Obscured Contribution of Oxygenated Intermediate-Volatility Organic Compounds to Secondary Organic Aerosol Formation from Gasoline Vehicle Emissions.

Secondary organic aerosol (SOA) formation from gasoline vehicles spanning a wide range of emission types was investigated using an oxidation flow reactor (OFR) by conducting chassis dynamometer tests. Aided by advanced mass spectrometric techniques, SOA precursors, including volatile organic compounds (VOCs) and intermediate/semivolatile organic compounds (I/SVOCs), were comprehensively characterized. The reconstructed SOA produced from the speciated VOCs and I/SVOCs can explain 69% of the SOA measured downstream of an OFR upon 0.5-3 days' OH exposure. While VOCs can only explain 10% of total SOA production, the contribution from I/SVOCs is 59%, with oxygenated I/SVOCs (O-I/SVOCs) taking up 20% of that contribution. O-I/SVOCs (e.g., benzylic or aliphatic aldehydes and ketones), as an obscured source, account for 16% of total nonmethane organic gas (NMOG) emission. More importantly, with the improvement in emission standards, the NMOG is effectively mitigated by 35% from China 4 to China 6, which is predominantly attributed to the decrease of VOCs. Real-time measurements of different NMOG components as well as SOA production further reveal that the current emission control measures, such as advances in engine and three-way catalytic converter (TWC) techniques, are effective in reducing the "light" SOA precursors (i.e., single-ring aromatics) but not for the I/SVOC emissions. Our results also highlight greater effects of O-I/SVOCs to SOA formation than previously observed and the urgent need for further investigation into their origins, i.e., incomplete combustion, lubricating oil, etc., which requires improvements in real-time molecular-level characterization of I/SVOC molecules and in turn will benefit the future design of control measures.

Reactions of C12-C14 n-Alkylcyclohexanes with Cl Atoms: Kinetics and Secondary Organic Aerosol Formation.

Long-chain alkanes are a type of intermediate volatility organic compound (IVOC) in the atmosphere and a potential source of secondary organic aerosols (SOAs). C12-C14 n-alkylcyclohexanes are important compositions of IVOCs, with considerable concentrations and emission rates. The reaction rate constants and SOA formation of the reactions of C12-C14 n-alkylcyclohexanes with Cl atoms were investigated in the present study. The reaction rate constants of the long-chain alkanes obtained via the relative-rate method at 298 ± 0.2 K (in units of ×10-10 cm3 molecule-1 s-1) were as follows: khexylcyclohexane = 5.11 ± 0.28, kheptylcyclohexane = 5.56 ± 0.30, and koctylcyclohexane = 5.74 ± 0.31. The gas-phase products of the reactions were identified as mainly small molecules of aldehydes, ketones, and acids. The particle-phase products were mostly monomers and oligomers, but there were still trimers even under high-NOx conditions. Moreover, under high-NOx conditions (urban atmosphere), the SOA yields of hexylcyclohexane are higher than that under low-NOx conditions (remote atmosphere), indicating that more attention should be given to the SOA formation of Cl-initiated n-alkylcyclohexane oxidations in polluted regions. This research can further clarify the oxidation processes and SOA formation of n-alkylcyclohexanes in the atmosphere.

Volatility Distribution of Organic Compounds in Sewage Incineration Emissions.

Intermediate volatility and semivolatile organic compounds (IVOC/SVOC) are important precursors of secondary organic aerosol (SOA) while SVOC is an important contributor to primary organic aerosol (POA). However, combustion emissions data for volatility classes are limited. This study reports the gas and particle emissions that were sampled with various dilution factors from a sewage sludge incinerator burning fuel oil. Volatility distributions were determined using measurements from online mass spectrometry and offline organic compound analyses. In the low volatility organic compound (LVOC) to IVOC range, volatility bins with organic saturation concentrations of 10-100 µg m-3 were most abundant, which was due to organic acids generated from sludge burning. Organic aerosol (OA) emission factors (EFOA) increased 1.4 times after cooling to ambient temperatures in comparison to those of the samples from the hot stack. Upon further isothermal dilution at 25 °C, the EFOA decreased while organic gas phase EFs increased with increasing dilution. Phase partitioning in volatility bins with saturation concentrations of 10-100 µg m-3 was sensitive to isothermal dilution that influenced the EFs. Therefore, gas- and particle-phase measurements alone cannot constrain EFs for these volatility classes. Low dilution factors may overestimate the particle phase and underestimate the gas phase EFs compared with real-world emission conditions.

