Isoprene-derived secondary organic aerosol in the global aerosol–chemistry–climate model ECHAM6.3.0–HAM2.3–MOZ1.0

Abstract

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. Semi-volatile and low-volatile compounds 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 iSOA precursor. With this method, every single precursor is tracked in terms of condensation and evaporation in each aerosol size bin. This approach led to the identification of dihydroxy dihydroperoxide (ISOP(OOH)2) as a main contributor to iSOA formation. Further, the reactive uptake of isoprene epoxydiols (IEPOXs) and isoprene-derived glyoxal 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 average isoprene SOA yield of 15 % relative to the primary oxidation of isoprene by OH, NO3 and ozone. With 445.1 Tg (392.1 Tg C) isoprene emitted, an iSOA source of 138.5 Tg (56.7 Tg C) is simulated. The major part of iSOA in ECHAM–HAMMOZ is produced by IEPOX at 42.4 Tg (21.0 Tg C) and ISOP(OOH)2 at 78.0 Tg (27.9 Tg C). The main sink process is particle wet deposition, which removes 133.6 (54.7 Tg C). The average iSOA burden reaches 1.4 Tg (0.6 Tg C) in the year 2012.

A new model mechanism for atmospheric oxidation of isoprene: global effects on oxidants, nitrogen oxides, organic products, and secondary organic aerosol

“…IDHPE accounts for 51% of this total, with dihydroxy-dihydroperoxides and dihydroxy-hydroperoxy-carbonyls contributing over 10% each. This total carries high uncertainty, due both to the SOA uptake parameterization and the lack of constraints on other loss pathways of the C 5 tetrafunctional compounds, but is similar to a recent estimate by Stadtler et al (2018) and highlights the importance of further investigations of this iSOA formation pathway.…”

“…Clair et al, 2015;Bates et al, 2016) and to the GEOS-Chem v11-02c mechanism (183 Tg a −1 ). This results in 38 Tg a −1 (20 TgC a −1 ) of iSOA formation from IEPOX, slightly lower than a recent estimate by Stadtler et al (2018). While the uptake parameterization of used here varies with particle acidity and sulfate content as seen in chamber studies and field observations (Gaston et al, 2014;10 Nguyen et al, 2014;Liao et al, 2015), it does not include the known effects of organic coatings and aerosol phase state (Riva et al, 2016;Zhang et al, 2018), which may also be important for the uptake of other precursors.…”

“…Chamber studies isolating specific isoprene oxidation pathways have measured SOA mass yields in excess of 15% (Liu et al, 2016;Schwantes et al, 2019), while top-down (Hallquist et al, 2009Heald et al, 2010;Spracklen et al, 2011) and mass-balance 30 (Goldstein and Galbally, 2007) assessments of global SOA production consistently arrive at higher estimates than the models. Stadtler et al (2018) found better agreement with the top-down assessments by implementing a new isoprene mechanism (including the major tetrafunctional C 5 compounds) into global simulations, resulting in a 33% global iSOA mass yield (16% per carbon). Hodzic et al (2016) showed that discrepancies between observed SOA yields and modeled SOA budgets could be 14 Atmos.…”

“…The dominant contributor to iSOA worldwide Stadtler et al, 2018), IEPOX is a secondgeneration oxidation product of isoprene via the ISOPOO + HO 2 reaction pathway. IEPOX can form in high yields of up to 75% from isoprene in HO 2 -dominated conditions (Figure 10).…”

A new model mechanism for atmospheric oxidation of isoprene: global effects on oxidants, nitrogen oxides, organic products, and secondary organic aerosol

“…Early mechanisms focused on high-NO conditions representative of polluted regions and the role of isoprene in driving the production of ozone and organic nitrates (Lloyd et al, 1983;Brewer et al, 1984;Trainer et al, 1987;Madronich and Calvert, 1990). These model studies led to a number of chamber experiments to test and improve the mechanisms (Atkinson et al, 1989;Tuazon and Atkinson, 1990;Grosjean et al, 1993;Miyoshi et al, 1994;Kwok and Atkinson, 1995;Stevens et al, 1999;Ruppert and Becker, 2000) along with field observations of isoprene chemistry (Biesenthal and Shepson, 1997;Starn et al, 1998;Roberts et al, 1998;Wiedinmyer et al, 2001). Improved understanding of the chemistry under low-NO conditions and growing interest in formation of organic aerosol led to the development of increasingly complex mechanisms (Carter, 1996;Stockwell et al, 1997;Pöschl et al, 2000;Geiger et al, 2003;Aumont et al, 2005).…”