signal from m∕z 35 (35Cl+) being negative, which dominates over the positive difference signal from m∕z 36 (H35Cl+). Highly time-resolved experiments with NH4Cl, NaCl and KCl particles show that the signal response of m∕z 35 is non-ideal when the signal builds up and decreases slowly for all three salts, leading to a negative difference measurement. In contrast, the m∕z 36 signal exhibits a near step-change response for NH4Cl during the sampling and filter period, resulting in a positive difference signal. The response of m∕z 36 for NaCl and KCl is not as prompt as for NH4Cl but still fast enough to have a positive difference signal. Furthermore, it is shown that this behavior is mostly independent of vaporizer temperature. Based on these observations, this work presents an approach to correct the chloride concentration time series by adapting the standard fragmentation table coupled with a calibration of NH4Cl to obtain a relative ionization efficiency (RIE) based on the signal at m∕z 36 (H35Cl+). This correction can be applied to measurements in environments where chloride is dominated by NH4Cl. Caution should be exercised when other chloride salts dominate the ambient particulate chloride.

Gasoline direct injection (GDI) vehicles have recently been identified as a significant source of carbonaceous aerosol, of both primary and secondary origin. Here we investigated primary emissions and secondary organic aerosol (SOA) from four GDI vehicles, two of which were also retrofitted with a prototype gasoline particulate filter (GPF). We studied two driving test cycles under cold- and hot-engine conditions. Emissions were characterized by proton transfer reaction time-of-flight mass spectrometry (gaseous non-methane organic compounds, NMOCs), aerosol mass spectrometry (sub-micron non-refractory particles) and light attenuation measurements (equivalent black carbon (eBC) determination using Aethalometers) together with supporting instrumentation. Atmospheric processing was simulated using the PSI mobile smog chamber (SC) and the potential aerosol mass oxidation flow reactor (OFR). Overall, primary and secondary particulate matter (PM) and NMOC emissions were dominated by the engine cold start, i.e., before thermal activation of the catalytic after-treatment system. Trends in the SOA oxygen to carbon ratio (O : C) for OFR and SC were related to different OH exposures, but divergences in the H : C remained unexplained. SOA yields agreed within experimental variability between the two systems, with a tendency for higher values in the OFR than in the SC (or, vice versa, lower values in the SC). A few aromatic compounds dominated the NMOC emissions, primarily benzene, toluene, xylene isomers/ethylbenzene and C3-benzene. A significant fraction of the SOA was explained by those compounds, based on comparison of effective SOA yield curves with those of toluene, o-xylene and 1,2,4-trimethylbenzene determined in our OFR, as well as others from literature. Remaining discrepancies, which were smaller in the SC and larger in the OFR, were up to a factor of 2 and may have resulted from diverse reasons including unaccounted precursors and matrix effects. GPF retrofitting significantly reduced primary PM through removal of refractory eBC and partially removed the minor POA fraction. At cold-started conditions it did not affect hydrocarbon emission factors, relative chemical composition of NMOCs or SOA formation, and likewise SOA yields and bulk composition remained unaffected. GPF-induced effects at hot-engine conditions deserve attention in further studies.

Organic aerosols (OAs), which consist of thousands of complex compounds emitted from various sources, constitute one of the major components of fine particulate matter. The traditional positive matrix factorization (PMF) method often apportions aerosol mass spectrometer (AMS) organic datasets into less meaningful or mixed factors, especially in complex urban cases. In this study, an improved source apportionment method using a bilinear model of the multilinear engine (ME-2) was applied to OAs collected during the heavily polluted season from two Chinese megacities located in the north and south with an Aerodyne high-resolution aerosol mass spectrometer (HR-ToF-AMS). We applied a rather novel procedure for utilization of prior information and selecting optimal solutions, which does not necessarily depend on other studies. Ultimately, six reasonable factors were clearly resolved and quantified for both sites by constraining one or more factors: hydrocarbon-like OA (HOA), cooking-related OA (COA), biomass burning OA (BBOA), coal combustion (CCOA), less-oxidized oxygenated OA (LO-OOA) and more-oxidized oxygenated OA (MO-OOA). In comparison, the traditional PMF method could not effectively resolve the appropriate factors, e.g., BBOA and CCOA, in the solutions. Moreover, coal combustion and traffic emissions were determined to be primarily responsible for the concentrations of PAHs and BC, respectively, through the regression analyses of the ME-2 results.

Ambient ammonia (NH3) measurements were performed with a mobile platform in three European cities: Zurich (Switzerland), Tartu (Estonia) and Tallinn (Estonia) deploying an NH3 analyzer based on cavity ring-down spectroscopy. A heated inlet line along with an auxiliary flow was used to minimize NH3 adsorption onto the inlet walls. In addition, a detailed characterization of the response and recovery times of the measurement system was used to deconvolve the true NH3 signal from the remaining adsorption-induced hysteresis. Parallel measurements with an aerosol mass spectrometer were used to correct the observed NH3 for the contribution of ammonium nitrate, which completely evaporated in the heated line at the chosen temperature, in contrast to ammonium sulfate. In this way a quantitative measurement of ambient gaseous NH3 was achieved with sufficient time resolution to enable measurement of NH3 point sources with a mobile sampling platform. The NH3 analyzer and the aerosol mass spectrometer were complemented by an aethalometer and various gas-phase analyzers to enable a complete characterization of the sources of air pollution, including the spatial distributions and the regional background concentrations and urban increments of all measured components. Although at all three locations similar increment levels of organic aerosols were attributed to biomass burning and traffic, traffic emissions clearly dominated the city enhancements of NH3, equivalent black carbon (eBC) and carbon dioxide (CO2). Urban increments of 3.4, 1.8 and 3.0 ppb of NH3 were measured in the traffic areas in Zurich, Tartu and Tallinn, respectively, representing an enhancement of 36.6, 38.3 and 93.8% over the average background concentrations. Measurements in areas strongly influenced by traffic emissions (including tunnel drives) were used to estimate emission factors (EF) for the traffic-related pollutants. The obtained median EFs range between 136.8-415.1 mg kg−1 fuel for NH3, 157.1–734.8 mg kg−1 fuel for eBC and 39.9–324.3 mg kg−1 fuel for HOA. Significant differences were found between the EFs of certain components in the three cities, which were partially linked to an older vehicle fleet in Estonia compared to Switzerland. Using the determined EFs we show that traffic can fully explain the NH3 enhancements in the three cities and also presents a non-negligible fraction of the background concentrations, which are mostly related to agricultural activities. Moreover, the estimated total contribution of traffic to NH3 at all three locations is in good agreement with the available emission inventories.

It is well established that light-absorbing organic aerosols (commonly known as brown carbon, BrC) impact climate. However, uncertainties remain as their contributions to absorption at different wavelengths are often ignored in climate models. Further, BrC exhibits differences in absorption at different wavelengths due to the variable composition including varying sources and meteorological conditions. However, diurnal variability in the spectral characteristics of water-soluble BrC (hereafter BrC) is not yet reported. This study presents unique measurement hitherto lacking in the literature. Online measurements of BrC were performed using an assembled system including a particle-into-liquid sampler, portable UV–Visible spectrophotometer with liquid waveguid capillary cell, and total carbon analyzer (PILS-LWCC-TOC). This system measured the absorption of ambient aerosol extracts at the wavelengths ranging from 300 to 600 nm with 2 min integration time and water-soluble organic carbon (WSOC) with 4 min integration time over a polluted megacity, New Delhi. Black carbon, carbon monoxide (CO), nitrogen oxides (NOx), and the chemical composition of non-refractory submicron aerosols were also measured in parallel. Diurnal variability in absorption coefficient (0.05 to 65 Mm−1), mass absorption efficiency (0.01 to 3.4 m−2 gC−1) at 365 nm, and absorption angstrom exponent (AAE) of BrC for different wavelength range (AAE300–400: 4.2–5.8; AAE400–600: 5.5–8.0; and AAE300–600: 5.3–7.3) is discussed. BrC chromophores absorbing at any wavelength showed minimum absorption during afternoon hours, suggesting the effects of boundary layer expansion and their photo-sensitive/volatile nature. On certain days, a considerable presence of BrC absorbing at 490 nm was observed during nighttime that disappears during the daytime. It appeared to be associated with secondary BrC. Observations also infer that BrC species emitted from the biomass and coal burning are more absorbing among all sources. A fraction of BrC is likely associated with trash burning, as inferred from the spectral characteristics of Factor-3 from the PMF analysis of BrC spectra. Such studies are essential in understanding the BrC characteristics and their further utilization in climate models.

