3. Emission of Toxic Air Pollutants and Greenhouse Gases from Crop Residue Open Burning in Southeast Asia

Agricultural crop production plays an important role in the economic development of Southeast Asia (SEA) countries. Annually, large amounts of crop residues are generated and field open burning for land clearing is commonly practiced which emits considerable amounts of toxic air pollutants and climate forcing agents. This study estimated the emissions of toxic gases, aerosol, and greenhouse gases from the crop residue open burning (CROB) in SEA countries. Emission inventory (EI) was done using the activity data gathered from primary surveys and published records for the SEA countries. The best estimates of emission species were calculated using the emission factors and the activity data that were most relevant for the considered SEA countries. In 2010, the SEA CROB emissions, in Gg were: 16,160 for CO; 320 for NO_x; 28 for SO₂; 980 for NMVOC; 550 for NH₃; 2060 for PM₁₀; 1880 for PM_2.5; 80 for BC; 885 for OC; 178,370 for CO₂; 580 for CH₄; and 14 for N₂O. Indonesia was the top contributor of all emission species (25–39%) followed by Vietnam (17–30%), Myanmar (8–19%), and Thailand (7–16%). Among 8 crop types considered, rice straw field burning contributed dominantly (85–98%) to the total SEA CROB emissions, followed by sugarcane, maize, and soybean. Low and high emission estimates were calculated using the ranges of activity data and available emission factors, respectively, to assess the uncertainty of the emission estimate for each species. The obtained gridded SEA CROB emissions with a resolution of 0.1° × 0.1° revealed higher emission intensity over the agricultural land areas, especially of rice, sugarcane, and maize. Temporal emissions showed higher peaks in the months following major crop harvesting periods in the dry season. The EI data for CROB produced in this study provided a key input for assessment of relative contributions of the emission sources in the SEA for further development of emission reduction strategies.