Abstract
Abstract. Emissions from mobile sources are important contributors to both primary and secondary organic aerosols (POA and SOA) in urban environments. We compiled recently published data to create comprehensive model-ready organic emission profiles for on- and off-road gasoline, gas-turbine, and diesel engines. The profiles span the entire volatility range, including volatile organic compounds (VOCs, effective saturation concentration C*=107–1011 µg m−3), intermediate-volatile organic compounds (IVOCs, C*=103–106 µg m−3), semi-volatile organic compounds (SVOCs, C*=1–102 µg m−3), low-volatile organic compounds (LVOCs, C*≤0.1 µg m−3) and non-volatile organic compounds (NVOCs). Although our profiles are comprehensive, this paper focuses on the IVOC and SVOC fractions to improve predictions of SOA formation. Organic emissions from all three source categories feature tri-modal volatility distributions (“by-product” mode, “fuel” mode, and “lubricant oil” mode). Despite wide variations in emission factors for total organics, the mass fractions of IVOCs and SVOCs are relatively consistent across sources using the same fuel type, for example, contributing 4.5 % (2.4 %–9.6 % as 10th to 90th percentiles) and 1.1 % (0.4 %–3.6 %) for a diverse fleet of light duty gasoline vehicles tested over the cold-start unified cycle, respectively. This consistency indicates that a limited number of profiles are needed to construct emissions inventories. We define five distinct profiles: (i) cold-start and off-road gasoline, (ii) hot-operation gasoline, (iii) gas-turbine, (iv) traditional diesel and (v) diesel-particulate-filter equipped diesel. These profiles are designed to be directly implemented into chemical transport models and inventories. We compare emissions to unburned fuel; gasoline and gas-turbine emissions are enriched in IVOCs relative to unburned fuel. The new profiles predict that IVOCs and SVOC vapour will contribute significantly to SOA production. We compare our new profiles to traditional source profiles and various scaling approaches used previously to estimate IVOC emissions. These comparisons reveal large errors in these different approaches, ranging from failure to account for IVOC emissions (traditional source profiles) to assuming source-invariant scaling ratios (most IVOC scaling approaches).
Highlights
Atmospheric particulate matter imposes health risks (Di et al, 2017) and influences climate (Kanakidou et al, 2005)
Organic aerosol (OA) is commonly classified as primary OA (POA), which is directly emitted by sources, or secondary OA (SOA), which is formed in the atmosphere through photooxidation gas-phase organics
Mobile sources contribute about one-third of the anthropogenic organic emissions in the 2014 EPA National Emission Inventory (NEI); they are an important source of POA and SOA
Summary
Atmospheric particulate matter imposes health risks (Di et al, 2017) and influences climate (Kanakidou et al, 2005). Lu et al.: Comprehensive organic emission profiles for gasoline, diesel, and gas-turbine engines precursor gases especially in urban environments (Gentner et al, 2017; USEPA-OAQPS, 2015) Traditional emissions inventories such as the NEI account for emissions of gas-phase volatile organic compounds (VOCs, typically smaller than C12) and non-volatile particulate matter (PM). These emissions are speciated for use in chemical transport models using source-specific emission profiles. Recent studies have reported comprehensive IVOC, SVOC and/or low-volatile organic compound (LVOC, C∗ ≤ 0.1 μg m−3) emissions and gas-particle partitioning on POA emissions from mobile sources (May et al, 2014; Presto et al, 2011; Zhao et al, 2015, 2016). We present box model calculations of SOA formation to demonstrate the importance to implement the new profiles in SOA modelling
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