도시지역 PM<sub>2.5</sub>의 HULIS 화학 특성 및 발생 과정 조사

Abstract

Little information on HUmic-Like Substances (HULIS) in ambient particulate matter has been reported yet in Korea. HULIS makes up a significant fraction of the water-soluble organic mass in the atmospheric aerosols and influence their water uptake properties. In this study 24-hr PM2.5 samples were collected between December 2013 and October 2014 at an urban site in Gwangju and analyzed for organic carbon (OC), elemental carbon (EC), watersoluble OC (WSOC), HULIS, and ionic species, to investigate possible sources and formation processes of HULIS. HULIS was separated using solid phase extraction method and quantified by total organic carbon analyzer. During the study period, HULIS concentration ranged from 0.19 to 5.65 μgC/m with an average of 1.83±1.22 μgC/m, accounting for on average 45% of the WSOC (12~73%), with higher in cold season than in warm season. Strong correlation of WSOC with HULIS (R = 0.91) indicates their similar chemical characteristics. On the basis of the relationships between HULIS and a variety of chemical species (EC, K, NO3-, SO4, and oxalate), it was postulated that HULIS observed during summer and winter were likely attributed to secondary formation and primary emissions from biomass burning (BB) and traffics. Stronger correlation of HULIS with K, which is a BB tracer, in winter (R = 0.81) than in summer (R = 0.66), suggests more significant contribution of BB emissions in winter to the observed HULIS. It is interesting to note that BB emissions may also have an influence on the HULIS in summer, but further study using levoglucosan that is a unique organic marker of BB emissions is required during summer. Higher correlation between HULIS and oxalate, which is mainly formed through cloud processing and/or photochemical oxidation processes, was found in the summer (R = 0.76) than in the winter (R = 0.63), reflecting a high fraction of secondary organic aerosol in the summer.