Search

Open burning of household solid waste is a large source of air pollutants worldwide, especially in the Global South. However, waste burning emissions are either missing or have large uncertainties in local, regional, or global emission inventories due to limited emission factor (EF) and activity data. Detailed particulate matter (PM) chemical speciation data are even less available. This paper reports source profiles and EFs for PM2.5 species as well as acidic and alkali gases measured from laboratory combustion of 10 waste categories that represent open burning in South Africa. Carbonaceous materials contributed more than 70 % of PM2.5 mass. Elemental carbon (EC) was most abundant from flaming materials (e.g., plastic bags, textiles, and combined materials), and its climate forcing exceeded the corresponding CO2 emissions by a factor of 2–5. Chlorine had the highest EFs among elements measured by X-ray fluorescence (XRF) for all materials. Vegetation emissions showed high abundances of potassium, consistent with its use as a marker for biomass burning. Fresh PM2.5 emitted from waste burning appeared to be acidic. Moist vegetation and food discards had the highest hydrogen fluoride (HF) and PM fluoride EFs due to fluorine accumulation in plants, while burning rubber had the highest hydrogen chloride (HCl) and PM chloride EFs due to high chlorine content in the rubber. Plastic bottles, plastic bags, rubber, and food discards had the highest EFs for polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs as well as their associated toxicities. Distinct differences between odd and even carbon preferences were found for alkanes from biological and petroleum-based materials: dry vegetation, paper, textiles, and food discards show preference for the odd-numbered alkanes, while the opposite is true for plastic bottles, plastic bags, and rubber. As phthalates are used as plasticizers, their highest EFs were found for plastic bottles and bags, rubber, and combined materials. Data from this study will be useful for health and climate impact assessments, speciated emission inventories, source-oriented dispersion models, and receptor-based source apportionment.

Peat fuels representing four biomes of boreal (western Russia and Siberia), temperate (northern Alaska, USA), subtropical (northern and southern Florida, USA), and tropical (Borneo, Malaysia) regions were burned in a laboratory chamber to determine gas and particle emission factors (EFs). Tests with 25 % fuel moisture were conducted with predominant smoldering combustion conditions (average modified combustion efficiency (MCE) =0.82±0.08). Average fuel-based EFCO2 (carbon dioxide) are highest (1400 ± 38 g kg−1) and lowest (1073 ± 63 g kg−1) for the Alaskan and Russian peats, respectively. EFCO (carbon monoxide) and EFCH4 (methane) are ∼12 %–15 % and ∼0.3 %–0.9 % of EFCO2, in the range of 157–171 and 3–10 g kg−1, respectively. EFs for nitrogen species are at the same magnitude as EFCH4, with an average of 5.6 ± 4.8 and 4.7 ± 3.1 g kg−1 for EFNH3 (ammonia) and EFHCN (hydrogen cyanide); 1.9±1.1 g kg−1 for EFNOx (nitrogen oxides); and 2.4±1.4 and 2.0 ± 0.7 g kg−1 for EFNOy (total reactive nitrogen) and EFN2O (nitrous oxide). An oxidation flow reactor (OFR) was used to simulate atmospheric aging times of ∼2 and ∼7 d to compare fresh (upstream) and aged (downstream) emissions. Filter-based EFPM2.5 varied by > 4-fold (14–61 g kg−1) without appreciable changes between fresh and aged emissions. The majority of EFPM2.5 consists of EFOC (organic carbon), with EFOC ∕ EFPM2.5 ratios in the range of 52 %–98 % for fresh emissions and ∼14 %–23 % degradation after aging. Reductions of EFOC (∼7–9 g kg−1) after aging are most apparent for boreal peats, with the largest degradation in low-temperature OC1 that evolves at ∘C, indicating the loss of high-vapor-pressure semivolatile organic compounds upon aging. The highest EFLevoglucosan is found for Russian peat (∼16 g kg−1), with ∼35 %–50 % degradation after aging. EFs for water-soluble OC (EFWSOC) account for ∼20 %–62 % of fresh EFOC. The majority (> 95 %) of the total emitted carbon is in the gas phase, with 54 %–75 % CO2, followed by 8 %–30 % CO. Nitrogen in the measured species explains 24 %–52 % of the consumed fuel nitrogen, with an average of 35 ± 11 %, consistent with past studies that report ∼1/3 to 2∕3 of the fuel nitrogen measured in biomass smoke. The majority (> 99 %) of the total emitted nitrogen is in the gas phase, with an average of 16.7 % as NH3 and 9.5 % as HCN. N2O and NOy constituted 5.7 % and 2.9 % of consumed fuel nitrogen. EFs from this study can be used to refine current emission inventories.

