Seasonal distribution and vertical structure of different types of aerosols in southwest China observed from CALIOP

Abstract

Different types of aerosols play a crucial role in the climate system according to their vertical distributions and optical-radiative properties. Southwest China (SWC), consisting of the Sichuan Basin (SCB), the Yunnan-Guizhou Plateau (YGP) and the Tibetan Plateau (TP), is one of the most topographically complex regions in the world and is also facing varying degrees of air pollution problems caused by local, high-intensity anthropogenic emissions and trans-regional transport of aerosols from surrounding areas. However, a comprehensive understanding of the regional three-dimensional (3D) characteristics of aerosol distribution and evolution over SWC has not to be achieved yet. Here, the seasonal distributions and vertical structures of four types of aerosols, including dust, polluted continental/smoke, polluted dust and elevated smoke, were detected by using the quality controlled CALIPSO Level 2 nighttime aerosol profile product from 2007 to 2016 in this study. The loading of aerosols over the SCB was higher than that over the other regions, and of the sources, polluted continental/smoke and polluted dust, related to anthropogenic sources, contributed the most to the aerosols. However, we also found that polluted continental/smoke and polluted dust have declined since 2013, which was due to the strict regulatory measures implemented for industry emissions and biomass burning in agriculture in recent years. The elevated smoke aerosols over the YGP at an altitude of 3 km in spring were significantly higher than those in other seasons, while the polluted continental/smoke aerosols at an altitude of 1–2 km were higher in autumn and winter than in the other seasons and was considered to be from local biomass burning. The aerosol optical depth (AOD) over the TP was nearly one magnitude lower than that over the other two regions. However, either the dust or polluted continental/smoke from the Qaidam Basin or elevated smoke elevated from the Indo-Gangetic Basin could have been transported to the layer as high as 6 km over the TP. Additionally, the heights of the highest frequencies of AOD for all types of aerosols for the SCB, YGP and TP were 0–2 km, 2–4 km and 4–6 km, respectively. In summer, elevated smoke can rise to heights of 8–10 km on the TP. The results of this study provide an observational basis for further understanding the trans-regional transport of aerosols and their climate effects in SWC.