Abstract
ABSTRACT The Community Multiscale Air Quality (CMAQ) model, with modifications to track precursor-specific SOA, was applied to model SOA formation from aromatic compounds and monoterpenes in Shanghai in November 2018. The modeled total aromatic SOA showed a strong correlation with measured 2,3-dihydroxy-4-oxopentanoic acid (DHOPA) concentrations in the ambient aerosols (R > 0.5 for hourly data and R > 0.75 for daily average data). The ratios of observed DHOPA and modeled aromatic SOA with all components included is around (0.5–1.6) × 10–3, lower than the commonly used ratio of 4 × 10–3 determined for toluene in a series of smog chamber experiments. This suggests that aromatic SOA could be underestimated when directly using the chamber-derived ratios. The predicted monoterpene SOA shows a stronger correlation with the sum of two α-pinene tracers (α-pinT), pinic acid and 3-MBTCA, with R > 0.6 and R > 0.8 for hourly and daily data, respectively. The α-pinT to modeled monoterpene SOA ratios are 0.13–0.25, which generally match the ratio of 0.168 ± 0.081 reported in chamber studies. However, since the current model does not treat α-pinene and its SOA explicitly, future modeling studies should include a more detailed treatment of monoterpene emissions and reactions to predict SOA from these important precursors and compare with the ambient precursor-specific SOA-tracers.
Highlights
Carbonaceous aerosols generally account for 20–50% of total ambient aerosols globally (Novakov et al, 1997; Kanakidou et al, 2005; Putaud et al, 2010; Contini et al, 2018). Cao et al (2007) reported that elemental carbon (EC) and organic matter combined accounted for 39–44% of PM2.5 in 14 Chinese cities, and in Shanghai, 40% of the PM2.5 were carbonaceous aerosols (Ye et al, 2003)
The predicted hourly aromatic and monoterpene Secondary organic aerosol (SOA) strongly correlates with the hourly tracers dihydroxy-4-oxopentanoic acid (DHOPA) (R ~0.6) and α-pinene tracers (α-pinT) (R ~0.6–0.65)
The mass fraction of hourly and daily DHOPA is in the range of 5–6 × 10–3 when SOA components from oligomers, glyoxal (GLY), and methylglyoxal (MGLY) are excluded
Summary
Carbonaceous aerosols generally account for 20–50% of total ambient aerosols globally (Novakov et al, 1997; Kanakidou et al, 2005; Putaud et al, 2010; Contini et al, 2018). Cao et al (2007) reported that elemental carbon (EC) and organic matter combined accounted for 39–44% of PM2.5 in 14 Chinese cities, and in Shanghai, 40% of the PM2.5 were carbonaceous aerosols (Ye et al, 2003). Predicted SOA concentrations are affected by the model representation of the emission, photochemical oxidation, gas-to-particle partitioning, and the multiphase reaction processes (Lannuque et al, 2016; Li et al, 2017; Jo et al, 2019). Many of these physical and chemical processes remain uncertain due to an incomplete understanding of the SOA formation mechanisms and large differences between the atmospheric conditions in the ambient environment and the chamber conditions under which the SOA formation experiments were conducted to determine parameters used in the models (Deng et al, 2017; Jorga et al, 2019)
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