Abstract
Abstract. In this paper, the diurnal variations of aerosol optical properties and their influences on the estimation of daily average direct aerosol radiative effect (DARE) in the North China Plain (NCP) are investigated based on in situ measurements from Haze in China campaign. For ambient aerosol, the diurnal patterns of single scattering albedo (SSA) and asymmetry factor (g) in the NCP are both highest at dawn and lowest in the late afternoon, and quite different from those of dry-state aerosol. The relative humidity (RH) is the dominant factor which determines the diurnal pattern of SSA and g for ambient aerosol. Basing on the calculated SSA and g, several cases are designed to investigate the impacts of the diurnal changes of aerosol optical properties on DARE. The results demonstrate that the diurnal changes of SSA and g in the NCP have significant influences on the estimation of DARE at the top of the atmosphere (TOA). If the full temporal coverage of aerosol optical depth (AOD), SSA and g are available, an accurate estimation of daily average DARE can be achieved by using the daily averages of AOD, SSA and g. However, due to the lack of full temporal coverage data sets of SSA and g, their daily averages are usually not available. Basing on the results of designed cases, if the RH plays a dominant role in the diurnal variations of SSA and g, we suggest that using both SSA and g averaged over early morning and late afternoon as inputs for radiative transfer model to improve the accurate estimation of DARE. If the temporal samplings of SSA or g are too few to adopt this method, either averaged over early morning or late afternoon of both SSA and g can be used to improve the estimation of DARE at the TOA.
Highlights
The direct effect of atmospheric aerosol on the radiation budget of earth is commonly described by direct aerosol radiative effect (DARE)
The daily average aerosol optical depth (AOD) at 550 nm is 0.47, which means that the North China Plain (NCP) is highly polluted
single scattering albedo (SSA) and g are both important parameters in the estimation of DARE (McComiskey et al, 2008), but their diurnal variations are rarely investigated, especially in the NCP
Summary
The direct effect of atmospheric aerosol on the radiation budget of earth is commonly described by direct aerosol radiative effect (DARE). Arola et al (2013) exploited data from a large number of AERONET sites, and assessed the influence of diurnal AOD variability on the estimates of daily average DARE at the top of atmosphere (TOA). This is the first time, in the NCP, that the diurnal cycles of SSA and g are both taken into account in the prediction of daily average DARE This is important for studying the direct aerosol effect in the NCP, where absorbing and scattering aerosols may contribute significantly to the climate change of the earth system (Chung et al, 2005; Bond et al, 2013).
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