Extreme Air Pollution Events Spiking Ionic Levels at Urban and Rural Sites of Indo-Gangetic Plain

Manisha Mishra,U.C Kulshrestha

doi:10.4209/aaqr.2019.12.0622

Abstract

ABSTRACT The present study is a modest attempt to quantify the water-soluble inorganic ions (WSIIs) in the early morning (fog-forming) ambient air on the central Indo-Gangetic Plain (IGP) during winter via dissolution using a low-cost refluxing mist chamber. The chemical composition of the bulk samples showed significant differences in the WSIIs between the two monitored sites, one urban and the other rural, with NH4+ (47% and 37%, respectively) and Ca2+ (18% and 8%, respectively) being the major cations and NO3– (10% and 16%, respectively) and SO42– (9% and 14%, respectively) being the major anions. The WSII concentration spiked during November at both locations (∑WSII = 159.6 and 141.9 µg m–3) due to two extreme air pollution events, viz., i) the burning of crop residue and ii) the Diwali festival. These changes, which were corroborated by observations of the meteorological conditions, played an essential role in the wintertime atmospheric chemistry. On foggy days, significant scavenging of ions associated with crustal dust (Ca2+, Na+, Mg2+ and Cl–) occurred, although the ambient concentrations of other species (K+, NH4+, NO2–, NO3– and SO42–) remained relatively unaffected. Furthermore, the relationship between the cations and anions demonstrated that NH3 and HONO, as the primary gaseous species, were involved in heterogeneous aqueous-phase reactions and the formation of secondary aerosols. Source apportionment based on principal component analysis and the mass ratios also indicated that local anthropogenic sources, in addition to natural ones such as soil/road dust and biogenic emissions, influenced the WSII composition. Vehicular exhaust, solid waste and biofuel burning were identified as the major contributors of WSIIs at the urban site, whereas biomass burning, agricultural activity and coal combustion in brick kilns were the predominant sources at the rural site.

Highlights

The onset of winter season in the Indo-Gangetic Plain (IGP) region has been found to be associated with the formation of a thick blanket of brown clouds within two to three kilometers above the surface (Ramanathan et al, 2005; Chung and Ramanathan, 2006; Nakajima et al, 2007)
Source apportionment based on principal component analysis and the mass ratios indicated that local anthropogenic sources, in addition to natural ones such as soil/road dust and biogenic emissions, influenced the water-soluble inorganic ionic (WSII) composition
Solid waste and biofuel burning were identified as the major contributors of WSIIs at the urban site, whereas biomass burning, agricultural activity and coal combustion in brick kilns were the predominant sources at the rural site

Summary

Introduction

The onset of winter season in the Indo-Gangetic Plain (IGP) region has been found to be associated with the formation of a thick blanket of brown clouds within two to three kilometers above the surface (Ramanathan et al, 2005; Chung and Ramanathan, 2006; Nakajima et al, 2007). As to the anthropogenic factors, the increased emissions of harmful pollutants from residential, industrial and transport sectors to meet the energy demands of this densely populated region undermines air quality (Singh et al, 2014; Pan et al, 2015; Liu et al, 2018) Moving further, another vital connection between the deteriorating air quality and certain extraneous extreme pollution episodes such as stubble burning in the states falling upwind of the IGP and the use of firecrackers during the celebration of Diwali festival needs to be factored in while accounting for the overall atmospheric profile of the region during the winter season (Kulshrestha et al, 2004; Singh et al, 2010; Perrino et al, 2011; Jain et al, 2014; Singh and Kaskaoutis, 2014; Izhar et al, 2018). These cumulatively result in the reduction of visibility, poor air quality and jeopardizing of health indicators (Seaton et al, 1995; Gautam et al, 2007; Balakrishnan et al, 2019)

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Conclusion