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- Title
Observations of relative humidity effects on aerosol light scattering in the Yangtze River Delta of China.
- Authors
Zhang, L.; Sun, J. Y.; Shen, X. J.; Zhang, Y. M.; Che, H. C.; Ma, Q. L.; Zhang, Y. W.; Zhang, X. Y.; Ogren, J. A.
- Abstract
Scattering of solar radiation by aerosol particles is highly dependent on relative humidity (RH) as hygroscopic particles take up water with increasing RH. To achieve a better understanding of the effect of aerosol hygroscopic growth on light scattering properties and radiative forcing, a field campaign was carried out in the Yangtze River Delta of China in March 2013. During the observation period, the mean and standard deviation of enhancement factors at RH = 85% for the scattering coefficient (f (85%)), backscattering coefficient (fβ(85%)) and hemispheric backscatter fraction f (85%)) were 1.58 ± 0.12, 1.25 ± 0.07 and 0.79 ± 0.04, respectively, i.e. aerosol scattering coefficient and backscattering coefficient increased by 58 and 25% as the RH increased from 40 to 85 %. Meanwhile, the aerosol hemispheric backscatter fraction decreased by 21 %. The relative amount of organic matter (OM) and inorganics in PM1 was found to be a main factor determining the magnitude of f (RH), the highest values of f (RH) corresponded to the aerosols with a small fraction of organic matter (OM), and vice versa. The relative amount of NO3- in fine particles was strongly correlated to f (85%), which suggests NO3- played a vital role in aerosol hygroscopic growth during this study. The mass percentage of nitrate also had a close relation to the curvature of humido- grams, namely, the higher the nitrate concentration is, the straighter the humidogram will be. Air masses that arrived at LinAn in March can be classified into northerly- polluted, locally-polluted and dust-influenced types, the scattering enhancement factors at 85% RH were 1.52 ± 0.10, 1.64 ± 0.09 and 1.48 ± 0.05, respectively. The sensitivity of the aerosol radiative forcing to f (RH) at the measured mean ambient RH 67% for various aerosol types was also estimated. The direct radiative forcing increased by 11.8, 19.5, and 10.5%, respectively, for locally-polluted, northerly-polluted and dust-influenced aerosols due to aerosol hygroscopic growth at LinAn in March 2013.
- Subjects
YANGTZE River Delta (China); ATMOSPHERIC aerosols; LIGHT scattering; SOLAR radiation; HUMIDITY; RADIATIVE forcing
- Publication
Atmospheric Chemistry & Physics Discussions, 2015, Vol 15, Issue 2, p2853
- ISSN
1680-7367
- Publication type
Article
- DOI
10.5194/acpd-15-2853-2015