Chemical speciation of fine particles or PM2.5 collected on filters is still a costly and time-consuming task.In this study,filter-based PM2.5 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-z 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 (PM2.5 ＞ 75 μg/m3) than during clean days (PM2.5 ≤ 75 μg/m3).With the evolution of a haze episode during our field campaign,the concentrations of the major PM2.5 components displayed consistent variations with their infrared absorption peak heights,suggesting ATR-FTIR could be a fast and useful technique to characterize filter-based PM2.5 compositions particularly during pollution events although cautions should be taken when PM2.5 levels are low.Notably,elevated PM2.5 mass concentrations occurred with enhanced ratios of [NO3-]/[SO42-] and [NH4+]/[SO42-],implying that nitrogenous components play vital roles in the PM2.5 pollution events in the study region.