Secondary Organic Aerosol Precursors Research Articles

A field investigation into the characteristics and formation mechanisms of particles during the operation of laser printers and photocopiers

Indoor particle release from toner printing equipment (TPE) is a major health concern and has received wide attention. In this study, nine printing centers were randomly selected and three working phases were simulated, namely, non-working, normal printing/copying, and heavy printing/copying. The dynamics of the ozone (O3), volatile organic compound (VOC), and particle emissions from TPE were determined by portable detectors. Results showed that particles, VOCs, and O3 were indeed discharged, and particles and VOCs concentrations remained at high levels. Among them, 44% of the rooms represented high-level particle releases. Submicrometer-sized particles, especially nanoparticles, were positively correlated with VOCs, but were inversely proportional to the O3 concentration. Four elements, Ca, Al, Mg and Ni, were usually present in nanoparticles because of the discharge of paper. Si, Al, K, Ni and Pb were found in the submicrometer-sized particles and were consistent with the toner composition. The potential particle precursors were identified, which suggested that styrene was the most likely secondary organic aerosol (SOA) precursor. Overall, the use of the toner formulation and the discharge of paper attribute to the TPE-emitted particles, in which styrene is a specific monitoring indicator for the formation of SOA.

An experimental study of the reactivity of terpinolene and <i>β</i>-caryophyllene with the nitrate radical

Abstract. Biogenic volatile organic compounds (BVOCs) are intensely emitted by forests and crops into the atmosphere. They can rapidly react with the nitrate radical (NO3) during the nighttime to form a number of functionalized products. Among them, organic nitrates (ONs) have been shown to behave as reservoirs of reactive nitrogen and consequently influence the ozone budget and secondary organic aerosols (SOAs), which are known to have a direct and indirect effect on the radiative balance and thus on climate. Nevertheless, BVOC + NO3 reactions remain poorly understood. Thus, the primary purpose of this study is to furnish new kinetic and mechanistic data for one monoterpene (C10H16), terpinolene, and one sesquiterpene (C15H24), β-caryophyllene, using simulation chamber experiments. These two compounds have been chosen in order to complete the few experimental data existing in the literature. Rate constants have been measured using both relative and absolute methods. They have been measured to be (6.0 ± 3.8) ×10-11 and (1.8 ± 1.4) ×10-11 cm3 molec.−1 s−1 for terpinolene and β-caryophyllene respectively. Mechanistic studies have also been conducted in order to identify and quantify the main reaction products. Total organic nitrates and SOA yields have been determined. Both terpenes appear to be major ON precursors in both gas and particle phases with formation yields of 69 % for terpinolene and 79 % for β-caryophyllene respectively. They are also major SOA precursors, with maximum SOA yields of around 60 % for terpinolene and 90 % for β-caryophyllene. In order to support these observations, chemical analyses of the gas-phase products were performed at the molecular scale using a proton transfer reaction–time-of-flight–mass spectrometer (PTR-ToF-MS) and FTIR. Detected products allowed proposing chemical mechanisms and providing explanations through peroxy and alkoxy reaction pathways.

Chemical identification and quantification of volatile organic compounds emitted by sewage sludge

The recycling of organic waste products (e.g. sewage sludge, SS) is currently being promoted as a substitute for mineral fertilizers for agricultural lands. The spreading of SS allows the recycling of the nutrients and organic matter it contains. SS contains various pollutants such as volatile organic compounds (VOCs) that adversely affect the ecosystem and human health through ozone production and serve as critical precursors of atmospheric secondary organic aerosols. There are very few studies quantifying the gaseous compounds emitted from SS, and those studies primarily address their odorant properties for identifying suitable odour abatement techniques. There is an urgent need for more comprehensive quantitative information on VOCs emitted from SS as aerosol precursors. In this context, an experimental study was performed on SS samples taken from a wastewater treatment plant located in France. Undigested SS (UDSS), digested SS (DSS) and SS with 30% and 60% dryness were collected from different stages of treatment sequence and analyzed using atmospheric simulation chambers coupled to proton-transfer-reaction quadrupole ion-guide time-of-flight mass spectrometer. Our study revealed that SS samples emitted a large spectrum of VOCs. 380 compounds were detected, quantified and classified into different chemical groups. The VOC emissions increased with the increase in the dryness of the sample; the highest being in SS 60%, followed by SS 30%, UDSS and DSS. OVOCs were dominant in SS 60%. The statistical analysis showed that the anaerobic digestion and the dewatering to 60% of dryness decreased the emissions of sulphuric compounds. Aromatic compounds and indoles (e.g. skatole) were emitted significantly from the UDSS. Some of these VOCs can serve as precursor gases for atmospheric aerosol formation. The experimental dataset obtained in this study provides an accurate inventory reference for the VOC emissions from SS samples and shows the impacts of the treatment on emission characteristics of VOCs.

