Intermediate Volatility Organic Compounds Research Articles

Intermediate volatile organic compounds in Canadian residential air in winter: Implication to indoor air quality

Intermediate volatile organic compounds (IVOCs) have recently been characterized for their contributions to the formation of secondary organic aerosol in atmospheric air. However, IVOCs in air in various indoor environments have not been characterized yet. In this study, we characterized and measured IVOCs, volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs), in residential indoor air in Ottawa, Canada. IVOCs, including n-alkanes, branched-chain alkanes (b-alkanes), unspecified complex mixtures (UCM) IVOCs, and oxygenated IVOCs (such as fatty acids), were found to have a large impact on indoor air quality. The results indicate that the indoor IVOCs behave differently from those in the outdoor environment. IVOCs in the studied residential air ranged from 14.4 to 69.0 μg/m3, with a geometric mean of 31.3 μg/m3, accounting for approximately 20% of the total organic compounds (IVOCs, VOCs and SVOCs) in indoor air. The total b-alkanes and UCM-IVOCs were found to have statistically significant positive correlations with indoor temperature but have no correlations with airborne particulate matter less than 2.5 μm (PM2.5) as well as ozone (O3) concentration. However, indoor oxygenated IVOCs behaved differently from b-alkanes and UCM-IVOCs, with a statistically significant positive correlation with indoor relative humidity but no correlation with other indoor environmental conditions.

A lumped species approach for the simulation of secondary organic aerosol production from intermediate-volatility organic compounds (IVOCs): application to road transport in PMCAMx-iv (v1.0) (Geoscientific Model Development)

A lumped species approach for the simulation of secondary organic aerosol production from intermediate-volatility organic compounds (IVOCs): application to road transport in PMCAMx-iv (v1.0) (Geoscientific Model Development)

Non-target scanning of organics from cooking emissions using comprehensive two-dimensional gas chromatography-mass spectrometer (GC×GC-MS)

Cooking emission is a major source influencing human health and air quality. To elucidate the emission pattern of cooking fumes, gaseous and particulate organics were sampled by Tenax TA desorption tubes and quartz filters, respectively. Organics were analyzed by a comprehensive two-dimensional gas chromatography-quadrupole mass spectrometer (GC × GC-qMS) coupled with a thermal desorption system (TDS). A non-target analysis was conducted identifying 166 (gas-phase) and 349 (particle-phase) compounds emitted from cooking fumes. We propose a four-step identification procedure, containing comparison with standards, homologs identification by selected ion chromatograms (SICs), searching spectrums in the National Institute of Standard Technology (NIST) library, and recognitions of unresolved complex mixtures (UCMs). The identified organics are then quantified or semi-quantified by surrogates in the same chemical class with an uncertainty of 27%. Intermediate volatility organic compounds (IVOCs) are extensively detected accounting for 20.5% and 81.4% of the total mass concentration and emission rates (ERs) in gas- and particle-phase samples. Aldehydes (30.6%) and acids (82.7%) dominate the mass concentration of organics in the gas- and particle-phase, respectively. Our work provides a detailed identification procedure in the non-target analysis and emphasizes the importance of IVOC measurement in cooking emissions.

Measurement of Atmospheric Volatile and Intermediate Volatility Organic Compounds: Development of a New Time-of-Flight Mass Spectrometer

A new gas inlet port combined with a novel ionization scheme have been developed and coupled to a high-resolution time-of-flight mass spectrometer (TOF MS) for the detection and measurement of atmospheric volatile (VOCs) and intermediate volatility organic compounds (IVOCs). Ions are produced predominantly by charge transfer reactions in a low-temperature plasma ionization source with minimal fragmentation. Enhanced sensitivity is accomplished by incorporating an increased-size inlet capillary in a transverse arrangement to maximize throughput in the ionization source. Additional design aspects of the new mass spectrometer enabling superior transmission include a large acceptance ion funnel and a segmented radio frequency (RF) ion guide with increased space charge storage capacity. An orthogonal TOF analyzer equipped with a two-stage reflectron and tuned to second order is employed for the determination of the mass-to-charge ratio of the ions, with a mass resolving power of >20 k at mass 500 Th. The performance of the instrument was evaluated in tests using VOC standards and in atmospheric chamber experiments to demonstrate the ability to measure a wide range of organic compounds with different functional groups. Linear signal response is demonstrated over a wide range of VOCs used in the calibration processes in the ppb range, while the instrument exhibits linear response in the ppt range as well. Detection limits as low as 1 ppt are accomplished. The potential applications of this new TOF MS instrument were demonstrated in a pilot atmospheric simulation chamber experiment.

