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The health effects of atmospheric particulate matter (PM) have become a major environmental concern in urban areas. Most PM studies are mainly designed to measure the “ambient” or “emitted” concentrations of PM. Some studies are specifically designed to address exposure to PM for pedestrians and/or commuters on-board vehicles or at bus stops, but less attention is paid to the exposure during physical exercise such as jogging. To this end, concentrations of both fine particulate matter (PM2.5) and black carbon (BC) were measured along three jogging trails in the densely populated city Macau in China. The three jogging trails include the campus of University of Macau (UM), Guia Municipal Park (GP), and Saivan Lake (SL). In our measurements, PM2.5 and BC ranged from 2.9 to 84.1 and 0.4–19.5 μg/m³, respectively. BC/PM2.5 ratio ranged from 0.016 to 0.448. Among all three jogging trails, the highest BC concentration was found at SL (19.5 μg/m³), and the highest PM2.5 concentration was found at UM (84.1 μg/m³). On the contrary, the BC and PM2.5 concentrations at the elevated (about 50 m above sea level) GP trail were lower than those at the other two jogging trails. BC and PM2.5 concentrations were generally lower in the night loops (21:30–23:00) than those in the morning loops (07:30–09:00), which coincide with morning rush hours, with only a few exceptions. The difference in geographical locations also affects the BC and PM2.5 concentrations measured, with locations near bus terminals, busy roads, or with congested street canyons having higher concentrations. Doses of BC and PM2.5 after 60 min of exposure during typical jogging exercise are also estimated to evaluate the exposure to PM pollution at these three jogging trails when exercising. The results from the current studies provide information both on personal choice for the time/venue for jogging exercise and on future abatement policy to mitigate such risks of exposure to BC and PM2.5.

The toxic effects of lead on human health and the environment have long been a focus of research. To explore sources of lead in Guangzhou, China, we investigated atmospheric lead-containing particles (LCPs) during wintertime using a single particle aerosol mass spectrometer (SPAMS). Based on mass spectral features, LCPs were classified into eight major particle types, including Pb-Cl and Pb-Cl-Li (coal combustion and waste incineration), Pb-Cl-EC and Pb-Cl-OC (diesel trucks and coal combustion), Pb-Cl-Fe (iron and steel industry), Pb-Cl-AlSi (dust), Pb-Sec (secondary formation), and Pb-Cl-Zn (industrial process); these sources (in parentheses) were identified by comparing atmospheric LCP mass spectra with authentic Pb emission source mass spectra. Sampling periods with LCP number fractions (NFs) more than three times the average LCP NF (APF = 4.35%) and below the APF were defined as high LCP NF periods (HLFPs: H1, H3, and H5) and low LCP NF APF periods (LLFPs: L2 and L4), respectively. Diurnal patterns and high Pb-Sec content during LLFPs indicate that photochemical activity and heterogeneous reactions may have controlled Pb-Sec particle formation. The inverse Pb-Cl and Pb-Sec particle diurnal trends during LLFPs suggest the replacement of Cl by sulfate and nitrate. On average over the five periods, ~ 76% of the LCPs likely arose from coal combustion and/or waste incineration, which were dominant sources during all five periods, followed by diesel trucks during LLFPs and iron- and steel-related sources during HLFPs; HLFP LCPs arose mainly from primary emissions. These results can be used to more efficiently control Pb emission sources and prevent harm to human and environmental health from Pb toxicity.

Interest in exhaled breath has grown considerably in recent years, as breath biosampling has shown promise for non-invasive disease diagnosis, therapeutic drug monitoring, and environmental exposure. Real time breath analysis can be accomplished via direct online mass spectrometry (MS)-based methods, which can provide more accurate and detailed data and an enhanced understanding of the temporal evolution of exhaled VOCs in the breath; however, the complicated chemical composition and large raw datasets involved in breath analysis have hindered the discovery of sources contributing to the exhaled VOCs. The positive matrix factorization (PMF) receptor model has been widely used for source apportionment in atmospheric studies. Since the exhaled VOCs contain compounds from various sources, such as alveolar air, mouth air and respiratory dead-space air, PMF may be also helpful for source apportionment of exhaled VOCs in the breath. Thus, this study explores the application of PMF in the pretreatment of direct breath measurement data. The results indicate that (i) endogenous compounds and background contaminants sources can be readily distinguished by PMF in data obtained from replicate measurements of human exhaled breath at single time points (~30 s/measurement), which may benefit both exhalome investigations and the identification of exposure biomarkers; (ii) sources resolved from online measurement data collected over longer periods (1.5 h) can be used to isolate the evolution of exhaled VOCs and investigate processes such as the pharmacokinetics of ketamine and its major metabolites. Therefore, PMF has shown promise for both data processing and subsequent data mining for the ambient MS-based breath analysis.

