Observed and simulated global distribution and budget of atmospheric C ₂-C ₅ alkanes

The primary sources and atmospheric chemistry of C ₂-C ₅ alkanes were incorporated into the atmospheric chemistry general circulation model EMAC. Model output is compared with new observations from the NOAA/ESRL GMD Cooperative Air Sampling Network. Based on the global coverage of the data, two different anthropogenic emission datasets for C ₄-C ₅ alkanes, widely used in the modelling community, are evaluated. We show that the model reproduces the main atmospheric features of the C ₂-C ₅ alkanes (e.g., seasonality). While the simulated values for ethane and propane are within a 20% range of the measurements, larger deviations are found for the other tracers. According to the analysis, an oceanic source of butanes and pentanes larger than the current estimates would be necessary to match the observations at some coastal stations. Finally the effect of C ₂-C ₅ alkanes on the concentration of acetone and acetaldehyde are assessed. Their chemical sources are largely controlled by the reaction with OH, while the reactions with NO ₃ and Cl contribute only to a little extent. The total amount of acetone produced by propane, i-butane and i-pentane oxidation is 11.2 Tg/yr, 4.3 Tg/yr, and 5.8 Tg/yr, respectively. Moreover, 18.1, 3.1, 3.4, 1.4 and 4.8 Tg/yr of acetaldehyde are formed by the oxidation of ethane, propane, n-butane, n-pentane and i-pentane, respectively.