Opposite Long-term Trends in Aerosols between Lower and Higher Altitudes: A Testimony to the Aerosol-PBL Feedback
Other literature type
(issn: 1680-7324, eissn: 1680-7324)
Interactions between absorbing aerosols and the planetary boundary layer (PBL) play an important role in enhancing air pollution near the surface. In this study, a unique feature of the interaction is found that has important implications in monitoring and combating air pollution. Opposite trends in aerosol loading between the lower and upper PBL are found on a wide range of time scales and from different types of data acquired by various platforms: from a short-term field experiment to decadal satellite observations, and multi-decadal ground observations in China. A novel method is proposed to obtain the vertical profiles of aerosol loading from passive sensors by virtue of varying elevations. Trend analyses of three particulate variables having different temporal scales, namely, visibility, aerosol optical depth, and extinction, all exhibit the same trend: increasing at the lower atmosphere, but decreasing in the upper. Column-integrated quantities are much less variable. The reversal trend is consistent with the strong vertical gradients in the aerosol-induced atmospheric heating rate that unevenly modifies the atmospheric temperature profile and alters the stability differently. These findings have multiple implications in understanding and combating air pollution, especially in many developing countries producing large amounts of black and brown carbon aerosols.