To reduce the influence of biomass burning on air quality, consumers are encouraged to replace their old woodstove with new and cleaner appliances. While their primary emissions have been extensively investigated, the impact of atmospheric aging on these emissions, including secondary organic aerosol (SOA) formation, remains unknown. Here, using an atmospheric smog chamber, we aim at understanding the chemical nature and quantify the emission factors of the primary organic aerosols (POA) from three types of appliances for residential heating, and to assess the influence of aging thereon. Two, old and modern, logwood stoves and one pellet burner were operated under typical conditions. Emissions from an entire burning cycle (past the start-up operation) were injected, including the smoldering and flaming phases, resulting in highly variable emission factors. The stoves emitted a significant fraction of POA (up to 80%) and black carbon. After ageing, the total mass concentration of organic aerosol (OA) increased on average by a factor of 5. For the pellet stove, flaming conditions were maintained throughout the combustion. The aerosol was dominated by black carbon (over 90% of the primary emission) and amounted to the same quantity of primary aerosol emitted by the old logwood stove. However, after ageing, the OA mass was increased by a factor of 1.7 only, thus rendering OA emissions by the pellet stove almost negligible compared to the other two stoves tested. Therefore, the pellet stove was the most reliable and least polluting appliance out of the three stoves tested. The spectral signatures of the POA and aged emissions by a High Resolution – Time of Flight – Aerosol Mass Spectrometer (Electron Ionization (EI) at 70 eV) were also investigated. The m/z 44 (CO2+) and high molecular weight fragments (m/z 115 (C9H7+), 137 (C8H9O2+), 167 (C9H11O3+) and 181 (C9H9O4+, C14H13+)) correlate with the modified combustion efficiency (MCE) allowing us to discriminate further between emissions generated from smoldering vs flaming conditions.

We report highly time-resolved estimates of airborne bacteria-like particle concentrations in ambient aerosol using an Aerodyne aerosol mass spectrometer (AMS). AMS measurements with a newly developed PM 2.5 and the standard (PM 1 ) aerodynamic lens were performed at an urban background site (Zurich) and at a rural site (Payerne) in Switzerland. Positive matrix factorization using the multilinear engine (ME-2) implementation was used to estimate the contribution of bacteria-like particles to non-refractory organic aerosol. The success of the method was evaluated by a size-resolved analysis of the organic mass and the analysis of single particle mass spectra, which were detected with a light scattering system integrated into the AMS. Use of the PM 2.5 aerodynamic lens increased measured bacteria-like concentrations, supporting the analysis method. However, at all sites, the low concentrations of this component suggest that airborne bacteria constitute a minor fraction of non-refractory PM 2.5 organic aerosol mass. Estimated average mass concentrations were below 0.1 μg/m 3 and relative contributions were lower than 2% at both sites. During rainfall periods, concentrations of the bacteria-like component increased considerably reaching a short-time maximum of approximately 2 μg/m 3 at the Payerne site in summer.

Evaporation of sulfuric acid from particles can be important in the atmospheres of Earth and Venus. However, the equilibrium constant for the dissociation of H2SO4 to bisulfate ions, which is the one of the fundamental parameters controlling the evaporation of sulfur particles, is not well constrained. In this study we explore the volatility of sulfate particles at very low relative humidity. We measured the evaporation of sulfur particles versus temperature and relative humidity in the CLOUD chamber at CERN. We modelled the observed sulfur particle shrinkage with the ADCHAM model. Based on our model results, we conclude that the sulfur particle shrinkage is mainly governed by H2SO4 and potentially to some extent by SO3 evaporation. We found that the equilibrium constants for the dissociation of H2SO4 to HSO4−(KH2SO4) and the dehydration of H2SO4 to SO3 (xKSO3) are KH2SO4 = 2–4 × 109 mol kg−1 and xKSO3 ≥ 1.4 × 1010 at 288.8 ± 5 K.

Secondary organic aerosol (SOA) yields from the photo-oxidation of α-pinene were investigated in smog chamber (SC) experiments at low (23–29 %) and high (60–69 %) relative humidity (RH), various NOx ∕ VOC ratios (0.04–3.8) and with different aerosol seed chemical compositions (acidic to neutralized sulfate-containing or hydrophobic organic). A combination of a scanning mobility particle sizer and an Aerodyne high-resolution time-of-flight aerosol mass spectrometer was used to determine SOA mass concentration and chemical composition. We used a Monte Carlo approach to parameterize smog chamber SOA yields as a function of the condensed phase absorptive mass, which includes the sum of OA and the corresponding bound liquid water content. High RH increased SOA yields by up to 6 times (1.5–6.4) compared to low RH. The yields at low NOx ∕ VOC ratios were in general higher compared to yields at high NOx ∕ VOC ratios. This NOx dependence follows the same trend as seen in previous studies for α-pinene SOA. A novel approach of data evaluation using volatility distributions derived from experimental data served as the basis for thermodynamic phase partitioning calculations of model mixtures in this study. These calculations predict liquid–liquid phase separation into organic-rich and electrolyte phases. At low NOx conditions, equilibrium partitioning between the gas and liquid phases can explain most of the increase in SOA yields observed at high RH, when in addition to the α-pinene photo-oxidation products described in the literature, fragmentation products are added to the model mixtures. This increase is driven by both the increase in the absorptive mass and the solution non-ideality described by the compounds' activity coefficients. In contrast, at high NOx, equilibrium partitioning alone could not explain the strong increase in the yields with RH. This suggests that other processes, e.g. reactive uptake of semi-volatile species into the liquid phase, may occur and be enhanced at higher RH, especially for compounds formed under high NOx conditions, e.g. carbonyls.

Characteristics and sources of volatile organic compounds (VOCs) were investigated with highly time-resolved simultaneous measurements by two proton-transfer-reaction time-of-flight mass spectrometers (PTR-ToF-MS) at an urban and a suburban site in New Delhi, India from January to March 2018. During the measurement period, high mixing ratios of VOCs and trace gases were observed, with high nocturnal mixing ratios and strong day-night variations. The positive matrix factorization (PMF) receptor model was applied separately to the two sites, and six major factors of VOCs were identified at both sites, i.e., two factors related to traffic emissions, two to solid fuel combustion, and two secondary factors. At the urban IITD site, traffic-related emissions comprising mostly mono-aromatic compounds were the dominant sources, contributing 56.6 % of the total mixing ratio, compared to 36.0 % at the suburban MRIU site. Emissions from various solid fuel combustion processes, particularly in the night, were identified as a significant source of aromatics, phenols and furans at both sites. The secondary factors accounted for 15.9 % of the total VOC concentration at IITD and for 33.6 % at MRIU. They were dominated by oxygenated VOCs and exhibited substantially higher contributions during daytime.

Delhi, the capital of India, suffers from heavy local emissions as well as regional transport of air pollutants, resulting in severe aerosol loadings. To determine the sources of these pollutants, we have quantified the mass concentrations of 26 elements in airborne particles, measured by an online X-ray fluorescence spectrometer with time resolution between 30 min and 1 h. Measurements of PM10 and PM2.5 (particulate matter

Real-time investigation of the intraparticle reactions in secondary organic aerosol., Highly oxygenated organic molecules (HOMs) are formed from the oxidation of biogenic and anthropogenic gases and affect Earth’s climate and air quality by their key role in particle formation and growth. While the formation of these molecules in the gas phase has been extensively studied, the complexity of organic aerosol (OA) and lack of suitable measurement techniques have hindered the investigation of their fate post-condensation, although further reactions have been proposed. We report here novel real-time measurements of these species in the particle phase, achieved using our recently developed extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF). Our results reveal that condensed-phase reactions rapidly alter OA composition and the contribution of HOMs to the particle mass. In consequence, the atmospheric fate of HOMs cannot be described solely in terms of volatility, but particle-phase reactions must be considered to describe HOM effects on the overall particle life cycle and global carbon budget.

