Sources of humic-like substances in the Pearl River Delta, China: positive matrix factorization analysis of PM&amp;lt;sup&amp;gt;2.5&amp;lt;/sup&amp;gt; major components and source markers

B Y Kuang,P Lin,X H H Huang,J Z Yu

doi:10.5194/acp-15-1995-2015

Abstract

Abstract. Humic-like substances (HULIS), the hydrophobic part of water-soluble organic carbon (WSOC), account for a significant fraction of PM2.5 mass. Their source studies are so far largely qualitative. In this study, HULIS and WSOC were determined in 100 PM2.5 samples collected in 2009 at an urban site (Guangzhou) and a suburban site (Nansha) in the Pearl River Delta in South China. The annual average concentration of HULIS was 4.83 and 4.71 μg m−3, constituting 8.5 and 10.2% of the PM2.5 mass, while HULIS-C (the carbon component of HULIS) contributed 48 and 57% of WSOC at the two sites, respectively. HULIS were found to correlate with biomass burning (BB) tracers (i.e., levoglucosan and K) and secondary species (e.g., SO42− and NH4+), suggesting its association with BB emissions and secondary formation processes. Sources of HULIS were investigated using positive matrix factorization analysis of PM2.5 chemical composition data, including major components and source markers. In addition to secondary formation process and BB emissions, residual oil combustion related to shipping was identified for the first time as a significant source of HULIS. Secondary formation process contributed the most, accounting for 49–82% of ambient HULIS at the two sites in different seasons. BB emissions contributed a seasonal average of 8–28%, with more contributions observed in the winter months (November–February) due to crop residue burning during harvest season. Residual oil combustion was revealed to be an important source at the suburban site in summer (44% of HULIS-C) due to its proximity to one of the ports and the shipping lane in the region. Vehicle emissions were found to contribute little to HULIS, but had contributions to the hydrophilic WSOC fraction. The contrast in contributions from different combustion sources to HULIS and hydrophilic WSOC suggests that primary sources of HULIS are linked to inefficient combustion. This source analysis suggests further study of HULIS be focused on secondary formation process and source characteristics of HULIS from BB and residual oil combustion.

Highlights

Humic-like substances (HULIS) are a mixture of organic species extracted from atmospheric aerosol particles with characteristics similar to humic and fulvic acids (Graber and Rudich, 2006)
The objective of this study is to identify major sources of HULIS and quantify their contributions in PM2.5 samples in the Pearl River Delta (PRD)
organic matter (OM) accounted for one-fourth to one-third of PM2.5 mass in summer and winter (Fig. S5), indicating the importance of sources analysis of OM

Summary

Introduction

Humic-like substances (HULIS) are a mixture of organic species extracted from atmospheric aerosol particles with characteristics similar to humic and fulvic acids (Graber and Rudich, 2006). It is operationally defined by procedures used for its isolation from the bulk water-soluble aerosol components by removing inorganic salts and low-molecular weight hydrophilic organic compounds (e.g., oxalate). Solid phase extraction (SPE) methods have been widely used to isolate HULIS (e.g., Varga et al, 2001; Lin et al 2010a, 2010b). Other methods have been utilized, such as capillary electrophoresis (Havers et al, 1998a), ultrafiltration (Havers et al, 1998b), ion-exchange chromatography (Decesari et al, 2000), and size-exclusion chromatography (Krivacsy et al, 2000; Samburova et al, 2005a, b)

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Results

Conclusion