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Daily PM2.5 samples were collected in Guangzhou — the largest megacity in South China, for a period of one month in each season during 2009–2010. Mass concentrations of water-soluble inorganic ions, organic carbon (OC) and elemental carbon (EC) in PM2.5 were determined, and aerosol scattering coefficient (bsp) was synchronously measured. The daily PM2.5 mass concentrations ranged from 21.0 to 213.6μgm−3 with an annual average of 76.8±41.5μgm−3. The highest seasonal average PM2.5 was observed in winter (103.3±50.1μgm−3) and the lowest in summer (38.6±15.7μgm−3). Annual average PM2.5 mass scattering efficiency (MSE) was 3.5±0.9m2 g−1, with obvious seasonal variations in sequence of autumn (4.5±0.2m2 g−1)>winter (3.9±0.5m2 g−1)>spring (3.0±0.4m2 g−1)>summer (2.3±0.3m2 g−1). To determine the relationship between bsp and the chemical components of PM2.5, bsp was reconstructed in each season using the original IMPROVE formula with a modification of including sea salt aerosols. The estimated bsp using this method was 22±28% smaller on annual average compared to the measurements. Multiple linear regression of measured bsp against (NH4)2SO4, NH4NO3, OM (Organic Mass), SS (Sea Salt), FS (Fine Soil), and CM (Coarse Mass) were also performed in all the four seasons. The estimated bsp from using the regression equation was 4±12% larger than the measured values. On average, (NH4)2SO4, NH4NO3, OM, SS, FS and CM accounted for 50±11%, 18±10%, 19±5%, 5±4%, 3±2% and 5±6%, respectively, of the estimated bsp. [ABSTRACT FROM AUTHOR]

Abstract: Daily PM2.5 samples were collected in Chengdu, a megacity in southwest China, for a period of one month in every season during 2009–2010. Mass concentrations of water-soluble inorganic ions, organic carbon (OC), elemental carbon (EC), levoglucosan (LG), water soluble organic carbon (WSOC), and elements were determined to identify the chemical characteristics and potential sources of PM2.5. The data obtained in spring were discussed in detail to explore the impacts of dust storms and biomass burning on the chemical aerosol properties. The daily PM2.5 mass concentrations ranged from 49.2 to 425.0μgm−3 with an annual average of 165.1±85.1μgm−3. The highest seasonal average of PM2.5 concentrations was observed in the winter (225.5±73.2μgm−3) and the lowest in the summer (113.5±39.3μgm−3). Dust storm influence was observed only during the spring, while biomass burning activities occurred frequently in late spring and early summer. In the spring season, water-soluble ions, total carbonaceous aerosols, and the sum of the dominant elements (Al, Si, Ca, Ti, Fe, Mn, Zn, Pb, and Cu) accounted for 30.0±9.3%, 38.6±11.4%, and 6.2±5.3%, respectively, of the total PM2.5 mass. Crustal element levels evidently increased during the dust storm episode and LG, OC, WSOC, Cl− and K+ concentrations increased by a factor of 2-7 during biomass burning episodes. Using the Positive Matrix Factorization (PMF) receptor model, four sources for spring aerosols were identified, including secondary sulfate and nitrate, motor vehicle emissions, soil dust, and biomass burning. The four sources were estimated to contribute 24.6%, 18.8%, 23.6% and 33.0%, respectively, to the total PM2.5 mass. [Copyright &y& Elsevier]

Abstract: Daily samples of ambient sub-micrometer particles (PM1, particles with an aerodynamic diameter≤1.0μm) were collected from July 2009 to April 2010 at an urban site over Guangzhou in southern China. Mass concentrations of water-soluble inorganic ions, organic carbon (OC) and elemental carbon (EC) were determined to characterize the chemical composition of PM1. The mass concentration of PM1 ranged from 14.6μgm−3 to 143.3μgm−3, with an annual mean value of 52.4±27.3μgm−3. Seasonally-averaged PM1 concentrations decreased in the order winter>autumn>spring>summer. The annual mean concentrations of OC and EC were 6.2±3.5 and 5.0±2.9μgm−3, respectively. The OC and EC concentrations were measured following the IMPROVE_A thermal/optical reflectance (TOR) protocol. Total carbonaceous aerosol (the sum of organic matter and elemental carbon) accounted for 23.0±4.4% of PM1 mass. Clear seasonal variations in OC and EC suggested sources of these two constituents were remarkable difference among the four seasons. Seasonally averaged OC/EC ratios were 1.2, 1.7, 1.4, and 1.5, from spring to winter respectively. Low OC/EC ratios in comparison with other cities in China revealed that vehicle emissions play an important role in carbonaceous aerosol levels in Guangzhou. SO4 2−, NO3 − and NH4 + were the three major inorganic ions in PM1, collectively contributing 30.0%±6.3% of the PM1 mass. SO4 2− and NH4 + were both the highest in autumn and the lowest in summer. In contrast, NO3 − was the highest in winter. Sulfur oxidation ratio was positively correlated with solar radiation and O3, but negatively correlated with SO2. Nitrogen oxidation ratio was positively correlated with NO2, NH4 + and Cl−, but showed a negative correlation with temperature. By applying the IMPROVE equation, PM1 mass was reconstructed and showed that (NH4)2SO4, NH4NO3, OM and EC accounted for (30.7±11.4) %, (9.7±5.2) %, (22.6±5.0) % and (9.7±2.3) % of PM1, respectively. Finally, source apportionment by positive matrix factorization revealed that (1) secondary aerosol and biomass burning, (2) diesel emissions, (3) gasoline emissions and sea salt, and (4) coal combustion were the greatest contributors to PM1. [Copyright &y& Elsevier]