Modeling of wintertime regional formation of secondary organic aerosols around Beijing: sensitivity analysis and anthropogenic contributions

Modeling of secondary organic aerosol (SOA) has remained a big challenge due to the various precursors and complex processes involved. In this study, the WRF-CAMx model was used to predict the ambient SOA concentrations in urban Beijing as well as the North China Plain (NCP) during a polluted period in winter. To identify the major uncertainties and improve the model performance, a series of model tests were performed to assess the sensitivity of model prediction to the key factors. Then the sources of SOA in Beijing were identified using the optimized model. Both the volatility basis set (VBS) approach and the two-product approach were used for SOA simulation. Although the modeled SOA was underpredicted compared with the SOA estimated through filter-based measurements, the VBS scheme produced higher SOA than the traditional two-product scheme. According to the sensitivity tests with the VBS scheme, the emissions of volatile organic compounds (VOC) and intermediate volatility organic compounds (IVOC) as well as the oxidant levels were the key factors that affected SOA prediction. Based on the optimized simulation scenario, the potential contributions from different anthropogenic sources and source areas were identified, with over 80% of SOA in urban Beijing from regional transport of SOA or its precursors from the surrounding areas during the polluted period. Residential emission in the North China Plain appeared as the dominant source of SOA in urban Beijing from the perspective of regional contribution.Graphical

Trends of Full-Volatility Organic Emissions in China from 2005 to 2019 and Their Organic Aerosol Formation Potentials

Emissions of organic compounds have strong influences on the environment. Most previous emission inventories only cover the emissions of particulate organic carbon and nonmethane volatile organic compounds (NMVOC) but neglect the semivolatile and intermediate volatile organic compounds (S/IVOC), which considerably contribute to the organic aerosol (OA) burden. Herein, we developed a full-volatility emission inventory of organic compounds in China from 2005 to 2019 and analyzed the OA formation potential (OAFP) of each volatility bin and source using a two-dimensional volatility basis set (2D-VBS) box model. The emissions of low/extremely low/ultralow VOC (xLVOC) decreased substantially during 2005–2019, while the emissions of SVOC showed significant decline after 2014, mainly because of reduced residential biomass consumption. IVOC and VOC emission amounts in 2019 were similar to those in 2005; however, the major sources of emissions changed substantially. Emissions from volatile chemical products (VCP) increased significantly and became the dominant source of IVOC and VOC emissions. The S/IVOC from VCP contributed 1322 kt of OAFP in 2019, higher than the total anthropogenic xLVOC emissions. Considering the high of S/IVOC, future air pollution control policies should prioritize VCP, residential biomass burning, and diesel vehicles.

Emission characteristic of OVOCs, I/SVOCs, OC and EC from wood combustion at different moisture contents

Wood combustion is an important source of organic compounds, and its emission characteristics are affected by many factors, among which fuel moisture content (MC) is poorly understood. In this study, wood with MC of 2.5%, 10.9%, 19.2%, 31.4%, and 43.2% were prepared by stepwise dehydration of fresh pine, and burned separately in a quartz tube furnace at different ignition temperatures (400, 600, and 800 °C), in order to discuss the effects of MC on the emission characteristics of gas- and particle-phase organic compounds. The results showed that the effects of MC on the emission factors (EFs) of organic compounds were significant. When MC was close to 10%, the average EFs of carbonyl compounds (CCs), intermediate volatile organic compounds (IVOCs), polycyclic aromatic hydrocarbons (PAHs), n-alkanes, organic carbon (OC), and elemental carbon (EC) were 832.0 ± 518.5, 439.3 ± 111.6, 44.3 ± 6.6, 59.3 ± 9.3 mg/kg, and 2.4 ± 0.2, 0.8 ± 0.8 g/kg, respectively whereas when MC was near 30%, all the EFs reached the maximum and were 2.4, 3.1, 2.6, 4.2, and 3.1 times the lowest values, respectively. The MC and ignition temperature together affected the composition of organic compounds, with different organic profiles observed at various MCs when the temperature increased from 400 to 800 °C. For example, at MC ≈ 10%, the proportion of unresolved complex mixture (UCM) in IVOCs decreased from 59.7% to 43.4%, while the proportion of 5-6-ring PAHs increased from 7.4% to 35.4%. However, at MC ≈ 30%, formaldehyde and acetaldehyde in CCs decreased from >60% to ∼40%. In brief, the influence of MC may explain to a large extent the differences in organic emission characteristics of wood burned in the stove and open burning, and MC should be further considered in the experiments on the measurement of organic compound emissions from biomass burning.

