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.

Automated summary

Organosulfates derived from monoterpene oxidation (MT-OSs) are widely found in atmospheric aerosol particles, but potential sampling artifacts from SO2 have been largely ignored. This study showed a significant increase in OS numbers and abundances when collecting aerosol particles from alpha-pinene oxidation in the presence of SO2. Field study results also demonstrated a decrease in MT-OSs abundances when SO2 was removed during particle sampling under atmospheric conditions. This highlights the importance of considering SO2 artifacts in both classical filter sampling and emerging analytical techniques in future studies.