| Hygroscopic growth is one of the important characteristics of atmospheric aerosols.The accurate description of the hygroscopic of aerosols is very important to reduce the uncertainty in the evaluation of aerosol radiative forcing and to more accurately simulate aerosol radiative forcing and atmospheric visibility.In order to accurately describe the hygroscopic growth characteristics of aerosols,we had carried out 14-month observation study on the aerosol hygroscopicity growth factor in urban Beijing.The scattering and hygroscopicity growth characteristics of PM100 and PM1 aerosols were analyzed.During the whole observation period,The mean values?±standard deviation?of aerosol scattering coefficient,scattering?ngstr?m exponent,and the mass scattering efficiency of PM100 were 238.1?±272.2?Mm-1,1.46?±0.27?,and 2.07?±1.26?m2 g-1,respectively.The variation trend of scattering coefficient of PM1aerosol was basically the same as that of PM10.The submicron scattering fraction reflects the proportion of PM1 scattering coefficient in PM10,and its average value?±standard deviation?was 71.6?±20?%.,which suggested that the scattering coefficient of PM100 aerosol was mainly contributed by PM1 aerosol.The average?±standard deviation?PM100 and PM1 aerosol scattering hygroscopic growth factor f?80%?were 1.61?±0.21?and 1.60?±0.19?,respectively.There was no significant difference between f?80%?of PM100 and PM1.The aerosol scattering hygroscopic growth factor in spring and summer was relatively large,and it was small in autumn and winter.The higher the mass fraction of inorganic matter,the stronger the hygroscopic growth ability of aerosols was.The high value of sulfate mass fraction often occured in the relatively clean period?low scattering coefficient?,when the mass fraction of nitrate was low?<0.1?,f?80%?varied between 1.4 and 1.8.The high value of nitrate mass fraction occured in the pollution period,f?80%?lied between 1.7 and 1.9;when the mass fraction of sulfate and nitrate were relatively high,The hygroscopicity of aerosols was the strongest,with f?80%?varied between1.8 and 2.0.The relationship between f?80%?and scattering coefficient,mass scattering efficiency?MSE?,scattering?ngstr?m exponent?SAE?,submicron scattering ratio?Rsp?and ambient relative humidity?RH?was studied.It was found that the variation trend of f?80%?with mass scattering efficiency was similar to that of f?80%?with scattering coefficient.f?80%?increased with the increase of scattering coefficient(<400 Mm-1,or MSE<3 m2 g-1),when the scattering coefficient was greater than 400 Mm-1(MSE was greater than 3 m2 g-1),f?80%?was maintained at around 1.8.f?80%?had a positive linear relationship with the SAE,f?80%?=?0.43±0.02?×SAE+?1.00±0.03?,SAE could be used to estimate f?80%?according to the fitting formula.Analysis of the relationship between f?80%?and ambient RH found that the higher the ambient RH,the more favorable the formation of secondary inorganic aerosols,and the hygroscopicity of aerosols was stronger.In the spring,Beijing is not only vulnerable to pollution events but also is affected by dust when strong winds blow away pollution.March 25-30,2018 was a very special period,in a few days,it had passed a pollution,dust and new particle formation?NPF?event.The aerosol optical properties and aerosol hygroscopicity of two sizes(PM100 and PM1)during the pollution period,dust period and a NPF events were analyzed.During the pollution period,the scattering and absorption coefficients increased dramatically with the accumulation of pollutants,while scattering?ngstr?m exponent?SAE?,submicron scattering fraction?Rsp?,submicron absorption fraction?Rap?decreased,as well as single scattering albedo?SSA?rose slightly,which indicated the increasing contribution of larger particle to scattering and absorption,and enhanced the scattering ability of aerosols.The average?±standard deviation?PM100 mass scattering efficiency was 3.86?±1.19?m2 g-11 with a range of 2.055.74 m2 g-1during the pollution period,and 0.40?±0.05?m2 g-11 during the dust period.The average?±standard deviation?PM100 and PM1 aerosol scattering hygroscopic growth factors f?80%?were 1.75?±0.05?and 1.75?±0.04?during the pollution period,1.14?±0.09?and1.15?±0.06?during the dust period,1.59?±0.05?and 1.60?±0.06?during the NPF event period,respectively.Aerosol scattering hygroscopic growth factors showed a strong correlation with the scattering?ngstr?m exponent which suggests the hygroscopicity is much stronger for fine particles?SAE>1.5?than the coarse particles?SAE<1.0?. |
PDF Full Text Request