Fast screening compositions of PM2.5 by ATR-FTIR： Comparison with results from IC and OC/EC analyzers

摘要

Chemical speciation of fine particles or PM_(2.5) collected on filters is still a costly and timeconsuming task. In this study, filter-based PM_(2.5) samples were collected during November–December 2013 at four sites in Guangzhou, and the major components were fast screened(~7 min per filter sample) by Attenuated Total Reflectance(ATR)-Fourier Transform Infrared Spectroscopic(FTIR) in comparison with that measured by Organic carbon/Element carbon(OC/EC) analyzer and Ion Chromatography(IC). The concentrations of nitrate, ammonium, sulfate,primary organic carbon(POC) and secondary organic carbon(SOC) measured by OC/EC and IC analyzers were better correlated with their infrared absorption peak heights at 1320 cm^(-1) for nitrate, 1435, 3045 and 3215 cm^(-1) for ammonium, 615 cm^(-1) for sulfate, 690, 760 and 890 cm^(-1) for POC and 1640 and 1660 cm^(-1) for SOC respectively, during polluted days(PM_(2.5)> 75 μg/m^3) than during clean days(PM_(2.5)≤ 75 μg/m^3). With the evolution of a haze episode during our field campaign, the concentrations of the major PM_(2.5) components displayed consistent variations with their infrared absorption peak heights, suggesting ATR-FTIR could be a fast and useful technique to characterize filter-based PM_(2.5) compositions particularly during pollution events although cautions should be taken when PM_(2.5) levels are low. Notably, elevated PM_(2.5) mass concentrations occurred with enhanced ratios of [NO_(-3)]/[SO_4^(2-)] and [NH^(+4)]/[SO_4^(2-)], implying that nitrogenous components play vital roles in the PM_(2.5) pollution events in the study region.