Abstract
Abstract. In this study we modeled secondary organic aerosol (SOA) mass loadings from the oxidation (by O3, OH and NO3) of five representative biogenic volatile organic compounds (BVOCs): isoprene, endocyclic bond-containing monoterpenes (α-pinene and limonene), exocyclic double-bond compound (β-pinene) and a sesquiterpene (β-caryophyllene). The simulations were designed to replicate an idealized smog chamber and oxidative flow reactors (OFRs). The Master Chemical Mechanism (MCM) together with the peroxy radical autoxidation mechanism (PRAM) were used to simulate the gas-phase chemistry. The aim of this study was to compare the potency of MCM and MCM + PRAM in predicting SOA formation. SOA yields were in good agreement with experimental values for chamber simulations when MCM + PRAM was applied, while a stand-alone MCM underpredicted the SOA yields. Compared to experimental yields, the OFR simulations using MCM + PRAM yields were in good agreement for BVOCs oxidized by both O3 and OH. On the other hand, a stand-alone MCM underpredicted the SOA mass yields. SOA yields increased with decreasing temperatures and NO concentrations and vice versa. This highlights the limitations posed when using fixed SOA yields in a majority of global and regional models. Few compounds that play a crucial role (>95 % of mass load) in contributing to SOA mass increase (using MCM + PRAM) are identified. The results further emphasized that incorporating PRAM in conjunction with MCM does improve SOA mass yield estimation.
Highlights
Atmospheric secondary organic aerosols, formed from gasto-particle phase conversion of the oxidation products of volatile organic compounds (VOCs), significantly impact the organic aerosol mass loadings (Griffin, 1999; Kanakidou et al, 2005)
secondary organic aerosol (SOA) mass yields were simulated for the oxidation of various biogenic volatile organic compounds by dominant atmospheric oxidants oxidants: the hydroxyl radical (OH), O3 and NO3
We simulated SOA mass yields derived from the oxidation of various biogenic volatile organic compounds (BVOCs)
Summary
Atmospheric secondary organic aerosols, formed from gasto-particle phase conversion of the oxidation products of volatile organic compounds (VOCs), significantly impact the organic aerosol mass loadings (Griffin, 1999; Kanakidou et al, 2005). The most important BVOCs for SOA formation are isoprene (C5H8), monoterpenes (C10H16) and sesquiterpenes (C15H24) These compounds are all alkenes containing at least one carbon–carbon double bond, enabling them to undergo oxidation by the dominant atmospheric oxidants: the hydroxyl radical (OH), ozone (O3) and the nitrate radical (NO3). For some of the terpenes, initial oxidation steps can lead to formation of highly oxygenated organic molecules (HOMs). These HOMs generally have low volatilities and can condense nearly irreversibly, thereby producing SOA (Ehn et al, 2014). HOMs, detected in both the ambient atmosphere and chamber experiments (Ehn et al, 2012) are formed by autoxidation (Berndt et al, 2016; Crounse and Nielsen, 2013) wherein peroxy radicals (RO2) undergo sub-
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