Atmospheric particulate matter (PM) pollution has become a major health threat accompanying the rapid economic development in China. For decades, filter-based offline chemical analyses have been the most widely adopted means to investigate PM and have provided much information for understanding this type of pollution in China. However, offline analyses have low time resolutions and the chemical information thus obtained fail to reflect the dynamic nature of the sources and the rapid processes leading to the severe PM pollution in China. In recent years, advances in real-time PM chemical characterization have created a new paradigm for PM studies in China. In this review, we summarize those advances, focusing on the most widely used mass spectrometric and ion chromatographic techniques. We describe the findings from those studies in terms of spatiotemporal variabilities, degree of neutralization and oxygenation, source apportionment, secondary formation, as well as collocated measurements of the chemical and physical (hygroscopic and optical) properties of PM. We also highlight the new insights gained from those findings and suggest future directions for further advancing our understanding of PM pollution in China via real-time chemical characterization.

A sampling campaign was conducted at an urban roadside site in Hong Kong from Nov. to Dec. in 2017 using a suite of state-of-the-art instruments to monitor compositions of non-refractory sub-micron particulate matter (NR-PM1) and gaseous pollutants. Results showed that the average NR-PM1 concentration was 26.1 ± 0.7 μg/m3 (average ± 95% confidence interval) and organic aerosol (OA) contributed the most to NR-PM1 with a proportion of 57.7 ± 0.2%. The aerosol size distributions of bulk composition of NR-PM1 presented a peak at ~600 nm with internal mixtures of the organic and inorganic components, while there were a larger proportion of primary organic particles at C 3 H 3 O + / C 3 H 5 O + (2.01 ± 0.01) and the opposite pattern of C 3 H 3 O + / C 3 H 5 O + to Ox during daytime hours suggested that the COA was oxidized to some extent when transported to the site. The findings implied that cooking activities are a significant source of organic aerosols in Hong Kong, even at a busy road. Control measures should focus on both cooking and traffic emissions in Hong Kong.

Clean surface of graphene was obtained at 500 °C and characterized by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). In the XPS C1s spectrum of graphene, besides an asymmetric sp2 carbon peak and a π-π∗ shake-up peak appeared, an additional sp3 carbon peak representing sp3 defects was also present. In the ToF-SIMS positive ion spectrum of graphene, a series of CxH2+ ions originated from the defects of graphene was found. To determine the origin of the CxH2+ ions, defects were created on the surface of nearly defect-free highly oriented pyrolytic graphite (HOPG) by bombarding it with a Cs+ ion beam at various sputtering doses. A detailed examination of the positive ion spectra of ion-bombarded HOPG surfaces reveals the presence of the CxH2+ ions, confirming that these CxH2+ ions, which came from the defects created on the sputtered HOPG surfaces, are similar to the defects present on graphene surface. A sp3 carbon peak at 285.3 eV, representing sp3 defects appeared in the XPS spectra of sputtered HOPG samples, confirms that the surface of the sputtered HOPG is similar to that of graphene. Fragmentation mechanisms of selected ions in the ToF-SIMS spectra of graphene and HOPG were proposed.