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.

Development of Volatility Distributions for Organic Matter in Biomass Burning Emissions.

The volatility distribution of organic emissions from biomass burning and other combustion sources can determine their atmospheric evolution due to partitioning/aging. The gap between measurements and models predicting secondary organic aerosol has been partially attributed to the absence of semi- and intermediate volatility organic compounds (S/I-VOC) in models and measurements. However, S/I-VOCs emitted from these sources and typically quantified using the volatility basis framework (VBS) are not well understood. For example, the amount and composition of S/I-VOCs and their variability across different biomass burning sources such as residential woodstoves, open field burns, and laboratory simulated open burning are uncertain. To address this, a novel filter-in-tube sorbent tube sampling method collected S/I-VOC samples from biomass burning experiments for a range of fuels and combustion conditions. Filter-in-tube samples were analyzed using thermal desorption-gas chromatography-mass spectrometry (TD/GC/MS) for compounds across a wide range of volatilities (saturation concentrations; -2 ≤ logC* ≤ 6). The S/I-VOC measurements were used to calculate volatility distributions for each emissions source. The distributions were broadly consistent across the sources with IVOCs accounting for 75% - 90% of the total captured organic matter, while SVOCs and LVOCs were responsible for 6% - 13% and 1% - 12%, respectively. The distributions and predicted partitioning were generally consistent with literature. Particulate matter emission factors spanned two orders of magnitude across the sources. This work highlights the potential of inferring gas-particle partitioning behavior of biomass burning emissions using filter-in-tube sorbent samples analyzed offline. This simplifies both sampling and analysis of S/I-VOCs for studies focused on capturing the full range of organics emitted.

Secondary Organic Aerosol Formation from Semi-Volatile and Intermediate Volatility Organic Compounds in the Fall in Beijing

Intermediate volatility organic compounds (IVOCs) and semi-volatile organic compounds (SVOCs) have recently been proposed as important precursors of secondary organic aerosol (SOA). In the present work, 97 volatile organic compounds (VOCs) and 80 intermediate volatility and semi-volatile organic compounds (IVOCs and SVOCs) were measured by online gas chromatography-mass spectrometer/flame ionization detection (GC-MS/FID), and offline thermal desorption gas chromatography-mass spectrometer (TD-GC-MS), respectively. The average concentration of speciated VOCs, IVOCs, and SVOCs were 22.36 ± 9.02 μg m−3, 1.01 ± 0.32 μg m−3, and 0.10 ± 0.17 μg m−3. Alkanes and polycyclic aromatic hydrocarbons (PAHs) are the main compounds of total S/IVOCs. With the increase in molecular weight, the concentrations decreased in the gas phase, while increasing in the particle phase. Vehicular emission is the most significant source according to the carbon preference index (CPI) and the carbon of the most abundant alkane (Cmax). The yield method was used to estimate SOA from the oxidation of VOCs and S/IVOCs. The estimated SOA mass from IVOCs and SVOCs (0.70 ± 0.57 μg m−3) was comparable to that of VOCs (0.62 ± 0.61 μg m−3), and the oxidation of PAHs and alkanes took up 28.70 ± 8.26% and 51.97 ± 20.77% of the total SOA estimation, respectively. Compared to previous work, our study provided detailed molecular information of ambient S/IVOC species and elucidated their importance on SOA formation. Despite their low concentration, S/IVOCs species are important SOA precursors which shared comparable contribution compared with VOCs.