Emissions of intermediate volatility organic compound from waste cooking oil biodiesel and marine gas oil on a ship auxiliary engine.

Ship auxiliary engines contribute large amounts of air pollutants when at berth. Biodiesel, including that from waste cooking oil (WCO), can favor a reduction in the emission of primary pollutant when used with internal combustion engines. This study investigated the emissions of gaseous intermediate-volatile organic compounds (IVOCs) between WCO biodiesel and marine gas oil (MGO) to further understand the differences in secondary organic aerosol (SOA) production of exhausts. Results revealed that WCO exhaust exhibited similar IVOC composition and volatility distribution to MGO exhaust, despite the differences between fuel contents. While WCO biodiesel could reduce IVOC emissions by 50% as compared to MGO, and thus reduced the SOA production from IVOCs. The compositions and volatility distributions of exhaust IVOCs varied to those of their fuels, implying that fuel-component-based SOA predicting model should be used with more cautions when assessing SOA production of WCO and MGO exhausts. WCO biodiesel is a cleaner fuel comparing to conventional MGO on ship auxiliary engines with regard to the reductions in gaseous IVOC emissions and corresponding SOA productions. Although the tests were conducted on test bench, the results could be considered as representative due to the widely applications of the test engine and MGO fuel on real-world ships.

Emission of intermediate volatility organic compounds from a ship main engine burning heavy fuel oil.

Intermediate volatility organic compounds (IVOCs) are crucial precursors of secondary organic aerosol (SOA). In this study, gaseous IVOCs emitted from a ship main engine burning heavy fuel oil (HFO) were investigated on a test bench, which could simulate the real-world operations and emissions of ocean-going ships. The chemical compositions, emission factors (EFs) and volatility distributions of IVOC emissions were investigated. The results showed that the main engine burning HFO emitted a large amount of IVOCs, with average IVOC EFs of 20.2-201 mg/kg-fuel. The IVOCs were mainly comprised of unspeciated compounds. The chemical compositions of exhaust IVOCs were different from that of HFO fuel, especially for polycyclic aromatic compounds and alkylcyclohexanes. The volatility distributions of IVOCs were also different between HFO exhausts and HFO fuel. The distinctions in IVOC emission characteristics between HFO exhausts and HFO fuel should be considered when assessing the IVOC emission and related SOA formation potentials from ocean-going ships burning HFO, especially when using fuel-surrogate models.

Size distribution dynamics reveal particle-phase chemistry in organic aerosol formation.

Organic aerosols are ubiquitous in the atmosphere and play a central role in climate, air quality, and public health. The aerosol size distribution is key in determining its optical properties and cloud condensation nucleus activity. The dominant portion of organic aerosol is formed through gas-phase oxidation of volatile organic compounds, so-called secondary organic aerosols (SOAs). Typical experimental measurements of SOA formation include total SOA mass and atomic oxygen-to-carbon ratio. These measurements, alone, are generally insufficient to reveal the extent to which condensed-phase reactions occur in conjunction with the multigeneration gas-phase photooxidation. Combining laboratory chamber experiments and kinetic gas-particle modeling for the dodecane SOA system, here we show that the presence of particle-phase chemistry is reflected in the evolution of the SOA size distribution as well as its mass concentration. Particle-phase reactions are predicted to occur mainly at the particle surface, and the reaction products contribute more than half of the SOA mass. Chamber photooxidation with a midexperiment aldehyde injection confirms that heterogeneous reaction of aldehydes with organic hydroperoxides forming peroxyhemiacetals can lead to a large increase in SOA mass. Although experiments need to be conducted with other SOA precursor hydrocarbons, current results demonstrate coupling between particle-phase chemistry and size distribution dynamics in the formation of SOAs, thereby opening up an avenue for analysis of the SOA formation process.

Uncovering the dominant contribution of intermediate volatility compounds in secondary organic aerosol formation from biomass-burning emissions.

