| Large amount of fusil fuel consumption in North China Plain (NCP) has important effect on chemical and physical properties of atmospheric aerosol. A three wave integrated nephelometer (TSI 3563) was deployed in urban Beijing to characterize aerosol scattering properties during heating periods of 2013 and early 2014. The results showed that the average scattering coefficients, backscattering coefficients and backscattering ratios at 550nm were 332.8 ±378.5 Mm-1,44.5±44.9 Mm-1 and 0.16±0.31, respectively. The mean aerosol scattering Angstrom exponent (SAE), asymmetry parameter and mass scattering efficient is 1.4±0.3,0.5±0.1 and 3.9±0.2 m2g, respectively. Meanwhile, an air mass backward trajectory showed that air mass from southern part (cluster 5) of Beijing has the most fraction of 31%, with average PM2.5 concentration of 90.3 μg·m-3, average scattering coefficient of 422.5 Mm-1, hemisphere backscattering coefficients of 64.8 Mm-1 and backscattering ratio of 0.15, respectively. We also found that an increasing of relative humidity, companied with elevated air pollution level, has significant effect on aerosol optical properties, leading to an increased fraction of coarse particle due to aerosol hygroscopic growth, gas-particle conversion, coagulation and uptake of gases by hydrated aerosol particle. Our results indicated that aerosol pollution is serious in Beijing and has significant effect on visibility degradation, radiative forcing and climate change on regional scale.Severe haze pollution over eastern China in January of 2013 received worldwide attention. A HR-ToF-AMS was deployed to characterize submicron aerosol chemical properties in urban Beijing. Aerosol hygroscopic growth factors (HGF) during this month were calculated at a subsaturation relative humidity of 85% based on a simplified Kohler theory and ZSR (Zdanovskii Stokes Robinson) mixing role. When the κ of organic aerosol was set to 0.1, the average HGF values in haze days and in none haze days are 1.4±0.02 (hourly averaged value ±standard deviation) and 1.35±0.04, respectively, with a difference of 4%. Moreover, the O:C ratio and m/z 44 exhibited higher values in haze days, which indicates a enhanced hygroscopic properties of organic aerosol and the difference maybe much more than 4% compared with that in none haze days. Size-resolved hygroscopic growth factor showed that the results may contribuate to our knowledge visibility degenerations and radiative forcing under a server pollution atmosphere.The evolution of physical, chemical and optical properties of urban aerosol particles was characterized during an extreme haze episode in Beijing, PRC, from January 24 through January 31,2013 based on in-situ measurements. The average mass concentrations of PM1, PM2.5 and PM10 were 99±67μg·m-3 (average ± stdev), 188±128 μg·m-3 and 265±157μg·m-3, respectively. A significant increase in PM1-2.5 fraction was observed during the most heavily polluted period. The average scattering coefficient at 550 nm was 877 Mm-1±624 Mm-1. An increasing relative amount of coarse particles can be deduced from the variations of backscattering ratios, asymmetry parameter and scattering Angstrom exponent. Particle number size distributions between 14 nm-2500 nm diameters showed high number concentrations, particularly in the nucleation mode and accumulation mode. Size-resolved chemical composition of submicron aerosol from a High Resolution-ToF-Aerosol Mass Spectrometer showed that the mass concentrations of organic, sulfate, nitrate, ammonium and chlorine mainly resided on 500nm to 800nm (vacuum diameter) particles, and nitrate and ammonium contributed greatly to particle growth during the heavily polluted day (January 28).Increasing relative humidity and stable synoptic conditions on January 28 combined with heavy pollution on 28 January, lead to enhanced water uptake by the hygroscopic submicron particles and formation of secondary aerosol, which might be the main reasons for the severity of the haze episode. Light scattering apportionment showed that organic, sulfate, ammonium nitrate and ammonium chloride compounds contributed to light scattering fractions of 54%,24%,12% and 10%, respectively. This study indicated that the organic component in submicron aerosol played an important role in visibility degradation during the haze episode in Beijing. |
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