Oxygenated hydrocarbons are ubiquitous in the atmosphere with levels ranging from low ppt (acetaldehyde) to low ppb (methanol). As an OH sink and an atmospheric HOx and ozone source, oxygenated hydrocarbons have a direct impact on the oxidative capacity of the atmosphere. The oceans are one of the largest sources of uncertainty in current atmospheric budget estimates of these species. A better understanding of the processes that produce and destroy these species in seawater would improve our understanding of the role of the oceans in cycling these species into or out of the atmosphere. We have measured the degradation rate of acetaldehyde in unfiltered and filtered southern California coastal waters. Rates were determined by following the concentrations of D-4 labelled acetaldehyde in spiked (nM levels) seawater in 100ml glass syringes as a function of time. Concentrations were determined by isotope dilution purge and trap gas chromatography mass spectrometry using C-13 labelled acetaldehyde as the internal standard. Degradation rates in 0.2um filtered seawater were not measurable. Degradation rates in unfiltered seawater were first order and ranged from 0.046 to 0.32 hr-1. Bacteria levels were also measured in all samples. Acetaldehyde degradation rates scale with bacteria levels. Variability as a function of time, rainfall and other water quality parameters will be discussed