We have performed long-term measurements of organic carbon (OC) and elemental carbon (EC) in atmospheric aerosols at Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS). Large-scale East Asian continental outflows of aerosols have frequently been observed at CHAAMS in both winter and spring, but large-scale air pollution (LSP) events in winter have not yet been described in the literature. Examination of PM 2.5 in LSP events showed that it consisted mainly of carbonaceous aerosols and sulfate. We compared OC and EC concentrations measured at CHAAMS during LSP events with those measured at the same time in East Asian cities, and with concentrations measured at CHAAMS during an Asian dust event in spring 2006. The maximum OC and EC concentrations at Cape Hedo during LSP events were comparable to those at China Atmosphere Watch Network sites in China. The average OC concentration was also similar to concentrations measured at urban sites in Taipei (Taiwan), Seoul (Korea), and Tokyo (Japan); EC, however, was several times lower at Cape Hedo than EC concentrations at these urban sites. We identified three types of air masses associated with LSP events: Type 1, a polluted air mass composed of freshly emitted pollutants; Type 2, an air mass that underwent photochemical aging during transport from China to Okinawa; and Type 3, an air mass that was almost fully aged in China before being transported to Japan. Simulations of LSP events with a 3-D chemical transport model (Chemical Weather Forecasting System) indicated that Type 1 air masses were associated with “cone type” transport in a low-pressure system, and Type 2 air masses were associated with “giant puff type” transport by a migratory high-pressure system. Generally speaking, air pollutants are transported from China to CHAAMS in winter in association with the north or northwest monsoon. High levels of air pollutants in China in winter are due to higher emissions and poorer dispersion because of the low boundary layer height and low wind speeds. Our results suggest that LSP events occur when a cold front forms under accumulated air pollutants. The mass contribution of carbonaceous materials to PM 2.5 during the LSP event in winter 2008 was 36%, much larger than the contribution of 19% during the spring 2006 dust event.

Single Particle Aerosol Mass Spectrometers (SPAMS) have been increasingly deployed for aerosol studies in Asia. To date, SPAMS is most often used to provide unscaled information for both the size and chemical composition of individual particles. The instrument's lack of accuracy is primarily due to only a fraction of particles being detected after collection, and the instrumental sensitivity is un-calibrated for various chemical species in mixed ambient aerosols. During a campaign from January to April 2013 at a coastal site in Hong Kong, the particle number information and ion intensity of major PM 2.5 components collected by SPAMS were scaled by comparing with collocated bulk PM 2.5 measurements of hourly or higher resolution. The bulk measurements include PM 2.5 mass by a SHARP 5030 Monitor, major ions by a Monitor for Aerosols & Gases in ambient Air (MARGA), and organic carbon (OC) and elemental carbon (EC) by a Sunset OCEC analyzer. During the data processing, both transmission efficiency (scaled with the Scanning Mobility Particle Sizer) and hit efficiency conversion were considered, and component ion intensities quantified as peak area (PA) and relative peak area (RPA) were analyzed to track the performance. The comparison between the scaled particle mass assuming a particle density of 1.9 g cm −3 from SPAMS and PM 2.5 concentration showed good correlation (R 2 = 0.81) with a slope of 0.814 ± 0.004. Regression analysis results suggest an improved scaling performance using RPA compared with PA for most of the major PM 2.5 components, including sulfate, nitrate, potassium, ammonium, OC and EC. Thus, we recommend preferentially scaling these species using the RPA. For periods of high K + concentrations (>1.5 μg m −3 ), under-estimation of K + by SPAMS was observed due to exceeding the dynamic range of the acquisition board. When only applying the hit efficiency correction, data for sulfate, nitrate, ammonium, potassium and OC were in reasonably good correlation (R 2 = 0.56–0.79) with the bulk measurements, suggesting semi-quantified data by the hit efficiency correction can be utilized when transmission efficiency correction is not available. More inter-comparisons of this type are needed to assess the inter-instrument variability among different SPAMS instruments.

Many field studies have investigated the formation mechanisms of organic aerosol (OA) based on bulk analysis, yet the source and formation process of individual organic particles may be quite different due to the diversity of chemical composition and mixing state in single particles. Here we present the observation results of chemical composition and mixing state of carbonaceous single particles at an urban site in Guangzhou. The carbonaceous particles accounted for 74.6% of the total detected single particles, and were grouped into four types including elemental carbon-aged (EC-aged), elemental and organic carbon (ECOC), organic carbon-rich (OC-rich) and secondary ions-rich (SEC) particles. The formation of EC-aged particles was closely associated with the absorption of organics onto fresh EC particles from primary sources, and the further enrichment of organics in EC-aged particles resulted in the production of ECOC particles. In the daytime OC-rich and SEC particles were mainly produced from the photochemical reactions, while in the nighttime their sharp increases were found along with the enrichment of nitrate and organic nitrogen fragments, suggesting the heterogeneous formation of nitrate and organic nitrogen in OC-rich and SEC particles. The production rates of carbonaceous particles were also investigated in an episodic event, and the EC-aged particles showed the highest production rate compared to the other carbonaceous particles both in the daytime and nighttime, suggesting a significant role of EC in the formation and aging process of carbonaceous particles. The results from this work have revealed different formation processes and production rates of carbonaceous particles due to their diversity in mixing state, providing further insights into the formation mechanisms of OA in field studies.

