Spatial distribution of pollutant emissions from crop residue burning in the Punjab and Sindh provinces of Pakistan: uncertainties and challenges.

Emissions of gaseous and particulate pollutants from burning of wheat straw, rice straw, cotton straw, and bagasse were studied for the two agricultural-activity-dominated provinces of Pakistan: the Punjab and Sindh. Emission estimates, inventory, and allocation maps indicated distinct patterns of pollutant emissions in the two provinces. Comparative pollutant emission analysis revealed that the Punjab province produced higher pollutants from agricultural biomass burning than Sindh province. Total emissions from these two provinces were estimated to be 16,084.04 Gg (16.08 Tg) for the year 2006/2007. Wheat straw was found to be the dominant source of CO, CO2, SO2, NOx, and EC emissions in the both provinces. However, for the emissions of CH4, NH3, EC, and OC, the Punjab and Sindh provinces differed markedly for the crop residue share in these pollutant emissions. Rice straw was found to be the largest contributor of CH4 (51%) and NH3 (65%) in Sindh province. When total emissions from biomass burning were considered at provincial level, wheat straw and bagasse were the major crop residues which accounted for 72 and 14% of pollutant emissions, respectively, in the Punjab province, whereas, in Sindh province, the order of crop residue contribution in total emission was as follows: wheat (59%) > bagasse (19%) > rice (14%) > cotton (7%). Emission inventory data of total pollutants per unit area under cultivation (Mg ha(-1)) revealed that Sindh province produced higher emissions per hectare for wheat straw, rice straw, and bagasse than the Punjab province.