Effect of Crop Residue Burning Over North India

Abstract

During harvesting period over north India, large amount agricultural residues are burnt in field to clear the field and prepare for next season of sowing. Biomass burning emits large amount of trace gases and particulates to the atmosphere. This emitted particulate even reaches long distance through airmass modifying the air quality at the local as well as regional level. Viewing this large impact of burning on the composition of particulates, a study was conducted to analyze the contribution of wheat and rice stubble burning practices on concentration levels of PM2.5 which were monitored in the ambient air at several sites over North India which included Delhi, Patiala, Chandigarh, Amritsar, Nainital and Kullu. Aerosol samples were collected on Quartz filter papers of 45mm of Whattman brand using dual channel dust sampler and fine dust sampler units for a 24 h period during rice harvesting season (October,2015-November,2015). Results pointed out a distinct increase in aerosols during the crop stubble burning periods and the impact remained in the atmosphere for many days even after burning period. Total Suspended Particulate Matter (TSPM) was also measured at three different agricultural sites near Patiala during the peak time of burning for two hours and results indicated distinct increase in TSPM also. The concentration weighted trajectory (CWT) receptor model was used to identify spatial source distribution and contribution of regional-scale transported aerosols. Three-dimensional 5-day backward trajectories arriving at all the sites, 500m above ground level were calculated using HYSPLIT-4 trajectory model during burning episodes. Results indicated that states undergoing crop residue burning are potential sources contributing the major PM2.5 in all the monitored cities. PM2.5 samples of Delhi and Patiala were further analyzed for ionic composition using ion analyzer. High concentration levels of K+ and Na+ were obtained during burning season of rice crops. Although, increase in K+ levels was observed at all the sites, but a strong association in K+ levels and Crop Residue Burning was obtained at an agricultural site only. Using these data, PCA Model source apportionment was made to understand the depth of effect of agricultural residue burning. Principal component analysis with varimax rotation was used to qualify the source contributions to PM2.5. Vehicular emissions and biomass burning were two major sources that contributed to PM2.5 concentrations in Delhi, whereas in Patiala, two major sources identified were industrial pollution and biomass burning.