Comment on acp-2022-219

Abstract

To identify the long-term trend of particle size variation, we analyzed aerosol optical depth (AOD, τ) separated as dust (τD) and coarse-(τPC) and fine-pollution particles (τPF) depending on emission sources and size. Ångström Exponent values are also identified separately as total and fine-mode particles (αT and αPF). We checked these trends in various ways; 1) first-order linear regression analysis of the annual average values, 2) percent variation using the slope of linear regression method, and 3) a reliability analysis using the Mann-Kendall (MK) test. We selected 17 AERONET sun/sky radiometer sites classified into six regions, i.e., Europe, North Africa, the Middle East, India, Southeast Asia, and Northeast Asia. τ decreased in Europe and Asian regions and increased in the Middle East, India, and North Africa. Values of τPC and τPF, show that aerosol loading caused by non-dust aerosols decreased in Europe and Asia and increased in India. In particular, τPF considerably decreased in Europe and Northeast Asia (95 % confidential levels in MK-test), and τPC decreased in Northeast Asia (Z-values for Seoul and Osaka are -2.95 and -2.31, respectively). The change in τPC reflects the reduction of primary emissions from plants and other anthropogenic sources as the result of regulations by air policies. Values of αT decreased by -3.3 to -30.5 % in Europe, North Africa, and the Middle East, which means the mean size of aerosol particles increased. Particle size on average became smaller over India and Asian regions considered in our study. We find that αT increased by 1.3 to 13.1 %. In particular, αPF increased in most areas., showing the probability that the average particle size of fine-mode aerosols became smaller in recent years.