In many parts of the developing world and economies in transition, small-scale traditional brick kilns are a notorious source of urban air pollution. Many are both energy inefficient and burn highly polluting fuels that emit significant levels of black carbon (BC), organic carbon (OC) and other atmospheric pollutants into local communities, resulting in severe health and environmental impacts. However, only a very limited number of studies are available on the emission characteristics of brick kilns; thus, there is a need to characterize their gaseous and particulate matter (PM) emission factors to better assess their overall contribution to emissions inventories and to quantify their ecological, human health, and climate impacts. In this study, the fuel-, energy-, and brick-based emissions factors and time-based emission ratios of BC, OC, inorganic PM components, CO, SO2, CH4, NOx, and selected volatile organic compounds (VOCs) from three artisanal brick kilns with different designs in Mexico were quantified using the tracer ratio sampling technique. Simultaneous measurements of PM components, CO, and CO2 were also obtained using a sampling probe technique. Additional measurements included the internal temperature of the brick kilns, mechanical resistance of bricks produced, and characteristics of fuels employed. Average fuel-based BC emission factors ranged from 0.15 to 0.58 g (kg fuel)−1, whereas BC∕OC mass ratios ranged from 0.9 to 5.2, depending on the kiln type. The results show that both techniques capture similar temporal profiles of the brick kiln emissions and produce comparable emission factors. A more integrated inter-comparison of the brick kilns' performances was obtained by simultaneously assessing emissions factors, energy efficiency, fuel consumption, and the quality of the bricks produced.

A thermal/optical carbon analyzer equipped with seven-wavelength light source/detector (405–980 nm) for monitoring spectral reflectance (R) and transmittance (T) of filter samples allowed "thermal spectral analysis (TSA)" and wavelength (λ)-dependent organic-carbon (OC)–elemental-carbon (EC) measurements. Optical sensing was calibrated with transfer standards traceable to absolute R and T measurements, adjusted for loading effects to report spectral light absorption (as absorption optical depth (τa, λ)), and verified using diesel exhaust samples. Tests on ambient and source samples show OC and EC concentrations equivalent to those from conventional carbon analysis when based on the same wavelength (~ 635 nm) for pyrolysis adjustment. TSA provides additional information that evaluates black-carbon (BC) and brown-carbon (BrC) contributions and their optical properties in the near infrared to the near ultraviolet parts of the solar spectrum. The enhanced carbon analyzer can add value to current aerosol monitoring programs and provide insight into more accurate OC and EC measurements for climate, visibility, or health studies.

This study investigates the causes of elevated PM2.5 episodes and potential exceedences of the US National Ambient Air Quality Standards (NAAQS) in Truckee Meadows, Nevada, an urban valley of the Western US, during winter 2009/2010, an unusually cold and snowy winter. Continuous PM2.5 mass and time-integrated chemical speciation data were acquired from a central valley monitoring site, along with meteorological measurements from nearby sites. All nine days with PM2.5 > 35 μg m−3 showed 24-h average temperature inversion of 1.5–4.5 °C and snow cover of 8–18 cm. Stagnant atmospheric conditions limited wind ventilation while highly reflective snow cover reduced daytime surface heating creating persistent inversion. Elevated ammonium nitrate (NH4NO3) and water associated with it are found to be main reasons for the PM2.5 exceedances. An effective-variance chemical mass balance (EV-CMB) receptor model using locally-derived geological profiles and inorganic/organic markers confirmed secondary NH4NO3 (27–37%), residential wood combustion (RWC; 11–51%), and diesel engine exhaust (7–22%) as the dominant PM2.5 contributors. Paved road dust and de-icing materials were minor, but detectable contributors. RWC is a more important source than diesel for organic carbon (OC), but vice versa for elemental carbon (EC). A majority of secondary NH4NO3 is also attributed to RWC and diesel engines (including snow removal equipment) through oxides of nitrogen (NOx) emissions from these sources. Findings from this study may apply to similar situations experienced by other urban valleys.

