Abstract
Volatile chemical products (VCPs) are commonly-used consumer and industrial items that are an important source of anthropogenic emissions. Organic compounds from VCPs evaporate on atmospherically relevant time scales and include many species that are secondary organic aerosol (SOA) precursors. However, the chemistry leading to SOA, particularly that of intermediate volatility organic compounds (IVOCs), has not been fully represented in regional-scale models such as the Community Multiscale Air Quality (CMAQ) model, which tend to underpredict SOA concentrations in urban areas. Here we develop a model to represent SOA formation from VCP emissions. The model incorporates a new VCP emissions inventory and employs three new classes of emissions: siloxanes, oxygenated IVOCs, and nonoxygenated IVOCs. VCPs are estimated to produce 1.67 μg m-3 of noontime SOA, doubling the current model predictions and reducing the SOA mass concentration bias from -75% to -58% when compared to observations in Los Angeles in 2010. While oxygenated and nonoxygenated intermediate volatility VCP species are emitted in similar quantities, SOA formation is dominated by the nonoxygenated IVOCs. Formaldehyde and SOA show similar relationships to temperature and bias signatures indicating common sources and/or chemistry. This work suggests that VCPs contribute up to half of anthropogenic SOA in Los Angeles and models must better represent SOA precursors from VCPs to predict the urban enhancement of SOA.
Highlights
Organic aerosol (OA) is a major component of fine particulate matter (PM2.5) in urban areas throughout the world (Zhang et al, 2007)
Secondary organic aerosol (SOA) is often the dominant component of OA (Jimenez et al, 2009) and is formed when gas-phase volatile organic compounds (VOCs) react with atmospheric oxidants to form products that condense into the aerosol phase, where they can undergo further reaction
The remaining 43.6 % (3.7 × 107 kg yr−1) of Los Angeles County emissions are assigned to model surrogates that form SOA
Summary
Organic aerosol (OA) is a major component of fine particulate matter (PM2.5) in urban areas throughout the world (Zhang et al, 2007). Secondary organic aerosol (SOA) is often the dominant component of OA (Jimenez et al, 2009) and is formed when gas-phase volatile organic compounds (VOCs) react with atmospheric oxidants to form products that condense into the aerosol phase, where they can undergo further reaction. SOA is formed via thousands of atmospheric reactions (Goldstein and Galbally, 2007), so understanding its sources remains a challenge. Volatile chemical products (VCPs) are an important source of organic emissions that lead to SOA formation Pennington et al.: Modeling secondary organic aerosol formation et al, 2018; Qin et al, 2021). Previous work suggests that during the 2010 California Research at the Nexus of Air Quality and Climate Change (CalNex) campaign in southern California (Ryerson et al, 2013), VCPs contributed approximately 1.1 μg m−3, or 41 %, of observed SOA above background levels in the Los Angeles Basin (Qin et al, 2021)
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