Extreme smog challenge of India intensified by increasing lower tropospheric stability

Abstract

Extreme smog in India widely impacts air quality in late autumn and winter months. While the links between emissions and air quality 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 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 an increase in relative humidity, leading to over fivefold increase in poor visibility days. Given this crucial aerosol-radiation-meteorological feedback driving the smog intensification, we anticipate results from this study will help inform mitigation strategies supporting stronger region-wide measures, which are critical for solving the smog challenge in India.

Cascading Delays in the Monsoon Rice Growing Season and Postmonsoon Agricultural Fires Likely Exacerbate Air Pollution in North India

“…Gautam et al. (2021) and Pan et al. (2015) previously underscored the role of secondary aerosol formation in the context of heavy aerosol pollution in northern India.…”

“…For north India, Gautam et al. (2021) used satellite, ground‐based, and reanalysis data to show that a decadal trend in aerosol‐induced warming potentially strengthened lower tropospheric stability and increased smog‐heavy, low visibility days. Due to computational cost, many atmospheric modeling studies do not account for two‐way aerosol interactions with meteorology (Li et al., 2017; Petäjä et al., 2016).…”

“…Superposing smoke PM 2.5 on higher background PM 2.5 later in the burning season increases the risk of extremely polluted days (>250 μg m −3 ), when wide-reaching emergency measures are taken to protect public health and safety, such as by canceling flights, halting construction, and closing schools (The Guardian, 2017; The Times of India, 2017). As experienced in early-to-mid-November in 2017, the buildup of smoke aerosols in northwest India can lead to both large spikes in PM 2.5 concentrations and regional smog that persists into the early afternoon, a phenomenon typically observed in winter (Gautam et al, 2007(Gautam et al, , 2021Ghude et al, 2017;Liu et al, 2021). Due to the heterogeneity in the postmonsoon fire season delay across districts, the timing of burning across all districts is now more closely aligned, increasing regional smoke concentrations on peak burning days.…”

“…A key question is whether the ∼2-week delay in postmonsoon fires from 2003 to 2018 may have worsened air pollution, regardless of any trends in anthropogenic emissions levels (Liu et al, 2021). Peak fire activity shifts from late October to early November, when meteorological conditions (i.e., cooler temperatures, weak winds) are more conducive to trapping haze within the shallow boundary layer (Gautam et al, 2021;Liu et al, 2018Liu et al, , 2021Ojha et al, 2020;Sembhi et al, 2020).…”

Physico-Chemical Properties and Deposition Potential of PM2.5 during Severe Smog Event in Delhi, India

“…In addition, very few studies are available on morphology of particles during smog conditions around the globe [ 35 , 36 ]. Since, limited studies are available for smog episodes in different parts of India [ 4 , 6 , 37 ], and extremely limited studies are available in Delhi for variations in PM concentrations [ 38 ] and inorganic components of PM (C, N, S components only) [ 5 ] during smog, this study is very useful for providing detailed variations in PM’s elemental and organic compositions along with morphological variations during smog episodes in Delhi. In addition, we found no such study on exposure assessment for deposition doses of PM (using the MPPD model) and associated elements during smog episodes available in Delhi and other parts of India.…”