Decreasing trends of elemental carbon (EC) have been reported at US Interagency Monitoring of PROtected Visual Environments (IMPROVE) network from 1990 to 2004, consistent with the phase-in of cleaner engines, residential biomass burning technologies, and prescribed burning practices. EC trends for the past decade are examined due to an upgrade of IMPROVE carbon instruments and the thermal/optical analysis protocol since 2005. Filter reflectance (τR) values measured as part of the carbon analysis were retrieved from archived data and compared with EC for 65 sites with more complete records within 2000–2009. EC–τR relationships suggest minor changes of EC quantified by the original and upgraded instruments for most IMPROVE samples. EC and τR show universal decreasing trends across the US. The EC and τR trends are correlated, with national average downward rates (relative to the 2000–2004 baseline medians) of 4.5% yr−1 for EC and 4.1% yr−1 for τR. The consistency between independent EC and τR measurements adds to the weight of evidence that EC reductions are real rather than an artifact of changes to the measurement process.

Airglow imaging at mid-latitude stations often show intensity modulations associated with medium scale travelling ionospheric disturbances (MSTID), while those carried out near the equatorial regions reveal depletions caused by equatorial plasma bubbles (EPB). Two all sky cameras are used to observe plasma depletions in the 630.0 nm emission over the equatorial ionization anomaly (EIA) region, Taiwan (23° N, 121° E; 13.5° N Magnetic) during 1998–2002 and 2006–2007. The results show EPB and MSTID depletions in different solar activity conditions. Several new features of the EPB depletions such as bifurcation, secondary structure on the walls, westward tilt, etc., are discussed in this paper. Evidence of tilted depletions with secondary structures developing on the eastern wall that later evolve to appear as bifurcations, are presented for the first time. Moreover, detail investigations are carried out using International Reference Ionosphere (IRI) model as well as the electron density from Ionosonde and Global Positioning System (GPS) Occultation Experiment (GOX) onboard FORMOSAT-3/COSMIC satellite, to understand the conditions that favor the propagation of MSTID to the latitude of Taiwan.

Thermal/optical methods have been widely used for quantifying total carbon (TC), organic carbon (OC), and elemental carbon (EC) in ambient and source particulate samples. Thermally defined carbon fractions have been used for source identification. Temperature precision in thermal carbon analysis is critical to the allocation of carbon fractions. The sample temperature is determined by a thermocouple, which is usually located in the oven near the sample. Sample and thermocouple temperature may differ owing to different thermal properties between the sample filter punch and the thermocouple, or inhomogeneities in the heating zone. Quick-drying temperature-indicating liquids (Tempil Inc., South Plainfield, NJ) of different liquefying points are used as temperature calibration standards. These consist of chemicals that change their appearance at specific temperatures and can be optically monitored to determine the sample temperature. Temperature measures were evaluated for three different models of carbon analyzers. Sample temperatures were found to differ from sensor temperatures by 10 to 50°C. Temperature biases of 14 to 22°C during thermal analysis were found to change carbon fraction measurements. The temperature indicators allow calibration curves to be constructed that relate the sample temperature to the temperature measured by a thermocouple.