The cleanliness of the surface of graphene is important for its proper functioning in devices and sensors. Impurities including residual poly(methyl methacrylate) (PMMA) and hydrocarbon contaminants can alter its electronic and chemical properties. In this study, we used two surface-sensitive techniques, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), to monitor the chemical composition of the surface of graphene after washing it with acetone and annealing at high temperatures. The concentration of residual PMMA and hydrocarbon contaminants decreased as the annealing temperature increased. The atomic ratio of sp3 carbons to sp2 carbons of a clean graphene surface determined using XPS can be used to estimate the amounts of sp3 defects in graphene. ToF-SIMS spectra indicate that residual PMMA was removed from the surface of graphene at 400 °C, while hydrocarbon contaminants required a higher temperature of 500 °C to remove. In ToF-SIMS spectra obtained at 500 °C, the characteristic ions for graphene, which are related to cleavage of ring structure, include Cx+ (x = 1, 2, 3…), CxH+ and CxH2+ as well as Cx− and CxH−. For the first time, we developed a process to produce a very clean graphene surface which was verified by ToF-SIMS and XPS analyses.

Secondary organic aerosols (SOAs) are some of the most important components of aerosol over south China, especially, in the Pearl River Delta (PRD). However, traditional SOA simulations usually result in severe underestimates because of the limited understanding of SOA formation. Furthermore, the source contribution features of SOAs in the PRD region remain poorly understood. In this study, a 1-D Volatility Basis-Set (VBS) scheme, and a 1.5-D VBS scheme are implemented in the Comprehensive Air Quality Model with Extensions (CAMx) to improve the poor model performance with the traditional SOA scheme, and a 1-year simulation of SOAs over the PRD region are conducted for each scheme. A comparison of the simulated results with the observational data reveals that the 1-D VBS scheme shows better model performance for SOA simulation in both absolute concentrations and time series agreement, which suggests that the VBS scheme effectively reduces the underestimation in SOA simulations. The missing processes [oxidation of intermediate-volatility organic compound (IVOC)/semi-volatility organic compound (SVOC)] contribute to SOA concentration of 4–7 μg/m3, (relatively as high as about 400–500%) at the center of the PRD region and of 1–2 μg/m3 (relatively about 100–300%) in the rural areas of the PRD region. By implementing the SOA source apportionment technology (SSAT) with 1-D VBS scheme in CAMx, the source contributions from geographic source regions and source types are discussed. The results at a rural supersite (HKUST) with SOA observation data show that the super-regional transport accounts for 56.5%–76.9% of SOA concentration, PRD region contribution accounts for 13.1%–32.7% of SOA concentration. Of the SOAs from the PRD region, mobile emission takes the largest contribution among the emissions categories, which suggests that the anthropogenic emission significantly contribute to the SOAs over the PRD region. Our results also indicate that the applications of VBS models and SSAT algorithm provide new insights into policy implications for improving local and regional air quality.

