Effects of two transition metal sulfate salts on secondary organic aerosol formation in toluene/NO_x photooxidation

Abstract

Aerosol phase reactions play a very important role on secondary organic aerosol (SOA) formation, and metal-containing aerosols are important components in the atmosphere. In this study, we tested the effects of two transition metal sulfate salts, manganese sulfate (MnSO₄) and zinc sulfate (ZnSO₄), on the photochemical reactions of a toluene/NO_x photooxidation system in a 2 m³ smog chamber. By comparing photochemical reaction products of experiments with and without transition metal sulfate seed aerosols, we evaluated the effects of transition metal sulfate seed aerosols on toluene consumption, NO_x conversion and the formation of ozone and SOA. MnSO₄ and ZnSO₄ seed aerosols were found to have similar effects on photochemical reactions, both enhance the SOA production, while showing negligible effects on the gas phase compounds. These observations are consistent when varying metal sulfate aerosol concentrations. This is attributed to the catalytic effects of MnSO₄ and ZnSO₄ seed aerosols which may enhance the formation of condensable semivolatile compounds. Their subsequent partitioning into the aerosol phase leads to the observed SOA formation enhancement.

Keywords

manganese sulfate / zinc sulfate / seed aerosols / toluene photooxidation / secondary organic aerosol

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Acknowledgements

This work was financially and technically supported by the National Natural Science Foundation of China (Grant Nos. 20937004, 21107060, and 21190054), Toyota Motor Corporation and Toyota Central Research and Development Laboratories Inc. We would like to thank Dr. Jeremy Wentzell for his help editing this paper.

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg