Isoprene derived secondary organic aerosol in a global aerosol chemistry climate model

Abstract

Within the framework of the global chemistry climate model ECHAM-HAMMOZ a novel explicit coupling between the sectional aerosol model HAM-SALSA and the chemistry model MOZ was established to form isoprene derived secondary organic aerosol (iSOA). Isoprene oxidation in the chemistry model MOZ is described by a semi-explicit scheme consisting of 147 reactions, embedded in a detailed atmospheric chemical mechanism with a total of 779 reactions. Low volatile compounds 5 (LVOC) produced during isoprene photooxidation are identified and explicitly partitioned by HAM-SALSA. A group contribution method was used to estimate their evaporation enthalpies and corresponding saturation vapor pressures, which are used by HAM-SALSA to calculate the saturation concentration of each LVOC. With this method, every single precursor is tracked in terms of condensation and evaporation in each aerosol size bin. This approach lead to the identification of ISOP(OOH)2 as a main contributor to iSOA formation. Further, reactive uptake of isoprene epoxidiols (IEPOX) and isoprene derived glyoxal 10 were included as iSOA sources. The parameterization of IEPOX reactive uptake includes a dependency on aerosol pH value.This model framework connecting semi-explicit isoprene oxidation with explicit treatment of aerosol tracers leads to a global, annual isoprene SOA yield of 16% relative to the primary oxidation of isoprene by OH, NO 3 , and ozone. With 445 Tg (392 TgC) isoprene emitted, an iSOA source of 148 Tg (61 TgC) is simulated. The major part of iSOA in ECHAM-HAMMOZ is produced by IEPOX (24.4 TgC) and ISOP(OOH)2 (28.3 TgC). The main sink process is particle wet deposition which removes 15 143 Tg (59 TgC). The iSOA burden reaches 1.6 Tg (0.7 TgC) in the year 2012.

A simplified parameterization of isoprene-epoxydiol-derived secondary organic aerosol (IEPOX-SOA) for global chemistry and climate models

“…50 Ground-based and aircraft field measurements have shown that IEPOX-SOA can contribute to total OA concentrations by as much as 36%, especially for forested regions under low NO across the globe (Hu et al, 2015). Several modeling studies have explicitly simulated IEPOX-SOA by considering detailed isoprene gas-phase chemistry and IEPOX uptake Budisulistiorini et al, 2017;Stadtler et al, 2017). Figure 1 shows the main chemical pathways of the IEPOX-SOA chemistry in (a) 55 HO2 and (b) NO dominant conditions simulated by GEOS-Chem.…”

The chemistry–climate model ECHAM6.3-HAM2.3-MOZ1.0

“…Shorter test simulations with the SALSA microphysics package reveal minor differences compared to the M7 simulations presented in this work (Stadtler et al, 2018).…”

“…If run without, then climatological fields from MOZ are used to prescribe monthly mean mixing ratios of oxidants, i.e., ozone, OH, H 2 O 2 , NO 2 , and NO 3 . If run interactively, the surface areas of HAM aerosols are used as input for the calculation of heterogeneous reaction rates (Stadtler et al, 2017). At present there is no interaction of aerosols with gas-species photolysis (MOZ uses a climatology of aerosols and lookup tables).…”

“…Details on the heterogeneous reactions in ECHAM-HAMMOZ and a discussion of their relevance are given in Stadtler et al (2017). The stratospheric chemistry scheme explicitly treats the oxidation and photolysis of 21 halogenated compounds listed in Table 2 together with their approximate lifetimes.…”

“…As described above, the released model version has very low lightning NO emissions, and the parameterization of the heterogeneous reaction of HNO 3 neglects the potential of reevaporation of aerosol nitrate to gaseous HNO 3 (Stadtler et al, 2017), which has an impact on the total amount of deposited nitrogen and also affects the budgets of ozone and nitrogen oxides as shown below. In order to investigate the impacts of these two factors we performed a small series of sensitivity simulations for the year 2008 based on restart files of the reference run.…”