Assessment of Global Distribution and Temporal Changes of Background Aerosol Optical Depth

Aerosol emissions from natural and anthropogenic activities produce consistent non-zero aerosol loading in background condition without any specific emission events. The aerosols existent in the background condition, a background aerosol hereafter, has been investigated to estimate aerosol contribution to attenuation of incoming solar energy. A quantified background aerosol itself can also be an indicator of local air quality. In this study we investigated spatiotemporal variation of background aerosol using Background Aerosol Otical Depth (BAOD) from both Aerosol Robotic Network (AERONET) and the Visible Infrared Imaging Radiometer Suite (VIIRS).

The high-level BAODs were mostly found in Africa, Asia, and South America. Also BAODs showed significant seasonal variation associated with natural activities such as biomass burning and dust. Meanwhile, air pollutants by anthropogenic activities cause higher BAOD level in South Asia and Northeast Asia throughout a year. On the contrary, Europe and North America under a strict environmental regulation maintained low-level BAOD. Long-term trends of regional BAOD showed that decrease of BAOD is dominant in the Europe, North America, and Northeast Asia.

The BAODs from VIIRS showed significant correlation with the AERONET. The VIIRS BAOD captured not only high-level AOD near source region, but also sea-salt induced and long-range transported BAOD over the North Pacific Ocean and the Antarctic Ocean. The regional and seasonal BAODs information provides accurate baseline of aerosol extinction in atmosphere for estimating radiative forcing and consequently will support improving aerosol retrieval.