Continuous measurements of atmospheric organic and elemental carbon (OC and EC) were taken during the high-pollution fall and winter seasons at Xi'an, Shaanxi Province, China from September 2003 through February 2004. Battery-powered mini-volume samplers collected PM2.5 samples daily and PM10 samples every third day. Samples were also obtained from the plumes of residential coal combustion, motor-vehicle exhaust, and biomass burning sources. These samples were analyzed for OC/EC by thermal/optical reflectance (TOR) following the Interagency Monitoring of Protected Visual Environments (IMPROVE) protocol. OC and EC levels at Xi'an are higher than most urban cities in Asia. Average PM2.5 OC concentrations in fall and winter were 34.1±18.0 μg m−3 and 61.9±;33.2 μg m−3, respectively; while EC concentrations were 11.3±6.9 μg m−3 and 12.3±5.3 μg m−3, respectively. Most of the OC and EC were in the PM2.5 fraction. OC was strongly correlated (R>0.95) with EC in the autumn and moderately correlated (R=0.81) with EC during winter. Carbonaceous aerosol (OC×1.6+EC) accounted for 48.8%±10.1% of the PM2.5 mass during fall and 45.9±7.5% during winter. The average OC/EC ratio was 3.3 in fall and 5.1 in winter, with individual OC/EC ratios nearly always exceeding 2.0. The higher wintertime OC/EC corresponded to increased residential coal combustion for heating. Total carbon (TC) was associated with source contributions using absolute principal component analysis (APCA) with eight thermally-derived carbon fractions. During fall, 73% of TC was attributed to gasoline engine exhaust, 23% to diesel exhaust, and 4% to biomass burning. During winter, 44% of TC was attributed to gasoline engine exhaust, 44% to coal burning, 9% to biomass burning, and 3% to diesel engine exhaust.

Open burning of household and municipal solid waste is a frequent practice in many developing countries. Due to limited resources for collection and proper disposal, solid waste is often disposed of in neighborhoods and open-burned in piles to reduce odors and create space for incoming waste. Emissions from these ground-level and low-temperature burns cause air pollution, leading to adverse health effects among community residents. In this study, laboratory combustion experiments were conducted to characterize gas and particle emissions from 10 waste categories representative of those burned in South Africa: paper, leather/rubber, textiles, plastic bottles, plastic bags, vegetation (with three different moisture content levels), food discards, and combined materials. Carbon dioxide (CO2) and carbon monoxide (CO) were measured in real time to calculate modified combustion efficiencies (MCEs). MCE is used along with video observations to determine fuel-based emission factors (EFs) during flaming and smoldering phases as well as the entire combustion process. Fuel elemental composition and moisture content have strong influences on emissions. Plastic bags have the highest carbon content and the highest combustion efficiency, leading to the highest EFs for CO2. Textiles have the highest nitrogen and sulfur content, resulting in the highest EFs for nitrogen oxides (NOx) and sulfur dioxide (SO2). Emissions are similar for vegetation with 0 % and 20 % moisture content; however, EFs for CO and particulate matter (PM) from the vegetation with 50 % moisture content are 3 and 20–30 times, respectively, those from 0 % and 20 % moisture content. This study also shows that neglecting carbon in the ash and PM can lead to significant overestimation of EFs. Results from this study are applicable to emission inventory improvements as well as air quality management to assess the health and climate effects of household-waste open burning.

Biomass burning (BB) is a significant source of dicarboxylic acids (diacids) and related compounds that play important roles in atmospheric chemistry and climate change. In this study, a combustion chamber and oxidation flow reactor were used to generate fresh and aged aerosols from burned rice, maize and wheat straw to investigate atmospheric aging and the stable carbon isotopic (δ13C) composition of these emissions. Succinic acid (C4) was the most abundant species in fresh samples, while oxalic acid (C2) became dominant after atmospheric aging. Of all diacids, C2 had the highest aged to fresh emission ratios (A/F), suggesting that C2 is largely produced through secondary photochemical processes. Compared with fresh samples, the emission factors of ketocarboxylic acids and α-dicarbonyls increased after 2 d but decreased after 7 d aging, indicating a short residence time and further atmospheric degradation from 2 to 7 d. The δ13C values of C2 for aged biomass samples were higher than those of urban aerosols but lower than marine or mountain aerosols, and the δ13C values of C2 became isotopically heavier during aging. Relationships between the reduction in volatile organic compounds (VOCs), such as toluene, benzene and isoprene, and increase in diacids after 2 d aging indicate that these VOCs led to the formation of diacids. However, no significant correlation was found between decreases in VOCs and increases in 7 d aged diacids. In addition, the A/F of C2 was 50.8 at 2 d and 64.5 at 7 d, indicating that the conversion of VOCs to C2 was almost completed within 2 d. For the longer aging times, the particulate-phase compounds may undergo further degradation in the oxidation processes.

