The Role of Boundary Layer Height in India on Transboundary Pollutions to the Tibetan Plateau

Abstract

The aerosols over the Tibetan Plateau (TP) play an important role in radiative budget and hydrologic cycle over Asia even the northern hemisphere. Adjacent to the major emission sources of air pollutants, transboundary pollutions transported to the TP due to the unique geographical location and climatic characteristics, is an important exogenous driver of multi-layer changes over the TP. The influence of boundary layer height (BLH) in India to the transboundary pollution over the TP from 1980 to 2018 was investigated in the study. Results showed that air pollutants transported to the TP is more efficient within the boundary layer compared with free troposphere. The BLH decrease with the rate of 1.8 m/season in these decades. Moreover, it has a correlation with AOD (-0.4), moisture (-0.95), temperature (0.29), and shows a good spatial distribution with horizontal motion in India. Accompanied with westerly wind and the topographic forcing in the higher boundary layer, dust particles were uplifted from the northern India to the high altitude. Compared with a higher BLH, the lower BLH is difficult for the long transport of pollutants with weaker westerly wind over the TP and its difference of dust concentration with 0.2 μg m -3  in the upper troposphere. The solar radiation enhancement increases the sensible heat and the near-surface wind increase the turbulence, which provide thermodynamic conditions for the development of BLH. This study provides confidence for the source, long-term transport of the TP aerosol, and its environmental and climatic impacts on climate systems in the Northern Hemisphere.

Keywords: Boundary Layer Height, Transboundary pollution, Dust aerosols, Tibetan Plateau, India Pre-Monsoon