Enhanced secondary organic aerosol formation during dust episodes by photochemical reactions in the winter in Wuhan

To investigate the effect of frequently occurring mineral dust on the formation of secondary organic aerosol (SOA), 106 volatile organic compounds (VOCs), trace gas pollutants and chemical components of PM2.5 were measured continuously in January 2021 in Wuhan, Central China. The observation period was divided into two stages that included a haze period and a following dust period, based on the ratio of PM2.5 and PM10 concentrations. The average ratio of secondary organic carbon (SOC) to elemental carbon (EC) was 1.98 during the dust period, which was higher than that during the haze period (0.69). The contribution of SOA to PM2.5 also increased from 2.75% to 8.64%. The analysis of the relationships between the SOA and relative humidity (RH) and the odd oxygen (e.g., OX = O3 + NO2) levels suggested that photochemical reactions played a more important role in the enhancement of SOA production during the dust period than the aqueous-phase reactions. The heterogeneous photochemical production of OH radicals in the presence of metal oxides during the dust period was believed to be enhanced. Meanwhile, the ratios of trans-2-butene to cis-2-butene and m-/p-xylene to ethylbenzene (X/E) dropped significantly, confirming that stronger photochemical reactions occurred and SOA precursors formed efficiently. These results verified the laboratory findings that metal oxides in mineral dust could catalyse the oxidation of VOCs and induce higher SOA production.

The Effect of Land Use Classification on the Gas‐Phase and Particle Composition of the Troposphere: Tree Species Versus Forest Type Information

AbstractRelationships between vegetation and air quality are intricate and still not fully understood. For regional air quality assessments, a better understanding of the diverse feedback mechanisms is crucial. The present article investigates the impact of land use data set detailedness on air quality predictions. Therefore, two different land use data sets were applied for simulations with COSMO‐MUSCAT for Germany in May 2014. One data set includes detailed information about tree species while the second one obtains generalized widely applied land use classes including mixed and coniferous forests. Moreover, we examined the role of agricultural NO soil emissions, agricultural biomass density enhancements, and model resolution. For a more comprehensive implementation of the secondary organic aerosol (SOA) formation, the SOA module was extended considering additional biogenic volatile organic compound (BVOC) precursor groups from isoprene, α‐pinene, limonene, and sesquiterpene oxidations. The model studies showed substantial differences in BVOC emission patterns between the two land use data sets. The application of detailed tree species information leads to complex BVOC emission patterns with high emission spots. In contrast, coarser forest information lead to standardized comprehensive emissions which result in 50% higher BVOC emissions. These differences affect both the atmospheric oxidizing potential and the production rates of SOA precursors. Land use induced regional differences (tree species minus forest information) in NOx (±2.5%), ozone (−2.5%), OH (±50%), NO3 radical (+70%) concentrations, and SOA (−60%) mass are modeled. Overall, the simulations demonstrate that detailed land use information, extended organic chemistry treatment, and high spatial resolution are mandatory for air quality assessments.

Molecular characterization of carbonyl compounds in atmospheric fine particulate matters (PM2.5) in Beijing by derivatization with Girard's reagent T combined with positive-ion ESI Orbitrap MS

Carbonyl compounds in aerosols endanger human health, affect atmospheric light absorption and cloud condensation nuclei activity, and are important precursors of secondary organic aerosols, but their composition is poorly understood. In the present study, we developed a new analytical method to characterize carbonyl compounds in PM2.5 (particles with aerodynamic diameter ≤ 2.5 μm) by chemical derivatization with Girard's reagent T combined with positive-ion ESI high resolution-mass spectrometry (HR-MS). Girard's reagent T selectively labels carbonyl compounds, and HR-MS provides accurate elemental composition of derivatives. This method realized the comprehensive molecular characterization of carbonyl compounds in PM2.5. Thousands of carbonyl formulas (2330) were identified, including aliphatic carbonyls and a series of aromatic carbonyls. This method was further applied to the quantification of carbonyl compounds in PM2.5 samples collected in summer and winter from 2016 to 2017. In winter, carbonyl compounds had the highest contribution to organic matter (10%) and PM2.5 (4%), respectively, and the concentration of carbonyls showed obvious seasonal variation characteristics: 2.04 μg/m3 in winter and 0.35 μg/m3 in summer. The detailed characterization of the molecular composition of carbonyl compounds in PM2.5 provides basic data for further evaluating its impact on the climate effect of organic aerosols.

