Chemical characterization of PM2.5 from a southern coastal city of China:applications of modeling and chemical tracers in demonstrationof regional transport

An intensive sampling campaign of airborne fine particles (PM2.5) was conducted at Sanya, a coastal city in Southern China, from January to February 2012. Chemical analyses and mass reconstruction were used identify potential pollution sources and investigate atmospheric reaction mechanisms. A thermodynamic model indicated that low ammonia and high relative humidity caused the aerosols be acidic and that drove heterogeneous reactions which led to the formation of secondary inorganic aerosol. Relationships among neutralization ratios, free acidity, and air-mass trajectories suggest that the atmosphere at Sanya was impacted by both local and regional emissions. Three major transport pathways were identified, and flow from the northeast (from South China) typically brought the most polluted air to Sanya. A case study confirmed strong impact from South China (e.g., Pearl River Delta region) (contributed 76.8% to EC, and then this result can be extended to primary pollutants) when the northeast winds were dominant. The Weather Research Forecasting Black carbon model and trace organic markers were used to apportion local pollution versus regional contributions. Results of the study offer new insights into the atmospheric conditions and air pollution at this coastal city

Effects of day-of-week trends and vehicle types on PM2.5-boundedcarbonaceous compositions

Carbonaceous compositions of PM2.5 were measured in the heart of Bangkok from 17th November 2010 to 19th January 2012, and a data set of 94 samples was constructed. Effects of day-of-week trends and vehicle types on PM2.5-bound TC, OC, and EC were carefully investigated. In this study, OC was the most important contributor to the total PM2.5 mass concentration. The average PM2.5-bound OC content measured at CHAOS (18.8 &plusmn; 9.18 &mu;g m&minus;3) was approximately 11 times higher than at Chaumont, Switzerland (1.7 &mu;g m&minus;3), but approximately five times lower than at Xi&#39;an, China (93.0 &mu;g m&minus;3). The application of diagnostic binary ratios of OC/EC and estimations of secondary organic carbon (SOC) coupled with autocorrelation plots (Box and Jenkins) highlight the enhanced impacts of traffic emissions, especially from diesel vehicles, on PM2.5-bound carbonaceous compositions on weekdays relative to weekends. Hierarchical cluster analysis (HCA) coupled with principal component analysis (PCA) underline the importance of diesel emissions as the primary contributors of carbonaceous aerosols, particularly during weekdays.</p

Chemical composition and sources of PM2.5 and TSP collected at Qinghai Lake during summertime

PM2.5 and total suspended particulate (TSP) samples were collected from June to September 2010 at Qinghai Lake, northeastern Tibetan Plateau. The concentrations of major water-soluble ions, 10 elements, elemental carbons (ECs) and organic carbons (OCs) were quantified. Mass concentrations of PM2.5 and TSP were 21.27&plusmn;10.70&mu;gm-3 and 41.47&plusmn;20.25&mu;gm-3, respectively, and the mean ratio of PM2.5/TSP was 0.51. The greatest anion and cation in both PM2.5 and TSP samples were SO42- and Ca2+, respectively. Crustal elements, such as Ca, Fe and K, were the main elements in our aerosol samples, and their enrichment factors (EFs) were lower than 10. EFs for Pb, As, and Zn were greater than 10, indicating that they were influenced by anthropogenic sources. EC concentrations were 0.33&plusmn;0.17&mu;gm-3 and 0.47&plusmn;0.28&mu;gm-3, whereas OC concentrations were 1.49&plusmn;0.63&mu;gm-3 and 2.30&plusmn;0.95&mu;gm-3 in PM2.5 and TSP, respectively. Based on the calculated ratios of EC/TC and K+/EC, most of the ECs were found to be related to biomass burning emissions. Because of the pollution from local sources, the ratios of OC/EC were 4.77&plusmn;1.32 and 5.23&plusmn;1.39 in PM2.5 and TSP, respectively, which were lower than those of other remote sites. Salt particles produced by the salty lake reacted with acid gases and caused most of the nitrates and a small fraction of sulfate to be distributed in coarse mode; Cl deficit was also observed in our aerosol samples. Results of backward trajectories and correlation analysis show that the concentrations of SO42-, OCs, As, Pb, and Zn, were influenced by the long-distance transport from eastern China.</p

Characteristics of surface ozone at an urban site of Xi'an in Northwest China

Surface ozone concentrations in Xi&#39;an, China were monitored from March 23, 2008 to January 12, 2009 using the Model ML/EC9810 ozone analyzer. The daily average O(3) ranged from &lt;1 ppb to 64.2 ppbv with an annual average of 16.0 ppbv. The seasonal average of O(3) in summer (32.5 ppbv) was more than 10 times higher than that in winter (3.0 ppbv). A significant positive correlation was found between ozone concentration and ambient temperature, indicating that the intensity of solar radiation was one of the several major factors controlling surface ozone production. Using the NOAA HYSPLIT 4 trajectory model, the three longest O(3) pollution episodes were found to be associated with the high biogenic volatile organic carbon (BVOC) emissions from the vegetation of Qinling Mountains. No significant weekday and weekend difference in O(3) levels was detected due to the non-significant change in NO(x) emissions. O(3) depletion by NO emission directly emitted from vehicles, low oxygenated VOC concentrations, and low-level solar radiation caused by high aerosol loading all contributed to the low levels of O(3) found in Xi&#39;an compared to other cities and rural areas.</p

