Chemical composition of pre-monsoon air in the Indo-Gangetic Plain measured using a new air quality facility and PTR-MS: high surface ozone and strong influence of biomass burning

Abstract

One seventh of the world's population lives in the Indo-Gangetic Plain (IGP) and the fertile region sustains agricultural food crop production for much of South Asia, yet it remains one of the most under-studied regions of the world in terms of atmospheric composition and chemistry. In particular, the emissions and chemistry of volatile organic compounds (VOCs) that form surface ozone and secondary organic aerosol through photochemical reactions involving nitrogen oxides are not well understood. In this study, ambient levels of VOCs such as methanol, acetone, acetaldehyde, acetonitrile and isoprene were measured for the first time in the IGP. A new atmospheric chemistry facility that combines India's first highsensitivity proton transfer reaction mass spectrometer, an ambient air quality station and a meteorological station, was used to quantify in situ levels of several VOCs and air pollutants in May 2012 at a suburban site in Mohali (northwest IGP). Westerly winds arriving at high wind speeds (5-20 m s −1 ) in the pre-monsoon season at the site were conducive for chemical characterization of regional emission signatures. Average levels of VOCs and air pollutants in May 2012 ranged from 1.2 to 2.7 nmol mol −1 for aromatic VOCs, 5.9 to 37.5 nmol mol −1 for the oxygenated VOCs, 1.4 nmol mol −1 for acetonitrile, 1.9 nmol mol −1 for isoprene, 567 nmol mol −1 for carbon monoxide, 57.8 nmol mol −1 for ozone, 11.5 nmol mol −1 for nitrogen oxides, 7.3 nmol mol −1 for sulfur dioxide, 104 µg m −3 for PM 2.5 and 276 µg m −3 for PM 10 . By analyzing the one-minute in situ data with meteorological parameters and applying chemical tracers (e.g., acetonitrile for biomass burning) and inter-VOC correlations, we were able to constrain major emission source

Pre-monsoon air quality over Lumbini, a world heritage site along the Himalayan foothills

“…CO concentration observed in Lumbini is lower than that of Mohali, western India, where the average concentration was 566.7 ppbv during pre-monsoon season due to intense biomass and agro-residue burning over the region (Sinha et al, 2014). Temporal variation of CO concentrations is similar to that of BC, exhibiting very strong correlation (r = 0.9).…”

“…Different sites located at urban, semi-urban and remote locations were used for comparison to get a clear comparative picture of the situation at Lumbini amongst other locations in the region. Pre-monsoon seasonal average PM 2.5 concentration in Lumbini has been found to be lower than in the megacity Delhi and northwestern IGP (Sinha et al, 2014), possibly due to higher levels of emissions (from traffic and biomass burning, respectively) over those regions. In addition, average BC and CO concentrations in Lumbini fell between concentrations observed at rural sites (up to 6 times higher) and cities in the region (see Table 2), indicating that Lumbini, in a way, can still be considered a semi-urban location.…”

“…In a separate analysis (not shown here), we considered only the WS > 1 m s −1 and calculated the correlation coefficients to investigate the influence of regional emissions. Past studies near this site have been focused on cities like Kathmandu (Sharma et al, 2012;Panday and Prinn, 2009;Putero et al, 2015) and Kanpur (Ram et al, 2010) and regions of IGP dominated by agro-residue burning (Rastogi et al, 2016;Sinha et al, 2014;Sarkar et al, 2013), all of which reported very high levels of pollution. Our study adds to the growing list of scientific observations in the IGP by providing data from the foothills of the central Himalayas.…”

Tropospheric ozone and its precursors from the urban to the global scale from air quality to short-lived climate forcer

“…Ojha et al, 2014;Cristofanelli et al, 2010), land clearing, agriculture and human settlements may cause occasional elevated ozone concentrations (Jacob et 1996). The seasonal ozone variation may be affected by these activities which can be influenced by seasonal meteorological conditions such as the occurrence of a wet/dry seasons (Valks et al, 2014;Rama Gopal et al, 2014;Cristofanelli et al, 2010;Sinha et al, 2014). Under stable conditions, ozone depletion due to ozone deposition and NO titration will occur.…”

Seasonal and diurnal variations in methane and carbon dioxide in the Kathmandu Valley in the foothills of the central Himalayas

“…Furthermore, a major segment of the population in South Asia has an agrarian economy and uses biofuel for cooking activities. Agro-residue burning is also common practice in the region, which is an important major source of air pollutants and greenhouse gases in the region (CBS, 2011;Pandey et al, 2014;Sinha et al, 2014).…”