Carbonaceous aerosol is a major contributor to the total aerosol load and being monitored by diverse measurement approaches. Here, 10 years (2005–2015) of continuous carbonaceous aerosol measurements collected at the Centre of Atmospheric Research Experiments (CARE) in Egbert, Ontario, Canada, on quartz-fiber filters by three independent networks (Interagency Monitoring of Protected Visual Environments, IMPROVE; Canadian Air and Precipitation Monitoring Network, CAPMoN; and Canadian Aerosol Baseline Measurement, CABM) were compared. Specifically, the study evaluated how differences in sample collection and analysis affected the concentrations of total carbon (TC), organic carbon (OC), and elemental carbon (EC). Results show that different carbonaceous fractions measured by various networks were consistent and comparable in general among the three networks over the 10-year period, even with different sampling systems/frequencies, analytical protocols, and artifact corrections. The CAPMoN TC, OC, and EC obtained from the DRI model 2001 thermal–optical carbon analyzer following the IMPROVE-TOR protocol (denoted as DRI-TOR) method were lower than those determined from the IMPROVE_A TOR method by 17 %, 14 %, and 18 %, respectively. When using transmittance for charring correction, the corresponding carbonaceous fractions obtained from the Sunset-TOT were lower by as much as 30 %, 15 %, and 75 %, respectively. In comparison, the CABM TC, OC, and EC obtained from a thermal method, EnCan-Total-900 (ECT9), were higher than the corresponding fractions from IMPROVE_A TOR by 20 %–30 %, 0 %–15 %, and 60 %–80 %, respectively. Ambient OC and EC concentrations were found to increase when ambient temperature exceeded 10 ∘C. These increased ambient concentrations of OC during summer were possibly attributed to secondary organic aerosol (SOA) formation and forest fire emissions, while elevated EC concentrations were potentially influenced by forest fire emissions and increased vehicle emissions. Results also show that the pyrolyzed organic carbon (POC) obtained from the ECT9 protocol could provide additional information on SOA although more research is still needed.

Residential solid biomass cookstoves are important sources of aerosol emissions in India. Cookstove emissions rates are largely based on laboratory experiments conducted using the standard water-boiling test, but real-world emissions are often higher owing to different stove designs, fuels, and cooking methods. Constraining mass emissions factors (EFs) for prevalent cookstoves is important because they serve as inputs to bottom-up emissions inventories used to evaluate health and climate impacts. Real-world EFs were measured during winter 2015 for a traditional cookstove (chulha) burning fuel wood, agricultural residue, and dung from different regions of India. Average (±95 % confidence interval) EFs for fuel wood, agricultural residue, and dung were (1) PM2.5 mass: 10.5 (7.7–13.4) g kg−1, 11.1 (7.7–15.5) g kg−1, and 22.6 (14.9–32.9) g kg−1, respectively; (2) elemental carbon (EC): 0.9 (0.6–1.4) g kg−1, 1.6 (0.6–3.0) g kg−1, and 1.0 (0.4–2.0) g kg−1, respectively; and (3) organic carbon (OC): 4.9 (3.2–7.1) g kg−1, 7.0 (3.5–12.5) g kg−1, and 12.9 (4.2–15.01) g kg−1, respectively. The mean (±95 % confidence interval) OC ∕ EC mass ratios were 6.5 (4.5–9.1), 7.6 (4.4–12.2), and 12.7 (6.5–23.3), respectively, with OC and EC quantified by the IMPROVE_A thermal-optical reflectance protocol. These real-world EFs are higher than those from previous laboratory-based measurements. Combustion conditions have larger effects on EFs than the fuel types. We also report the carbon mass fractions of our aerosol samples determined using the thermal-optical reflectance method. The mass fraction profiles are consistent between the three fuel categories but markedly different from those reported in past literature – including the source profiles for wood stove PM2.5 emissions developed as inputs to receptor modeling studies conducted by the Central Pollution Control Board of India. Thermally stable OC (OC3 in the IMPROVE_A protocol) contributed nearly 50 % of the total carbon mass for emissions from all fuels.

