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. 2020 Apr 3;10(1):5862.
doi: 10.1038/s41598-020-62710-8.

On the widespread enhancement in fine particulate matter across the Indo-Gangetic Plain towards winter

Narendra Ojha  1 , Amit Sharma  2   3 , Manish Kumar  4 , Imran Girach  5 , Tabish U Ansari  6 , Som K Sharma  7 , Narendra Singh  8 , Andrea Pozzer  4 , Sachin S Gunthe  9
Affiliations

On the widespread enhancement in fine particulate matter across the Indo-Gangetic Plain towards winter

Narendra Ojha et al. Sci Rep. .

Abstract

Fine particulate matter (PM2.5, aerodynamic diameter ≤2.5 µm) impacts the climate, reduces visibility and severely influences human health. The Indo-Gangetic Plain (IGP), home to about one-seventh of the world's total population and a hotspot of aerosol loading, observes strong enhancements in the PM2.5 concentrations towards winter. We performed high-resolution (12 km × 12 km) atmospheric chemical transport modeling (WRF-Chem) for the post-monsoon to winter transition to unravel the underlying dynamics and influences of regional emissions over the region. Model, capturing the observed variations to an extent, reveals that the spatial distribution of PM2.5 having patches of enhanced concentrations (≥100 µgm-3) during post-monsoon, evolves dramatically into a widespread enhancement across the IGP region during winter. A sensitivity simulation, supported by satellite observations of fires, shows that biomass-burning emissions over the northwest IGP play a crucial role during post-monsoon. Whereas, in contrast, towards winter, a large-scale decline in the air temperature, significantly shallower atmospheric boundary layer, and weaker winds lead to stagnant conditions (ventilation coefficient lower by a factor of ~4) thereby confining the anthropogenic influences closer to the surface. Such changes in the controlling processes from post-monsoon to winter transition profoundly affect the composition of the fine aerosols over the IGP region. The study highlights the need to critically consider the distinct meteorological processes of west-to-east IGP and changes in dominant sources from post-monsoon to winter in the formulation of future pollution mitigation policies.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
(a) The study region (also the domain of the regional model WRF-Chem), and the locations of observation sites used in the study. Correlation between the model and observations for the day-to-day variations in (b) AOD at 550 nm, and (c) PM2.5 during October-December 2016. Solid black line shows a 1:1 relation and dashed lines show an agreement within a factor of 2.
Figure 2
Figure 2
Mean distribution of PM2.5 (µgm−3) over the northern Indian region during October, November, and December 2016 as simulated by the WRF-Chem model.
Figure 3
Figure 3
Near surface temperature (°C), boundary layer height (m), mean winds (ms−1), and ventilation coefficient (m2s−1) over the northern Indian subcontinent during October, November and December 2016, based on the WRF-Chem model.
Figure 4
Figure 4
Reduction in PM2.5 (%) concentrations due to switching off the biomass-burning (left panel) and anthropogenic emissions (right panel) as compared to the reference simulation.
Figure 5
Figure 5
Relative effects of regional biomass burning and anthropogenic emissions on the modeled PM2.5 at selected stations in the IGP region.
See this image and copyright information in PMC

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