Abstract: Aerosol optical properties were continuously measured at an urban site in Shanghai of China from December 2010 to March 2011, and aerosol scattering (σscat) and absorption (σabs) coefficients and single scattering albedo (SSA) were examined. During the entire period, mean σscat, σabs, SSA were 293Mm−1, 66Mm−1 and 0.81, respectively. Higher σscat and σabs occurred in December while relatively lower values were observed in March, and SSA was just opposite to them. σscat and σabs coefficients behaved an apparent bi-peak pattern in diurnal variation: maxima of 319, 76Mm−1 at 8:00 LT during traffic rush hours and sub-maxima of 280, 71Mm−1 at 20:00 LT. SSA also behaved a bi-peak diurnal cycle with maximum 0.85 at 13:00 LT and sub-maximum 0.82 at 4:00 LT. σscat and σabs coefficients showed a clear negative correlation with atmospheric visibility. PM2.5 and black carbon were major contributors to large optical parameters because their concentrations were 2 times higher during haze episode than in clean days. σscat and σabs were low in magnitude when northeasterly winds bring “clean” air from the China Yellow Sea arriving the observation site, and were relatively high when air masses from the north or northwest pass through continental areas or/and industrial regions, indicating impacts of various aerosol origins on aerosol optical properties. [Copyright &y& Elsevier]

Concentrations and compositions of PAHs and oxygenated PAHs (OPAHs) in four size ranges of ambient particles (< 1.1, 1.1–3.3, 3.3–9.0 and > 9.0 μm) collected in Xi'an and Guangzhou, two megacities of China, during the winter and summer of 2013 were measured and compared with those in 2003. The TSP-equivalent concentrations of Σ14PAHs in Xi'an and Guangzhou are 57 ± 20 and 18 ± 23 ng m − 3 in winter, 5–10 times higher than those in summer. PAHs in both cities are dominated by 5- and 6-ring congeners in summer. In contrast, they are dominated by 4- and 5-ring congeners in winter, probably due to enhanced gas-to-particle phase partitioning of the semi-volatile PAHs. TSP-equivalent Σ7OPAHs during winter are 54 ± 15 and 23 ± 32 ng m − 3 in Xi'an and Guangzhou and dominated by 5-ring OPAHs. Size distribution results showed that the fine modes (< 3.3 μm) of PAHs and OPAHs in both cities are dominated by 4- and 5-ring congeners in winter and 5- and 6-ring congeners in summer. Relative abundances of 3-ring PAHs and OPAHs increased along with an increase in particle sizes, accounting for from about 1% of the total PAHs or OPAHs in the smallest particles (< 1.1 μm) to > 90% of the total in the largest particles (> 9.0 μm). The toxicity of PAH assessment indicated that atmospheric particles in Xi'an and Guangzhou during winter are much more toxic than those during summer and fine particles are more toxic than coarse particles. Compared to those in 2003, fine particulate PAHs and OPAHs in both cities during winter decreased by 50–90%, most likely due to the replacement of coal by natural gas in the country. [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosol was measured continuously at an urban site in Shanghai (31°18′N, 121°30′E) from January 2011 to January 2012, and the characteristics and relevant remote sources of BC were examined. Daily BC concentrations varied within the range of 0.3–11.4μgm−3 with an annual average of 2.3μgm−3. Comparably, monthly BC concentrations were usually high in the dry season (November–April) but low in the wet season (May–October). Hourly BC showed a similar diurnal pattern with two peaks, one at 7:00–9:00 LT and another at 19:00–21:00 LT, in the four seasons. BC level was always relatively higher during daytime than nighttime. There also existed a workday/weekend difference of BC due to anthropogenic activities. The correlation analyses between BC and meteorological factors indicated that (1) wind speed was an important contributor to BC diffusion in the boundary atmosphere, (2) atmospheric visibility was not highly sensitive to BC, and (3) northwesterly, westerly and southwesterly wind directions related closely to BC. The increase of BC is likely associated with fossil fuel combustion during the winter heating period and agricultural waste burning over the surrounding areas during the summer harvest period, as well as the air masses originating from and/or transiting through these regions. [ABSTRACT FROM AUTHOR]

