Speciation of carboxylic components in humic-like substances (HULIS) and source apportionment of HULIS in ambient fine aerosols (PM2.5) collected in Hong Kong.

Humic-like substances (HULIS) are an important mixture of organic compounds, which account for a great part of water-soluble organic compounds in ambient aerosols. In this study, individual carboxylic and hydroxylic species in HULIS extracts of PM_2.5 samples collected in Hong Kong during summer were measured by gas chromatography mass spectrometry with prior chemical derivatization. Significantly higher levels of HULIS were observed on days mainly impacted by regional pollution (regional days, 4.11 ± 1.76 μg m⁻³) than on days under local emission influences (local days, 0.56 ± 0.30 μg m⁻³). Positive matrix factorization was applied to identify the major sources and apportion their contributions to HULIS. Simultaneous monitoring and analysis data from four different sampling sites showed that sources of HULIS in Hong Kong were mainly regional with small spatial variations. Secondary aerosol formation (both organic and inorganic) had a predominant contribution (52.7%) to HULIS during the whole sampling period. It accounted for 1.88 ± 0.91 μg m⁻³ of HULIS on regional days, which was about 5 times higher than its contribution (0.39 ± 0.34 μg m⁻³) on local days. Of the three identified primary sources, biomass burning had the largest contribution on both regional (34.9%) and local days (24.6%). Marine vessels were also a significant contributor, especially on local days (20.3%). Vehicle exhaust, on the other hand, showed a negligible contribution to HULIS (2.1%) in Hong Kong in this study. [ABSTRACT FROM AUTHOR]