Influence of post-harvest crop residue fires on surface ozone mixing ratios in the N.W. IGP analyzed using 2years of continuous in situ trace gas measurements

• Published in: Journal of geophysical research. Atmospheres 2016-04, Vol.121 (7), p.3619-3633
• Main Authors: Kumar, V, Sarkar, C, Sinha, V
• Format: Article
• Language: English
• Subjects: Air masses; Air quality; Air quality standards; Atmospheric chemistry; Cloud cover; Crop residues; Crops; Daytime; Fires; Fog; Geophysics; Harvesting; Maxima; Monsoons; Ozone; Photochemistry; Population density; Seasonal variations; Seasons
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1002/2015JD024308

O sub(3), CO, and NO sub(x) affect air quality and tropospheric chemistry but factors that control them in the densely populated N.W. Indo-Gangetic Plain (IGP) are poorly understood. This work presents the first simultaneous 2year long in situ data set acquired from August 2011 to September 2013 at a N.W. IGP site (30.667 degree N, 76.729 degree E; 310masl). We investigate the impact of emissions and meteorology on the diel and seasonal variability of O sub(3), CO, and NO sub(x). Regional post-harvest crop residue fires contribute majorly to an enhancement of 19ppb in hourly averaged ozone concentrations under similar meteorological conditions in summer and 7ppb under conditions of lower radiation during the post monsoon. d[O sub(3)]/dt (from sunrise to daytime O sub(3) maxima) was highest during periods influenced by post-harvest fires in post monsoon season (9.2ppbh super(-1)) and lowest during monsoon season (4.1ppbh super(-1)). Analysis of air mass clusters revealed that enhanced chemical formation of O sub(3) and not transport was the driver of the summertime and post monsoon ambient O sub(3) maxima. Despite having high daytime NO sub(x) (>12ppb) and CO (>440ppb) in winter, average daytime O sub(3) was less than 40ppb due to reduced photochemistry and fog. Average daytime O sub(3) during the monsoon was less than 45ppb due to washout of precursors and suppressed photochemistry due to cloud cover. The 8h ambient air quality O sub(3) standard was violated on 451days in the period August 2011-September 2013. The results show that substantial mitigation efforts are required to reduce regional O sub(3) pollution in the N.W. IGP. Key Points * First simultaneous multiyear in situ data set on O sub(3), CO, and NO sub(x) from N.W. IGP * Agricultural fires enhanced chemical ozone production * Ozone exceedance of 8h standard occurred on 451days (62% of the time)