Global atmospheric budget of acetaldehyde: 3D model analysis and constraints from in-situ and satellite observations

Acetaldehyde plays an important role in the atmosphere as a source of ozone (O₃), peroxyacetyl nitrate (PAN), and HO_x radicals, and is classified as a hazardous air pollutant by the US EPA. Here we use a 3-D model of atmospheric chemistry (GEOS-Chem) to carry out the first detailed analysis of the global acetaldehyde budget, and use an ensemble of observations to evaluate present understanding of its sources and sinks. The analysis includes a new approach to quantifying the global air-sea acetaldehyde flux based on SeaWiFS satellite observations (see figure). We estimate net ocean emissions of 58 Tg/y, the second largest global source of acetaldehyde after hydrocarbon oxidation (130 Tg/y). A key uncertainty is the acetaldehyde turnover time in the ocean mixed layer. We introduce the Model of Emissions of Gases and Aerosols from Nature (MEGANv2.1) for acetaldehyde and ethanol and use it to quantify their net flux from living terrestrial plants. Our simulation underestimates acetaldehyde levels in urban outflow, suggesting a missing source in polluted air, but we find no compelling evidence for a widespread missing acetaldehyde source in the free troposphere, as previously conjectured. We estimate current US sources of ethanol and acetaldehyde at approximately 60% and 400% of the corresponding increases expected for a national transition from gasoline to ethanol fuel. For more details see Millet et al., (submitted, 2010).

Please click here to see previous research highlights.