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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: 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]

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]