GENerator of reduced Organic Aerosol mechanism (GENOA v1.0): an automatic generation tool of semi-explicit mechanisms

Abstract

Abstract. This paper describes the GENerator of reduced Organic Aerosol mechanism (GENOA) that produces semi-explicit mechanisms for simulating the formation and evolution of secondary organic aerosol (SOA) in air quality models. Using a series of predefined reduction strategies and evaluation criteria, GENOA trains and reduces SOA mechanisms from near-explicit chemical mechanisms (e.g., the Master Chemical Mechanism – MCM) under representative atmospheric conditions. As a consequence, these trained SOA mechanisms can preserve the accuracy of detailed gas-phase chemical mechanisms on SOA formation (e.g., molecular structures of crucial organic compounds, the effect of “non-ideality”, and the hydrophilic/hydrophobic partitioning of aerosols), with a size (in terms of reaction and species numbers) that is manageable for three-dimensional (3-D) aerosol modeling (e.g., regional chemical transport models). Applied to the degradation of sesquiterpenes (as β-caryophyllene) from MCM, GENOA builds a concise SOA mechanism (2 % of the MCM size) that consists of 23 reactions and 15 species, with 6 of them being condensable. The generated SOA mechanism has been evaluated regarding its ability to reproduce SOA concentrations under the varying atmospheric conditions encountered over Europe, with an average error lower than 3 %.

Implementation of a Parallel Reduction Algorithm in the Generator of Reduced Organic Aerosol Mechanisms (Genoa V2.0): Application to Multiple Monoterpene Aerosol Precursors

“…GENOA is a reduction algorithm that generates concise SOA mechanisms based on detailed VOC mechanisms under representative atmospheric conditions. Since a detailed description of the first version of the GENOA algorithm (GENOA v1.0) is available in Wang et al (2022), only the main concepts are reviewed here.…”

“…GENOA v1.0 was applied to the degradation scheme of sesquiterpene of MCM v3.3.1 (Jenkin et al, 2012), resulting in a reduction from 1 625 reactions and 579 species to 23 reactions and 15 species (2% of the original size) with less than 3% error on average (Wang et al, 2022).…”

“…The second limitation of GENOA v1.0 is its inability to reduce mechanisms with multiple SOA precursors simultaneously, whereas some precursors may share common or similar chemical pathways. As presented in Wang et al (2022), only one initial SOA precursor (i.e., beta-caryophyllene) is considered in the sesquiterpene mechanism adopted in GENOA v1.0. The reduction was performed with a single initial concentration of sesquiterpene of 10 μg/m 3 for all conditions.…”

“…In addition to the restrictions for the sesquiterpene reduction of GENOA v1.0 (detailed in Wang et al, 2022), more stringent restrictions are used for the monoterpene mechanism reduction of GENOA v2.0. Lumping is now restricted according to the saturation vapor pressure (P 𝑠𝑎𝑡 ) and oxygen atom numbers (indicating the oxidation state) of the species.…”

“…4 illustrates the locations of the training, pre-testing, and testing datasets adopted for the monoterpene mechanism reduction. All the selected atmospheric conditions were extracted from the same database used for the sesquiterpene reductions reported in Wang et al (2022). This database includes CHIMERE simulation results performed over a one-year period (2015) over Europe.…”