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

Narendra Ojha,Imran Girach,Narendra Singh,Andrea Pozzer,Amit Sharma,Tabish U Ansari,Sachin S Gunthe,Manish Kumar,Som K Sharma

doi:10.1038/s41598-020-62710-8

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.

Highlights

Fine particulate matter (PM2.5, aerodynamic diameter ≤2.5 μm) impacts the climate, reduces visibility and severely influences human health
Aerosol optical depth (AOD) at 550 nm is simulated to be higher over the Indo-Gangetic Plain (IGP) region (0.5–1) in the results of the standard simulation, which is in good agreement with the satellite-based observations from moderate resolution imaging spectroradiometer (MODIS) and multiangle imaging spectroradiometer (MISR) (Fig. S1)
Model captures the variations in the AOD (r = ~0.6) at Kanpur and Jaipur stations as obtained from the Aerosol Robotic Network (AERONET) observations in this region, to a reasonable extent (Fig. 1b) with underestimated magnitudes

Summary

Introduction

Fine particulate matter (PM2.5, aerodynamic diameter ≤2.5 μm) impacts the climate, reduces visibility and severely influences human health. Regional modeling studies, exploiting the potential of high-resolution input emissions together with a well-resolved meteorology[28,29,30,31,32], are essential to unravel the effects of dynamics and emissions (biomass-burning versus anthropogenic) on the widespread PM2.5 build-up across the IGP from post-monsoon to winter transition In this direction, here we performed high-resolution (12 km × 12 km) simulations using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem)[33], configured on the basis of the previous evaluations of meteorology, wind patterns, and chemical fields over the South Asian region[30,32,34,35] (Table S1). Besides the reference simulation, called as “WRF-Chem”, two additional simulations have been performed by alternatively switching off the anthropogenic (anthro_off) and biomass burning (fire_off) emissions in the model

Methods

Results

Conclusion