An updated comprehensive anthropogenic S/IVOCs emission inventory in Central China: Spatial and Temporal characteristics

Semi-volatile organic compounds (SVOCs) and intermediate volatile organic compounds (IVOCs) are key precursors for the formation of SOA, which is an important component of PM2.5, a representative pollutant of complex atmospheric pollution. It is important to understand the emissions of SVOCs and IVOCs. Based on the collected anthropogenic activity data and ratio of SVOCs and IVOCs to primary organic aerosols (POA), in this study, a newly 2017-based high-resolution S/IVOCs emission inventory in Central China represented by Henan Province was developed. The total emissions of SVOCs and IVOCs were 101.3 kt and 447.9 kt, respectively. SVOCs emission was mainly originated from residential combustion and industrial process, with the contribution of 44.4% and 20.8%, respectively. Industrial process and on-road mobile were the main contributors to IVOCs emission, accounting for 56.1% and 14.5% of total emission, respectively. This study further analyzes and compares S/IVOCs emissions of different cities based on the urban population. S/IVOCs emissions in 10 megacities, 5 large cities, and 3 small cities account for 74.9%, 16.4%, and 8.7% of total emissions, respectively. High SVOCs emissions were mainly distributed in eastern regions such as Shangqiu and Zhoukou which are agricultural cities, and that was in cities with developed industries and transportation, such as Zhengzhou and Jiaozuo, as for IVOCs. The uncertainties of SVOCs and IVOCs emissions established in this study are −60.7% - 62.2% and − 122.1% - 119.1%, respectively. Industrial process and on-road mobile are the emission sources with higher uncertainty of SVOCs and IVOCs emissions, respectively. It hopes to better understand the emission characteristics of S/IVOCs and provide more detailed basic data for air quality modelling simulation and various emission control policies.

Online measurements of cycloalkanes based on NO+ chemical ionization in proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS)

Abstract. Cycloalkanes are important trace hydrocarbons existing in the atmosphere, and they are considered a major class of intermediate volatile organic compounds (IVOCs). Laboratory experiments showed that the yields of secondary organic aerosols (SOAs) from oxidation of cycloalkanes are higher than acyclic alkanes with the same carbon number. However, measurements of cycloalkanes in the atmosphere are still challenging at present. In this study, we show that online measurements of cycloalkanes can be achieved using proton transfer reaction time-of-flight mass spectrometry with NO+ chemical ionization (NO+ PTR-ToF-MS). Cyclic and bicyclic alkanes are ionized with NO+ via hydride ion transfer, leading to major product ions of CnH2n-1+ and CnH2n-3+, respectively. As isomers of cycloalkanes, alkenes undergo association reactions with major product ions of CnH2n ⚫ (NO)+, and concentrations of 1-alkenes and trans-2-alkenes in the atmosphere are usually significantly lower than cycloalkanes (about 25 % and <5 %, respectively), as a result inducing little interference with cycloalkane detection in the atmosphere. Calibrations of various cycloalkanes show similar sensitivities associated with small humidity dependence. Applying this method, cycloalkanes were successfully measured at an urban site in southern China and during a chassis dynamometer study of vehicular emissions. Concentrations of both cyclic and bicyclic alkanes are significant in urban air and vehicular emissions, with comparable cyclic alkanes / acyclic alkanes ratios between urban air and gasoline vehicles. These results demonstrate that NO+ PTR-ToF-MS provides a new complementary approach for the fast characterization of cycloalkanes in both ambient air and emission sources, which can be helpful to fill the gap in understanding the importance of cycloalkanes in the atmosphere.

