Global Modeling of Secondary Organic Aerosol With Organic Nucleation

Organic nucleation has been identified as an important way to form secondary organic aerosol (SOA) and change the number concentration of aerosol and thus its climate effect. A global atmospheric chemistry model is developed to include a comprehensive organic nucleation scheme that includes heteromolecular nucleation of sulfuric acid and organics, neutral pure organic nucleation, and ion‐induced pure organic nucleation. Our model simulation shows reasonable agreement with the seasonal as well as spatial pattern of organic carbon concentration in America, while it fails to predict the seasonal pattern of organic carbon in Europe due to the lack of sharp increases in primary organic aerosol emissions in the winter. Including organic nucleation decreases the bias of the annual average particle number concentration at 54% of the available observation sites and increases the temporal correlation coefficients at 58% of the sites. Ion‐induced pure organic nucleation contributes the most to the total organic nucleation rate, which peaks around 400 hPa in the tropics. Heteromolecular nucleation of sulfuric acid and organics dominates the total organic nucleation rate in the summer and mostly occurs in the lower troposphere. The number concentration of particles formed from organic nucleation (newSOA) in the nucleation and Aitken modes is highest in the tropics, while accumulation mode newSOA is highest in the Northern Hemisphere due to growth as a result of the condensation of sulfate. Three sensitivity experiments suggest that more studies are needed to investigate the formation mechanism of newSOA, so that a more accurate simulation of the spatial and size distribution of newSOA can be developed.Key PointsA new version of the CESM/IMPACT atmospheric model is developed to include three organic nucleation schemesIncluding organic nucleation improves the model’s ability to simulate aerosol number concentrationIon‐induced pure organic nucleation is the largest contributor to the global new organic particle formationPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151313/1/jgrd55629_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151313/2/jgrd55629.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151313/3/jgrd55629-sup-0001-Figure_SI-S01.pd