Organic vapors from biomass burning are a major source of secondary organic aerosols (SOAs). Previous smog chamber studies found that the SOA contributors in biomass-burning emissions are mainly volatile organic compounds (VOCs). While intermediate volatility organic compounds (IVOCs) are efficient SOA precursors and contribute a considerable fraction of biomass-burning emissions, their contribution to SOA formation has not been directly observed. Here, by deploying a newly-developed oxidation flow reactor to study SOA formation from wood burning, we find that IVOCs can contribute ∼70% of the formed SOA, i.e. >2 times more than VOCs. This previously missing SOA fraction is interpreted to be due to the high wall losses of semi-volatile oxidation products of IVOCs in smog chambers. The finding in this study reveals that SOA production from biomass burning is much higher than previously thought, and highlights the urgent need for more research on the IVOCs from biomass burning and potentially other emission sources.

Elucidating the unexpected importance of intermediate-volatility organic compounds (IVOCs) from refueling procedure.

Evaporative emissions release organic compounds comparable to gasoline exhaust in China. However, the measurement of intermediate volatility organic compounds (IVOCs) is lacking in studies focusing on gasoline evaporation. This study sampled organics from a real-world refueling procedure and analyzed the organic compounds using comprehensive two-dimensional gas chromatography coupled with a mass spectrometer (GC×GC-MS). The non-target analysis detected and quantified 279 organics containing 93 volatile organic compounds (VOCs, 64.9 ± 7.4 % in mass concentration), 182 IVOCs (34.9 ± 7.4 %), and 4 semivolatile organic compounds (SVOCs, 0.2 %). The refueling emission profile was distinct from that of gasoline exhaust. The b-alkanes in the B12 volatility bin are the most abundant IVOC species (1.9 ± 1.4 µg m-3) in refueling. A non-negligible contribution of 17.5 % to the ozone formation potential (OFP) from IVOCs was found. Although IVOCs are less in concentration, secondary organic aerosol potential (SOAP) from IVOCs (58.1 %) even exceeds SOAP from VOCs (41.6 %), mainly from b-alkane in the IVOC range. At the molecular level, the proportion of cyclic compounds in SOAP (12.1 %) indeed goes above its mass concentration (3.1 %), mainly contributed by cyclohexanes and cycloheptanes. As a result, the concentrations and SOAP of cyclic compounds (>50 %) could be overestimated in previous studies. Our study found an unexpected contribution of IVOCs from refueling procedures to both ozone and SOA formation, providing new insights into secondary pollution control policy.

Source apportionment of anthropogenic and biogenic organic aerosol over the Tokyo metropolitan area from forward and receptor models.

Organic aerosol (OA) is a dominant component of PM2.5, and accurate knowledge of its sources is critical for identification of cost-effective measures to reduce PM2.5. For accurate source apportionment of OA, we conducted field measurements of organic tracers at three sites (one urban, one suburban, and one forest) in the Tokyo Metropolitan Area and numerical simulations of forward and receptor models. We estimated the source contributions of OA by calculating three receptor models (positive matrix factorization, chemical mass balance, and secondary organic aerosol (SOA)-tracer method) using the ambient concentrations, source profiles, and production yields of OA tracers. Sensitivity simulations of the forward model (chemical transport model) for precursor emissions and SOA formation pathways were conducted. Cross-validation between the receptor and forward models demonstrated that biogenic and anthropogenic SOA were better reproduced by the forward model with updated modules for emissions of biogenic volatile organic compounds (VOC) and for SOA formation from biogenic VOC and intermediate-volatility organic compounds than by the default setup. The source contributions estimated by the forward model generally agreed with those of the receptor models for the major OA sources: mobile sources, biomass combustion, biogenic SOA, and anthropogenic SOA. The contributions of anthropogenic SOA, which are the main focus of this study, were estimated by the forward and receptor models to have been between 9 % and 15 % in summer 2019. The observed percent modern carbon data indicate that the amounts of anthropogenic SOA produced during daytime have substantially declined from 2007 to 2019. This trend is consistent with the decreasing trend of anthropogenic VOC, suggesting that reduction of anthropogenic VOC has been effective in reducing anthropogenic SOA in the atmosphere.

Detailed Speciation of Semi-Volatile and Intermediate-Volatility Organic Compounds (S/IVOCs) in Marine Fuel Oils Using GC × GC-MS.