Moderate Contribution of Gasoline Intermediate Volatility Organic Compounds to Secondary Organic Aerosol Formation in Summer of Beijing

Moderate Contribution of Gasoline Intermediate Volatility Organic Compounds to Secondary Organic Aerosol Formation in Summer of Beijing

Simulations of Organic Aerosol with CAMx over the Po Valley during the Summer Season

A new sensitivity analysis with the Comprehensive Air Quality Model with Extensions (CAMx) using a traditional two-product scheme (SOAP) and the newer Volatility Basis Set (VBS) algorithm for organic aerosol (OA) calculations is presented. The sensitivity simulations include the default versions of the SOAP and VBS schemes, as well as new parametrizations for the VBS scheme to calculate emissions and volatility distributions of semi- and intermediate-volatile organic compounds. The focus of the simulations is the summer season (May to July 2013), in order to quantify the sensitivity of the model in a period with relatively large photochemical activity. In addition to the model sensitivity, we validate the results with ad hoc OA measurements obtained from aerosol mass spectrometers at two monitoring sites. Unlike winter cases previously published, the comparison with experimental data showed limited sensitivity to total OA amount, with an estimated increase in OA concentrations limited to a few tenths of µg m−3, for both the primary and secondary components. We show that the lack of pronounced sensitivity is related to the effect of the new parametrizations on different emissions sectors. Furthermore, the minor sensitivity to the new parametrizations could be related to the greater partitioning of OA towards the gaseous phase in the summer period, thus reducing the organic fraction in the aerosol phase.

A lumped species approach for the simulation of secondary organic aerosol production from intermediate-volatility organic compounds (IVOCs): application to road transport in PMCAMx-iv (v1.0)

Abstract. Secondary organic aerosol (SOA) is formed in the atmosphere through the oxidation and condensation of organic compounds. Intermediate-volatility compounds (IVOCs), compounds with effective saturation concentration (C∗) at 298 K between 103 and 106 µg m−3, have high SOA yields and can be important SOA precursors. The first efforts to simulate IVOCs in chemical transport models (CTMs) used the volatility basis set (VBS), a highly parametrized scheme that oversimplifies their chemistry. In this work we propose a more detailed approach for simulating IVOCs in CTMs, treating them as lumped species that retain their chemical characteristics. Specifically, we introduce four new lumped species representing large alkanes, two lumped species representing polyaromatic hydrocarbons (PAHs) and one species representing large aromatics, all in the IVOC range. We estimate IVOC emissions from road transport using existing estimates of volatile organic compound (VOC) emissions and emission factors of individual IVOCs from experimental studies. Over the European domain, for the simulated period of May 2008, estimated IVOC emissions from road transport were about 21 Mmol d−1, a factor of 8 higher than emissions used in previous VBS applications. The IVOC emissions from diesel vehicles were significantly higher than those from gasoline ones. SOA yields under low-NOx and high-NOx conditions for the lumped IVOC species were estimated based on recent smog chamber studies. Large cyclic alkane compounds have both high yields and high emissions, making them an important, yet understudied, class of IVOCs.

Mobile Sources Are Still an Important Source of Secondary Organic Aerosol and Fine Particulate Matter in the Los Angeles Region.

Secondary organic aerosol (SOA) is a significant component of atmospheric fine particulate matter. Mobile sources have historically been a major source of SOA precursors in urban environments, but decades of regulations have reduced their emissions. Less regulated sources, such as volatile chemical products (VCPs), are of growing importance. We analyzed ambient and emissions data to assess the contribution of mobile sources to SOA formation in Los Angeles during the period of 2009-2019. During this period, air quality in the Los Angeles region has improved, but organic aerosol (OA) concentrations did not decrease as much as primary pollutants. This appears to be largely due to SOA, whose mass fraction in OA increased over this period. In 2010, about half of the freshly formed SOA measured in Pasadena, CA appears to be formed from hydrocarbon (non-oxygenated) precursors. Chemical mass balance analysis indicates that these hydrocarbon SOA precursors (including intermediate volatility organic compounds) can largely be explained by emissions from mobile sources in 2010. Our analysis indicates that continued reduction in emissions from mobile sources should lead to additional significant decreases in atmospheric SOA and PM2.5 mass in the Los Angeles region.

Source Diversity of Intermediate Volatility n-Alkanes Revealed by Compound-Specific δ13C-δD Isotopes.

