Molecular characterization of biomass burning tracer compounds in fine particles in Nanjing, China

Abstract

Abstract In this work, a sensitive method based on the High Performance Liquid Chromatography-Electrospray Ionization-Mass spectrometry/Mass spectrometry (HPLC-ESI-MS/MS) technique was established and validated, and successfully applied to quantify biomass burning tracer species (in total 20 compounds) in fine aerosol particles (PM2.5) collected during the full year of 2016 in Nanjing, China. The annual levoglucosan concentration was determined to be 328.3 ng m−3, at a similar level as it in other Chinese cities; the concentration peaked in fall, indicating influences of crop/straw burning during harvest periods. Concentrations of other species were a few orders of magnitude lower than that of levoglucosan, with salicylic acid (1.53 ng m−3), cis-pinonic acid (0.60 ng m−3) and vanillic acid (0.51 ng m−3) as the three most abundant ones. Total concentrations of tracers indicative of softwood, hardwood and grass burning were about equal. Seasonal concentrations of these tracers were generally similar, and all peaked in winter, different from that of levolglucosan. Further positive matrix factorization (PMF) identified four types of biomass (cellulose, harwood lignin, softwood lignin and grass). Celluose was dominated in fall, while softwood and hardwood were both dominated in winter, and seasonal contributions (except summer) were relatively even to grass. On an annual basis, softwood, hardwood and grass contributions were almost on par to the selected tracers, in agreement with the results based only on concentrations, but seasonally, grass was the major one in spring, summer and fall, but much less important in winter.