Source apportionment and characterization of primary and secondary aerosols remains a challenging research field. In particular, the organic composition of primary particles and the formation mechanism of secondary organic aerosols (SOAs) warrant further investigations. Progress in this field is strongly connected to the development of novel analytical techniques. In this study an off-line aerosol mass spectrometric technique based on filter samples, a hyphenated thermal–optical analyzer photo-ionization time-of-flight mass spectrometer (PI-TOFMS) system, was developed. The approach extends the capability of the widely used particulate matter (PM) carbon analysis (for elemental / organic carbon, EC / OC) by enabling the investigation of evolved gaseous species with soft and selective (resonance enhanced multi-photon ionization, REMPI) and non-selective photo-ionization (single-photon ionization, SPI) techniques. SPI was tuned to be medium soft to achieve comparability with results obtained by the electron ionization aerosol mass spectrometer (AMS). Different PM samples including wood combustion emission samples, smog chamber samples from the reaction of ozone with different SOA precursors, and ambient samples taken at Ispra, Italy, in winter as well as in summer were tested. The EC / OC–PI-TOFMS technique increases the understanding of the processes during thermal–optical analysis and identifies marker substances for the source apportionment. Composition of oligomeric or polymeric species present in PM can be investigated by the analysis of the thermal breakdown products. In the case of wood combustion, in addition to the well-known markers at m/z ratios of 60 and 73, two new characteristic masses (m/z 70 and 98) have been revealed as potentially linked to biomass burning. All four masses were also the dominant signals in an ambient sample taken in winter time in Ispra, Italy, confirming the finding that wood burning for residential heating is a major source of PM in winter at this location. The summer sample from the same location showed no influence of wood burning, but seems to be dominated by SOAs, which was confirmed from the comparison with chamber experiment samples. The experiments conducted with terpenes as precursors showed characteristic masses at m/z 58 and 82, which were not observable in any other emission samples and could serve as a marker for SOA from terpenes.

Open biomass burning is an important source of air pollution in China and globally. Joint observations of air pollution were conducted in five cities (Shanghai, Hangzhou, Ningbo, Suzhou and Nanjing) of the Yangtze River delta, and a heavy haze episode with visibility 2.9–9.8 km was observed from 28 May to 6 June 2011. The contribution of biomass burning was quantified using both ambient monitoring data and the WRF/CMAQ (Weather Research and Forecasting (WRF) and Community Multiscale Air Quality (CMAQ)) model simulation. It was found that the average and maximum daily PM2.5 concentrations during the episode were 82 and 144 μgm−3, respectively. Weather pattern analysis indicated that stagnation enhanced the accumulation of air pollutants, while the following precipitation event scavenged the pollution. Mixing depth during the stagnant period was 240–399 m. Estimation based on observation data and CMAQ model simulation indicated that biomass open burning contributed 37% of PM2.5, 70% of organic carbon and 61% of elemental carbon. Satellite-detected fire spots, back-trajectory analysis and air quality model simulation were integrated to identify the locations where the biomass was burned and the pollutants transport. The results suggested that the impact of biomass open burning is regional, due to the substantial inter-province transport of air pollutants. PM2.5 exposure level could be reduced 47% for the YRD region if complete biomass burning is forbidden and significant health benefit is expected. These findings could improve the understanding of heavy haze pollution, and suggest the need to ban open biomass burning during post-harvest seasons.

