Abstract
Abstract. The dicarbonyls glyoxal (Gly) and methylglyoxal (Mgly) have been recognized as important precursors of secondary organic aerosols (SOAs) through the atmospheric heterogeneous process. In this study, field measurement was conducted at a receptor site in the Pearl River Delta (PRD) region in southern China, and an observation-based photochemical box model was subsequently applied to investigate the production and evolution of Gly and Mgly as well as their contributions to SOA formation. The model was coupled with a detailed gas-phase oxidation mechanism of volatile organic compounds (VOCs) (i.e., Master Chemical Mechanism, MCM, v3.2), heterogeneous processes of Gly and Mgly (i.e., reversible partitioning in aqueous phase, irreversible volume reactions and irreversible surface uptake processes), and the gas–particle partitioning of oxidation products. The results suggested that without considering the heterogeneous processes of Gly and Mgly on aerosol surfaces, the model would overpredict the mixing ratios of Gly and Mgly by factors of 3.3 and 3.5 compared to the observed levels. The agreement between observation and simulation improved significantly when the irreversible uptake and the reversible partitioning were incorporated into the model, which in total both contributed ∼ 62 % to the destruction of Gly and Mgly during daytime. Further analysis of the photochemical budget of Gly and Mgly showed that the oxidation of aromatics by the OH radical was the major pathway producing Gly and Mgly, followed by degradation of alkynes and alkenes. Furthermore, based on the improved model mechanism, the contributions of VOC oxidation to SOA formed from gas–particle partitioning (SOAgp) and from heterogeneous processes of Gly and Mgly (SOAhet) were also quantified. It was found that o-xylene was the most significant contributor to SOAgp formation (∼ 29 %), while m,p-xylene and toluene made dominant contributions to SOAhet formation. Overall, the heterogeneous processes of Gly and Mgly can explain ∼ 21 % of SOA mass in the PRD region. The results of this study demonstrated the important roles of heterogeneous processes of Gly and Mgly in SOA formation and highlighted the need for a better understanding of the evolution of intermediate oxidation products.
Highlights
Organic aerosols (OAs) are important components of atmospheric aerosols, with important impacts on radiation balance, air quality, atmospheric oxidative capacity and climate change (Zhu et al, 2011; Carlton et al, 2009; Hoyle et al, 2009)
Li et al (2013) concluded that secondarily produced (SOA) formed from the heterogeneous processes of dicarbonyls may contribute more than 50 % to the total SOA mass in the Pearl River Delta (PRD) region, while our study showed that the contribution of SOAhet to total SOA mass was ∼ 21 % (i.e., ∼ 11 % of SOAhet formed from Gly; ∼ 10 % of SOAhet formed from Mgly)
A photochemical box model coupled with MCM (v3.2) (PBM-MCM) and further improvements on the evolution of semi- and non-volatile oxidation products to a condensed particle-phase was used to investigate the production and heterogeneous processes of Gly and Mgly, as well as the SOA–precursor relationship at a receptor site for the first time in the PRD region
Summary
Organic aerosols (OAs) are important components of atmospheric aerosols, with important impacts on radiation balance, air quality, atmospheric oxidative capacity and climate change (Zhu et al, 2011; Carlton et al, 2009; Hoyle et al, 2009). In addition to the primary organic components (primary OA, POA) directly emitted from various sources. Z. Ling et al.: Formation and sink of glyoxal and methylglyoxal in the PRD in the particulate form, a large fraction of OAs are secondarily produced (SOA) through the aging of POAs and through complex homogenous and/or heterogeneous reactions of volatile or semivolatile organic compounds (VOCs, SVOCs) (Jimenez et al, 2009; Steinfeld et al, 1998). The characteristics of SOAs are still poorly understood because of their complicated formation mechanisms, various chemical compositions and multitude of precursors from diverse emissions, making SOAs an important research topic in the field of the atmospheric environment
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