Characteristics and sources of ambient particle elements in urban Beijing were studied by hourly observations in two size fractions (PM10 and PM2.5) during November and December 2017 using an online multi-element analyzer. The reconstructed oxide concentrations of 24 elements (from Al to Pb) comprise an appreciable fraction of PM10 and PM2.5, accounting for 37% and 17%, respectively on average. We demonstrate the benefit of using high-time-resolution chemical speciation data in achieving robust source apportionment of the total elemental PM10 (PM10el) and elemental PM2.5 (PM2.5el) mass using positive matrix factorization (PMF). Biomass burning, coal combustion, secondary sulfate, industry, non-exhaust traffic and dust were identified in both size fractions (with varying relative concentrations), which accounted on average for 4%, 12%, 5%, 2%, 14%, and 63%, respectively to the total PM10el, and 14%, 35%, 21%, 6%, 12% and 12%, respectively to the total PM2.5el. Biomass burning and coal combustion exhibited higher concentrations during haze episodes of the heating season. In contrast, secondary sulfate and industry contributed more to haze episodes during the non-heating season. The fractional contribution of dust was mostly high during clean days, while the fractional non-exhaust traffic emission contribution was similar throughout the measurement period. The non-exhaust traffic emissions contributed locally, while the remaining sources were dominated by neighboring areas. Furthermore, trajectory analysis showed that the origin of the industrial sources roughly agreed with the locations of the main point sources. Overall, this work provides detailed information on the characteristics of the elements during different haze events during heating and non-heating seasons.

This study examines the light absorption characteristics of fine atmospheric particulates using the co-located real-time measurements of chemical and optical aerosol characteristics at a site located in Delhi during winter. The contribution of absorption by black carbon and brown carbon (BC and BrC) to the total absorption (babs) is computed using the absorption Angstrom exponent (AAE) method. The period average contribution of BrC absorption (babs_BrC) to babs is found to be highest at 370 nm (23%) that decreased exponentially with increasing wavelengths, i.e.,18, 12, 10, and 4% at 470, 520, 590, and 660 nm, respectively. The absorption spectrum of BrC is used to study the bulk composition of BrC, which indicates that primary BrC was dominant during morning and night time, whereas secondary BrC was significant during the rest of the time. Further, organic aerosols (OA) were divided into different factors using positive-matrix factorization (PMF) analysis, and the mass absorption efficiency (Eabs) of each factor was assessed through multivariate linear regression of babs_BrC with OA factors. The biomass burning OA (BBOA) exhibited the highest Eabs at 370 nm (0.86 m2 g−1), followed by semi-volatile oxygenated OA (SVOOA; 0.67 m2 g−1) and hydrocarbon-like OA (HOA; 0.42 m2 g−1). Further, although the composition of OA was dominated by LVOOA (32%) and BBOA (32%), followed by SVOOA (22%), and HOA (14%), their contribution to bBrC followed different order due to differences in their mass absorption efficiencies. The BBOA contributed almost half (48%) of babs_BrC followed by SVOOA (26%), and HOA (10%). This study provides quantitative information on the sources of BrC and their relative contribution to BrC absorption over a heavily polluted region, which is still lacking in the literature. These results have implications in understanding the source-specific BrC absorption.

The widespread use of Aerodyne aerosol mass spectrometers (AMS) has greatly improved real-time organic aerosol (OA) monitoring, providing mass spectra that contain sufficient information for source apportionment. However, AMS field deployments remain expensive and demanding, limiting the acquisition of long-term datasets at many sampling sites. The offline application of aerosol mass spectrometry entailing the analysis of nebulized water extracted filter samples (offline-AMS) increases the spatial coverage accessible to AMS measurements, being filters routinely collected at many stations worldwide. PM1 (particulate matter with an aerodynamic diameter + fragment contribution, whose intensity is typically assumed to be equal to that of CO2+. Offline-AMS spectra reveal that the water-soluble CO2+ : CO+ ratio not only shows values systematically > 1 but is also dependent on season, with lower values in winter than in summer. AMS WSOA spectra were analyzed using positive matrix factorization (PMF), which yielded four factors. These factors included biomass burning OA (BBOA), local OA (LOA) contributing significantly only in Vilnius, and two oxygenated OA (OOA) factors, summer OOA (S-OOA) and background OOA (B-OOA), distinguished by their seasonal variability. The contribution of traffic exhaust OA (TEOA) was not resolved by PMF due to both low concentrations and low water solubility. Therefore, the TEOA concentration was estimated using a chemical mass balance approach, based on the concentrations of hopanes, specific markers of traffic emissions. AMS-PMF source apportionment results were consistent with those obtained from PMF applied to marker concentrations (i.e., major inorganic ions, OC / EC, and organic markers including polycyclic aromatic hydrocarbons and their derivatives, hopanes, long-chain alkanes, monosaccharides, anhydrous sugars, and lignin fragmentation products). OA was the largest fraction of PM1 and was dominated by BBOA during winter with an average concentration of 2 µg m−3 (53 % of OM), while S-OOA, probably related to biogenic emissions, was the prevalent OA component during summer with an average concentration of 1.2 µg m−3 (45 % of OM). PMF ascribed a large part of the CO+ explained variability (97 %) to the OOA and BBOA factors. Accordingly, we discuss a new CO+ parameterization as a function of CO2+ and C2H4O2+ fragments, which were selected to describe the variability of the OOA and BBOA factors.

Aerodyne aerosol mass spectrometer (AMS) and Aerodyne aerosol chemical speciation monitor (ACSM) mass spectra are widely used to quantify organic aerosol (OA) elemental composition, oxidation state, and major environmental sources. The OA CO2+ fragment is among the most important measurements for such analyses. Here, we show that a non-OA CO2+ signal can arise from reactions on the particle vaporizer, ion chamber, or both, induced by thermal decomposition products of inorganic salts. In our tests (eight instruments, n = 29), ammonium nitrate (NH4NO3) causes a median CO2+ interference signal of +3.4% relative to nitrate. This interference is highly variable between instruments and with measurement history (percentiles P10–90 = +0.4 to +10.2%). Other semi-refractory nitrate salts showed 2–10 times enhanced interference compared to that of NH4NO3, while the ammonium sulfate ((NH4)2SO4) induced interference was 3–10 times lower. Propagation of the CO2+ interference to other ions during standard AMS and ACSM d...

