Global atmospheric budget of simple monocyclic aromatic compounds

Abstract. The global atmospheric budget and distribution of monocyclic aromatic compounds is estimated, using an atmospheric chemistry general circulation model. Simulation results are evaluated with an ensemble of surface and aircraft observations with the goal of understanding emission, production and removal of these compounds.

Anthropogenic emissions provided by the RCP database represent the largest source of aromatics in the model (≃ 23 TgC year⁻¹) and biomass burning from the GFAS inventory the second largest (≃ 5 TgC year⁻¹). The simulated chemical production of aromatics accounts for  ≃ 5 TgC year⁻¹. The atmospheric burden of aromatics sums up to 0.3 TgC. The main removal process of aromatics is photochemical decomposition (≃ 27 TgC  year⁻¹), while wet and dry deposition are responsible for a removal of  ≃ 4 TgC year⁻¹.

Simulated mixing ratios at the surface and elsewhere in the troposphere show good spatial and temporal agreement with the observations for benzene, although the model generally underestimates mixing ratios. Toluene is generally well reproduced by the model at the surface, but mixing ratios in the free troposphere are underestimated. Finally, larger discrepancies are found for xylenes: surface mixing ratios are not only overestimated but also a low temporal correlation is found with respect to in situ observations.