Ship emissions contribute substantial air pollutants when at berth. However, the complexity and diversity of the marine fuels utilized hinder our understanding and mapping of the characteristics of ship emissions. Herein, we applied GC × GC-MS to analyze the components of marine fuel oils. Owing to the high separation capacity of GC × GC-MS, 11 classes of organic compounds, including b-alkanes, alkenes, and cyclo-alkanes, which can hardly be resolved by traditional one-dimensional GC-MS, were detected. Significant differences are observed between light (-10# and 0#) and heavy (120# and 180#) fuels. Notably, -10# and 0# diesel fuels are more abundant in b-alkanes (44~49%), while in 120# and 180#, heavy fuels b-alkanes only account for 8%. Significant enhancement of naphthalene proportions is observed in heavy fuels (20%) compared to diesel fuels (2~3%). Hopanes are detected in all marine fuels and are especially abundant in heavy marine fuels. The volatility bins, one-dimensional volatility-based set (VBS), and two-dimensional VBS (volatility-polarity distributions) of marine fuel oils are investigated. Although IVOCs still take dominance (62-66%), the proportion of SVOCs in heavy marine fuels is largely enhanced, accounting for ~30% compared to 6~12% in diesel fuels. Furthermore, the SVOC/IVOC ratio could be applied to distinguish light and heavy marine fuel oils. The SVOC/IVOC ratios for -10# diesel fuel, 0# diesel fuel, 120# heavy marine fuel, and 180# heavy marine fuel are 0.085 ± 0.046, 0.168 ± 0.159, 0.504, and 0.439 ± 0.021, respectively. Our work provides detailed information on marine fuel compositions and could be further implemented in estimating organic emissions and secondary organic aerosol (SOA) formation from marine fuel storage and evaporation processes.

Emission factors and chemical profile of I/SVOCs emitted from household biomass stove in China.

Household combustion of biomass straw for cooking or heating is one of the most important emission sources of intermediate volatility and semi-volatile organic compounds (I/SVOCs). However, there are limited studies on the emission factors (EFs) and speciation profiles of I/SVOCs from household stoves burning biomass straw. In this study, experiments were conducted in a typical Chinese stove to test the EFs and species of I/SVOCs in three commonly used straws. It was revealed that EFs of I/SVOCs emitted from the burning of corn straw, rice straw, and wheat straw were 6.7, 1.9, and 9.8 g/kg, respectively, which accounted for 48.3 %, 36.8 %, and 48.6 % of total organic compounds emitted. Particulate organic compounds were dominated by ketones, oxygenated aromatics, acids, esters, and nitrogen-containing compounds, whereas the gaseous phase was dominated by aldehydes, acids, and aromatics. Although I/SVOCs only accounted for 18.1-23.6 % of the gaseous emissions from burning of straw, they represented 64.8-72.9 % of the secondary organic aerosol formation potential (SOAFP). The EFs of 16 priority polycyclic aromatic hydrocarbons (PAHs) were 362.0, 262.5, and 1145.2 mg/kg for corn straw, rice straw, and wheat straw, respectively, among which 3-ring and 4-ring PAHs were the main components. Thus, the results of this study provide new reliable I/SVOCs data that are useful for the development of an accurate emission inventory of organic compounds, simulation of secondary organic aerosol (SOA) formation, and health risk assessment.

Measurement-based intermediate volatility organic compound emission inventory from on-road vehicle exhaust in China.

Intermediate volatility organic compounds (IVOCs) have great potential to form secondary organic aerosols (SOA) in the atmosphere. Thus, a high-resolution IVOC emission inventory is essential for the accurate simulation of SOA formation. This study developed the first nationwide on-road vehicular IVOC emission inventory in China based on localized measurement of the IVOC emission factors and volatility distributions for various vehicle types. The total vehicular IVOC emissions in China in 2019 were estimated to be 241.2 Gg. Heavy-duty trucks, light-duty trucks, and light-duty passenger vehicles contributed the most, accounting for 47.6%, 24.6%, and 16.9% of total vehicular IVOC emissions, respectively. Although much higher in number, gasoline vehicles contributed 15.0%, which was far less than the contribution of diesel vehicles. The two peaks in volatility bins B12-B13 and B16-B17 accounted for 42.2% and 23.7% of the total IVOC emissions, respectively. By gridding the emission inventory into a relatively high resolution of 0.1° × 0.1°, high-emission areas and hotspots were clearly identified. In general, eastern China had substantially higher vehicular IVOC emissions than western China. High-emission areas with emission intensity >10 Mg·grid-1 covered most of the North China Plain, Yangtze River Delta, and Pearl River Delta. The emission intensity over the downtown areas of Beijing and Shanghai exceeded 50 Mg·grid-1. In contrast, IVOC emissions over western China were relatively lower, with a network structure gathering around the traffic arteries serving inter-provincial transportation. This study underscored the importance of having a localized emission factor to better reflect the IVOC emission characteristics from Chinese vehicles and to improve the assessment of their environmental impacts.