Multi-Year Analyses of Columnar Aerosol Opticaland Microphysical Properties in Xi’an, a Megacity inNorthwestern China

A thorough understanding of aerosol optical properties and their spatio-temporal variability are required to accurately evaluate aerosol effects in the climate system. In this study, a multi-year study of aerosol optical and microphysical properties was firstly performed in Xi’an based on three years of sun photometer remote sensing measurements from 2012 to 2015. The multi-year average of aerosol optical depth (AOD) at 440 nm was about 0.88 ± 0.24 (mean ± SD), while the averaged Ångström Exponent (AE) between 440 and 870 nm was 1.02 ± 0.15. The mean value of single scattering albedo (SSA) was around 0.89 ± 0.03. Aerosol optical depth and AE showed different seasonal variation patterns. Aerosol optical depth was slightly higher in winter (0.99 ± 0.36) than in other seasons (~0.85 ± 0.20), while AE showed its minimum in spring (0.85 ± 0.05) due to the impact of dust episodes. The seasonal variations of volume particle size distribution, spectral refractive index, SSA, and asymmetry factor were also analyzed to characterize aerosols over this region. Based on the aerosol products derived from sun photometer measurements, the classification of aerosol types was also conducted using two different methods in this region. Results show that the dominant aerosol types are absorbers in all seasons, especially in winter, demonstrating the strong absorptivity of aerosols in Xi’an

Measuring and Modeling Black Carbon (BC) Contamination in the SE Tibetan Plateau,

Black carbon (BC) concentrations were measured in the southeast (SE) Tibetan Plateau along the valley of the Yarlung Tsangpo River during winter (between November, 2008 and January, 2009). The measured mean concentration (0.75 &mu;g m&minus;3) is significantly higher than the concentrations (0.004&ndash;0.34 &mu;g m&minus;3) measured in background and remote regions of the globe, indicating that Tibetan glaciers are contaminated by BC particles in the Plateau. Because BC particles play important roles for the climate in the Tibetan Plateau, the sources and causes of the BC contamination need to be understood and investigated. In this study, a mesocale dynamical model (WRF) with BC particle modules is applied for analyzing the measurement. The analysis suggests that the major sources for the contamination in the SE Plateau were mainly from the BC emissions in eastern Indian and Bangladesh. Because of the west prevailing winds, the heavy emissions in China had no significant effects on the SE Plateau in winter. Usually, the high altitude of the Himalayas acts a physical wall, inhibiting the transport of BC particles across the mountains to the plateau. This study, however, finds that the Yarlung Tsangpo River valley causes a &#39;leaking wall&#39;, whereby under certain meteorological conditions, BC particles are being transported up onto the glacier. This too causes variability of BC concentrations (ranging from 0.3 to 1.5 &mu;g m&minus;3) in a time scale of a few days. The analysis of the variability suggests that the &ldquo;leaking wall&rdquo; effect cannot occur when the prevailing winds were northwest winds, during which the BC transport along the valley of the Yarlung Tsangpo River was obstructed. As a result, large variability of BC concentration was observed due to the change of prevailing wind directions.</p

Comparison and implications of PM2.5 carbon fractionsin different environments

The concentrations of PM2.5 carbon fractions in rural, urban, tunnel and remote environments were measured using the IMPROVE thermal optical reflectance (TOR) method. The highest OC1 and EC1 concentrations were found for tunnel samples, while the highest OC2, OC3, and OC4 concentrations were observed for urban winter samples, respectively. The lowest levels of most carbon fractions were found for remote samples. The percentage contributions of carbon fractions to total carbon (TC) were characterized by one peak (at rural and remote sites) and two peaks (at urban and tunnel sites) with different carbon fractions, respectively. The abundance of char in tunnel and urban environments was observed, which might partly be due to traffic-related tire-wear. Various percentages of optically scattering OC and absorbing EC fractions to TC were found in the four different environments. In addition, the contribution of heating carbon fractions (char and soot) indicated various warming effects per unit mass of TC. The ratios of OC/EC and char/soot at the sites were shown to be source indicators. The investigation of carbon fractions at different sites may provide some information for improving model parameters in estimating their radiative effects.</p

Association between exposure to ambientparticulate matter and chronic obstructivepulmonary disease: results from a cross-sectionalstudy in China

