Global Modeling of Secondary Organic Aerosol With Organic Nucleation

Abstract

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.

Comment on acp-2021-838

“…Our results are consistent with the model-derived importance of pure organic NPF in remote regions (Gordon et al, 2017;Zhu and Penner, 2019), however, they raise important questions about the extent to which pristine NPF conditions still exist in the present-day atmosphere. At the vast majority of remote sites studied so far, NPF is exclusively a daytime 480 phenomenon, suggesting dominance of H2SO4 as the controlling species.…”

Frequent new particle formation at remote sites in the temperate/boreal forest of North America

“…Our results are consistent with the model-derived importance of pure organic NPF in remote regions (Gordon et al, 2017;Zhu and Penner, 2019), however, they raise important questions about the extent to which pristine NPF conditions still exist in the present-day atmosphere. At the vast majority of remote sites studied so far, NPF is exclusively a daytime 480 phenomenon, suggesting dominance of H2SO4 as the controlling species.…”

Particulate Oxalate‐To‐Sulfate Ratio as an Aqueous Processing Marker: Similarity Across Field Campaigns and Limitations

“…Oxygenated organic species comprise 60%-95% of total organic aerosol mass across urban and remote sites (Zhang et al, 2007), while SOA from VOCs explains up to 70% of global organic carbon mass (Hallquist et al, 2009). More recent work reports reduced discrepancy between models and observations for SOA concentrations (Hodzic et al, 2016;Pai et al, 2020;Zhu & Penner, 2019). However, despite improvements in modeling organic aerosol (Heald et al, 2005(Heald et al, , 2011, atmospheric chemistry models still underestimate SOA (Schroder et al, 2018) due partly to an incomplete understanding and representation of aqueous processes, resulting in poor model parameterization (Hallquist et al, 2009;McNeill, 2015).…”