Trends in the types and absorption characteristics of ambient aerosols over the Indo-Gangetic Plain and North China Plain in last two decades

Climatology and trends in different types of aerosols with focus on absorbing aerosols over Kanpur located in Indo-Gangetic Plain (IGP) in South Asia and Beijing in North China Plain (NCP) in East Asia are investigated. We perform a first analysis of high-quality time series of columnar aerosols observations over a period of nearly two-decades, along with satellite observations to provide a broader regional perspective. Satellite retrieved aerosol Ångström exponent (AE) values have increased (10–20%) suggesting an increasing contribution of fine aerosols to aerosol optical depth (AOD) over Asia in last 2-decades. Among three aerosol types [urban-industrial (UI), biomass burning (BB), and dust (DU)], only UI and BB aerosols are present over Kanpur throughout the year, while DU is present along with UI and BB aerosols only during pre-monsoon and monsoon. Overall, there is a positive trend in BB aerosols over both Kanpur and Beijing, a positive (negative) trend in UI aerosols over Kanpur (Beijing), and positive (negative) trend in dust over Beijing (Kanpur). Positive trend in BB aerosols over Kanpur is statistically significant. Among three absorbing aerosol types [mostly black carbon (MBC), mostly dust (MDU), and mixed (MIX) containing BC and dust], only MBC and MIX are present in post-monsoon and winter over IGP, and MDU is present along with MBC and MIX only during pre-monsoon and monsoon, in agreement with aerosol types found. Trends in MBC, MIX and MDU over Kanpur in IGP and in MIX over Beijing are statistically significant. These trends are attributed mainly to changes in anthropogenic aerosol emissions, and not to natural and climatic factors as their changes are relatively small. These findings on hitherto unavailable climatology and trends in aerosols and absorbing aerosols over two global aerosol hotspots and identified contrasts will be crucial in model simulations to better decipher aerosol-climate interactions over Asia.