Photochemical Production of Carbonyl Compounds in the North Pacific and Northwest Atlantic Ocean

Low molecular weight (LMW) carbonyl compounds are ubiquitous, oxygenated volatile organic compounds in the troposphere that are important in the oxidative capacity and secondary organic aerosol formation in the atmosphere. The sea to air flux is a potentially significant source of several LMW carbonyls to the lower atmosphere, but parameterization of these fluxes has been hindered by a poor understanding of carbonyl cycling in seawater. Although it is considered an important source, the photochemical production of carbonyl compounds in seawater is poorly understood. We determined the photochemical efficiencies (AQYs) for the production of acetaldehyde, glyoxal and methylglyoxal in seawater from several stations in the North Pacific Ocean and the Northwest Atlantic Ocean employing a monochromatic irradiation system. Wavelength dependent AQYs decreased exponentially with increasing wavelength (290-400 nm) at 20 ˚C. AQYs decreased after several hours of irradiation at 320 nm, possibly due to a depletion of photochemical precursors or carbonyl photolysis. AQYs of acetaldehyde, glyoxal and methylglyoxal decreased with decreasing temperature at 0-40 ˚C, suggesting possible secondary photochemical pathways. Given the similarities between wavelength-dependent AQYs among samples from the Pacific and Atlantic Oceans, it is possible to use AQY spectra to determine global-scale photochemical fluxes for these compounds in the surface ocean. The importance of these findings in the oceanographic and atmospheric aspects for the cycling of carbonyl compounds will be discussed.