Air pollution is one of the main environmental concerns in urban areas, where anthropogenic emissions strongly affect air quality. This work presents the first spatially resolved detailed characterization of PM2.5 (particulate matter with aerodynamic equivalent diameter daero ≤ 2.5 µm) in two major Estonian cities, Tallinn and Tartu. The measurements were performed in March 2014 using a mobile platform. In both cities, the non-refractory (NR)-PM2.5 was characterized by a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) using a recently developed lens which increases the transmission of super-micron particles. Equivalent black carbon (eBC) and several trace gases including carbon monoxide (CO), carbon dioxide (CO2), and methane (CH4) were also measured. The chemical composition of PM2.5 was found to be very similar in the two cities. Organic aerosol (OA) constituted the largest fraction, explaining on average about 52 to 60 % of the PM2.5 mass. Four sources of OA were identified using positive matrix factorization (PMF): hydrocarbon-like OA (HOA, from traffic emissions), biomass burning OA (BBOA, from biomass combustion), residential influenced OA (RIOA, probably mostly from cooking processes with possible contributions from waste and coal burning), and oxygenated OA (OOA, related to secondary aerosol formation). OOA was the major OA source during nighttime, explaining on average half of the OA mass, while during daytime mobile measurements the OA was affected by point sources and dominated by the primary fraction. A strong increase in the secondary organic and inorganic components was observed during periods with transport of air masses from northern Germany, while the primary local emissions accumulated during periods with temperature inversions. Mobile measurements offered the identification of different source regions within the urban areas and the assessment of the extent to which pollutants concentrations exceeded regional background levels (urban increments). HOA, eBC, CO2, and CO showed stronger enhancements on busy roads during the morning and evening traffic rush hours; BBOA had its maximum enhancement in the residential areas during the evening hours and RIOA was enhanced in both the city center (emissions from restaurants) and in the residential areas (emissions from residential cooking). In contrast, secondary components (OOA, sulfate (SO4), nitrate (NO3), ammonium (NH4), and chloride (Cl)) had very homogeneous distributions in time and space. We were able to determine a total PM2.5 urban increment in Tartu of 6.0 µg m−3 over a regional background concentration of 4.0 µg m−3 (i.e., a factor of 2.5 increase). Traffic exhaust emissions were identified as the most important source of this increase, with eBC and HOA explaining on average 53.3 and 20.5 % of the total increment, respectively.

We have systematically examined the gas and particle phase emissions from seven wood combustion devices. Among total carbon mass emitted (excluding CO2), CO emissions were dominant, together with nonmethane volatile organic compounds (NMVOCs) (10–40%). Automated devices emitted 1–3 orders of magnitude lower CH4 (0.002–0.60 g kg–1 of wood) and NMVOCs (0.01–1 g kg–1 of wood) compared to batch-operated devices (CH4: 0.25–2.80 g kg–1 of wood; NMVOCs: 2.5–19 g kg–1 of wood). 60–90% of the total NMVOCs were emitted in the starting phase of batch-operated devices, except for the first load cycles. Partial-load conditions or deviations from the normal recommended operating conditions, such as use of wet wood/wheat pellets, oxygen rich or deficit conditions, significantly enhanced the emissions. NMVOCs were largely dominated by small carboxylic acids and alcohols, and furans. Despite the large variability in NMVOCs emission strengths, the relative contribution of different classes showed large similarities among d...

Aerosols and organic source apportionment were characterized using data collected during two measurement campaigns. These campaigns were conducted during the summer and winter seasons at Măgurele, a site located southwest of Bucharest, the capital of Romania and one of the largest cities in southeastern Europe (raking seven in Europe based on population). The summer campaign was conducted between 7 June&ndash, 18 July 2012, and the winter campaign from 14 January&ndash, 6 February 2013. Approximately 50% of the organic fraction contribution to the total submicron particulate matter sampled by aerosol mass spectrometer was evidenced during both seasons. Submicronic organic aerosol sources were quantified using the positive matrix factorization approach. For warm (summer) and cold (winter) seasons, more than 50% from total organics was represented by oxidized factors. For the summer season, separate analyses were conducted on data influenced by urban and non-urban sources. The influence of pollution from Bucharest on the measurement site was observed in aerosol concentration and composition. The primary organic aerosols have different contribution percentage during summer, depending on their main origin. The influence of Bucharest, during summer, included cooking contribution of 13%. The periods with more regional influence were characterized by lower contribution from traffic and biomass burning in a total proportion of 28%. In winter, the influence of local non-traffic sources was dominant. For more than 99% of the measurements, the biomass burning indicator, f 60 , exceeded the background value, with residential heating being an important source in this area. Fossil fuel contribution was confirmed for one week during the winter campaign, when 14 C analysis of total and elemental carbon revealed the presence of 17% fossil contributions to total carbon. Mass spectrometry, 14 C and absorption data suggest biomass burning as the predominant primary source of organic aerosols for the winter season.

Wood combustion emissions can induce oxidative stress in the human respiratory tract by reactive oxygen species (ROS) in the aerosol particles, which are emitted either directly or formed through oxidation in the atmosphere. To improve our understanding of the particle-bound ROS (PB-ROS) generation potential of wood combustion emissions, a suite of smog chamber (SC) and potential aerosol mass (PAM) chamber experiments were conducted under well-determined conditions for different combustion devices and technologies, different fuel types, operation methods, combustion regimes, combustion phases, and aging conditions. The PB-ROS content and the chemical properties of the aerosols were quantified by a novel ROS analyzer using the DCFH (2′,7′-dichlorofluorescin) assay and a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). For all eight combustion devices tested, primary PB-ROS concentrations substantially increased upon aging. The level of primary and aged PB-ROS emission factors (EFROS) were dominated by the combustion device (within different combustion technologies) and to a greater extent by the combustion regimes: the variability within one device was much higher than the variability of EFROS from different devices. Aged EFROS under bad combustion conditions were ∼ 2–80 times higher than under optimum combustion conditions. EFROS from automatically operated combustion devices were on average 1 order of magnitude lower than those from manually operated devices, which indicates that automatic combustion devices operated at optimum conditions to achieve near-complete combustion should be employed to minimize PB-ROS emissions. The use of an electrostatic precipitator decreased the primary and aged ROS emissions by a factor of ∼ 1.5 which is however still within the burn-to-burn variability. The parameters controlling the PB-ROS formation in secondary organic aerosol were investigated by employing a regression model, including the fractions of the mass-to-charge ratios m∕z 44 and 43 in secondary organic aerosol (SOA; f44 − SOA and f43 − SOA), the OH exposure, and the total organic aerosol mass. The regression model results of the SC and PAM chamber aging experiments indicate that the PB-ROS content in SOA seems to increase with the SOA oxidation state, which initially increases with OH exposure and decreases with the additional partitioning of semi-volatile components with lower PB-ROS content at higher OA concentrations, while further aging seems to result in a decay of PB-ROS. The results and the special data analysis methods deployed in this study could provide a model for PB-ROS analysis of further wood or other combustion studies investigating different combustion conditions and aging methods.

During winter 2013–2014 aerosol mass spectrometer (AMS) measurements were conducted for the first time with a novel PM2.5 (particulate matter with aerodynamic diameter ≤ 2.5 µm) lens in two major cities of China: Xi'an and Beijing. We denote the periods with visibility below 2 km as extreme haze and refer to the rest as reference periods. During the measurements in Xi'an an extreme haze covered the city for about a week and the total non-refractory (NR)-PM2.5 mass fraction reached peak concentrations of over 1000 µg m−3. During the measurements in Beijing two extreme haze events occurred, but the temporal extent and the total concentrations reached during these events were lower than in Xi'an. Average PM2.5 concentrations of 537 ± 146 and 243 ± 47 µg m−3 (including NR species and equivalent black carbon, eBC) were recorded during the extreme haze events in Xi'an and Beijing, respectively. During the reference periods the measured average concentrations were 140 ± 99 µg m−3 in Xi'an and 75 ± 61 µg m−3 in Beijing. The relative composition of the NR-PM2.5 evolved substantially during the extreme haze periods, with increased contributions of the inorganic components (mostly sulfate and nitrate). Our results suggest that the high relative humidity present during the extreme haze events had a strong effect on the increase of sulfate mass (via aqueous phase oxidation of sulfur dioxide). Another relevant characteristic of the extreme haze is the size of the measured particles. During the extreme haze events, the AMS showed much larger particles, with a volume weighted mode at about 800 to 1000 nm, in contrast to about 400 nm during reference periods. These large particle sizes made the use of the PM2.5 inlet crucial, especially during the severe haze events, where 39 ± 5 % of the mass would have been lost in the conventional PM1 (particulate matter with aerodynamic diameter ≤ 1 µm) inlet. A novel positive matrix factorization procedure was developed to apportion the sources of organic aerosols (OA) based on their mass spectra using the multilinear engine (ME-2) controlled via the source finder (SoFi). The procedure allows for an effective exploration of the solution space, a more objective selection of the best solution and an estimation of the rotational uncertainties. Our results clearly show an increase of the oxygenated organic aerosol (OOA) mass during extreme haze events. The contribution of OOA to the total OA increased from the reference to the extreme haze periods from 16.2 ± 1.1 to 31.3 ± 1.5 % in Xi'an and from 15.7 ± 0.7 to 25.0 ± 1.2 % in Beijing. By contrast, during the reference periods the total OA mass was dominated by domestic emissions of primary aerosols from biomass burning in Xi'an (42.2 ± 1.5 % of OA) and coal combustion in Beijing (55.2 ± 1.6 % of OA). These two sources are also mostly responsible for extremely high polycyclic aromatic hydrocarbon (PAH) concentrations measured with the AMS (campaign average of 2.1 ± 2.0 µg m−3 and frequent peak concentrations above 10 µg m−3). To the best of our knowledge, this is the first data set where the simultaneous extraction of these two primary sources could be achieved in China by conducting on-line AMS measurements at two areas with contrasted emission patterns.

