Contribution of methane to aerosol carbon mass

Abstract

Small volatile organic compounds (VOC) such as methane (CH4) have long been considered non-relevant to aerosol formation due to the high volatility of their oxidation products. However, even low aerosol yields from CH4, the most abundant VOC in the atmosphere, would contribute significantly to the total particulate carbon budget. In this study, organic aerosol (OA) mass yields from CH4 oxidation were evaluated at the Paul Scherrer Institute (PSI) smog chamber in the presence of inorganic and organic seed aerosols. Using labeled 13C methane, we could detect its oxidation products in the aerosol phase, with yields up to 0.09 +0.26−0.09 %. Overall, we estimate a maximum contribution of CH4 oxidation of 0.13% to the total global organic aerosol budget. We present evidence that oxidation of formaldehyde, a product of methane oxidation, contributes only a minor fraction to the observed aerosol yields. Therefore, other mechanisms appear to be more important for OA production from CH4 oxidation. A thorough elucidation of such mechanisms is still required. However, our results imply that many other small, volatile, and abundant hydrocarbons thus far considered irrelevant for OA production may contribute to the atmospheric OA budget.