The origin of potential precursors of secondary organic aerosols during combustion of biochar and softwood in residential heating

Compounds that are potential precursors of secondary organic –aerosols account for up to 33.4 ± 7.1 mg/m3 in softwood combustion emissions, while biochar can be considered zero-emission fuel (0.18 ± 0.06 mg/m3). The characteristic feature of gaseous emissions from biochar combustion is the presence of n-alkanes (70.3 ± 6.6 µg/m3), which arise from the thermal degradation of waxes, cuticles, and plant lipids. In addition to alkanes, carboxylic acids (4.9 ± 0.2 µg/m3) are present in biochar emissions at significantly lower concentrations. In deposits from biochar combustion (6.1 ± 0.8 g/kg), the internal parts of the boiler capture 20% more organic compounds than in wood-burning deposits (4.84 ± 0.91 g/kg). The greater uptake of organic compounds in biochar combustion deposits (513.8 ± 6.2 g/kg) than in softwood (382.7 ± 27.3 g/kg) is related to the higher elemental carbon content in biochar. The organic compounds present in deposits from biochar are mainly methyl ketone, fatty acids such and alkanes. In deposits from softwood, the compounds of chemical groups of phenols, anhydrosaccharides and acetic acids are present. The novelty lies in identifying and determining the quantity of organic compounds that form precursors of the solid organic aerosols in the combustion of biochar.

Spatial characteristics of VOCs and their ozone and secondary organic aerosol formation potentials in autumn and winter in the Guanzhong Plain, China

As critical precursors of tropospheric ozone (O3) and secondary organic aerosol (SOA), volatile organic compounds (VOCs) largely influence air quality in urban environments. In this study, measurements of 102 VOCs at all five major cities in the Guanzhong Plain (GZP) were conducted during Sep.09-Oct. 13, 2017 (autumn) and Nov. 14, 2017–Jan. 19, 2018 (winter) to investigate the characteristics of VOCs and their roles in O3 and SOA formation. The average concentrations of total VOCs (TVOCs) at Xi'an (XA), Weinan (WN), Xianyang (XY), Tongchuan (TC), and Baoji (BJ) sites were in the range of 55.2–110.2 ppbv in autumn and 42.4–74.3 ppbv in winter. TVOCs concentrations were reduced by 22.4%–43.5% from autumn to winter at XA, WN and BJ. Comparatively low concentrations of TVOCs were observed in XY and TC, ranging from 53.5 to 62.7 ppbv across the sampling period. Alkanes were the major components at all sites, accounting for 26.4%–48.9% of the TVOCs during the sampling campaign, followed by aromatics (4.2%–26.4%). The average concentration of acetylene increased by a factor of up to 4.8 from autumn to winter, indicating the fuel combustion in winter heating period significantly impacted on VOCs composition in the GZP. The OH radical loss rate and maximum incremental reactivity method were employed to determine photochemical reactivities and ozone formation potentials (OFPs) of VOCs, respectively. The VOCs in XA and WN exhibited the highest reactivities in O3 formation, with the OFP of 168–273 ppbv and the OH loss rates of 19.3–40.8 s−1. Alkenes and aromatics primarily related to on-road and industrial emissions contributed 57.8%–76.3% to the total OFP. The contribution of aromatics to the SOA formation at all sites reached 94.1%–98.6%. Considering the potential source-area of VOCs, regional transport of VOCs occurred within the GZP cities.

Secondary Organic and Inorganic Aerosol Formation from a GDI Vehicle under Different Driving Conditions

This study investigated the primary emissions and secondary aerosol formation from a gasoline direct injection (GDI) passenger car when operated over different legislative and real-world driving cycles on a chassis dynamometer. Diluted vehicle exhaust was photooxidized in a 30 m3 environmental chamber. Results showed elevated gaseous and particulate emissions for the cold-start cycles and higher secondary organic aerosol (SOA) formation, suggesting that cold-start condition will generate higher concentrations of SOA precursors. Total secondary aerosol mass exceeded primary PM emissions and was dominated by inorganic aerosol (ammonium and nitrate) for all driving cycles. Further chamber experiments in high temperature conditions verified that more ammonium nitrate nucleates to form new particles, forming a secondary peak in particle size distribution instead of condensing to black carbon particles. The results of this study revealed that the absorption of radiation by black carbon particles can lead to changes in secondary ammonium nitrate formation. Our work indicates the potential formation of new ammonium nitrate particles during low temperature conditions favored by the tailpipe ammonia and nitrogen oxide emissions from gasoline vehicles.

