Abstract
Abstract. A new detailed aqueous phase mechanism named the Cloud Explicit Physico-chemical Scheme (CLEPS 1.0) is proposed to describe the oxidation of water soluble organic compounds resulting from isoprene oxidation. It is based on structure activity relationships (SARs) which provide global rate constants together with branching ratios for HO⋅ abstraction and addition on atmospheric organic compounds. The GROMHE SAR allows the evaluation of Henry's law constants for undocumented organic compounds. This new aqueous phase mechanism is coupled with the MCM v3.3.1 gas phase mechanism through a mass transfer scheme between gas phase and aqueous phase. The resulting multiphase mechanism has then been implemented in a model based on the Dynamically Simple Model for Atmospheric Chemical Complexity (DSMACC) using the Kinetic PreProcessor (KPP) that can serve to analyze data from cloud chamber experiments and field campaigns. The simulation of permanent cloud under low-NOx conditions describes the formation of oxidized monoacids and diacids in the aqueous phase as well as a significant influence on the gas phase chemistry and composition and shows that the aqueous phase reactivity leads to an efficient fragmentation and functionalization of organic compounds.
Highlights
Clouds favor chemical reactions that would not occur in the gas phase or at a rate much slower than in the aqueous phase (Epstein and Nizkorodov, 2012; Herrmann, 2003; Herrmann et al, 2015)
∗ Electron transfer reaction. (*) electron transfer reaction reactivity could be extended to all the considered alcohol functions in our mechanism, we investigated whether the process appears thermodynamically feasible by calculating the relative reaction free energies (Gibbs energies) using density functional theory (DFT; see details and references in Supplement SM1)
The mechanism resulting from the coupling of CLEPS with MCM v3.3.1 is integrated into a model based on the Dynamically Simple Model for Atmospheric Chemical Complexity (DSMACC; Emmerson and Evans, 2009) using the Kinetic PreProcessor (KPP: see Damian et al, 2002), which has been modified to account for an aqueous phase, as described in the following
Summary
Clouds favor chemical reactions that would not occur in the gas phase or at a rate much slower than in the aqueous phase (Epstein and Nizkorodov, 2012; Herrmann, 2003; Herrmann et al, 2015). A new mechanism, the Cloud Explicit Physicochemical Scheme (CLEPS 1.0), including organic compounds up to C4, has been developed under low-NOx (< 1 ppbv) and cloudy conditions and uses recent available laboratory data and empirical estimation methods It is implemented in a box model including gas phase chemistry and kinetic mass transfer of soluble species between the gas phase and cloud droplets. Recent developments in empirical estimates of kinetic and thermodynamic parameters (e.g., rate constants, Henry’s law constants) for aqueous phase chemistry (Doussin and Monod, 2013; Minakata et al, 2009; Monod and Doussin, 2008; Raventos-Duran et al, 2010) are included in the CLEPS mechanism These structure activity relationships (SARs) are based on experimental data and rely on robust hypotheses about the rate constants
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