Objective The association between exposure to ambient particles with a median aerodynamic diameter less than 10/2.5 &micro;m (particulate matter, PM10/2.5) and COPD remains unclear. Our study objective was to examine the association between ambient PM10/2.5 concentrations and lung functions in adults. Methods A cross-sectional study was conducted in southern China. Seven clusters were randomly selected from four cities across Guangdong province. Residents aged &ge;20 years in the participating clusters were randomly recruited; all eligible participants were examined with a standardised questionnaire and spirometry. COPD was defined as a post-bronchodilator FEV1/FVC less than 70%. Atmosphere PM sampling was conducted across the clusters along with our survey. Results Of the subjects initially recruited, 84.4% (n=5993) were included for analysis. COPD prevalence and atmosphere PM concentration varied significantly among the seven clusters. COPD prevalence was significantly associated with elevated PM concentration levels: adjusted OR 2.416 (95% CI 1.417 to 4.118) for &gt;35 and &le;75 &micro;g/m3 and 2.530 (1.280 to 5.001) for &gt;75 &micro;g/m3 compared with the level of &le;35 &micro;g/m3 for PM2.5; adjusted OR 2.442 (95% CI 1.449 to 4.117) for &gt;50 and &le;150 &micro;g/m3 compared with the level of &le;50 &micro;g/m3 for PM1. A 10 &micro;g/m3 increase in PM2.5 concentrations was associated with a 26 mL (95% CI &minus;43 to &minus;9) decrease in FEV1, a 28 mL (&minus;49 to &minus;8) decrease in FVC and a 0.09% decrease (&minus;0.170 to &minus;0.010) in FEV1/FVC ratio. The associations of COPD with PM10 were consistent with PM2.5 but slightly weaker. Conclusions Exposure to higher PM concentrations was strongly associated with increased COPD prevalence and declined respiratory function

Physiochemical characteristics ofindoor PM2.5 with combustion ofdried yak dung as biofuel in TibetanPlateau, China

People inhabiting the Tibetan Plateau rely for survival on the yak, the region&rsquo;s native cattle. One of the important products of yak is dung, which has been served as cooking and heating fuels in the traditional Tibetan pastoralist society for several thousand years. The indoor air quality (IAQ) at eight residential homes with altitudes ranging from 3212 m to 4788 m was investigated in November 2012 to obtain a shot-term profile of emission from combustion of dried yak dung as biofuel in pastoral and agro-pastoral regions on the Tibetan Plateau. The indoor temperature, relative humidity, CO2 and mass concentrations of PM2.5 were monitored for around a 4-h period (5 kg dried fuel was consumed) at each site. Filter-based aerosol samples were also collected to characterize their elemental compositions, water-soluble ions, carbonaceous species and individual particle morphologies. The results showed that combustion of solid biomass fuel in cast-iron stove is the preliminary source of indoor particulate pollution. The average indoor and outdoor PM2.5 mass concentrations were 330.7 and 29.1 lg/m3, respectively. Individual particle analysis showed that most of the particles in smoke from dung burning were in the submicrometer size range. Regular and irregular organic balls and soot aggregates were the predominant species in the smoke (&gt;90% in numbers). The data set in this study can provide significant basis for IAQ and epidemiology study on the Tibetan Plateau.</p

Chemical profiles of urban fugitive dust over Xi'an in the south margin of the Loess Plateau, China

Urban fugitive dust samples were collected to determine the chemical profiles of fugitive dust over Xi&#39;an. Seventy eight samples were collected and divided into categories of paved road dust, construction dust, cement dust, and soil dust. Eighteen elements, including Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Ba, and Pb, and eight water-soluble inorganic ions, including Na+, Mg2+, Ca2+, NH4+, F-, Cl-, NO3- and SO42-, were measured. The most abundant elements in these urban dust samples were Al, Si, Ca, and Fe. Al, Si, K, and Ti and showed strong positive correlations with each other, indicating they are typical dust trace elements. In contrast, elements of Ca, Zn, As, and Pb had negative correlations to crustal elements. Si/Al, K/Al, Ti/Al, Mn/Al, and Fe/Al ratios varied insignificantly among these four samples types; these ratios are similar to the properties of loess, desert, and Gobi soil dust reported in previous studies. A significantly higher Ca/Al ratio was dominant in the chemical profile of the cement samples. In addition, high Pb/Al and Zn/Al ratios were detected in comparison with those in the Gobi soil, desert soil, and loess soil samples, which indicated that Pb/Al and Zn/Al ratios can be considered as markers of urban dust. Total water-soluble ions occupied only a small fraction (&lt;5%) in the urban fugitive soil samples indicating that most of the materials in the fugitive dust were insoluble. Ca2+ and SO42- were the most abundant ions in all samples. Most of the Ca and K in the fugitive soil samples were in insoluble phases, which differ significantly in comparison with combustion sources. A strong correlation was observed between Ca2+ and estimated CO32- levels indicating that most of Ca2+ was in the form of CaCO3 rather than other calcium minerals in Xi&#39;an fugitive dust.</p