Production of oxygenated volatile organic compounds from the ozonolysis of coastal seawater

Abstract

Dry deposition of ozone (O3) to the ocean surface and the ozonolysis of organic material found in the sea surface microlayer (SSML) is a potential source of volatile organic compounds (VOC) to the marine atmosphere. We use a gas chromatography system coupled to a Vocus proton transfer reaction time-of-flight mass spectrometer to determine the chemical composition and product yield of select VOC formed from ozonolysis of coastal seawater collected from Scripps Pier in La Jolla, California. We interpret these laboratory-derived results in the context of direct VOC vertical flux measurements made at Scripps Pier. The dominant products of O3 deposition in both the laboratory and field measurements are measured at CxHy+ and CxHyOz+ ions on the Vocus. GC analysis suggests that C5-C11 oxygenated VOC, primarily aldehydes, are the largest contributors to these ion signals. In the laboratory, using a flow reactor experiment, we determine a VOC yield of 0.43-0.62. In the field at Scripps Pier, we determine a VOC yield of 0.04-0.06. Scaling the field and lab VOC yields for an average O3 deposition flux and an average VOC structure results in an emission source of 12.6 to 136 Tg C yr-1, competitive with the DMS source of 21.1 Tg C yr-1. This study reveals that O3 reactivity to dissolved organic carbon can be a significant carbon source to the marine atmosphere and warrants further investigation into the speciated VOC composition from different seawater samples, and the reactivities and secondary organic aerosol yields of these molecules in marine-relevant, low NOx conditions.