Organic gases undergoing conversion to form secondary organic aerosol (SOA) during atmospheric aging are largely unidentified, particularly in regions influenced by anthropogenic emissions. SOA dominates the atmospheric organic aerosol burden and this knowledge gap contributes to uncertainties in aerosol effects on climate and human health. Here we characterize primary and aged emissions from residential wood combustion using high resolution mass spectrometry to identify SOA precursors. We determine that SOA precursors traditionally included in models account for only ~3–27% of the observed SOA, whereas for the first time we explain ~84–116% of the SOA by inclusion of non-traditional precursors. Although hundreds of organic gases are emitted during wood combustion, SOA is dominated by the aging products of only 22 compounds. In some cases, oxidation products of phenol, naphthalene and benzene alone comprise up to ~80% of the observed SOA. Identifying the main precursors responsible for SOA formation enables improved model parameterizations and SOA mitigation strategies in regions impacted by residential wood combustion, more productive targets for ambient monitoring programs and future laboratories studies, and links between direct emissions and SOA impacts on climate and health in these regions.

Due to current and upcoming regulations to address the adverse impacts of particulate matter (PM) from shipping emissions, the maritime sector is required to find energy-efficient ways to comply mainly by using low fuel sulfur content (FSC) in regulated seas. We studied the PM emission from a research ship diesel engine with fuel switching capability, optimized for HFO used at cruising, operated at representative engine loads resulting to varying excess O2 emission which was an indirect measurement of air–fuel mixture (k), using heavy fuel oil (HFO, 1.6 S (%m)) and diesel fuel (DF

A variety of tools are used to simulate atmospheric aging, including smog chambers and flow reactors. Traditional, large-scale smog chambers age emissions over the course of hours to days, whereas flow reactors rapidly age emissions using high oxidant concentrations to reach higher degrees of oxygenation than typically attained in smog chamber experiments. The atmospheric relevance of the products generated under such rapid oxidation warrants further study. However, no previously published studies have compared the yields and chemical composition of products generated in flow reactors and smog chambers from the same starting mixture. The yields and composition of the organic aerosol formed from the photo-oxidation of α-pinene and of wood-combustion emissions in a smog chamber (SC) and two flow reactors: a potential aerosol mass reactor (PAM) and a micro-smog chamber (MSC), were determined using aerosol mass spectrometry. Reactants were sampled from the SC and aged in the MSC and the PAM using a range of hydroxyl radical (OH) concentrations and then photo-chemically aged in the SC. The chemical composition, as well as the maximum yields and emission factors, of the products in both the α-pinene and wood-combustion systems determined with the PAM and the SC agreed reasonably well. High OH exposures have been shown previously to lower yields by breaking carbon–carbon bonds and forming higher volatility species, which reside largely in the gas phase; however, fragmentation in the PAM was not observed. The yields determined using the PAM for the α-pinene system were slightly lower than in the SC, possibly from increased wall losses of gas phase species due to the higher surface area to volume ratios in the PAM, even when offset with better isolation of the sampled flow from the walls. The α-pinene SOA results for the MSC were not directly comparable, as particles were smaller than the optimal AMS transmission range. The higher supersaturation in the flow reactors resulted in more nucleation than in the SC. For the wood-combustion system, emission factors measured from the MSC were typically lower than those measured from the SC. Lower emission factors in the MSC may have been due to considerable nucleation mode particles formed in the MSC which were not detected by the AMS or due to condensational loss of gases to the walls inside or after the MSC. More comprehensive coverage of the potential particle size range is needed in future SOA measurements to improve our understanding of the differences in yields when comparing the MSC to the SC. The PAM and the SC agreed within measurement uncertainties in terms of yields and composition for the systems and conditions studied here and this agreement supports the continued use of the PAM to study atmospheric aging.

International audience; Residential coal combustion is a significant contributor to particulate urban air pollution in Chinese mega cities and some regions in Europe. While the particulate emission factors and the chemical characteristics of the organic and inorganic aerosol from coal combustion is extensively studied, the chemical composition and non methane organic gas (NMOG) emission factors from residential coal combustion are mostly unknown. We conducted 23 individual burns in a traditional Chinese stove used for heating and cooking using five different coals with Chinese origins, characterizing the NMOG emissions using a proton transfer reaction time-of-fight mass spectrometer. The measured emission factors range from 1−15 g/kgcoal for bituminous coals and are below 0.1 g/kgcoal for anthracite coals. The emission factors from the bituminous coals are mostly influenced by the time until the coal is fully ignited. The emissions from the bituminous coals are dominated by aromatic and oxygenated aromatic compounds with a significant contribution of hydrocarbons. The results of this study can help to improve urban air pollution modeling in China and eastern Europe and can be used to constrain a coal burning factor in ambient gas phase positive matrix factorization studies.

Vapor wall loss has only recently been shown a potentially significant bias in atmospheric chamber studies. Yet, previous works aimed at the determination of the degradation rate of semi-volatile organic compounds (SVOCs) often did not account for this process. Here we evaluate the influence of vapor wall loss on the determination of the gas phase reaction rate kOH of several biomass burning markers (levoglucosan, mannosan, coniferyl aldehyde, 3-guaiacyl propanol, and acetosyringone) with hydroxyl radicals (OH). Emissions from the combustion of beech wood were injected into a 5.5 m3 Teflon atmospheric chamber, and aged for 4 hours (equivalent to 5–8 hours in the atmosphere). The particle phase compound concentrations were monitored using a Thermal Desorption Aerosol Gas Chromatograph coupled to a High-Resolution – Time of Flight – Mass Spectrometer (TAG-AMS). The observed depletion of the concentration was later modeled using two different approaches: the previously published approach which does not take into consideration partitioning and vapor wall loss, and an approach with a more complex theoretical framework which integrates all the processes likely influencing the particle phase concentration. We find that with the first approach one fails to predict the measured markers concentration time evolution. With the second approach, we determine that partitioning and vapor wall loss play a predominant role in the particle phase concentration depletion of all the compounds, while the reactivity with OH has a non-significative effect. Furthermore we show that kOH cannot be determined precisely without a strong constraint of the whole set of physical parameters necessary to formally describe the various processes involved. It was found that the knowledge of the saturation mass concentration C* is especially crucial. Therefore previously published rate constants of levoglucosan and more generally SVOCs with hydroxyl radicals inferred from atmospheric chamber experiments must be, at least, considered with caution.