In many cities worldwide, modern fleets have been introduced to reduce gaseous and particle emissions from city buses. To date, most emission studies are limited to a few vehicles, making a statistically significant assessment of control options difficult, especially under real-world driving conditions. Exhaust emissions of 234 individual city buses were measured under real-world stop-and-go traffic conditions at a bus stop in Gothenburg, Sweden. The buses comprised models fulfilling Euro III-VI and EEV (Enhanced Environmentally Friendly Vehicle) standards with different engine technologies, fuels, and exhaust after-treatment systems, and also included hybrid-electric buses (HEV). Both gaseous (NOx, CO, HC, and SO2) and size-resolved particle number (PN) and mass (PM) emission factors (EF) were calculated for vehicles using compressed natural gas (CNG), diesel (DSL), Rapeseed Methyl Ester (RME) and Hydro-treated Vegetable Oil (HVO) equipped with various after-treatment technologies, e.g., diesel particulate filter (DPF), selective catalytic reduction (SCR) and exhaust gas recirculation (EGR) systems. The highest median EFPN was obtained from Euro VHEV-HVO-SCR buses (MdEFPN = 18×1014 # kg-1) when their combustion engines were used though 53% of their accelerations were below detection limits indicating the use of their electrical engine. The highest MdEFPM was obtained from the Euro V-DSL-SCR buses (MdEFPM = 150 mg kg-1) and the lowest from EEV-CNG buses (below detection threshold) and Euro VIHEV-HVO- SCR+EGR+DPF buses (MdEFPM = 19 mg kg-1). The highest MdEFNOx was obtained from the Euro V-RME-SCR (MdEFNOx = 30 g kg-1) and Euro VHEV-HVO-SCR buses (MdEFNOx = 24 g kg-1), and the lowest from CNG buses (MdEFNOx = 4.8 g kg-1) and Euro VIHEV-HVO-SCR+EGR+DPF buses (MdEFNOx = 7.4 g kg-1). Hybrid buses can give higher PN emissions compared to traditional diesel engines, likely due to downsized combustion engines. Replacing diesel by biodiesel fuel reduced MdEFPM significantly but increased MdEFNOx which may be due to the higher combustion temperature and oxygen contents of the fuel (for RME). Overall, the EEV-CNG buses performed the best regarding both the MdEF and low contribution to the high emitters. It was also found that a small (5%) proportion of the buses contributed significantly (14-30%) to the total emissions. Identification and monitoring the maintenance of the high emitters in the fleets should be considered for the improvement of air quality. Keywords: Vehicle emissions, Emission factor, Roadside measurement, Hybrid-electric vehicles (HEV), Rapeseed methyl ester (RME), Hydro-treated vegetable oil (HVO), Compressed natural gas (CNG)

A simple computationally efficient model which is capable of replicating the basic features of cardiac cell action potential is proposed. The model is a four-dimensional map and demonstrates good correspondence with real cardiac cells. Various regimes of cardiac activity, which can be reproduced by the proposed model, are shown. Bifurcation mechanisms of these regimes transitions are explained using phase space analysis. The dynamics of 1D and 2D lattices of coupled maps which model the behavior of electrically connected cells is discussed in the context of synchronization theory.

In this study, 24-h PM2.5 samples were collected using Harvard Honeycomb denuder/filter-pack system during different seasons in 2006 and 2007 at an urban site in Guangzhou, China. The particles collected in this study were generally acidic (average strong acidity ([H+]) ~ 70 nmol m− 3). Interestingly, aerosol sulfate was not fully neutralized in the ammonia-rich atmosphere (NH3 ~ 30 ppb) and even when NH4+]/[SO42−] was larger than 2. Consequently, strong acidity ([H+]) as high as 170 nmol m− 3 was observed in these samples. The kinetic rate of neutralization of acidity (acidic sulfate) by ambient ammonia was significantly higher than the rate of formation of ammonium nitrate involving HNO3 and NH3 for [NH4+]/[SO42−] ≤ 1.5 and much lower for NH4+]/[SO42−] > 1.5. Therefore, higher nitrate principally formed via homogeneous gas phase reactions involving ammonia and nitric acid were observed for [NH4+]/[SO42−] > 1.5. However, little nitrate, probably formed via heterogeneous processes e.g. reaction of HNO3 with sea salt or crustal species, was observed for [NH4+]/[SO42−] ≤ 1.5. These demonstrate a clear transition in the pathways of ambient ammonia to form aerosol ammonium at [NH4+]/[SO42−] = 1.5 and evidently explain the observed high acidity due to the unneutralized sulfate in the ammonium-rich aerosol (NH4+]/[SO42−] > 1.5). In fact, the measured acidity was almost similar to the excess acid defined as the acid that remains at [NH4+]/[SO42−] = 1.5 due to the un-neutralized fraction of sulfate ([H+] = 0.5[SO42−]). The presence of high excess acid and ammonium nitrate significantly lowered the deliquescence relative humidity of ammonium sulfate (from 80% to 40%) in the ammonium-rich samples.

