Modeling SOA formation from the oxidation of intermediate volatility <i>n</i>-alkanes

Abstract

Abstract. The chemical mechanism leading to SOA formation and ageing is expected to be a multigenerational process, i.e. a successive formation of organic compounds with higher oxidation degree and lower vapor pressure. This process is here investigated with the explicit oxidation model GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere). Gas phase oxidation schemes are generated for the C 8 -C 24 series of n-alkanes. Simulations are conducted to explore the time evolution of organic compounds and the behavior of secondary organic aerosol (SOA) formation for various preexisting organic aerosol concentration (C OA ). As expected, simulation results show that (i) SOA yield increases with the carbon chain length of the parent hydrocarbon, (ii) SOA yield decreases with decreasing C OA , (iii) SOA production rates increase with increasing C OA and (iv) the number of oxidation steps (i.e. generations) needed to describe SOA formation and evolution grows when C OA decreases. The simulated oxidative trajectories are examined in a two dimensional space defined by the mean carbon oxidation state and the volatility. Most SOA contributors are not oxidized enough to be categorized as highly oxygenated organic aerosols (OOA) but reduced enough to be categorized as hydrocarbon like organic aerosols (HOA), suggesting that OOA may underestimate SOA. Results show that the model is unable to produce highly oxygenated aerosols (OOA) with large yields. The limitations of the model are discussed.

Organic aerosol concentration and composition over Europe: insights from comparison of regional model predictions with aerosol mass spectrometer factor analysis

“…Although most previous studies have considered OPOA as OOA (Robinson et al, 2007;Shrivastava et al, 2008;Murphy and Pandis, 2009;Hodzic et al, 2010;, it has been argued (Cappa and Wilson, 2012;Aumont et al, 2012) that not all OPOA is oxidized enough to be assigned to the OOA mass fraction by factor analysis. Zhang et al (2013) suggested that if some OPOA were measured as part of HOA, the CTM bias would be reduced.…”

Origin and variability in volatile organic compounds observed at an Eastern Mediterranean background site (Cyprus)

“…These latter react with atmospheric oxidants leading to increasingly functionalized products with sufficiently low volatility (Aumont et al, 2012;Jimenez et al, 2009;Kroll and Seinfeld, 2008) taking part in the formation of secondary organic aerosols (SOAs) by nucleation or condensation onto preexisting particles (Fuzzi et al, 2006;Kanakidou et al, 2005). Furthermore, numerical simulation models suggest that the secondary OVOCs are still reactive and multifunctionalized several days after emission, and they thus affect the oxidant budget as well as the formation of ozone and SOA at remote locations (Aumont et al, 2005;Madronich, 2006).…”

Organic carbon at a remote site of the western Mediterranean Basin: sources and chemistry during the ChArMEx SOP2 field experiment

“…The hydroxyl radical is the main oxidant in the atmosphere and therefore controls the fate of most VOCs through oxidation cycles that lead to the formation of tropospheric O 3 (Seinfeld and Pandis, 1998) and a large number of secondary oxygenated VOCs (OVOCs; Atkinson, 2000;Goldstein and Galbally, 2007). OVOCs subsequently react with atmospheric oxidants, leading to multifunctionalized compounds of lower volatility through a multigenerational oxidation process (Kroll and Seinfeld, 2008;Jimenez et al, 2009;Aumont et al, 2012). These semi-volatile compounds take part in the formation of secondary organic aerosols (SOAs) through condensation onto preexisting particles (Kanakidou et al, 2005).…”