Spatio-temporal variations and influential factors of anthropogenic NO<inf>2</inf> pollution over Western China

Abstract

Using the tropospheric NO2 columns observed by the satellite-based Ozone Monitoring Instrument (OMI), we analyzed the spatio-temporal variations and influential factors of NO2 pollution over Western China from 2005 to 2016. First, the anthropogenic NO2 columns were estimated dependent on the seasonal characteristics of NO2 pollution, excluding the source of natural NO2. The long-term trend and seasonal characteristics of NO2 columns over Western China were then extracted by the wavelet transform method. We compared the changes of NO2 columns over Western China and Eastern China. Finally, combined with economic and social data, the main drivers of NO2 pollution over Western China were analyzed. The results showed that the NO2 columns over Western China showed a rapidly increasing trend from 2005 to 2012. Specifically, the growth rate of northwestern provinces exceeded 10% a-1. After 2012, the NO2 columns over Western China began to decrease. We observed that most western provinces had completed the emission reduction targets of the "12th Five-Year Plan". In addition, coal consumption is the most important factor of NO2 pollution. Although part of thermal power in Yunnan and Sichuan Provinces has been replaced with hydropower and the growth rate of coal consumption has slowed down, traffic emissions have already become the main source of local NO2 pollution in the two provinces. As one of the key regions of the national "One Belt, One Road Initiative" new strategy, the results of this study will provide an important scientific basis for the Chinese government to formulate effective emission control policies and promote regional balance and sustainable development.