A hydrophilic/hydrophobic organic (H²O) aerosol model: Development, evaluation and sensitivity analysis

Abstract

A secondary organic aerosol (SOA) model, the Hydrophilic/Hydrophobic Organic model (H2O), is presented and evaluated over Europe. H2O uses surrogate organic molecules to represent the myriad of SOA species and distinguishes two kinds of surrogate species: hydrophilic species (which condense preferentially into an aqueous phase) and hydrophobic species (which condense only into an organic phase). These surrogate species are formed from the oxidation in the atmosphere of volatile organic compounds. H2O includes several important processes, including the effect of nitrogen oxides (NOX) on SOA formation, the dissociation of organic acids in an aqueous phase, the oligomerization of aldehydes, the non‐ideality of the particle phase and the hygroscopicity of organics. Concentrations of organic aerosols were simulated over Europe from July 2002 to July 2003 for comparison with measurements of the European Monitoring Evaluation Program (EMEP). In H2O, primary organic aerosols (POA) are considered as semi‐volatile organic compounds (SVOC) present in both the gas phase and the particle phase. Taking into account the gas‐phase fraction of SVOC increases significantly organic PM concentrations, particularly in winter, in better agreement with observations. The impacts on organic aerosol formation of ideality, of the choice of the parameterization for isoprene SOA formation, and of the OM/OC ratio of the model were also investigated. Assuming ideality in H2O was found to lead to a small decrease in OM. Compared to a two‐product parameterization, the parameterization of Couvidat and Seigneur [2011] for SOA formation from isoprene oxidation leads to a significant increase in isoprene SOA by taking into account their hydrophilic properties and suggests that most models may currently underestimate isoprene SOA.

Development of an inorganic and organic aerosol model (CHIMERE 2017<i>β</i> v1.0): seasonal and spatial evaluation over Europe

“…Following Couvidat et al (2012), primary organic aerosols (POAs) are assumed to be SVOCs and are split into three compounds: POAlP (Kp = 1.1 m 3 µg −1 ), POAmP (Kp = 0.0116 m 3 µg −1 ) and POAhP (Kp = 0.00031 m 3 µg −1 ) having, respectively, a low, medium and high volatility to follow the dilution curve of POA in Robinson et al (2007). The aging of these compounds is also taken into account with a reaction with OH which leads to less volatile compounds (SOAlP, SOAmP and SOAhP) via the following reactions:…”

“…In Couvidat et al (2012), a SVOC/POA factor of 5 was used on the basis that SVOC primary emissions are underestimated. With this factor, the model was able to simulate the strong concentrations of organic aerosols in winter and to give satisfactory results over most of Europe.…”

“…(1) For SVOC formation that leads to the formation of SOA compounds after partitioning, the mechanism of Couvidat et al (2012) is used. The mechanism is shown in Table 1.…”

“…-The SOA formation mechanism of Couvidat et al (2012) is used for toluene, xylene and biogenic VOCs.…”

Updated aerosol module and its application to simulate secondary organic aerosols during IMPACT campaign May 2008

“…The simulation with the CHIMERE model in Paris, spring 2007, was reported by Sciare et al (2010), who found that the SOA was underestimated possibly due to missing potential sources of SOA in the model such as the aging of POA and oligomerization. Couvidat et al (2012) simulated the SOA formation from isoprene oxidation with two sets of parameterizations (Henze and Seinfeld, 2006;Couvidat and Seigneur, 2011), and found out that the latter (Couvidat and Seigneur, 2011) calculated higher concentrations of isoprene SOA than the former (Henze and Seinfeld, 2006). The former is currently widely used in different CTMs and may underestimate isoprene produced SOA masses.…”