Multi-generational oxidation model to simulate secondary organic aerosol in a 3-D air quality model

Abstract

Abstract. Multi-generational gas-phase oxidation of organic vapors can influence the abundance, composition and properties of secondary organic aerosol (SOA). Only recently have SOA models been developed that explicitly represent multigenerational SOA formation. In this work, we integrated the statistical oxidation model (SOM) into SAPRC-11 to simulate the multi-generational oxidation and gas/particle partitioning of SOA in the regional UCD/CIT (University of California, Davis/California Institute of Technology) air quality model. In the SOM, evolution of organic vapors by reaction with the hydroxyl radical is defined by (1) the number of oxygen atoms added per reaction, (2) the decrease in volatility upon addition of an oxygen atom and (3) the probability that a given reaction leads to fragmentation of the organic molecule. These SOM parameter values were fit to laboratory smog chamber data for each precursor/compound class. SOM was installed in the UCD/CIT model, which simulated air quality over 2-week periods in the South Coast Air Basin of California and the eastern United States. For the regions and episodes tested, the two-product SOA model and SOM produce similar SOA concentrations but a modestly different SOA chemical composition. Predictions of the oxygen-tocarbon ratio qualitatively agree with those measured globally using aerosol mass spectrometers. Overall, the implementation of the SOM in a 3-D model provides a comprehensive framework to simulate the atmospheric evolution of organic aerosol.

Modeling of the chemistry in oxidation flow reactors with high initial NO

“…In the study of the air in a traffic tunnel (OFR185-iNO mode; Tkacik et al, 2014), where toluene is usually a major anthropogenic SOA precursor as in other urban environments (Dzepina et al, 2009;Borbon et al, 2013;Hayes et al, 2015;Jathar et al, 2015), NO x was several hundred ppb. This resulted in an estimated NO 3exp /OH exp range of ∼ 0.1-1 in which up to ∼ 30 % of cresols (intermediates of toluene oxidation) may have been consumed by NO 3 .…”

Investigating diesel engines as an atmospheric source of isocyanic acid in urban areas

“…Gas-phase chemistry was modeled using SAPRC-11. For more details, we refer the reader to previous model applications (Hu et al, 2012;Jathar et al, 2016) and evaluations (Jathar et al, 2015. Primary emissions of HNCO were calculated by first determining a source-specific HNCO : CO ratio (see Table 1) and then combining them with source-specific, spatiotemporally resolved CO emissions to build an inventory for HNCO emissions.…”

“…The UCD/CIT is a regional chemical transport model that has been extensively used to simulate the emissions, transport, chemistry, deposition and source contribution of pollutants in the lower troposphere (Kleeman and Cass, 2001) and evaluated against meteorological and gas-and particle-phase measurements (Hu et al, 2012(Hu et al, , 2015Jathar et al, 2015Jathar et al, , 2016 , 2010). Gas-phase chemistry was modeled using SAPRC-11.…”

Modelling organic aerosol concentrations and properties during ChArMEx summer campaigns of 2012 and 2013 in the western Mediterranean region

“…Furthermore, they tend to converge as they continue to be developed and refined. For example, I/S-VOCs from anthropogenic emissions, which are usually specified by volatility classes, can be included in a mechanistic model (Albriet et al, 2010;Couvidat et al, 2013a); also, the VBS scheme can take into account the oxidative state of SOA (Jimenez et al, 2009), in particular its elemental O / C ratio Jathar et al, 2015). The recently developed 1.5-VBS (Koo et al, 2014) assigned a molecular structure to VBS products.…”

“…SOA models used in mesoscale models can be grouped into two major categories: (1) models based on an empirical representation of SOA formation and (2) models based on a mechanistic representation of SOA formation. Models of the first category include the widely used two-compound Odum approach (Odum et al, 1996), the more recent volatility basis set (VBS) approach (Donahue et al, 2006 or the multi-generational oxidation model (Jathar et al, 2015). Models of the second category use experimental data on the molecular composition of SOA and represent the formation of SOA using surrogate molecules with representative physicochemical properties (Pun et al, 2006;Bessagnet et al, 2008;Carlton et al, 2010;Couvidat et al, 2012).…”