We investigate the optical properties of light-absorbing organic carbon (brown carbon) from domestic wood combustion as a function of simulated atmospheric aging. At shorter wavelengths, light absorption by brown carbon from primary organic aerosol (POA) and secondary organic aerosol (SOA) formed during aging was around 10 % and 20 %, respectively, of the total aerosol absorption (brown carbon plus black carbon). The mass absorption cross-section (MAC) determined for black carbon (BC, 13.7 m2 g−1 (geometric standard deviation GSD = 1.1) at 370 nm) was consistent with that recommended by Bond et al. (2006). The corresponding MAC of POA (5.5 m2 g−1 (GSD = 1.2)) was higher than that of SOA (2.4 m2 g−1 (GSD = 1.3)) at 370 nm. However, SOA presents a substantial mass fraction, with a measured average SOA / POA mass ratio after aging of ~ 5 and therefore contributes significantly to the overall light absorption, highlighting the importance of wood-combustion SOA as a source of atmospheric brown carbon. The wavelength dependence of POA and SOA light absorption between 370 nm and 660 nm is well described with absorption Ångström exponents of 4.6 and 5.6, respectively. UV-visible absorbance measurements of water and methanol-extracted OA were also performed showing that the majority of the light-absorbing OA is water insoluble even after aging.

Residential wood burning contributes significantly to the total atmospheric aerosol burden; however, large uncertainties remain in the magnitude and characteristics of wood burning products. Primary emissions are influenced by a variety of parameters, including appliance type, burner wood load and wood type. In addition to directly emitted particles, previous laboratory studies have shown that oxidation of gas phase emissions produces compounds with sufficiently low volatility to readily partition to the particles, forming significant quantities of secondary organic aerosol (SOA). However, relatively little is known about wood burning SOA and the effects of burn parameters on SOA formation and composition are yet to be determined. There is clearly a need for further study of primary and secondary wood combustion aerosols to advance our knowledge of atmospheric aerosols and their impacts on health, air quality and climate. For the first time, smog chamber experiments were conducted to investigate the effects of wood loading on both primary and secondary wood combustion products. Products were characterized using a range of particle and gas phase instrumentation, including an aerosol mass spectrometer (AMS). A novel approach for polycyclic aromatic hydrocarbon (PAH) quantification from AMS data was developed and results were compared to those from GC-MS analysis of filter samples. Similar total particle mass emission factors were observed under high and average wood loadings, however, high fuel loadings were found to generate significantly higher contributions of PAHs to the total organic aerosol (OA) mass compared to average loadings. PAHs contributed 15 ± 4% (mean ± 2 sample standard deviations) to the total OA mass in high load experiments, compared to 4 ± 1% in average load experiments. With aging, total OA concentrations increased by a factor of 3 ± 1 for high load experiments compared to 1.6 ± 0.4 for average load experiments. In the AMS, an increase in PAH and aromatic signature ions at lower m/z values, likely fragments from larger functionalized PAHs, was observed with aging. Filter samples also showed an increase in functionalized PAHs in the particles with aging, particularly oxidized naphthalene species. As PAHs and their oxidation products are known to have deleterious effects on health, this is a significant finding to aid in the mitigation of negative wood burning impacts by improving burner operation protocols.

The valence threshold photoionization of oleic acid has been studied using synchrotron VUV radiation and imaging photoelectron photoion coincidence (iPEPICO) spectroscopy. An oleic acid aerosol beam was impacted on a copper thermodesorber, heated to 130 °C, to evaporate the particles quantitatively. Upon threshold photoionization, oleic acid produces the intact parent ion first, followed by dehydration at higher energies. Starting at ca. 10 eV, a large number of fragment ions slowly rise suggesting several fragmentation coordinates with quasi-degenerate activation energies. However, water loss is the dominant low-energy dissociation channel, and it is shown to be closely related to the unsaturated carbon chain. In the lowest-barrier process, one of the four allylic hydrogen atoms is transferred to the carboxyl group to form the leaving water molecule and a cyclic ketone fragment ion. A statistical model to analyze the breakdown diagram and measured rate constants yields a 0 K appearance energy of 9.77 eV, which can be compared with the density functional theory result of 9.19 eV. Alternative H-transfer steps yielding a terminal C=O group are ruled out based on energetics and kinetics arguments. Some of the previous photoionization mass spectrometric studies also reported 2 amu and 26 amu loss fragment ions, corresponding to hydrogen and acetylene loss. We could not identify such peaks in the mass spectrum of oleic acid.

Oxidative processing of aircraft turbine-engine exhausts was studied using a potential aerosol mass (PAM) chamber at different engine loads corresponding to typical flight operations. Measurements were conducted at an engine test cell. Organic gases (OGs) and particle emissions pre- and post-PAM were measured. A suite of instruments, including a proton-transfer-reaction mass spectrometer (PTR-MS) for OGs, a multigas analyzer for CO, CO2, NOx, and an aerosol mass spectrometer (AMS) for nonrefractory particulate matter (NR-PM1) were used. Total aerosol mass was dominated by secondary aerosol formation, which was approximately 2 orders of magnitude higher than the primary aerosol. The chemical composition of both gaseous and particle emissions were also monitored at different engine loads and were thrust-dependent. At idling load (thrust 2.5–7 %), more than 90 % of the secondary particle mass was organic and could mostly be explained by the oxidation of gaseous aromatic species, e.g., benzene; toluene; xylenes; tri-, tetra-, and pentamethyl-benzene; and naphthalene. The oxygenated-aromatics, e.g., phenol, furans, were also included in this aromatic fraction and their oxidation could alone explain up to 25 % of the secondary organic particle mass at idling loads. The organic fraction decreased with thrust level, while the inorganic fraction increased. At an approximated cruise load sulfates comprised 85 % of the total secondary particle mass., Atmospheric Chemistry and Physics, 18 (10), ISSN:1680-7375, ISSN:1680-7367

Gasoline direct injection (GDI) vehicles have recently been identified as a significant source of carbonaceous aerosol, of both primary and secondary origin. Here we investigated primary emissions and secondary organic aerosol (SOA) formation from GDI vehicle exhaust for multiple vehicles and driving test cycles, and novel GDI after-treatment systems. Emissions were characterized by proton transfer reaction time-of-flight mass spectrometry (gaseous non-methane organic compounds, NMOCs), aerosol mass spectrometry (sub-micron non-refractory particles), and light attenuation measurements (equivalent black carbon (eBC) determination using Aethalometer measurements) together with supporting instrumentation. We evaluated the effect of retrofitted prototype gasoline particle filters (GPFs) on primary eBC, organic aerosol (OA), NMOCs, as well as SOA formation. Two regulatory driving test cycles were investigated, and the importance of distinct phases within these cycles (e.g. cold engine start, hot engine start, high speed driving) to primary emissions and secondary products was evaluated. Atmospheric processing was simulated using both the PSI mobile smog chamber (SC) and the potential aerosol mass oxidation flow reactor (OFR). GPF retrofitting was found to greatly decrease primary particulate matter (PM) through removal of eBC, but showed limited partial removal of the minor POA fraction, and had no detectable effect on either NMOC emissions (absolute emission factors or relative composition) or SOA production. In all tests, overall primary and secondary PM and NMOC emissions were dominated by the engine cold start, i.e. before thermal activation of the catalytic after-treatment system. Differences were found in the bulk compositional properties of SOA produced by the OFR and the SC (O : C and H : C ratios), while the SOA yields agree within our uncertainties, with a tendency for lower SOA yields in SC experiments. A few aromatic compounds are found to dominate the NMOC emissions (primarily benzene, toluene, xylene isomers and C3-benzenes). A large fraction (> 0.5) of the SOA production was explained by those compounds, based on investigation of reacted NMOC mass and comparison with SOA yield curves of toluene, o-xylene and 1,2,4-trimethylbenzene determined in our OFR within this study. Remaining differences in the obtained SOA yields may result from diverse reasons including aging conditions, unaccounted-for precursors and differences in SOA yields of aromatic hydrocarbons with different degrees of substitution, as well as experimental uncertainties in the assessment of particle and vapor wall losses.

