Overestimation Of Monoterpene Organosulfate Abundance In Aerosol Particles By Sampling In The Presence Of So2

Organosulfates derived from monoterpene oxidation (MT-OSs) are ubiquitously abundant in atmospheric aerosol particles. However, to date, potential sampling artifacts in MT-OS detection and quantification have been largely ignored. Here, it is demonstrated that collecting aerosol particles from alpha-pinene oxidation onto filters in the presence of SO2 strongly increased OS numbers and particle mass-normalized abundances by up to 72% and 3 orders of magnitude, respectively. Similarly, at much lower SO2 levels (i.e., atmospheric conditions), an average decrease of 43% in MT-OSs abundances was detected during a field study when SO2 was removed during particle sampling. Additionally, a tremendous increase in mass spectrometric ion signals of OSs was observed when particles were analyzed directly (i) by electrospray ionization (ESI) in the presence of S(VI) and (ii) by extractive ESI (EESI) in the presence of S(IV). Our findings raise concerns on the extent of the recently suggested formation of MT-OSs from S(IV) and organic peroxides, as none of these studies accounted for sampling artifacts from SO2. Furthermore, SO2 artifacts likely affected also earlier studies on MT-OSs. In future studies, SO2 artifacts should be considered more carefully for classical filter sampling and also for emerging analytical techniques.