We present the laboratory and ambient photoacoustic (PA) measurement of aerosol light absorption coefficients at ultraviolet wavelength (i.e., 355 nm) and compare with measurements at 405, 532, 870, and 1047 nm. Simultaneous measurements of aerosol light scattering coefficients were achieved by the integrating reciprocal nephelometer within the PA's acoustic resonator. Absorption and scattering measurements were carried out for various laboratory-generated aerosols, including salt, incense, and kerosene soot to evaluate the instrument calibration and gain insight on the spectral dependence of aerosol light absorption and scattering. Ambient measurements were obtained in Reno, Nevada, between 18 December 2009 and 18 January 2010. The measurement period included days with and without strong ground level temperature inversions, corresponding to highly polluted (freshly emitted aerosols) and relatively clean (aged aerosols) conditions. Particulate matter (PM) concentrations were measured and analyzed with other tracers of traffic emissions. The temperature inversion episodes caused very high concentration of PM2.5 and PM10 (particulate matter with aerodynamic diameters less than 2.5 μm and 10 μm, respectively) and gaseous pollutants: carbon monoxide (CO), nitric oxide (NO), and nitrogen dioxide (NO2). The diurnal change of absorption and scattering coefficients during the polluted (inversion) days increased approximately by a factor of two for all wavelengths compared to the clean days. The spectral variation in aerosol absorption coefficients indicated a significant amount of absorbing aerosol from traffic emissions and residential wood burning. The analysis of single scattering albedo (SSA), Ångström exponent of absorption (AEA), and Ångström exponent of scattering (AES) for clean and polluted days provides evidences that the aerosol aging and coating process is suppressed by strong temperature inversion under cloudy conditions. In general, measured UV absorption coefficients were found to be much larger for biomass burning aerosol than for typical ambient aerosols.

Aerosol samples were collected at a pasture site in the Amazon Basin as part of the project LBA-SMOCC-2002 (Large-Scale Biosphere-Atmosphere Experiment in Amazonia – Smoke Aerosols, Clouds, Rainfall and Climate: Aerosols from Biomass Burning Perturb Global and Regional Climate). Sampling was conducted during the late dry season, when the aerosol composition was dominated by biomass burning emissions, especially in the submicron fraction. A 13-stage Dekati low-pressure impactor (DLPI) was used to collect particles with nominal aerodynamic diameters (Dp) ranging from 0.03 to 0.10 μm. Gravimetric analyses of the DLPI substrates and filters were performed to obtain aerosol mass concentrations. The concentrations of total, apparent elemental, and organic carbon (TC, ECa, and OC) were determined using thermal and thermal-optical analysis (TOA) methods. A light transmission method (LTM) was used to determine the concentration of equivalent black carbon (BCe) or the absorbing fraction at 880 nm for the size-resolved samples. During the dry period, due to the pervasive presence of fires in the region upwind of the sampling site, concentrations of fine aerosols (Dp−3) were higher than coarse aerosols (Dp> 2.5 μm: 4.1 μg m−3). Carbonaceous matter, estimated as the sum of the particulate organic matter (i.e., OC × 1.8) plus BCe, comprised more than 90% to the total aerosol mass. Concentrations of ECa (estimated by thermal analysis with a correction for charring) and BCe (estimated by LTM) averaged 5.2 ± 1.3 and 3.1 ± 0.8 μg m−3, respectively. The determination of EC was improved by extracting water-soluble organic material from the samples, which reduced the average light absorption Ångström exponent of particles in the size range of 0.1 to 1.0 μm from >2.0 to approximately 1.2. The size-resolved BCe measured by the LTM showed a clear maximum between 0.4 and 0.6 μm in diameter. The concentrations of OC and BCe varied diurnally during the dry period, and this variation is related to diurnal changes in boundary layer thickness and in fire frequency.