Intermediate volatility organic compounds (IVOCs) are important precursors of secondary organic aerosols, and their sources remain poorly defined. N-alkanes represent a considerable portion of IVOCs in atmosphere, which can be well identified and quantified out of the complex IVOC pool. To investigate the potential source diversity of intermediate volatility n-alkanes (IVnAs, nC12-nC20), we apportioned the sources of IVnAs in the atmosphere of four North China cities, based on their compound-specific δ13C-δD isotope compositions and Bayesian model analysis. The concentration level of IVnAs reached 1195 ± 594 ng/m3. The δ13C values of IVnAs ranged -32.3 to -27.6‰ and δD values -161 to -90‰. The δD values showed a general increasing trend toward higher carbon number alkanes, albeit a zigzag odd-even prevalence. Bayesian MixSIAR model using δ13C and δD compositions revealed that the source patterns of individual IVnAs were inconsistent; the relative contributions of liquid fossil combustion were higher for lighter IVnAs (e.g., nC12-nC13), while those of coal combustion were higher for heavier IVnAs (e.g., nC17-nC20). This result agrees with principal component analysis of the dual isotope data. Overall, coal combustion, liquid fossil fuel combustion, and biomass burning contributed about 47.8 ± 0.1, 35.7 ± 4.0, and 16.3 ± 4.2% to the total IVnAs, respectively, highlighting the importance of coal combustion as an IVnA source in North China. Our study demonstrates that the dual-isotope approach is a powerful tool for source apportionment of atmospheric IVOCs.

Emission Characteristics and Formation Pathways of Intermediate Volatile Organic Compounds from Ocean-Going Vessels: Comparison of Engine Conditions and Fuel Types.

The lack of emission data for ocean-going vessels (OGVs) and the recent fuel switching make it urgent to enhance the onboard measurement of ship emissions, especially for intermediate volatile organic compounds (IVOCs). This study focused on the IVOC emission characteristics and formation pathways of three OGVs under various engine conditions (power and load) and fuel oils (heavy fuel oil (HFO) versus marine gas oil (MGO)). The results showed that the (1) IVOC emission factors (EFIVOC) of the three OGVs increased with engine power and were higher for MGO (1494.4 ± 421.7 mg/kg) than HFO (1830.5 ± 534.5 mg/kg) and engine load is an important parameter. (2) Engine load and oil type affect the composition and volatility distribution of IVOCs. The proportion of polycyclic aromatic hydrocarbons in IVOCs increased with a higher load, and using MGO shifted IVOC components to a higher volatility in contrast to HFO. (3) The compositions of IVOCs were more like those in fuel oils under low loads than under high loads, indicating that different formation pathways of IVOCs exist for different engine loads. (4) A higher EFIVOC was observed nearshore than in open sea owing to the lower and transient engine load, which indicates the necessity of paying attention to the IVOC emissions for ships.

Tracing the Formation of Secondary Aerosols Influenced by Solar Radiation and Relative Humidity in Suburban Environment

AbstractSecondary particulate matter exerts adverse effects on air quality and human health. The production or reaction rate of secondary aerosols in polluted environments remains uncertain and is complicated by diverse emissions and meteorological conditions. By concurrently measuring the mass spectra of compounds in both particulate (using an aerosol mass spectrometer) and gas phases (using proton‐transfer‐reaction mass spectrometry) in suburban Beijing, we linked the secondary organic aerosol (OA) and volatile organic compounds (VOCs) to photochemical age (tage) and obtained their reaction or production rates. Factorization analysis of the mass spectra of OA and the 108 VOC species resolved three oxygenated OAs (OOA) and three secondary VOC factors at different oxidation levels. Primary organic aerosols and VOCs from traffic sources were determined to be important sources for secondary aerosol formation. At high pollution levels under the conditions of weaker solar radiation and higher relative humidity, moderately oxygenated OA (O/C = 0.61) and secondary inorganics were coproduced in combination with rapid consumption of all VOCs. At lower pollution levels, the intense solar radiation caused substantial and rapid production of OOA (O/C = 0.81) and intermediate VOCs (both in a high oxidation state) at a rate of 15.0% h−1 and 14.0% h−1, respectively. These results highlight the feedback effects between radiation and moisture in terms of altering the formation mechanism of secondary aerosols. In particular, highly oxygenated secondary airborne products under strong radiation should be considered in regard to their environmental impact.

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.