Berberine is a natural quaternary ammonium alkaloid used clinically in the chloride salt form for the treatment of diarrhea in many Asian countries. Although the hydrate formation of berberine chloride (BCl) is well documented, the associated mechanism and implications in pharmaceutical formulation have not been studied in detail. In this study, pure BCl dihydrate and BCl tetrahydrate were recrystallized from water and their phase transformation behaviors under defined conditions were inves- tigated. Additionally, pharmacopoeial grade BCl material consisting predominantly of the dihydrate form was examined for potential phase changes when being subjected to a conventional wet granulation procedure for tablet production. Results from solubility measurements, thermal analysis, variable temperature-powder X-ray diffraction (VT- PXRD), and variable temperature-Fourier transform infrared spectroscopy (VT-FTIR) confirmed the solid-state interconversions between the tetrahydrate and dihydrate at 30-498C and between the dihydrate and anhydrate at 70-878C. Consistent with the observed phase changes of the two pure hydrates, wet massing of the pharmacopoeial grade BCl sample led to a thermodynamics-driven transition to the tetrahydrate form at room temperature while subsequent tray drying at 508C caused a reversion back to the dihydrate form. The rate and extent of such hydrate conversion depended largely on the water activity of the granulated powder matrix, which in turn was governed by the particular excipients employed. The present findings have important implications in the regulation of the hydrate forms of BCl in the finished products using specific excipients. 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:1942-1954

Interest in the role and contribution of fungi to atmospheric aerosols and processes grows in the past decade. Substantial data or information such as fungal mass or carbon loading to ambient aerosols is however still lacking. This study aimed to quantify the specific organic carbon content (OC per spore) of eleven fungal species commonly found airborne in the subtropics, and estimated their contribution to organic carbon in aerosols. The specific OC contents showed a size-dependent relationship (r = 0.64, p

As the world gets ready to begin the second decade of the twenty-first century, global climate change has been recognized as a real threat to civilization as we know it. The rapid and successful economic growth of developing nations, particularly China and India, is contributing to climate change. The route to initial economic success in China followed that of the developed nations through the development of industries. Unfortunately, China's environmental protection efforts have not been the same as in developed countries because China is vastly different culturally, socially, economically and, especially, politically from developed nations. When China started to deal with environmental concerns in the late 1970s, it took advantage of the experiences of other countries in establishing environmental standards and regulations, but it did not have a model to follow when it came to implementing these standards and regulations because of the abovementioned differences. Economically, China is transitioning from an agricultural base into an industrial base; however, even now, 60% of the population remains farmers. China has been and still is heavily dependent upon coal for energy, resulting in serious atmospheric particulate pollution. While growing efforts have been expended on the environment, at this juncture of its economic development, China would be well served to revisit the traditional “develop first and clean up later” approach and to find a balance between development and protecting the environment. Against this backdrop, a reflective look of the effort to manage air quality from 1949–2008 (with an emphasis on the past 30 years) in China is presented in this paper. The environmental component of the 2008 Olympic Games is examined as a special example to illustrate the current measures being used to improve air quality in China.

A novel approach to measure the corrosion effects of aerosols as a function of their aerodynamic size and chemical composition was used to study the effects of atmospheric aerosols on mild steel at a rural coastal site. The technique uses collocated micro-orifice uniform deposition impactor samplers to deposit ambient atmospheric particles on exposure steel coupons and collect aerosol samples for ionic analyses. Rusts were found on the coupons with aerosols but none on the blank coupons even the blanks were incubated at the same conditions. FTIR analysis shows that the composition of rusts changes gradually with the aerosol particle size.

Oleanolic acid is a naturally occurring compound used clinically in China for the treatment of hepatitis B. The solid-state chemistry of oleanolic acid recrystallized from a variety of solvents was investigated. Glassy materials were prepared from dichloromethane and chloroform solvents. The oleanolic acid non-solvate prepared from acetone (OA-acetone), and the two oleanolic acid solvates prepared from methanol (OA-methanol) and ethanol (OA-ethanol) were physicochemically characterized. Upon desolvation, both the methanol and ethanol solvates were found to undergo phase transformation to a crystalline phase similar to OA-acetone around 190–195 °C. The PXRD patterns of commercial pharmaceutical grade OA and the OA-methanol were similar, so the commercial form is probably desolvated oleanolic acid methanol solvate.