An updated comprehensive IVOC emission inventory for mobile sources in China.

Intermediate volatility organic compounds (IVOCs) from mobile sources contribute significantly to secondary organic aerosol (SOA) formation. However, the assessments of IVOC emissions remain considerably uncertain due to the lack of localized measured data and detailed emission source classifications. This study established a comprehensive database of IVOC emission factors (EFs) for mobile sources based on the diversified measured EFs and correlations with hydrocarbons. The provincial-level IVOC emission inventories over China were further established by integrating activity data of various mobile sources. The national mobile source IVOC emissions were 507.5 Gg in 2017. The IVOC emissions of on-road and non-road mobile sources were roughly the same. Trucks and non-road construction machineries were the major contributors to IVOC emissions, accounting for >66 % of the total. The IVOC emission characteristics and spatial distributions from various mobile sources varied significantly with different types and usages. The IVOC emission inventories with detailed classifications can be used to evaluate emission control policies for mobile sources. Incorporating localized measured data would be beneficial for a better understanding for the atmospheric impacts of mobile source IVOC emissions.

Investigation of partition coefficients and fingerprints of atmospheric gas- and particle-phase intermediate volatility and semi-volatile organic compounds using pixel-based approaches.

Ambient gas- and particle-phase intermediate volatility and semi-volatile organic compounds (I/SVOCs) of Beijing were analyzed by a thermal desorption comprehensive two-dimensional gas chromatography quadrupole mass spectrometry (TD-GC × GC-qMS). A pixel-based scheme combing the integration-based approach was applied for partition coefficients estimation and fingerprints identification. Blob-by-blob recognition was firstly utilized to characterize I/SVOCs from the molecular level. 412 blobs in gas-phase and 460 blobs in particle-phase were resolved, covering a total response of 47.5% and 43.5%. A large pool of I/SVOCs was found with a large diversity of chemical classes in both gas- and particle-phase. Acids (8.5%), b-alkanes (5.8%), n-alkanes (C8-C25, 5.3%), and aromatics (4.4%) were dominant in gas-phase while esters (7.0%, including volatile chemical product compounds, VCPs), n-alkanes (C9-C34, 5.7%), acids (4.6%), and siloxanes (3.6%) were abundant in particle-phase. Air pollutants were then evaluated by a two-parameter linear free energy relationship (LFER) model, which could be further implemented in the two-dimensional volatility basis set (2D-VBS) model. Multiway principal component analysis (MPCA) and partial least squares-discriminant analysis (PLS-DA) implied that naphthalenes, phenol, propyl-benzene isomers, and oxygenated volatile organic compounds (OVOCs) were key components in the gas-phase under different pollution levels. This work gives more insight into property estimation and fingerprints identification for complex ambient samples.

Primary organic gas emissions in vehicle cold start events: Rates, compositions and temperature effects.

Identification of air toxics emitted from light-duty gasoline vehicles (LDGVs) is expected to better protect human health. Here, the volatile organic compound (VOC) and intermediate VOC (IVOC) emissions in the high-emitted start stages were measured on a chassis dynamometer under normal and extreme temperatures for China 6 LDGVs. Low temperature enhanced the emission rates (ERs) of both VOCs and IVOCs. The VOC ERs were averaged 5.19 ± 2.74 times higher when the temperature dropped from 23 °C to 0 °C, and IVOCs were less sensitive to temperature change with an enlargement of 2.27 ± 0.19 times. Aromatics (46.75 ± 2.83%) and alkanes (18.46 ± 1.21%) dominated the cold start VOC emissions under normal temperature, which was quite different from hot running emission profiles. From the perspective of emission inventories, changes in the speciated composition of VOCs and IVOCs were less important than that in the actual magnitude of ERs under cold conditions. However, changes in the ERs and emission profiles were equally important at high temperatures. Furthermore, high time-resolved measurements revealed that low temperature enhanced both the emission peak and peak duration of fuel components and incomplete combustion products during cold start, while high temperature only increased the peak concentration of fuel components.

