Functionalization and fragmentation during ambient organic aerosol aging: application of the 2-D volatility basis set to field studies

Abstract

Abstract. Multigenerational oxidation chemistry of atmospheric organic compounds and its effects on aerosol loadings and chemical composition is investigated by implementing the Two-Dimensional Volatility Basis Set (2-D-VBS) in a Lagrangian host chemical transport model. Three model formulations were chosen to explore the complex interactions between functionalization and fragmentation processes during gas-phase oxidation of organic compounds by the hydroxyl radical. The base case model employs a conservative transformation by assuming a reduction of one order of magnitude in effective saturation concentration and an increase of oxygen content by one or two oxygen atoms per oxidation generation. A second scheme simulates functionalization in more detail using group contribution theory to estimate the effects of oxygen addition to the carbon backbone on the compound volatility. Finally, a fragmentation scheme is added to the detailed functionalization scheme to create a functionalization-fragmentation parameterization. Two condensed-phase chemistry pathways are also implemented as additional sensitivity tests to simulate (1) heterogeneous oxidation via OH uptake to the particle-phase and (2) aqueous-phase chemistry of glyoxal and methylglyoxal.The model is applied to summer and winter periods at three sites where observations of organic aerosol (OA) mass and O:C were obtained during the European Integrated Project on Aerosol Cloud Climate and Air Quality Interactions (EU-CAARI) campaigns. The base case model reproduces observed mass concentrations and O:C well, with fractional errors (FE) lower than 55 % and 25 %, respectively. The detailed functionalization scheme tends to overpredict OA concentrations, especially in the summertime, and also underpredicts O:C by approximately a factor of 2. The detailed functionalization model with fragmentation agrees well with the observations for OA concentration, but still underpredicts O:C. Both heterogeneous oxidation and aqueous-phase processing have small effects on OA levels but heterogeneous oxidation, as implemented here, does enhance O:C by about 0.1. The different schemes result in very different fractional attribution for OA between anthropogenic and biogenic sources.

Modeling the meteorological and chemical effects of secondary organic aerosols during an EUCAARI campaign

“…Hodzic et al (2010) showed that the addition of 40 % oxygen in mass and the drop of two orders of magnitude in volatility upon each oxidation step are found to improve oxygen to carbon atomic ratio predictions, though lead to unrealistically high SOA production. Nevertheless, a number of complex and more realistic schemes has been recently tested and showed that a one-volatility bin shift scheme resulted in the best agreement with the observations (Murphy et al, 2012).…”

“…To cope with this deficiency, a two-dimensional VBS scheme is developed, which uses the degree of oxidation as a second coordinate ). However, when tested against measurements in Europe it was found that the simple one-dimensional scheme had as good a performance as any of the more complex two dimensional VBS schemes probably due to uncertainties in our understanding of SOA evolution in the atmosphere (Murphy et al, 2012).…”

ORACLE 2-D (v2.0): an efficient module to compute the volatility and oxygen content of organic aerosol with a global chemistry–climate model

“…This may result in an overestimation of OA at long aging timescales up to thousands of kilometers downwind of the source regions. However, this overestimation can be partially offset by the conservative aging scheme used in ORACLE 2-D compared to the relatively aggressive functionalization scheme proposed by Murphy et al (2012). The same addition of oxygen atoms (one or two) is assumed for bSOA-v (SOA from the oxidation of biogenic VOCs); however, its volatility remains unchanged due to a balancing of fragmentation and functionalization effects (Murphy et al, 2012) (Fig.…”

“…Recent studies have suggested that the main difference between these two OOA types is often not so much their volatility, but mostly their oxygen content (Kostenidou et al, 2015;Louvaris et al, 2017). These two OOA types represent distinct oxidation states with O : C of 0.33-0.67 for SVOOA and 0.67-1.00 for LVOOA (Donahue et al, 2012). Therefore, SVOOA can be compared at least as a zero-order approximation against the simulated fresh SOA (Table 3) and LVOOA against the simulated aged SOA (Table 4).…”

“…However, the large number of additional surrogate organic compounds required by the 2-D VBS framework has hindered implementation in three-dimensional atmospheric models (Napier et al, 2014). Therefore, the 2-D VBS approach has been mostly adopted in box and 1-D Lagrangian models (Murphy et al, 2011(Murphy et al, , 2012Chacon-Madrid et al, 2013;Zhao et al, 2015;Paciga et al, 2016). Koo et al (2014) introduced a hybrid VBS approach for use in three-dimensional chemical transport models (CTMs) that combines the simplicity of the VBS with the ability to track the evolution of OA in the 2-D space of volatility and oxygen content.…”