Water uptake by hygroscopic constituents of atmospheric particles has implications for climate and health. This article focuses on three topics related to calculating particle water uptake. First, an electrodynamic balance (EDB) is used to measure water activity for supersaturated binary KNO3 and KCl solutions. The EDB measurements for KNO3 confirm earlier predictions, while those for KCl confirm earlier measurements. Second, our earlier theory for the variation in mutual deliquescence relative humidity (MDRH) with temperature (T) is extended to double salt systems. The MDRH(T) equation for double salt systems reduces to the earlier equation under some conditions, and predictions for two systems are in reasonable agreement with solubility-based calculations. Finally, an approximate treatment of water uptake in the MDRH region (i.e., near the eutectic) is evaluated, and a new approach is developed that accounts for particle composition. The new approach represents predictions of a benchmark model well and eliminates most of the error associated with the earlier method. Although simple treatments of water uptake near the eutectic may introduce error into equilibrium calculations, their use can sometimes be justified based on inherent limitations of aerosol representations in chemistry-transport models. Results of this study can be used to improve calculations of water content in atmospheric aerosol models.

The effect of H2O on the catalytic reduction of SO2 and NO on La2O2S was studied using temperature-programmed reaction coupled with fast mass spectrometry, powder X-ray diffraction and X-ray photoelectron spectroscopy. It is found that La2O2S can be completely and irreversibly deactivated in the presence of H2O at 700 °C when NO/SO2 is sufficiently high (∼1.0). This is caused by the formation of a layer of inactive and stable La2O2SO4 on the oxysulfide. When NO is absent or NO/SO2 is low (∼0.4), H2O inhibits the reduction and shifts the selectivity from sulfur to H2S. While the causes of the deactivation can be attributed to the Reverse Claus Reaction between H2O and sulfur in the oxysulfide, the competitive hydrolysis of the COS intermediate and the competitive adsorption of H2O, the shift in selectivity to H2S is attributable to the former two factors.

Due to its rapidly expanding economic and industrial developments, China is currently considered to be the engine of the world's economic growth. China's economic growth has been accompanied by an expansion of the urban area population and the emergence of a number of mega cities since the 1990. This expansion has resulted in tremendous increases in energy consumption, emissions of air pollutants and the number of poor air quality days in mega cities and their immediate vicinities. Air pollution has become one of the top environmental concerns in China. Currently, Beijing, Shanghai, and the Pearl River Delta region including Guangzhou, Shenzhen and Hong Kong, and their immediate vicinities are the most economically vibrant regions in China. They accounted for about 20% of the total GDP in China in 2005. These are also areas where many air pollution studies have been conducted, especially over the last 6 years. Based on these previous studies, this review presents the current state of understanding of the air pollution problems in China's mega cities and identifies the immediate challenges to understanding and controlling air pollution in these densely populated areas.

Ammonium nitrate (NH4NO3) is a common constituent of atmospheric particulate pollutants. It exists in five stable polymorphic forms, designated as phases V, IV, III, II and I, below its melting point of 170 °C. In atmospheric research, very little attention has been paid to the solid phase transitions of NH4NO3 because phase IV NH4NO3 particles are stable over a wide range of tropospheric temperatures. Potassium nitrate (KNO3) is often found to co-exist with NH4NO3 in atmospheric aerosols, and it can change the phase transition behaviors of solid NH4NO3 particles. In this study, we investigated the effects of KNO3 on the solid phase transitions of NH4NO3 particles using in situ microscopic Raman spectroscopy. Both the transition path and transition temperature of NH4NO3 single particles (40–700 μm) depend on the KNO3 mass percentage and the particle size. With the addition of KNO3, the IV→II transition, which appears at 52 °C for pure NH4NO3 particles, is replaced by the IV→III transition. The KNO3 mass percentage required for this change in transition path increases with decreasing particle size and the transition temperature decreases with increasing KNO3 mass percentage. At a relatively high mass percentage of KNO3 (⩾7.4 wt%), the KNO3/NH4NO3 mixed particles undergo the IV→III transition under ambient temperatures, or even crystallize directly in phase III from droplets with a further increase in the mass percentage of KNO3. Submicron KNO3/NH4NO3 particles crystallize to phase IV at low KNO3 mass percentages (⩽5.7 wt%) but to phase III at higher KNO3 mass percentages (⩾7.4 wt%). These results suggest that atmospheric solid NH4NO3 particles may exist in phase III and the phase transitions should not be ignored in atmospheric chemical models.

