Contributions of open crop straw burning emissions to PM2.5 concentrations in China

PM2.5 inventories have been developed inmajor Chinese cities to quantify the contributions from various sources based on annual emissions. This approach, however, could substantially underestimate the contribution fromopen straw burning during the harvest or other active burning periods. This study examines this issue by estimatingmonthly and annual straw-burning PM2.5 emissions in China and comparingwith themwith the corresponding emissions fromother anthropogenic sources. Annually burned strawPM2.5 emissions during 1997∼2013 for 31China provinces were calculated based on crop and related burning information for 12months based on satellite detection of agricultural burning. Annual emissions fromother anthropogenic sources were collected from the literature and allocated tomonthly values using air pollution indexmeasurements. The results indicate that the annual PM2.5 emissions fromopen straw burning inChinawere 1.036m tons. The monthly PM2.5 emission ratios of straw burning to other anthropogenic sources during June, the harvest period formany regions, were several times larger than the annual ratios at national, regional, and province levels, suggesting that, in contrast to annual emissions that were used in the PM2.5 inventories inChinese cities to assess the contributions fromother sources,monthly emissions should be used to assess the contributions from straw burning during the harvest or other active burning periods. The larger contributions from straw burning shown in this study also suggest that substantial reduction of openfield straw burningwould dramatically improve air quality inmanyChinese regions during the harvest or other active burning periods.