Extreme Smog Challenge of India Intensified by Increasing Lower Tropospheric Stability.

Extreme smog in India widely impacts air quality in late autumn and winter months. While the links between emissions, air quality and health impacts are well‐recognized, the association of smog and its intensification with climatic trends in the lower troposphere, where aerosol pollution and its radiative effects manifest, are not understood well. Here we use long‐term satellite data to show a significant increase in aerosol exceedances over northern India, resulting in sustained atmospheric warming and surface cooling trends over the last two decades. We find several lines of evidence suggesting these aerosol radiative effects have induced a multidecadal (1980–2019) strengthening of lower tropospheric stability and increase in relative humidity, leading to over fivefold increase in poor visibility days. Given this crucial aerosol‐radiation‐meteorological feedback driving the smog intensification, results from this study would help inform mitigation strategies supporting stronger region‐wide measures, which are critical for solving the smog challenge in India. Plain Language Summary: Severe air pollution in India and its impacts on air quality and public health are worsening. Extreme smog episodes are frequently observed in northern India associated with the highest aerosol concentrations and hazardous visibility conditions. It is well‐known that anthropogenic emissions directly affect pollution, but it remains unclear from an observational perspective how the stability of the lower troposphere, where aerosol pollution builds up, impacts the long‐term evolution of smog. Using a multidecadal analysis of satellite, ground and reanalysis data sets, here we show sustained intensification of extreme smog associated with the strengthening of lower tropospheric stability, potentially amplified by aerosol‐induced atmospheric warming. Solving the smog crisis in India is increasingly critical given the strongly linked aerosol‐radiation‐meteorological interactions. Key Point: Past 40‐year observations reveal aerosol‐induced radiation‐meteorological feedbacks have intensified extreme smog in India [ABSTRACT FROM AUTHOR]