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Zhao H.,Institute of Atmospheric Environment | Che H.,Chinese Academy of Meteorological Sciences | Ma Y.,Institute of Atmospheric Environment | Xia X.,CAS Institute of Atmospheric Physics | And 3 more authors.
Atmospheric Research | Year: 2015

Visibility, particulate matter (PM) mass concentration, and aerosol optical properties data from June 2009 to December 2011 were obtained at Shenyang in Northeast China. The characteristics and relationships between these parameters were statistically analyzed. The results demonstrate that the monthly averaged visibility over Shenyang was higher in spring and autumn but lower in summer and winter, and had an inverse trend to PM and aerosol optical depth (AOD). Higher AOD at 500nm was found year by year, with the maximum value (1.31±0.45) occurring in June 2011, and the minimum in June 2010 (0.72±0.31). The mean value of the Ångström exponent underwent a notable reduction during the period of 2011, with values less than 1.0 from February to September. The single scattering albedo was consistently around 0.90 during 2009-2011, which was higher in summer but lower in winter. The higher absorption aerosol optical depth at 440nm in 2011 indicates that there were more absorbing aerosol particles in this period compared with the corresponding absorption Ångström exponent in the same year (about 0.75). The direct radiative forcing at the bottom of the atmosphere increased to -200W/m2 in 2011, compared with -150W/m2 from June 2009 to December 2010, suggesting a stronger cooling effect of aerosols at the surface. The positive radiative forcing at the top of the atmosphere in November and December 2009 could have been due to snow cover, which has a large surface albedo that reflects shortwave radiation to the atmosphere. © 2015 Elsevier B.V.

Wang P.,Longfengshan Atmospheric Background Regional Station | Che H.,Chinese Academy of Meteorological Sciences | Zhang X.,Chinese Academy of Meteorological Sciences | Song Q.,Longfengshan Atmospheric Background Regional Station | And 4 more authors.
Atmospheric Environment | Year: 2010

Aerosol optical properties from 2005 to 2008 at the Longfengshan regional background station in Northeast China were measured and analyzed. The annual mean of aerosol optical depth (AOD) at 440nm for the four years was about 0.27±0.25, 0.39±0.37, 0.35±0.34, and 0.38±0.38, respectively, and the corresponding annual mean for the Angstrom exponent between 440nm and 870nm was about 1.43±0.48, 1.23±0.37, 1.53±0.47, and 1.55±0.42. The average monthly AOD440nm showed similar seasonal variation with a maximum in spring and a minimum in autumn. The monthly means of AOD at 440, 675, 870 and 1020 nm increase from the January to March with the maxima about 0.77±0.04, 0.65±0.04, 0.58±0.06, 0.57±0.07, respectively and decrease from September to February with the minima about 0.32±0.12, 0.22±0.09, 0.15±0.08, and 0.13±0.07 in January. The monthly mean of Angstrom exponent shows a minimum in March (0.97±0.52) and a maximum in September (1.66±0.29). Both the AOD and Angstrom exponent presents single peak distributions of occurrence frequencies. The Longfenshan data showed high AODs (>1.00) both clustering in the fine mode growth wing and the coarse mode. Two typical cases under dust and haze conditions showed that the AOD under dusty day decreased from 2.20 to 1.20 and the Angstrom exponent increased from 0.10 to 1.00. On the contrast, the AOD under haze day remained relatively stable about 0.90 and the Angstrom exponent was around 1.40. The 3-day backtrajectory analysis at Longfengshan illustrated that the air-masses near ground on the dust day were from Bohai Sea and passed through Liaodong Peninsula and Northeast plain in China. But the air-masses on 500m AGL were originated from western Mongolia and crossed Gobi deserts, Otindag Sand Land and Horqin Sand Land in Northeast China. The air-masses at Longfengshan near ground 500m and 1000m AGL on the haze days were from North China Region and passed through Northeast Heavy Industrial Base in Northeast China. © 2010 .

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