Simulating secondary organic aerosol formation in a global aerosol-climate model

Secondary organic aerosols (SOA), produced via the oxidation of gaseous precursor compounds in the atmosphere, contribute a substantial fraction of atmospheric airborne particles and affect both air quality and climate. Global aerosol-climate models often suffer from very simplified representations of atmospheric SOA formation or missing formation pathways, typically leading to underestimated SOA particle numbers and mass contributions in comparison to observational data. Here, we use the aerosol microphysics submodel MADE3 as part of the global chemistry-climate model EMAC and implement an improved scheme for SOA formation. While MADE3 in its previous version did not account for new particle formation from organic precursors, we included the nucleation parametrization for SOA particles from monoterpene precursors described in Riccobono et al. (2014), which depends on the concentration of sulfuric acid and oxidized organic molecules. Additionally, we consider isoprene as biogenic SOA precursor for the condensation on pre-existing particles, which has been neglected in the previous model version. In addition to biogenic precursors, we also consider anthropogenic precursors for SOA formation, e.g. benzene, toluene, and xylenes from anthropogenic activities like the combustion of fossil fuels. Particle nucleation from these anthropogenic precursors is parametrized similarly to the Riccobono et al. (2014) scheme. We show the effect on particle numbers and SOA mass fractions when using the new SOA scheme and evaluate our simulation results against various observational data sets. When the nucleation parameterization for monoterpene precursors is activated, the total near-surface number concentrations can increase regionally by up to one order of magnitude. With the new SOA scheme, the underestimation of particle numbers and SOA mass fractions in the lower troposphere is reduced and results show an improved agreement with observations.

 

References:

Francesco Riccobono et al., Oxidation Products of Biogenic Emissions Contribute to Nucleation of Atmospheric Particles. Science 344, 717 721 (2014). DOI: 10.1126/science.1243527