Temporal variations of the abundance and optical properties of water soluble Humic-Like Substances (HULIS) in PM2.5 at Guangzhou, China

Abstract

Humic-Like Substances (HULIS) are important macromolecular compounds that are present in PM2.5 and play significant roles in the atmospheric environment. In this study, 48 PM2.5 samples were collected from February 2010 to January 2011 at an urban site in Guangzhou, southern China. The water soluble HULIS fractions in PM2.5 were analyzed to explore the temporal variation of abundance and optical properties and to identify their possible sources. The HULIS concentrations were in the range of 0.4 to 8.2μgCm−3, with a mean of 2.4μgCm−3. HULIS are important components in organic aerosols, accounting for 17±5% of the organic carbon (OC), and 49±6 and 68±5% of water soluble organic carbon (WSOC) as determined with a total organic carbon (TOC) analyzer and UV absorbance at 250nm, respectively. The special UV absorbance (SUVA) at 254nm and 280nm and the E250/E365 ratio of HULIS were 3.2±0.5L (mmgC)−1, 2.2±0.4L (mmgC)−1, and 5.9±0.9, respectively. The HULIS fractions had higher concentrations, slightly higher SUVA values, and lower E250/E365 ratios from November to January, indicating the important contribution of aromatic compounds to HULIS in the dry season. The concentrations of HULIS were positively correlated with water soluble K+, secondary organic carbon (SOC), and secondary inorganic ions (NH4+, NO3−, and SO42−). These results suggest that biomass burning and secondary photochemical formation are both sources of HULIS in our study area. In addition, the SUVA280 of HULIS was strongly correlated with K+ and SOC, suggesting that HULIS properties were also influenced by their primary source of biomass burning and secondary atmospheric formation.