Heterogeneous sulfate aerosol formation mechanisms during wintertime Chinese haze events: air quality model assessment using observations of sulfate oxygen isotopes in Beijing

Abstract

Abstract. Air quality models have not been able to reproduce the magnitude of the observed concentrations of fine particulate matter (PM2.5) during wintertime Chinese haze events. The discrepancy has been at least partly attributed to low biases in modeled sulfate production rates, due to the lack of heterogeneous sulfate production on aerosols in the models. In this study, we explicitly implement four heterogeneous sulfate formation mechanisms into a regional chemical transport model, in addition to gas-phase and in-cloud sulfate production. We compare the model results with observations of sulfate concentrations and oxygen isotopes, Δ17O(SO42-), in the winter of 2014–2015, the latter of which is highly sensitive to the relative importance of different sulfate production mechanisms. Model results suggest that heterogeneous sulfate production on aerosols accounts for about 20 % of sulfate production in clean and polluted conditions, partially reducing the modeled low bias in sulfate concentrations. Model sensitivity studies in comparison with the Δ17O(SO42-) observations suggest that heterogeneous sulfate formation is dominated by transition metal ion-catalyzed oxidation of SO2.

The acidity of atmospheric particles and clouds

“…The formation of secondary organic aerosol material in atmospheric aerosols via multiphase processes is strongly related to the acidity. Many atmospheric organic accretion reactions, such as aldol condensation (Noziere and Esteve, 2007;Noziere et al, 2010;Sareen et al, 2010;Li et al, 2011), hemiacetal and acetal formation (Jang et al, 2002;Kalberer et al, 2004;Shapiro et al, 2009;Loeffler et al, 2006), and esterification of carboxylic acids (Barsanti and Pankow, 2006), are acid catalyzed. The acid-catalyzed reactive uptake of epoxide species, especially isoprene epoxydiols (IEPOX) (Paulot et al, 2009;Surratt et al, 2010), to aerosol water has also emerged as a significant source of secondary organic aerosol material Marais et al, 2016;Pye et al, 2013).…”

Exploring 2016–2017 surface ozone pollution over China: source contributions and meteorological influences

“…The GEOS-FP datasets are available at a native horizontal resolution of 0.25 • latitude by 0.3125 • longitude, a temporal resolution of 1 h for surface variables, and boundary layer height and 3 h for others. We use the nested-grid version of GEOS-Chem that has 0.25 • × 0.3125 • horizontal resolution over East Asia (70-140 • E, 15-55 • N) (Chen et al, 2009;Zhang et al, 2016;Shao et al, 2019), with boundary conditions archived from the global simulation at 2 • latitude × 2.5 • longitude resolution.…”

“…1). The datasets have been widely used to examine urban air quality issues over China in recent studies Li et al, 2017b;Gao et al, 2018;Shen et al, 2019;Li et al, 2019). Quality controls to remove unreliable hourly observations are applied following our previous work .…”

Importance of Bias Correction in Data Assimilation of Multiple Observations Over Eastern China Using WRF‐Chem/DART

“…In addition to the RH bias, works that explored the systematic bias between modeled and observed AOD values also suggested that the error within the emission used (Park et al, 2011) or the lack of a nitrate process (Li et al, 2016) may be the reason. GOCART also lacks processes concerning secondary organic aerosols and heterogeneous sulfate formation (Shao et al, 2019). The absence of such processes would bring underestimation of the portion of secondary aerosols which are rather efficient in extinction.…”