Aerosol Direct Radiative Effects over China Based on Long-Term Observations within the Sun-Sky Radiometer Observation Network (SONET)

To investigate aerosol radiative effects, the Sun-Sky Radiometer Observation Network (SONET) has performed long-term observations of columnar atmospheric aerosol properties at 20 distributed stations around China. The aerosol direct radiative forcing (RF) and efficiency (RFE, the rate at which the atmosphere is forced per unit of aerosol optical depth) were estimated using radiative transfer model simulations based on the ground-based observations dating back to 2009. Results of multi-year monthly average RF illustrated that: the dust-dominant aerosol population at arid and semi-arid sites exerted moderate cooling effects (-8.0 similar to-31.2 W/m(2)) at the top and bottom of atmosphere (TOA and BOA); RF at continental background site was very weak (-0.8 similar to-2.9 W/m(2)); fine-mode dominant aerosols at urban and suburban sites exerted moderate cooling effects (-9.3 similar to-24.1 W/m(2)) at TOA but more significant cooling effects (-19.4 similar to-50.6 W/m(2)) at BOA; RF at coastal sites was comparable with values of urban sites (-5.5 similar to-19.5 W/m(2) at TOA, and -15.6 similar to-44.6 W/m(2) at BOA), owing to combined influences by marine and urban-industrial aerosols. Differences between RFE at TOA and BOA indicated that coarse-mode dominant aerosols at arid, semi-arid, and continental background sites were less efficient to warm the atmosphere; but fine-mode dominant aerosols at urban, suburban, and coastal sites were shown to be more efficient to heat the atmosphere.