Abstract Saccharides are important constituents in atmospheric aerosols but studies in northwestern China are still very limited. Here, we have measured anhydrosugars (levoglucosan, mannosan and galactosan), primary sugars (glucose, fructose, sucrose and trehalose), and sugar alcohols (arabitol, mannitol, sorbitol and inositol) in ambient PM 2.5 samples during summer and winter in Xi'an city, northwestern China. The abundance of total saccharides showed no clear seasonal variation, but apparent distinctions on the levels of the three categories and individual saccharide compounds were found. Primary sugars and particularly sucrose were dominant in summer. In contrast, levoglucosan was the predominant species in winter, contributing 60% of total saccharides. Source apportionment by positive matrix factorization revealed that airborne pollen was a major source of PM 2.5 associated-saccharides in summer, accounting for 35% of total saccharides; while biomass burning activities contributed to 60% of the winter saccharides. Furthermore, an increasing trend of biomass/biofuel burning contribution to winter PM 2.5 was observed in comparison with previous studies in Xi'an, suggesting a change in emission sources may be underway in northwestern China. Graphical abstract Unlabelled Image Highlights • Sucrose dominates total saccharides during summer while levoglucosan was the dominant species during winter. • Biomass burning emissions are the predominant source of saccharides in winter. • A yearly increase of biomass burning contribution to PM 2.5 during winter was found over Xi'an. [ABSTRACT FROM AUTHOR]

A regional air quality model system (RAQMS), coupled with a biogenic emission model was applied to investigate the variations of summertime biogenic volatile organic compound (BVOC) emission and secondary organic aerosols (SOA) during 2001–2018 over China. During 2001–2018, evident land use changes occurred, especially in the Sichuan Basin, the Qinling Mountains, and the megacities over east China. Leaf aera index (LAI) increased significantly over the western parts of northeast China, the Qinling Mountains, the North China Plain (NCP), and most areas of south China. The domain-average LAI and BVOC emission increased by 0.2 m2 m−2 (19%) and 3.0 Tg (26%), respectively, over China during 2001–2018, mainly due to the increases in LAI and air temperature. It is found that near surface BSOA concentration increased apparently over China from 2001 to 2018, with the maximum increment exceeded 2 μg m−3 (75%) in the middle reaches of the Yangtze River. The domain-average surface BSOA concentration increased remarkably by 0.44 μg m−3 (41%) over China, resulting from the combined effect of LAI and anthropogenic emission increases, and meteorological change, in which the land use and LAI changes were the dominant driving factors, explaining over 50% of the BSOA increase, while the changes in meteorology and anthropogenic emission contributed almost equally to the remaining BSOA increase. The changes in near surface BSOA concentration (μg m−3) between summer 2001 and 2018 due to (a) land use and LAI changes; (b) meteorology change; (c) anthropogenic emission change; (d) all the above factor changes. [Display omitted] • Summer BVOC emissions and BSOA concentration over China during 2001–2018 are explored. • The domain-average LAI increased by 0.2 m2 m−2 (19%) over China from 2001 to 2018. • BVOC emissions in China increased by 3.0Tg (26%) due to increased LAI and air temperature. • BSOA concentration increased by 0.4 μg m−3 (41%) due to land use, meteorology, and anthropogenic emission variability. [ABSTRACT FROM AUTHOR]

Coal-to-clean energy programs (coal bans) can improve air quality and public health and welfare. However, the field measurements taken in rural areas are still insufficient to evaluate the efficacy of coal bans in China. In this study, more than three years of observations were made on organic carbon (OC), elemental carbon (EC, also called black carbon, BC) and PM 2.5 at a rural site (Xianghe) in the Beijing-Tianjin-Hebei region (BTH) of China in combination with auxiliary measurements in urban areas (Beijing, Tianjin, Langfang, Baoding and Shijiazhuang). As a result of the coal ban, the annual average PM 2.5 concentrations decreased in rural areas. Accordingly, the annual average concentrations of OC declined from 19.1 to 12.3 μg/m3, while those of EC declined from 4.7 to 3.0 μg/m3. The amplitudes of the decrease of total carbon (the sum of OC and EC) and PM 2.5 in the areas with implementation of coal ban were greater than those in the non-coal banned areas. Based on the simulation performed using the Weather Research and Forecasting model coupled with chemistry (WRF-Chem), the quantitative contributions ascribed to coal ban policy and meteorology are discussed. In contrast to those observed in the winter of 2016/2017, the declines in the observed EC concentration could be attributed to meteorological impact (45% and 15%), changes in other emissions (29% and 40%) and coal bans (26% and 45%) for the winter of 2017/2018 and 2018/2019, respectively. Besides, in primary OC and PM 2.5 concentrations, 50% and 33% of fractional changes respectively were resulted from the reduced residential emissions associated with coal ban in the winter of 2017/2018; and more surprisingly, they rose to 66% and 57% in the winter of 2018/2019, respectively. In summary, coal ban policy had worked effectively in the BTH of China and should be widely implemented in this region if the supply of natural gas and electricity is sufficient and affordable to the local residents. • An obvious decline in OC, EC and PM 2.5 concentrations was observed. • TC and PM 2.5 declined more obviously in the coal ban areas. • The quantitative contributions of coal bans and meteorology are assessed. [ABSTRACT FROM AUTHOR]