ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-10-6487-2010 Humic-like substances in fresh emissions of rice straw burning and in ambient aerosols in the Pearl River Delta Region, China Lin P. 1 Engling G. 2 Yu J. Z. 1 3 4 Division of Environment, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan Department of Chemistry, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China Atmospheric Research Center, HKUST Fok Ying Tung Graduate School, Nansha, Guangzhou 511458, China 16 07 2010 10 14 6487 6500 Copyright: © 2010 P. Lin et al. 2010 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/10/6487/2010/acp-10-6487-2010.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/10/6487/2010/acp-10-6487-2010.pdf

HUmic-LIke Substances (HULIS) are an abundant unresolved mixture of organic compounds present in atmospheric samples. Biomass burning (BB) has been recognized as an important primary source of HULIS, but measurements of HULIS in various fresh BB particles are lacking. In this work, HULIS in emissions of rice straw burning was measured in a number of field and chamber experiments. The average HULIS/OC ratio was 0.34&plusmn;0.05 in μg/μgC, showing small variance among emissions under different burning conditions. The influence of BB on ambient HULIS levels was investigated by examining the spatial and temporal variation of HULIS and other aerosol constituents and interspecies relations in ambient PM<sub>2.5</sub>. The PM<sub>2.5</sub> samples were collected at an urban and a suburban location in the Pearl River Delta (PRD), China over a period of one year. The HULIS concentrations in the ambient PM<sub>2.5</sub> were significantly higher in air masses originating from regions influenced by BB. Significant correlations between HULIS and water-soluble K<sup>+</sup> concentrations at both sites further support that BB was an important source of HULIS. Ambient concentrations of HULIS also correlated well with those of sulfate, oxalate, and oxidant (the sum of O<sub>3</sub> and NO<sub>2</sub>). The HULIS/OC ratios in BB-influenced ambient aerosols (~0.6) were much higher than those in the fresh BB emissions (0.34), implying that secondary formation was also an important source of HULIS in the atmosphere. The annual average HULIS concentrations were 4.9 μg m<sup>−3</sup> at the urban site and 7.1 μg m<sup>−3</sup> at the suburban site while the annual average concentrations of elemental carbon were 3.3 μg m<sup>−3</sup> and 2.4 μg m<sup>−3</sup>, respectively. The urban-suburban spatial gradient of HULIS was opposite to that of elemental carbon, negating vehicular exhaust as a significant primary emission source of HULIS.

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