Quantification of known and unknown terpenoid organosulfates in PM10 using untargeted LC-HRMS/MS: contrasting summertime rural Germany and the North China Plain

Abstract

Organosulfates (OSs) are a ubiquitous class of compounds in atmospheric aerosol particles. However, a detailed quantification of OSs is commonly hampered because of missing authentic standards and the abundance of unknown OSs. Using a combined targeted and untargeted approach of high-resolution liquid chromatography-Orbitrap mass spectrometry (LC-Orbitrap MS), we quantified for the first time the total concentrations of known and unknown monoterpene (MT) and sesquiterpene (SQT) OSs in summertime PM10 particulate matter from field studies in rural Germany (MEL) and the North China Plain (NCP). At each site, we observed more than 50 MT-OSs, 13 of which were detectable at both sites. For both locations, median concentrations of MT-OSs were in the range of 10 to 40 ng m-3, to which the 13 common MT-OSs contributed on average >50 %. The main contributor to MT-OSs was C9H16O7S (MT-OS 267) with average mass concentrations of 2.23 and 6.38 ng m-3 for MEL and NCP respectively. The concentrations of MT-OSs correlated with the concentrations of MT oxidation products only for MEL. For NCP, the low concentrations of MT oxidation products (i.e. typically <1 ng m-3) suggested a suppression of carboxylic acid formation under high concentrations of NOx and particulate sulfate. Furthermore, we observed 17 SQT-OSs for the MEL samples, whereas 40 SQT-OSs were detected in the NCP samples. Only five of these SQT-OSs were detectable at both sites. Correspondingly, the total concentrations of SQT-OSs were larger for NCP than for MEL, which suggested large differences in the particle chemistry. In particular, aerosol acidity was found to be a key factor during SQT-OS formation, and was probably not sufficient in the PM10 from MEL.