The Xact 625 Ambient Metals Monitor was tested during a 3-week field campaign at the rural, traffic-influenced site Härkingen in Switzerland during the summer of 2015. The field campaign encompassed the Swiss National Day fireworks event, providing increased concentrations and unique chemical signatures compared to non-fireworks (or background) periods. The objective was to evaluate the data quality by intercomparison with other independent measurements and test its applicability for aerosol source quantification. The Xact was configured to measure 24 elements in PM10 with 1g h time resolution. Data quality was evaluated for 10 24g h averages of Xact data by intercomparison with 24g h PM10 filter data analysed with ICP-OES for major elements, ICP-MS for trace elements, and gold amalgamation atomic absorption spectrometry for Hg. Ten elements (S, K, Ca, Ti, Mn, Fe, Cu, Zn, Ba, Pb) showed excellent correlation between the compared methods, with r2 values ≥ g 0.95. However, the slopes of the regressions between Xact 625 and ICP data varied from 0.97 to 1.8 (average 1.28) and thus indicated generally higher Xact elemental concentrations than ICP for these elements. Possible reasons for these differences are discussed, but further investigations are needed. For the remaining elements no conclusions could be drawn about their quantification for various reasons, mainly detection limit issues. An indirect intercomparison of hourly values was performed for the fireworks peak, which brought good agreement of total masses when the Xact data were corrected with the regressions from the 24g h value intercomparison. The results demonstrate that multi-metal characterization at high-time-resolution capability of Xact is a valuable and practical tool for ambient monitoring. © Author(s) 2017., This study has been partly funded by the Swiss Federal Office for the Environment (FOEN). M. C. Minguillón acknowledges the Ramón y Cajal Fellowship awarded by the Spanish Ministry of Economy, Industry and Competitiveness. We thank René Richter and Roland Scheidegger of PSI for their support during the field campaign. We are grateful to Chris Koch and John Cooper of Cooper Environmental Services for instructions on instrument operation and numerous discussions on the results. Andrés Alastuey, Xavier Querol, and laboratory personnel from IDAEA-CSIC are also acknowledged. We also thank Julie Swift and Randy Mercurio of ERG for the ICP-MS analyses.

A series of smog chamber (SC) experiments was conducted to identify factors responsible for the discrepancy between ambient and SC aerosol degree of oxygenation. An Aerodyne high-resolution time-of-flight aerosol mass spectrometer is used to compare mass spectra from α-pinene photooxidation with ambient aerosol. Composition is compared in terms of the fraction of particulate CO2+, a surrogate for carboxylic acids, vs. the fraction of C2H3O+, a surrogate for aldehydes, alcohols and ketones, as well as in the Van Krevelen space, where the evolution of the atomic hydrogen-to-carbon ratio (H : C) vs. the atomic oxygen-to-carbon ratio (O : C) is investigated. Low (near-ambient) organic mass concentrations were found to be necessary to obtain oxygenation levels similar to those of low-volatility oxygenated organic aerosol (LV-OOA) commonly identified in ambient measurements. The effects of organic mass loading and OH (hydroxyl radical) exposure were decoupled by inter-experiment comparisons at the same integrated OH concentration. An OH exposure between 3 and 25 × 107 cm−3 h is needed to increase O : C by 0.05 during aerosol aging. For the first time, LV-OOA-like aerosol from the abundant biogenic precursor α-pinene was produced in a smog chamber by oxidation at typical atmospheric OH concentrations. Significant correlation between measured secondary organic aerosol (SOA) and reference LV-OOA mass spectra is shown by Pearson's R2 values larger than 0.90 for experiments with low organic mass concentrations between 1.2 and 18 μg m−3 at an OH exposure of 4 × 107 cm−3 h, corresponding to about two days of oxidation time in the atmosphere, based on a global mean OH concentration of ~ 1 × 106 cm−3. α-Pinene SOA is more oxygenated at low organic mass loadings. Because the degree of oxygenation influences the chemical, volatility and hygroscopic properties of ambient aerosol, smog chamber studies must be performed at near-ambient concentrations to accurately simulate ambient aerosol properties.

The organic functional group composition of particles produced in laboratory “smog” chambers were characterized by scanning transmission X-ray microscopy (STXM) with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and characteristic spectral signatures for secondary organic aerosol (SOA) were identified. The main objective of this study is to compare the single particle functional group composition of SOA formed from five precursors (glyoxal, α-pinene, isoprene, 1,2,4-trimethylbenzene, and d-limonene) to the composition of ambient particles from multiple field campaigns. This has implications for understanding the potential contributions of particles similar to those produced in SOA chambers to ambient compositions during those campaigns. Glyoxal uptake studies showed absorption from mainly alkyl, carbon-nitrogen (C-N), and carboxylic carbonyl groups. The SOA formed from the photooxidation of α-pinene (with and without isoprene) showed stronger absorptions for alkyl and carbonyl groups tha...

Nonmethane organic gas emissions (NMOGs) from in-service aircraft turbine engines were investigated using a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) at an engine test facility at Zurich Airport, Switzerland. Experiments consisted of 60 exhaust samples for seven engine types (used in commercial aviation) from two manufacturers at thrust levels ranging from idle to takeoff. Emission indices (EIs) for more than 200 NMOGs were quantified, and the functional group fractions (including acids, carbonyls, aromatics, and aliphatics) were calculated to characterize the exhaust chemical composition at different engine operation modes. Total NMOG emissions were highest at idling with an average EI of 7.8 g/kg fuel and were a factor of ∼40 lower at takeoff thrust. The relative contribution of pure hydrocarbons (particularly aromatics and aliphatics) of the engine exhaust decreased with increasing thrust while the fraction of oxidized compounds, for example, acids and carbonyls increased. Exhaust chemical composition at idle was also affected by engine technology. Older engines emitted a higher fraction of nonoxidized NMOGs compared to newer ones. Idling conditions dominated ground level organic gas emissions. Based on the EI determined here, we estimate that reducing idle emissions could substantially improve air quality near airports.

Organic gases emitted during the flaming phase of residential wood combustion are characterized individually and by functionality using proton transfer reaction time-of-flight mass spectrometry. The evolution of the organic gases is monitored during photochemical aging. Primary gaseous emissions are dominated by oxygenated species (e.g., acetic acid, acetaldehyde, phenol and methanol), many of which have deleterious health effects and play an important role in atmospheric processes such as secondary organic aerosol formation and ozone production. Residential wood combustion emissions differ considerably from open biomass burning in both absolute magnitude and relative composition. Ratios of acetonitrile, a potential biomass burning marker, to CO are considerably lower ( ∼ 0.09 pptv ppbv−1) than those observed in air masses influenced by open burning ( ∼ 1–2 pptv ppbv−1), which may make differentiation from background levels difficult, even in regions heavily impacted by residential wood burning. A considerable amount of formic acid forms during aging ( ∼ 200–600 mg kg−1 at an OH exposure of (4.5–5.5) × 107 molec cm−3 h), indicating residential wood combustion can be an important local source for this acid, the quantities of which are currently underestimated in models. Phthalic anhydride, a naphthalene oxidation product, is also formed in considerable quantities with aging ( ∼ 55–75 mg kg−1 at an OH exposure of (4.5–5.5) × 107 molec cm−3 h). Although total NMOG emissions vary by up to a factor of ∼ 9 between burns, SOA formation potential does not scale with total NMOG emissions and is similar in all experiments. This study is the first thorough characterization of both primary and aged organic gases from residential wood combustion and provides a benchmark for comparison of emissions generated under different burn parameters.

Residential wood burning is a major source of poorly characterized, deleterious particulate matter, whose composition and toxicity may vary with wood type, burning condition and photochemical age. The causative link between ambient wood particle constituents and observed adverse health effects is currently lacking. Here we investigate the relationship between chemical properties of primary and atmospherically aged wood combustion particles and acute toxicity in human airway epithelial cells. Emissions from a log wood burner were diluted and injected into a smog chamber for photochemical aging. After concentration-enrichment and removal of oxidizing gases, directly emitted and atmospherically aged particles were deposited on cell cultures at the air-liquid interface for 2 hours in an aerosol deposition chamber mimicking physiological conditions in lungs. Cell models were fully differentiated normal and diseased (cystic fibrosis and asthma) human bronchial epithelia (HBE) and the bronchial epithelial cell line BEAS-2B. Cell responses were assessed at 24 hours after aerosol exposure. Atmospherically relevant doses of wood combustion particles significantly increased cell death in all but the asthma cell model. Expression of oxidative stress markers increased in HBE from all donors. Increased cell death and inflammatory responses could not be assigned to a single chemical fraction of the particles. Exposure to primary and aged wood combustion particles caused adverse effects to airway epithelia, apparently induced by several interacting components.

