Exploring the Drivers and Photochemical Impact of the Positive Correlation between Single Scattering Albedo and Aerosol Optical Depth in the Troposphere

Single scattering albedo (SSA), an important aerosol optical property, determines the effects of aerosols on actinic flux and ozone production. Similar to some measurement results in the United States and Europe, a strong positive correlation between SSA and aerosol optical depth (AOD) was also found in Beijing. Our results show that the enhancement of secondary aerosol formation induced by increased humidity and photochemical aging plays a major role in the positive correlation between SSA and AOD. Further analysis indicated that this positive correlation between SSA and AOD leads to a nonlinear relationship between photolysis frequencies and AOD. Omitting this positive correlation in radiative transfer models will lead to photolysis frequencies and ozone production rates being significantly overestimated under low AOD levels but significantly underestimated under high AOD levels. This result also implies that this positive correlation is conducive to the simultaneous occurrence of ozone and particulate matter pollution. We suggest that the positive correlation between SSA and AOD should be fully considered to accurately quantify the effect of aerosols on ozone production.

Automated summary

The study revealed a strong positive correlation between SSA and AOD, mainly influenced by the enhancement of secondary aerosol formation induced by increased humidity and photochemical aging. Neglecting this positive correlation could lead to significant overestimation of photolysis frequencies and ozone production rates at low AOD levels, and significant underestimation at high AOD levels.