Trace gas and particle emissions from open burning of three cereal crop residues: Increase in residue moistness enhances emissions of carbon monoxide, methane, and particulate organic carbon

We determined emission factors for open burning of straw of rice, wheat, and barley, as well as rice husks, and we incorporated the effects of moisture content on the emission factors for the straw. A closed system that simulated on-site backfiring of residues on the soil surface under moderate wind conditions was used to measure the gas and particle emissions from open burning of the residues on an upland field. Two moisture content conditions were evaluated: a dry condition (air-dried residues, 11-13% by weight) and a moist condition (20%). When a linear regression model with the initial moisture content of the residue as the explanatory variable showed good correlation between the primary emission data of a substance and the moisture content, the regression model was adopted as a function to give the emission factors. Otherwise, the unmodified primary data were used as the emission factors. The magnitudes of the gas and particle emissions differed among the residue types. For example, carbon monoxide (CO) emissions from straw of rice, wheat, and barley and rice husks burned under the dry condition were 27.2 ± 1.7, 41.8 ± 24.2, 46.9 ± 2.1, and 66.1 g kg−1 dry matter, and emissions of methane (CH4) were 0.75 ± 0.01, 2.01 ± 0.93, 1.47 ± 0.06, and 5.81 g kg−1 dry matter, respectively (n = 2 for straw with the standard deviation; n = 1 for husks). Emissions of carbon-containing gases and particles (e.g., CO, CH4, and particulate organic carbon) were higher under the moist condition than under the dry condition, which suggests that emission factors for open burning should incorporate the effects of moisture content except open burning performed in the dry season or arid zones.