Carbonaceous particulate matter (PM), comprising black carbon (BC), primary organic aerosol (POA) and secondary organic aerosol (SOA, from atmospheric aging of precursors), is a highly toxic vehicle exhaust component. Therefore, understanding vehicle pollution requires knowledge of both primary emissions, and how these emissions age in the atmosphere. We provide a systematic examination of carbonaceous PM emissions and parameterisation of SOA formation from modern diesel and gasoline cars at different temperatures (22, −7 °C) during controlled laboratory experiments. Carbonaceous PM emission and SOA formation is markedly higher from gasoline than diesel particle filter (DPF) and catalyst-equipped diesel cars, more so at −7 °C, contrasting with nitrogen oxides (NOX). Higher SOA formation from gasoline cars and primary emission reductions for diesels implies gasoline cars will increasingly dominate vehicular total carbonaceous PM, though older non-DPF-equipped diesels will continue to dominate the primary fraction for some time. Supported by state-of-the-art source apportionment of ambient fossil fuel derived PM, our results show that whether gasoline or diesel cars are more polluting depends on the pollutant in question, i.e. that diesel cars are not necessarily worse polluters than gasoline cars.

Cloud condensation nuclei (CCN) number concentrations alongside with submicrometer particle number size distributions and particle chemical composition have been measured at atmospheric observatories of the Aerosols, Clouds, and Trace gases Research InfraStructure (ACTRIS) as well as other international sites over multiple years. Here, harmonized data records from 11 observatories are summarized, spanning 98,677 instrument hours for CCN data, 157,880 for particle number size distributions, and 70,817 for chemical composition data. The observatories represent nine different environments, e.g., Arctic, Atlantic, Pacific and Mediterranean maritime, boreal forest, or high alpine atmospheric conditions. This is a unique collection of aerosol particle properties most relevant for studying aerosol-cloud interactions which constitute the largest uncertainty in anthropogenic radiative forcing of the climate. The dataset is appropriate for comprehensive aerosol characterization (e.g., closure studies of CCN), model-measurement intercomparison and satellite retrieval method evaluation, among others. Data have been acquired and processed following international recommendations for quality assurance and have undergone multiple stages of quality assessment.

[1] Major summertime aerosol emission sources in Paris were assessed using a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The application of positive matrix factorization (PMF) to the highly mass and time-resolved AMS measurements allowed the identification of primary and secondary sources of organic (OA) and sulfate aerosols. Primary anthropogenic emissions contributed on average ~27% (14.7% cooking, 12% traffic) to the total organic mass, while the major contribution to the organic fraction was associated with secondary formation products. Low-volatility oxygenated OA (LV-OOA, 25.2%) and semi-volatile oxygenated OA (SV-OOA, 32.4%) factors were classified as SOA. An additional component with high S : C and O : C ratios was identified and attributed to marine emissions (marine organic aerosol, MOA), owing to its high correlation with methanesulfonic acid (R2 = 0.84) and contributing on average 15.7% to the total OA mass, even in the continental megacity of Paris. Non-sea salt sulfate was apportioned by including both organic and sulfate ions in the PMF data matrix. This allowed apportionment of submicron sulfate to continental versus marine sources. A detailed source apportionment of PM1 combining AMS, aethalometer, and filter data is presented.

Here we explore the vapour pressure of sulphuric acid at very low relative humidity, where evaporation of sulphuric acid from particles can be important in the atmospheres of Earth and Venus. We performed experiments in the CLOUD chamber at CERN forming sulphuric acid particles via nucleation and then measuring evaporation versus temperature and relative humidity. We modelled the experiments with the ADCHAM model to constrain the thermodynamic properties governing the evaporation of sulphuric acid. ADCHAM includes a thermodynamics module coupled to an aerosol dynamics module. We derived the mole fractions and activity coefficients of H2SO4, HSO4−, SO42− and SO3 in the particles and then simulated the condensation and evaporation of H2SO4 and SO3. We constrained the equilibrium constants for the dissociation of H2SO4 to HSO4− (KH2SO4) and the dehydration of H2SO4 to SO3 (xKSO3). Our results suggest that particle shrinkage is mainly governed by H2SO4 evaporation, however, we cannot dismiss a contribution from SO3 evaporation. We conclude that KH2SO4 = 2–4 ∙ 109 mol ∙ kg−1 at 288.8 ± 5 K and xKSO3 ≥ 1.4 ∙ 1010.

17 páginas, 8 figuras., PM1 (particulate matter with an aerodynamic diameter, We thank the organizers of the DAURE project, including Mar Viana and everybody else at ICTJA for their work and help. We acknowledge the CCES project IMBALANCE and the EU-FP7 project EUCAARI for financial support and ’Accion Complementaria DAURE’ from the Spanish Ministry of Science and Innovation (CGL2007-30502-E/CLI) for infrastructure support. P. F. DeCarlo is grateful for the postdoctoral support from the US-NSF (IRFP# 0701013). J. Penuelas and R. Seco were sup- ˜ ported by the Spanish Government projects CGL2010-17172 and Consolider Ingenio Montes CSD2008-00040, and by a postdoctoral grant from Fundacion Ram ´ on Areces to R. Seco. The National ´ Center for Atmospheric Research is sponsored by the National Science Foundation. J. L. Jimenez was supported by NSF ATM- 0919189 and DOE (BER, ASR program) DE-FG02-11ER65293.

Organic aerosol (OA) represents a significant and often major fraction of the non-refractory PM1 (particulate matter with an aerodynamic diameter da < 1 μm) mass. Secondary organic aerosol (SOA) is an important contributor to the OA and can be formed from biogenic and anthropogenic precursors. Here we present results from the characterization of SOA produced from the emissions of three different anthropogenic sources. SOA from a log wood burner, a Euro 2 diesel car and a two-stroke Euro 2 scooter were characterized with an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) and compared to SOA from α-pinene. The emissions were sampled from the chimney/tailpipe by a heated inlet system and filtered before injection into a smog chamber. The gas phase emissions were irradiated by xenon arc lamps to initiate photo-chemistry which led to nucleation and subsequent particle growth by SOA production. Duplicate experiments were performed for each SOA type, with the averaged organic mass spectra showing Pearson's r values >0.94 for the correlations between the four different SOA types after five hours of aging. High-resolution mass spectra (HR-MS) showed that the dominant peaks in the MS, m/z 43 and 44, are dominated by the oxygenated ions C2H3O+ and CO2+, respectively, similarly to the relatively fresh semi-volatile oxygenated OA (SV-OOA) observed in the ambient aerosol. The atomic O:C ratios were found to be in the range of 0.25–0.55 with no major increase during the first five hours of aging. On average, the diesel SOA showed the lowest O:C ratio followed by SOA from wood burning, α-pinene and the scooter emissions. Grouping the fragment ions revealed that the SOA source with the highest O:C ratio had the largest fraction of small ions. The HR data of the four sources could be clustered and separated using principal component analysis (PCA). The model showed a significant separation of the four SOA types and clustering of the duplicate experiments on the first two principal components (PCs), which explained 79% of the total variance. Projection of ambient SV-OOA spectra resolved by positive matrix factorization (PMF) showed that this approach could be useful to identify large contributions of the tested SOA sources to SV-OOA. The first results from this study indicate that the SV-OOA in Barcelona is strongly influenced by diesel emissions in winter while in summer at SIRTA at the southwestern edge of Paris SV-OOA is more similar to alpha-pinene SOA. However, contributions to the ambient SV-OOA from SOA sources that are not covered by the model can cause major interference and therefore future expansions of the PCA model with additional SOA sources is recommended.