Pollution Characterizations and Oxidative Potentials of Water-Soluble Organic Matters at Different Polarity Levels in Winter PM2.5 Over Xi'an

Abstract

Atmospheric fine particulate matter (PM2.5) can produce reactive oxygen species (ROS), which have adverse effects on health. Acidic, neutral, and highly polar water-soluble organic matter (WSOM) is an important component of ROS in organic aerosols. PM2.5 samples were collected in winter 2019 in Xi'an City to deeply explore the pollution characteristics and health risks of WSOM components with different polarity levels. The results showed that the concentration of WSOM in PM2.5 in Xi'an was (4.62±1.89) μg·m-3, humic-like substances (HULIS) were an important part of WSOM (78.81%±10.50%), and the proportion of HULIS was higher in haze days. The concentration levels of three WSOM components with different polarities in haze and non-haze days were:neutral HULIS (HULIS-n)>acidic HULIS (HULIS-a)>highly-polarity WSOM(HP-WSOM) and HULIS-n>HP-WSOM>HULIS-a. The oxidation potential (OP) was measured using the 2',7'-dichlorodihydrofluorescein (DCFH) method. It was found that the law of OPm in haze and non-haze days was HP-WSOM>HULIS-a>HULIS-n, and the characteristic of OPv was HP-WSOM>HULIS-n>HULIS-a. During the whole sampling period, OPm was negatively correlated with the concentrations of the three components of WSOM. The OPm of HULIS-n (R2=0.8669) and HP-WSOM (R2=0.8582) in haze days were highly correlated with their respective concentrations. The OPm of HULIS-n, HULIS-a, and HP-WSOM in non-haze days were strongly dependent on their respective component concentrations.