Identification of two main origins of intermediate-volatility organic compound emissions from vehicles in China through two-phase simultaneous characterization.

Intermediate-volatility organic compounds (IVOCs) emitted from vehicles are generally in the gas phase but may partly partition into particle phase when measured under ambient temperature. To have a complete and accurate picture of IVOC emissions from vehicles, gas- and particle-phase IVOCs from a fleet of gasoline and diesel vehicles were simultaneously characterized by dynamometer testing in Guangzhou, China. The total IVOC emission factors of the diesel vehicles were approximately 16 times those of the gasoline vehicles, and IVOCs were mainly concentrated in the particle phase in the form of the unresolved complex mixture (UCM). The chemical compositions and volatility distributions of the gas-phase IVOCs differed much between gasoline and diesel vehicles, but were similar to those of their respective fuel content. This indicated that vehicle fuel is the main origin for the gas-phase IVOC emissions from vehicles. In comparison, the chemical compositions of the particle-phase IVOCs from gasoline and diesel vehicles were similar and close to lubricating oil content, implying that lubricating oil plays an important role in contributing to particle-phase IVOCs. The highest IVOC fraction in the particle phase occurred from B16-B18 volatility bins, overall accounting for more than half of the particle-phase IVOCs for both the gasoline and diesel vehicles. A conceptual model was developed to articulate the distributions of lubricating oil contents and their evaporation and nucleation/adsorption capabilities in the different volatility bins. The IVOCs-produced secondary organic aerosol (SOA) were 1.4-2.6 and 3.9-11.7 times POAs emitted from the gasoline and diesel vehicles, respectively. The tightening of emission standards had not effectively reduced IVOC emissions and the SOA production until the implementation of China VI emission standard. This underscores the importance of accelerating the promotion of the latest emission standard to alleviate pollution from vehicles in China.

A gridded emission inventory of semi-volatile and intermediate volatility organic compounds in China.

An emission inventory of precursors is a prerequisite for the simulation of secondary organic aerosol (SOA), which could provide valuable information on the evolution of precursors, formation of SOA, and its influence on fine particle (PM2.5) abundance, oxidative capacity, and climate change. However, an emission inventory of semi-volatile and intermediate volatility organic compounds (S/IVOCs), the key precursor of SOA, particularly the gridded inventory that is appropriate for input into regional air quality models, remains limited in China, leading to an incomplete understanding of S/IVOCs sources and roles in SOA formation and the atmospheric environment. Therefore, a gridded emission inventory of S/IVOCs in China for 2016 was developed based on ample source-specific measured data on emission ratios of S/IVOCs to primary organic aerosols (POA) from literatures. The total emission of S/IVOCs was estimated to be 9.6 Tg, and industry and residential sectors were major sources of S/IVOCs, with contributions of 48.0% and 30.2%, respectively. The spatial variations suggested that S/IVOC emissions were mainly distributed in the highly industrialized and urbanized regions in China, such as Beijing-Tianjin-Hebei (BTH), the Yangtze River Delta (YRD), the Pearl River Delta (PRD), and the Sichuan-Chongqing (SC) regions, though the contributions and temporal patterns varied between different regions. Furthermore, uncertainty of the emission inventory was estimated to be within the range of -66%-153%, which was mainly attributed to emission ratios of IVOCs/POA for industry, transportation, and power plants. The gridded emission inventory developed in this study can be used to estimate the emissions of S/IVOCs in different regions, and can be applied to different models for a better understanding of the environmental effects of S/IVOCs.

Primary organic gas emissions from gasoline vehicles in China: Factors, composition and trends.

