Global modeling of aerosol nucleation with an explicit chemical mechanism for highly oxygenated organic molecules (HOMs)
Abstract. New particle formation (NPF) involving organic compounds has been identified as an important process affecting aerosol particle number concentrations in the global atmosphere. Laboratory studies have shown that highly oxygenated organic molecules (HOMs) can make a substantial contribution to NPF, but there is a lack of global model studies of NPF with detailed HOMs chemistry. Here, we add a state-of-art biogenic HOMs chemistry scheme with 96 chemical reactions to a global chemistry-climate model and quantify the contribution to global aerosols through HOMs-driven NPF. The updated model captures the frequency of NPF events observed at continental surface sites (normalized mean bias changes from -96 % to -15 %) and shows reasonable agreement with measured rates of NPF and sub-20 nm particle growth. Sensitivity simulations show that the effect of HOMs on particle growth is more important for particle number than the effect on particle formation. Globally, organics contribute around 45 % of the annual mean vertically-integrated nucleation rate (at 1 nm) and 25 % of the vertically-averaged growth rate. The inclusion of HOMs-related processes leads to a 39 % increase in the global annual mean aerosol number burden and a 33 % increase in cloud condensation nuclei (CCN) burden at 0.5 % supersaturation compared to a simulation with only inorganic nucleation. Our work predicts a greater contribution of organic nucleation to NPF than previous studies due to the explicit HOMs mechanism and an updated inorganic NPF scheme. The large contribution of biogenic HOMs to NPF on a global scale could make global aerosol sensitive to changes in biogenic emissions.
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