Abstract
Rapid economic growth and development have exacerbated air quality problems across India, driven by many poorly understood pollution sources and understanding their relative importance remains critical to characterising the key drivers of air pollution. A comprehensive suite of measurements of 90 non-methane hydrocarbons (NMHCs) (C2-C14), including 12 speciated monoterpenes and higher molecular weight monoaromatics, were made at an urban site in Old Delhi during the pre-monsoon (28-May to 05-Jun 2018) and post-monsoon (11 to 27-Oct 2018) seasons using dual-channel gas chromatography (DC-GC-FID) and two-dimensional gas chromatography (GC×GC-FID). Significantly higher mixing ratios of NMHCs were measured during the post-monsoon campaign, with a mean night-time enhancement of around 6. Like with NOx and CO, strong diurnal profiles were observed for all NMHCs, except isoprene, with very high NMHC mixing ratios between 35-1485 ppbv. The sum of mixing ratios of benzene, toluene, ethylbenzene and xylenes (BTEX) routinely exceeded 100 ppbv at night during the post-monsoon period, with a maximum measured mixing ratio of monoaromatic species of 370 ppbv. The mixing ratio of highly reactive monoterpenes peaked at around 6 ppbv in the post-monsoon campaign and correlated strongly with anthropogenic NMHCs, suggesting a strong non-biogenic source in Delhi. A detailed source apportionment study was conducted which included regression analysis to CO, acetylene and other NMHCs, hierarchical cluster analysis, EPA UNMIX 6.0, principal component analysis/absolute principal component scores (PCA/APCS) and comparison with NMHC ratios (benzene/toluene and i-/n-pentane) in ambient samples to liquid and solid fuels. These analyses suggested the primary source of anthropogenic NMHCs in Delhi was from traffic emissions (petrol and diesel), with average mixing ratio contributions from Unmix and PCA/APCS models of 38% from petrol, 14% from diesel and 32% from liquified petroleum gas (LPG) with a smaller contribution (16%) from solid fuel combustion. Detailed consideration of the underlying meteorology during the campaigns showed that the extreme night-time mixing ratios of NMHCs during the post-monsoon campaign were the result of emissions into a very shallow and stagnant boundary layer. The results of this study suggest that despite widespread open burning in India, traffic-related petrol and diesel emissions remain the key drivers of gas-phase urban air pollution in Delhi.
Highlights
Poor urban air quality is a major global public health concern, in the developing world, as rapid urban growth has increased concentrations to harmful levels
Paper included some emissions from static diesel generators, were the dominant source of NMHCs at the site, with relative mean mixing ratio contributions predicted by the Principle component analysis (PCA)/absolute principle component scores (APCS) and Unmix models from petrol automobiles and motorbikes (38%), diesel trucks, trains and generators (14%), liquified petroleum gas (LPG) from cooking and vehicles (32%) and open burning of biomass and municipal solid waste (16%)
This study presented a comprehensive suite of NMHC measurements performed at an urban site in Delhi during the pre- and post-monsoon seasons in 2018
Summary
Poor urban air quality is a major global public health concern, in the developing world, as rapid urban growth has increased concentrations to harmful levels. This issue remains at the forefront of many governmental policies, as by 2050 approximately 66% of the global population are expected to live in urban environments.[1] Globally, an estimated 4.2 million premature deaths were a result of poor ambient air quality in 2016,2 mainly caused by exposure to particulate matter (PM) and ozone (O3). Biogenic NMHC emissions are the dominant source with an estimated ux of 377–760 TgC per year.[4,5,6] anthropogenic emissions, which have been estimated to be 130– 169 TgC per year,[5,7,8] can be important drivers of poor air quality in densely populated urban environments
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