Quantifying the contribution of long-range transport to particulate matter (PM) mass loadings at a suburban site in the north-western Indo-Gangetic Plain (NW-IGP)

Abstract

Abstract. Many sites in the densely populated Indo-Gangetic Plain (IGP) frequently exceed the national ambient air quality standard (NAAQS) of 100 μg m−3 for 24 h average PM10 and 60 μg m−3 for 24 h average PM2.5 mass loadings, exposing residents to hazardous levels of particulate matter (PM) throughout the year. We quantify the contribution of long-range transport to elevated PM levels and the number of exceedance events through a back-trajectory climatology analysis of air masses arriving at the IISER Mohali Atmospheric Chemistry facility (30.667° N, 76.729° E; 310 m a.m.s.l.) for the period August 2011–June 2013. Air masses arriving at the receptor site were classified into six clusters, which represent synoptic-scale air-mass transport patterns. Long-range transport from the west leads to significant enhancements in the average fine- and coarse-mode PM mass loadings during all seasons. The contribution of long-range transport from the west and south-west (source regions: Arabia, Thar Desert, Middle East and Afghanistan) to coarse-mode PM varied between 9 and 57 % of the total PM10–2.5 mass. Local pollution episodes (wind speed < 1 m s−1) contributed to enhanced PM2.5 mass loadings during both the winter and summer seasons and to enhanced coarse-mode PM only during the winter season. South-easterly air masses (source region: eastern IGP) were associated with significantly lower fine- and coarse-mode PM mass loadings during all seasons. The fraction of days in each season during which the PM mass loadings exceeded the national ambient air quality standard was controlled by long-range transport to a much lesser degree. For the local cluster, which represents regional air masses (source region: NW-IGP), the fraction of days during which the national ambient air quality standard (NAAQS) of 60 μg m−3 for 24 h average PM2.5 was exceeded varied between 36 % of the days associated with this synoptic-scale transport during the monsoon, and 95 % during post-monsoon and winter seasons; the fraction of days during which the NAAQS of 100 μg m−3 for the 24 h average PM10 was exceeded, varied between 48 % during the monsoon and 98 % during the post-monsoon season. Long-range transport was responsible for both, bringing air masses with a significantly lower fraction of exceedance days from the eastern IGP and air masses with a moderate increase in the fraction of exceedance days from the west (source regions: Arabia, Thar Desert, Middle East and Afghanistan). In order to bring PM mass loadings into compliance with the NAAQS and to reduce the number of exceedance days, mitigation of regional combustion sources in the NW-IGP needs to be given highest priority.

Vertical and horizontal distribution of submicron aerosol chemical composition and physical characteristics across northern India during pre-monsoon and monsoon seasons

“…Distinctive to the IGP were high OA : BC ratios (10-15), which are somewhat higher than for similar polluted environments such as China during summer with a ratio of ∼ 4 (Ho et al, 2006;Ni et al, 2018). It has been indicated that OA : BC ratios over India could be greater than expected due to the dominance of biomass burning rather than fossil fuel emissions, with the highest values in the pre-monsoon season (Ram and Sarin, 2011;Bisht et al, 2015;Kumar and Yadav, 2016) as seen in our data. Outside the IGP, the aerosol species concentrations are consistent with the aerosol sources, with more informal industries and manufacturing industries present that form high concentrations of SO 4 aerosol through the conversion of sulfur dioxide (SO 2 ) into sulfuric acid (H 2 SO 4 ).…”

“…The diverse living habits, fuel and land use make understanding the complexity of emissions and atmospheric dynamics challenging. The Indo-Gangetic Plain (IGP) in the Indian sub-continent is one such polluted region in South Asia; its unique geomorphology, meteorology and characteristic variations in aerosol particles have drawn the attention of aerosol researchers for many years (Pawar et al, 2015;Singh et al, 2017). Aerosol mass sources within the IGP are mostly dominated by natural sources such as dust, but also anthropogenic emissions associated with traffic, biomass burning, waste incineration, and crop and wood burning (Banerjee et al, 2015;Singh et al, 2017), with Delhi being one of the most polluted locations (Sharma et al, 2014).…”

Particulate matter air pollution may offset ozone damage to global crop production

“…Similar publicly available network surface ozone measurements are not available for India and China during this time period. We also compare ozone and PM surface observations from a site at the Indian Institute of Science Education and Research (IISER) Mohali in Chandigarh, India provided by Sinha et al (2015) and Pawar et al (2015), respectively, with simulated concentrations from GEOS-Chem (Fig. 3).…”

Black Carbon physical and optical properties across northern India during pre-monsoon and monsoon seasons

“…Understanding, identifying and characterising air pollution sources and their effect on local and regional areas, is important for health impact studies as well as radiative forcing assessments on local and global scales (Lawrence et al, 2007). The Indo-Gangetic Plain (IGP) in northern India is one such polluted region in south Asia (Pawar et al, 2015;Singh et al, 2017). Aerosol mass sources within the IGP are dominated by natural sources such as dust, but also anthropogenic emissions associated with traffic, biomass burning, waste incineration and crop and wood burning (Banerjee et al, 2015;Singh et al, 2017).…”