Representing Organic Compound Oxidation in Chemical Mechanisms for Policy-Relevant Air Quality Models under Background Troposphere Conditions

Abstract

This intercomparison has taken thirteen chemical mechanisms and compared how they treat VOC oxidation and degradation and its relationship to the photochemical formation of ozone and hydroxyl radicals. Here, we have looked in some detail at the incremental responses of hydroxyl radicals to incremental additions of a range of organic compounds under conditions appropriate to the background atmosphere. Most of the time, with most organic compounds and most chemical mechanisms, incremental additions of an organic compound led to depletion of hydroxyl radical concentrations. The chemical mechanisms studied demonstrated increasingly negative incremental hydroxyl radical reactivities with increasing carbon numbers for the alkanes ethane, propane and n-butane. Hydroxyl radical incremental reactivities for the simple alkenes, ethylene and propylene, were reasonably consistent across the chemical mechanisms studied. However, this consistent representation did not extend to trans but-2-ene, where reactivity estimates spanned a range of a factor of five. Incremental reactivities were reasonably well-defined for isoprene which was encouraging in view of its importance to background tropospheric chemistry. The most serious discrepancies emerging from this study were found with the aromatics toluene and o-xylene, and with the Master Chemical Mechanism and these are discussed in some detail.

Intercomparison of the representations of the atmospheric chemistry of pre-industrial methane and ozone in earth system and other global chemistry-transport models

“…References BCC-GEOS-CHEMv1.0 Wu et al (2019, 2020) Mao et al, 2010Parrella et al, 2012Emmerson and Evans (2009…”

“…This intercomparison employed a constrained box-model approach that has previously been applied to the polluted boundary layer (Derwent, 2017) and to the background troposphere (Derwent, 2020). Here, the constrained box-model is focussed on the representation of the atmospheric chemistry of O 3 and CH 4 in the pre-industrial atmosphere and its representation in earth system and other global chemistry-transport models.…”

Influence of Ammonium Sulfate Seed Particle on Optics and Compositions of Toluene Derived Organic Aerosol in Photochemistry

“…Glyoxal and methylglyoxal can be protonated by H + ion and hydrolyzed to tetrol product (1), as displayed in Figure 9. Additionally, the protonated α-dicarbonyls can react with NH 4 + ions to produce diimine product (2). Tetrol product (1) can react with diimine The high concentration of (NH4)2SO4 seed provides more surface area for condensation and reaction of gaseous α-dicarbonyls.…”

“…The photooxidation of toluene and other monocyclic aromatic compounds from anthropogenic emission sources leads to the formation of semi-and non-volatile oxygenated compounds, which result in secondary organic aerosol (SOA) particles [1,2]. Interest in SOA has been renewed because of its contribution to radiative balance and visibility degradation [3][4][5].…”