秸秆燃烧PM_(2.5)及其碳组分排放特征研究

Emission characteristics of PM_(2.5) and its carbonaceous components emitted from crop straw burning

采用自主设计的民用炉灶燃烧-烟气稀释采样装置,获得安徽淮南和湖北武汉的小麦、玉米、水稻、花生、大豆5类典型农作物秸秆燃烧排放PM_(2.5)及其碳组分的排放因子,分析了排放因子的差异,筛选了碳组分的标识组分。结果表明,秸秆燃烧PM_(2.5)的排放因子随秸秆种类和地区的不同而呈现明显差异,淮南的秸秆燃烧烟气PM_(2.5)排放因子在0.56～7.67 g·kg^(-1),武汉的秸秆燃烧烟气PM_(2.5)排放因子在3.53～7.91 g·kg^(-1);不同种类秸秆烟气PM_(2.5)排放因子有明显差异,花生秸秆燃烧烟气PM_(2.5)的排放因子最高(均值5.98 g·kg^(-1)),是大豆秸秆燃烧烟气PM_(2.5)排放因子(均值2.04 g·kg^(-1))的2.93倍。秸秆燃烧PM_(2.5)的排放因子随秸秆含水率的增加而明显增大。碳组分是5种秸秆燃烧PM_(2.5)的主要成分碳,总碳(TC)占PM_(2.5)的36.40%～65.84%,其中花生秸秆TC排放因子最高(均值2.58 g·kg^(-1)),是小麦秸秆的TC排放因子(均值1.07 g·kg^(-1))的2.41倍;秸秆燃烧PM_(2.5)中的有机碳(OC)浓度远高于元素碳(EC),OC/EC值为2.36～13.73,表明秸秆燃烧对二次气溶胶的形成具有重要影响。淮南及武汉的秸秆燃烧烟气PM_(2.5)中char-EC/soot-EC值为17.20～64.16,char-EC显著高于soot-EC,可作为判断秸秆燃烧源的一个重要指标。主成分分析结果表明,秸秆燃烧PM_(2.5)中的OC1、OC2和EC1在碳组分中贡献较大,因此,OC1、OC2和EC1可作为秸秆燃烧PM_(2.5)的标识性组分。

Five kinds of typical crop straws including wheat, corn, peanut, rice and soybean straws obtained from Huainan, Anhui Province and Wuhan, Hubei Province, were investigated for combustion experiment using self-designed combustion-dilution sampling device. The fine particulate matter(PM2.5)and carbonaceous components emitted from crop straws combustion were collected and the differences in emission factors of PM2.5 and the carbonaceous components in the two regions were analyzed,and the indicative components of carbonaceous components were screened. The result showed that emission factors of PM2.5 from crop straw burning were obviously different for the different crop straw species and regions. The emission factors of PM2.5 from crop straw burning in Huainan were 0.56~7.67 g·kg^-1, and that in Wuhan was 3.53~7.91 g·kg^-1. Moreover, the emission factor of PM2.5 was also significantly different for the different kinds of crop straws.The emission factor of PM2.5 of peanut straw reached the maximum value with an average value of 5.98 g·kg^-1 among the five crop straws,which was 2.93 times of that of soybean straw(the average value was 2.04 g·kg^-1). The emission factor of PM2.5 increased with increasing the moisture content in straw. Carbonaceous components were the main component of PM2.5 from crop straw burning, and the percentage of total carbon(TC)in PM2.5 ranged from 36.40% to 65.84%. Among the five crop straws, peanut straw showed the highest emission factor of TC in PM2.5 with an average value of 2.58 g·kg^-1, which was 2.41 times of that of wheat straw with the average value of 1.07 g·kg^-1. The percentage of organic carbon(OC)was much higher than that of elemental carbon(EC)in PM2.5, and the ratios of OC/EC ranged from 2.36 to 13.73, indicating that crop straw burning had an important effect on the formation of secondary aerosols. The ratios of char-EC/soot-EC in PM2.5 from crop straw in Huainan and Wuhan were between 17.20~64.16, and char-EC was significantly higher than soot-EC. So the ratios of char-EC/soot-EC could be used as an important indicator to judge the source of straw combustion. The result of principal component analysis(PCA)showed that OC1, OC2 and EC1 mainly contributed to the carbonaceous component in PM2.5 in Huainan and Wuhan, and therefore OC1, OC2 and EC1 could be used as indicative components of PM2.5 emitted from crop straw burning.