دانلود رایگان مقاله اثر رشد رطوبت پسند آئروسل در اثر تابش مستقیم آئروسل در تابستان

abstract

In this paper, relative humidity (RH) profiles and their impacts on the vertical variations of aerosol optical properties and the direct aerosol radiative effect (DARE) have been investigated based on surface measurements from the Haze in China campaign and sounding data from the North China Plain. Among the profiles obtained from July to September in 2008, about half have RHs greater than 80% within the mixed layer. The vertical variations in the aerosol optical properties at ambient RH, including the extinction coefficient (sext), single scattering albedo (SSA) and asymmetry factor (g), are remarkably different from the variations in the dry aerosols and are highly dependent on the RH profiles. Increases of the aerosol optical depth and column-averaged SSA and g due to aerosol water uptake can reach up to 64%, 0.052 and 0.079, respectively. The fractional contribution to the instantaneous DARE at the top of the atmosphere due to aerosol hygroscopic growth reaches 60% in high RH profiles. DARE estimates can be significantly biased if the RH dependence of SSA or g is not considered. We suggest that if their vertical profiles or column-averaged values are absent, then the ambient values of SSA and g at the surface should be used rather than the values of SSA and g obtained from dry aerosols when estimating DAREs.

4. Conclusions

From the vertical profiles of the meteorological parameters observed using radiosonde in Beijing at the local time of 13:30 from July to September in 2008, the vertical characteristics of RH on the NCP are characterized. The profiles with MRHs greater than 80% represent 52% of all the profiles that have distinct mixed layers. Which demonstrates that high RH profiles are prevalent during the summer on the NCP. The RH profiles are further coupled with surface measurements of aerosol properties to study the influences of RH profiles on aerosol optical properties. The ambient vertical structures of sext, SSA and g are remarkably different from those of dry aerosols and are highly dependent on RH profiles. Increases of the aerosol optical depth and column-averaged SSA and g due to aerosol water uptake can reach up to 64%, 0.052 and 0.079, respectively. These results demonstrate that aerosol hygroscopic growth has significant influences on aerosol optical properties and RH profiles play significant roles. Several cases have been designed to quantitatively estimate the influences of different levels of RH profiles on DARE estimates. The fractional contribution to the instantaneous DARE at the TOA due to aerosol hygroscopic growth reaches 60% in high RH profiles. Individual effects of the RH dependence of AOD, SSA and g on DARE are also studied. The calculated results demonstrate that DARE estimates can be significantly biased if the RH dependence of SSA or g is not considered. The results of designed cases also demonstrate that large biases occur if surface SSA and g are used to estimate the DARE at the TOA and surface, particularly for highly humid profiles. The ambient values of SSA and g at the surface, when used together, are better than the SSA and g values obtained from dry aerosols for estimating the DARE at the TOA and the surface. Thus, we suggest that the ambient values of SSA and g at the surface should be used rather than the values of SSA and g obtained from dry aerosols when estimating the DARE in the absence of their vertical profiles or column-averaged values.