Chemical composition and light absorption of carbonaceous aerosols emitted from crop residue burning: influence of combustion efficiency

Wang, Yujue; Hu, Min; Xu, Nan; Qin, Yanhong; Wu, Zhijun; Zeng, Liwu; Huang, Xiaofeng; He, Lingyan

Biomass burning is one of the major sources of carbonaceous aerosols, which affects air quality, the radiation budget and human health. Field straw residue burning is a widespread type of biomass burning in Asia, while its emissions are poorly understood compared with wood burning emissions. In this study, lab-controlled straw (wheat and corn) burning experiments were designed to investigate the emission factors and light absorption properties of different biomass burning organic aerosol (BBOA) fractions, including water-soluble organic carbon (WSOC), humic-like substances (HULIS) and water-insoluble organic carbon (WISOC). The influences of biofuel moisture content and combustion efficiency on emissions are comprehensively discussed. The emission factors of inline-formulaPM2.5, organic carbon (OC) and elemental carbon (EC) were inline-formula9.3±3.4, inline-formula4.6±1.9 and inline-formula0.21±0.07inline-formulag kg−1 for corn burning and inline-formula8.7±5.0, inline-formula3.9±2.8 and inline-formula0.22±0.05inline-formulag kg−1 for wheat burning, generally lower than wood or forest burning emissions. Though the mass contribution of WISOC to OC (32 %–43 %) was lower than WSOC, the light absorption contribution of WISOC (57 %–84 % at 300–400 inline-formulanm) surpassed WSOC due to the higher mass absorption efficiency (MAE) of WISOC. The results suggested that BBOA light absorption would be largely underestimated if only the water-soluble fractions were considered. However, the light absorption of WSOC in the near-UV range, occupying 39 %–43 % of the total extracted OC absorption at 300 inline-formulanm, cannot be negligible due to the sharper increase of absorption towards shorter wavelengths compared with WISOC. HULIS were the major light absorption contributors to WSOC, due to the higher MAE of HULIS than other high-polarity WSOC components. The emission levels and light absorption of BBOA were largely influenced by the burning conditions, indicated by modified combustion efficiency (MCE) calculated by measured inline-formulaCO and inline-formulaCO2 in this study. The emission factors of inline-formulaPM2.5, OC, WSOC, HULIS and organic acids were enhanced under lower MCE conditions or during higher moisture straw burning experiments. Light absorption coefficients of BBOA at 365 inline-formulanm were also higher under lower MCE conditions, which was mainly due to the elevated mass emission factors. Our results suggested that the influence of varied combustion efficiency on particle emissions could surpass the differences caused by different types of biofuels. Thus, the burning efficiency or conditions should be taken into consideration when estimating the influence of biomass burning. In addition, we observed that the ratios of inline-formula M16inlinescrollmathml chem normal K + / normal OC 38pt14ptsvg-formulamathimg8addf229fa84e9c7ad1a96c2a65d6ac9 acp-20-13721-2020-ie00001.svg38pt14ptacp-20-13721-2020-ie00001.png and inline-formula M17inlinescrollmathml chem normal Cl - / normal OC 41pt14ptsvg-formulamathimgae082a99c887f9c753460b8af1d5f8c3 acp-20-13721-2020-ie00002.svg41pt14ptacp-20-13721-2020-ie00002.png increased under higher MCE conditions due to the enhancement of potassium and chlorine released under higher fire temperatures during flaming combustion. This indicates that the potassium ion, as a commonly used biomass burning tracer, may lead topage13722 estimation uncertainty if the burning conditions are not considered.



Wang, Yujue / Hu, Min / Xu, Nan / et al: Chemical composition and light absorption of carbonaceous aerosols emitted from crop residue burning: influence of combustion efficiency. 2020. Copernicus Publications.


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