Vertical Fluxes and Atmospheric Cycling of Methanol, Acetaldehyde, and Acetone In a Coastal Environment

Oxygenated Volatile Organic Compounds (OVOCs) exist ubiquitously in the troposphere and are important for atmospheric chemistry and climate. They can be emitted from natural or anthropogenic sources, photochemically produced or destroyed in air, and deposited to the surface. We present here eddy covariance fluxes of methanol, acetaldehyde, and acetone measured during March to July 2012 near the southwest coast of the United Kingdom. OVOC concentrations and fluxes vary significantly with the time of day and wind direction. Higher concentrations and fluxes of acetaldehyde and acetone are usually observed in the daytime and from the direction of a forested park, most likely due to elevated emissions from terrestrial plants. Methanol concentration and flux do not demonstrate clear diel variability, suggesting sources in addition to plant emissions. The mean (1 sigma) acetaldehyde concentration of 0.13 (0.02) ppb at night is partly maintained by sea-to-air transfer, while photochemical destruction likely outpaces production during the day. Air-sea exchange and photochemistry are probably net sinks of methanol and acetone in this region. Their nighttime concentrations of 0.46 (0.20) and 0.39 (0.08) ppb are affected more by terrestrial emissions and long distance transport, respectively. To more accurately constrain the air-sea exchange of OVOCs, measurements at sea, rather than at a spatial inhomogeneous coastal site, are necessary.