Observations at national parks and other remote sites show that average elemental carbon and fine particle mass concentrations in the United States both decreased by over 25 % between 1990 and 2004. Percentage decreases in elemental carbon were much larger in winter than in summer. These data suggest that emissions controls have been effective in reducing particulate concentrations not only in polluted areas but also across the United States. Despite the reduction in elemental carbon, the simultaneous decrease in non-absorbing particles implies that the overall radiative forcing from these changes was toward warming. The use of a 2005 instead of 1990 as a baseline for climate-relevant emissions from the United States would imply a significantly lower baseline for aerosol emissions. The use of older data will overestimate the possibility for future reductions in warming due to black carbon controls.

Carbon (C) and nitrogen (N) released from biomass burning have multiple effects on the Earth's biogeochemical cycle, climate change, and ecosystem. These effects depend on the relative abundances of C and N species emitted, which vary with fuel type and combustion conditions. This study systematically investigates the emission characteristics of biomass burning under different fuel moisture contents, through controlled burning experiments with biomass and soil samples collected from a typical alpine forest in North America. Fuel moisture in general lowers combustion efficiency, shortens flaming phase, and introduces prolonged smoldering before ignition. It increases emission factors of incompletely oxidized C and N species, such as carbon monoxide (CO) and ammonia (NH3). Substantial particulate carbon and nitrogen (up to 4 times C in CO and 75% of N in NH3) were also generated from high-moisture fuels, maily associated with the pre-flame smoldering. This smoldering process emits particles that are larger and contain lower elemental carbon fractions than soot agglomerates commonly observed in flaming smoke. Hydrogen (H)/C ratio and optical properties of particulate matter from the high-moisture fuels show their resemblance to plant cellulous and brown carbon, respectively. These findings have implications for modeling biomass burning emissions and impacts.

Sources of PM2.5 at the Fresno Supersite during high PM2.5 episodes occurring from 15 December 2000–3 February 2001 were estimated with the Chemical Mass Balance (CMB) receptor model. The ability of source profiles with organic markers to distinguish motor vehicle, residential wood combustion (RWC), and cooking emissions was evaluated with simulated data. Organics improved the distinction between gasoline and diesel vehicle emissions and allowed a more precise estimate of the cooking source contribution. Sensitivity tests using average ambient concentrations showed that the gasoline vehicle contribution was not resolved without organics. Organics were not required to estimate hardwood contributions. The most important RWC marker was the water-soluble potassium ion. The estimated cooking contribution did not depend on cholesterol because its concentrations were below the detection limit in most samples. Winter time source contributions were estimated by applying the CMB model to individual and average sample concentrations. RWC was the largest source, contributing 29–31% of measured PM2.5. Hardwood and softwood combustion accounted for 16–17% and 12–15%, respectively. Secondary ammonium nitrate and motor vehicle emissions accounted for 31–33% and 9–15%, respectively. The gasoline vehicle contribution (3–10%) was comparable to the diesel vehicle contribution (5–6%). The cooking contribution was 5–19% of PM2.5. Fresno source apportionment results were consistent with those estimated in previous studies.

To determine the levels and variations of carbonaceous aerosol in Hong Kong, PM2.5 and PM10 samples were collected by high volume (Hi-vol) samplers at three monitoring stations (representing middle-scale roadside, urban-, and regional-scale environments) during winter (November 2000 to February 2001) and summer (June 2001 to August 2001) periods. The highest concentrations of organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC) were found at the middle-scale roadside site with the lowest at the regional-scale site. The percentages of WSOC in total carbon at these sites were inversely correlated with their concentrations (i.e., the highest percentages of WSOC were observed at the regional-scale site). A high WSOC fraction may be associated with aged aerosol because of the secondary formation by photochemical oxidation of organic precursors of anthropogenic pollutants during transport. The annual average of isotope abundances (δ13C) of OC and EC were –26.9±0.5‰ and –25.6±0.1‰, respectively. There were no notable differences for seasonal distributions of carbon isotopic composition, consistent with motor vehicle emissions being the main source contributors of carbonaceous aerosol in Hong Kong. OC 13C abundances at the regional-scale site were higher than those at the middle-scale roadside and urban sites, consistent with secondary organic aerosols of biogenic origin.