Continuous tightening emission standards (ESs) facilitate the reduction of organic gas emissions from gasoline vehicles. Correspondingly, it is essential to update the emissions and chemical speciation of total organic gases (TOGs), including volatile organic compounds (VOCs), intermediate volatility organic compounds (IVOCs), CH4, and unidentified non-methane hydrocarbons (NMHCs) for assessing the formation of ozone and secondary organic aerosol (SOA). In this study, TOG and speciation emissions from 12 in-use light-duty gasoline vehicle (LDGV) exhausts, covering the ESs from China II to China V, were investigated on a chassis dynamometer under the Worldwide Harmonized Light-duty Test Cycle (WLTC) in China. The results showed that the most effectively controlled subgroup in TOG emissions from LDGVs was VOCs, followed by the unidentified NMHCs and IVOCs. The mass fraction of VOCs in TOGs also reduced from 61 ± 9% to 46 ± 18% while the IVOCs gently increased from 2 ± 0.4% to 8 ± 4% along with the more stringent ESs. For the VOC subsets, the removal efficiency of oxygenated VOCs (OVOCs) was lower than those of other VOC subsets in the ESs from China IV to V, suggesting the importance of OVOC emission controls for relatively new LDGVs. The IVOC emissions were mainly subject to the ESs, then driving cycles and fuel use. The formation potentials of ozone and SOA from LDGVs decreased separately 96% and 90% along with the restricted ESs from China II-III to China IV. The major contributor of SOA formation transformed from aromatics in the VOC subsets for China II-III vehicles to IVOCs for China IV/V vehicles, highlighting that IVOC emissions from LDGVs are also needed more attentions to control in future.

Behaviour of traffic emitted semi-volatile and intermediate volatility organic compounds within the urban atmosphere.

Particulate matter originated from traffic has attracted major interest over the last few years. The semi-volatile organic component of the particles may evaporate with dispersion away from the emission source, creating vapour which may oxidise to form secondary organic aerosol. Air samples were collected from a street canyon, the adjacent park and an urban background site during the winter-spring period in central London, UK. Emissions of semi-volatile organic compounds (SVOCs) and intermediate volatility organic compounds (IVOCs) ranging from C10 to C36 in both the gas phase and particle phase were measured by using thermal desorption coupled to comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (TD-GC × GC-ToF-MS). Main compound groups identified and quantified were grouped alkanes (n-alkanes and branched alkanes), monocyclic alkanes, bicyclic alkanes and monocyclic aromatics. The carbon preference index (CPI) of n-alkanes was estimated to distinguish the emission sources. Pearson correlations between I/SVOCs and traffic tracers (black carbon, NOx and benzene) in different locations were compared to analyse the influence of this emission source. The results indicate that while the major emission source at the roadside site is traffic, the lower correlations at background sites are indicative of other source contributions and/or differential reactivity of compounds. Gas-particle phase partitioning of n-alkanes is evaluated and compared between sites. The potential influence of gas phase I/SVOCs upon OH reactivity and secondary organic aerosol (SOA) formation is estimated and found to be relatively small.

[Emission Inventory of Intermediate Volatility Organic Compounds from Vehicles in the Yangtze River Delta in 2017 and the Impact on the Formation Potential of Secondary Organic Aerosols].

Intermediate volatility organic compounds (IVOCs) have a significant contribution to the formation of secondary organic aerosols (SOA) in the atmosphere, but are not included in the current emission inventory. In this study, IVOC emissions from vehicles are estimated for the Yangtze River Delta region (YRD) for 2017 based on two methods:the emission factor method and the IVOCs/POA scaling factor method. Uncertainties in the estimated IVOCs emissions and the impact on their potential formation are discussed. The results based on the emission factor method showed that the total vehicular IVOCs emission in the YRD in 2017 was 35800 tons, and that the formation potential of SOA was an estimated 695 tons. IVOCs emissions from trucks accounted for>70% of total IVOCs emissions in most cities in the YRD region. In terms of fuel type, IVOCs emissions from diesel vehicles were much higher than of those from gasoline vehicles. Results based on the IVOCs/POA scaling factor method showed that the emissions calculated by different combinations of IVOCs/POA ratios and POA/PM2.5 ratios that could vary significantly, with a maximum of 64.2×104 tons and a minimum of just 5.2×104 tons. The resultant SOA formation potential was 1.55×104 tons and 1032 tons for the maximum and minimum, respectively. This study shows that the results of IVOCs emissions based on different estimation methods are associated with large uncertainties, which could directly affect the simulation results of SOA in subsequent air quality models. Therefore, it is necessary to use different inventory results in air quality models and perform model evaluation of SOA in order to obtain more accurate IVOCs emission inventories of vehicles in the YRD region.