Organic coatings have been commonly found in atmospheric particles and can affect the hygroscopicity of atmospheric particles. In this paper, we examine the effect of a water-insoluble coating on the hygroscopic growth and phase transformation properties of ammonium sulfate ((NH4)2SO4) particles using an electrodynamic balance. Octanoic acid was utilized as a model compound for water-insoluble coating. (NH4)2SO4 particles coated with octanoic acid (9 and 34 wt% octanoic acid) were subjected to relative humidity (RH) cycling to effect two cycles of deliquescence and crystallization. The coated particles exhibited very similar hygroscopicity in two cycles. Octanoic acid was likely present on the surface of solid (NH4)2SO4 cores and (NH4)2SO4 solution droplets throughout the RH cycling. Mass transfer effects were found in the deliquescence and evaporation of the heavily coated (34 wt%) particles. The mass transfer of water molecules to and through octanoic acid coating led to a significant delay in the deliquescence and crystallization of the coated particles, an increase in the observed deliquescence RH and a decrease in observed crystallization RH as compared to that of uncoated (NH4)2SO4 particles. A water accommodation coefficient in the order of 10−3 can explain these observations. When sufficient time was given to ensure equilibrium, the coating had no effect in altering the equilibrium phase transitions and hygroscopic growth of the (NH4)2SO4 particles. It is important to allow sufficient time for equilibration in hygroscopic measurements of aerosol particles coated with organic coatings.

Heterogeneous reactions of organic aerosols with atmospheric oxidants are important processes that affect the hygroscopicity and cloud condensation nuclei (CCN) activities of atmospheric aerosols. An electrodynamic balance (EDB) coupled with Raman spectroscopy is a particularly attractive platform for studying atmospheric reactions since it allows long-duration (days) particle levitation and reactions at atmospherically relevant low-oxidant concentrations can be investigated. In this study, we demonstrated the use of an EDB/Raman system to investigate the heterogeneous reactions of oleic acid particles with ozone (240–280 ppb) under ambient temperatures (22–24 °C) and dry conditions (relative humidity O groups of peroxides and/or ozonides), carbonyl (C O) and hydroxyl (O H) functional characteristics, which are consistent with the predictions of the Criegee mechanism as well as the results reported in the literature. We also confirmed that the Raman signatures of the reacted particles at atmospheric and much higher (>10 ppm) ozone concentrations are practically the same, which provides assurance to the use of elevated ozone concentrations in reaction studies of the oleic acid–ozone system in the literature. The ratio of the percentage of mass loss (due to evaporation of volatile organic products) to the percentage of oleic acid conversion was estimated to be 0.05. Furthermore, the oxidation products that remained in the particle phase were more hygroscopic than were their hydrophobic parent molecules.

Volume concentration data of submicron particles ( 0.1 – 1.0 μ m ) in on-road vehicle plumes ( NO x > 400 ppb ) gathered by the Mobile Real-time Air Monitoring Platform (MAP) on city streets, highways and in tunnels in Hong Kong are used to study the size distributions and growth of vehicular submicron particles due to gas condensation and, particularly, its dependency on ambient temperature. Three particle volume size distributions are observed: a uni-modal distribution with an accumulation mode at 0.2 ± 0.1 μ m , and two bi-modal distributions with a minor mode at 0.2 ± 0.1 μ m and the dominant mode at either 0.5 ± 0.1 or 0.7 ± 0.1 μ m . In tunnels, the ratio of particle volume concentration to black carbon (BC) mass concentration correlates negatively with ambient temperature ( r 2 = 0.57 ) ; the dominant mode tends to be at the large particle size when the temperature is low, and when the temperature is high, the uni-mode appears at the small particle size. Thus temperature seems to exert a significant influence on the condensation growth of fresh vehicular particles. On the other hand, this ratio correlates positively with ambient particle concentrations ( r 2 = 0.35 ) . Ambient particles measured in this study are mostly > 0.3 μ m while BC in vehicle plumes is generally believed to be mainly in the 0.3 μ m size range in the literature. Temperature-dependent gas-condensation competition between fresh BC and ambient particles is suggested to play a role in the bi-modal formation.