Observational Insights into Isoprene Secondary Organic Aerosol Formation through the Epoxide Pathway at Three Urban Sites from Northern to Southern China.

Isoprene is the most abundant precursor of global secondary organic aerosol (SOA). The epoxide pathway plays a critical role in isoprene SOA (iSOA) formation, in which isoprene epoxydiols (IEPOX) and/or hydroxymethyl-methyl-α-lactone (HMML) can react with nucleophilic sulfate and water producing isoprene-derived organosulfates (iOSs) and oxygen-containing tracers (iOTs), respectively. This process is complicated and highly influenced by anthropogenic emissions, especially in the polluted urban atmospheres. In this study, we took a 1-year measurement of the paired iOSs and iOTs formed through the IEPOX and HMML pathways at the three urban sites from northern to southern China. The annual average concentrations of iSOA products at the three sites ranged from 14.6 to 36.5 ng m-3. We found that the nucleophilic-addition reaction of isoprene epoxides with water dominated over that with sulfate in the polluted urban air. A simple set of reaction rate constant could not fully describe iOS and iOT formation everywhere. We also found that the IEPOX pathway was dominant over the HMML pathway over urban regions. Using the kinetic data of IEPOX to estimate the reaction parameters of HMML will cause significant underestimation in the importance of HMML pathway. All these findings provide insights into iSOA formation over polluted areas.

Long-chain alkanes in the atmosphere: A review

As a representative species of intermediate volatile organic compounds (IVOCs), long-chain alkanes are considered to be important precursors of secondary organic aerosols (SOA) in the atmosphere. This work reviews the previous studies on long-chain alkanes in the atmosphere: (1) the detection methods and filed observations of long-chain alkanes in both gas and particle phases are summarized briefly; (2) the laboratory studies of long chain alkanes are reviewed, the kinetic data, reaction mechanism, SOA yields, and physicochemical properties of SOA are included in detail; (3) the research progress related to model simulations of long-chain alkanes are also discussed. In addition, based on available research results, several perspective contents are proposed that can be used as a guideline for future research plans.

Enhanced summertime ozone and SOA from biogenic volatile organic compound (BVOC) emissions due to vegetation biomass variability during 1981–2018 in China

Abstract. Coordinated control of fine particulate matter (PM2.5) and ozone (O3) has become a new and urgent issue for China's air pollution control. Biogenic volatile organic compounds (BVOCs) are important precursors of O3 and secondary organic aerosol (SOA) formation. China experienced a rapid increase in BVOC emissions as a result of increased vegetation biomass. We applied WRF-Chem3.8 coupling with MEGAN2.1 to conduct long-term simulations for impacts of BVOC emissions on O3 and SOA during 1981–2018, using the emission factors extrapolated by localized emission rates and annual vegetation biomass. In summer 2018, BVOC emissions were 9.91 Tg (in June), which led to an average increase of 8.6 ppb (16.75 % of the total) in daily maximum 8 h (MDA8) O3 concentration and 0.84 µg m−3 (73.15 % of the total) in SOA over China. The highest contribution to O3 is concentrated in the Great Khingan Mountains, Qinling Mountains, and most southern regions while in southern areas for SOA. Isoprene has the greatest contribution to O3, while monoterpene has the largest SOA production. BVOC emissions have distinguished impacts in different regions. The Chengdu–Chongqing (CC) region has the highest O3 and SOA generated by BVOCs, while the Beijing–Tianjin–Hebei (BTH) region has the lowest. From 1981 to 2018, the interannual variation of BVOC emissions caused by increasing leaf biomass resulted in O3 concentration increasing by 7.38 % at an average rate of 0.11 ppb yr−1 and SOA increasing by 39.30 % at an average rate of 0.008 µg m−3 yr−1. Due to the different changing trends of leaf biomass by region and vegetation type, O3 and SOA show different interannual variations. The Fenwei Plain (FWP), Yangtze River Delta (YRD), and Pearl River Delta (PRD) regions have the most rapid O3 increment, while the increasing rate of SOA in CC is the highest. BTH has the smallest enhancement in O3 and SOA concentration. This study will help to recognize the impact of historical BVOC emissions on O3 and SOA and further provide a reliable scientific basis for the precise prevention and control of air pollution in China.

Improved Performance of PMF Source Apportionment for Volatile Organic Compounds Based on Classification of VOCs' Aging Degree in Air Mass

VOCs are the key precursors of ozone and secondary organic aerosols. The results of source apportionment for VOCs are very important for the coordinated control of ozone and second organic particulate matter. However, VOCs do not fully meet the assumption of the receptor model because the VOCs released from each source are relatively unstable in the transmission process for their reactivity. As a result, we do not accurately obtain the actual source contribution when the receptor model is used for the source apportionment of VOCs. In order to solve the problem that the relative changes in the components caused by VOCs reactivity are not consistent with the PMF model hypothesis, the aging degree of VOCs was introduced to distinguish the state characteristics after their photochemical reactions in the ambient air. According to the ratio of ethylbenzene to m/p-xylene, VOCs monitored at Wuhai were divided into three aging states:high, medium, and low. The results showed that the model parameters, such as regression equation parameters (slope and intercept), standard error, determination coefficient, and pass rate of residual error, were improved obviously compared to the sample set after classification. Because the degree of aging is closely related to the transport time of air mass and the atmospheric oxidation in the atmosphere, it also reflects the different sources of air mass to some extent. In the high-aging VOCs samples, the coking source occupied a high proportion (up to 47.20%). In the low-aging VOCs samples, the combustion source and coking source accounted for a higher proportion, 28.67% and 24.39%, respectively. After the classification according to the aging degree, the results of VOCs source apportionment by PMF are more consistent with the actual contribution of emission sources.

Field observational constraints on the controllers in glyoxal (CHOCHO) reactive uptake to aerosol

Abstract. Glyoxal (CHOCHO), the simplest dicarbonyl in the troposphere, is a potential precursor for secondary organic aerosol (SOA) and brown carbon (BrC) affecting air quality and climate. The airborne measurement of CHOCHO concentrations during the KORUS-AQ (KORea–US Air Quality study) campaign in 2016 enables detailed quantification of loss mechanisms pertaining to SOA formation in the real atmosphere. The production of this molecule was mainly from oxidation of aromatics (59 %) initiated by hydroxyl radical (OH). CHOCHO loss to aerosol was found to be the most important removal path (69 %) and contributed to roughly ∼ 20 % (3.7 µg sm−3 ppmv−1 h−1, normalized with excess CO) of SOA growth in the first 6 h in Seoul Metropolitan Area. A reactive uptake coefficient (γ) of ∼ 0.008 best represents the loss of CHOCHO by surface uptake during the campaign. To our knowledge, we show the first field observation of aerosol surface-area-dependent (Asurf) CHOCHO uptake, which diverges from the simple surface uptake assumption as Asurf increases in ambient condition. Specifically, under the low (high) aerosol loading, the CHOCHO effective uptake rate coefficient, keff,uptake, linearly increases (levels off) with Asurf; thus, the irreversible surface uptake is a reasonable (unreasonable) approximation for simulating CHOCHO loss to aerosol. Dependence on photochemical impact and changes in the chemical and physical aerosol properties “free water”, as well as aerosol viscosity, are discussed as other possible factors influencing CHOCHO uptake rate. Our inferred Henry's law coefficient of CHOCHO, 7.0×108 M atm−1, is ∼ 2 orders of magnitude higher than those estimated from salting-in effects constrained by inorganic salts only consistent with laboratory findings that show similar high partitioning into water-soluble organics, which urges more understanding on CHOCHO solubility under real atmospheric conditions.

Photochemical Reactions of Glyoxal during Particulate Ammonium Nitrate Photolysis: Brown Carbon Formation, Enhanced Glyoxal Decay, and Organic Phase Formation.

Glyoxal is an important precursor of aqueous secondary organic aerosol (aqSOA). Its photooxidation to form organic acids and oligomers and reactions with reduced nitrogen compounds to form brown carbon (BrC) have been extensively investigated separately, although these two types of reactions can occur simultaneously during the daytime. Here, we examine the reactions of glyoxal during photooxidation and BrC formation in premixed NH4NO3 + Glyoxal droplets. We find that nitrate photolysis and photosensitization can enhance the decay rates of glyoxal by a factor of ∼5 and ∼6 compared to those under dark, respectively. A significantly enhanced glyoxal decay rate by a factor of ∼12 was observed in the presence of both nitrate photolysis and photosensitization. Furthermore, a new organic phase was formed in irradiated NH4NO3 + Glyoxal droplets, which had no noticeable degradation under prolonged photooxidation. It was attributed to the imidazole oxidation mediated by nitrate photolysis and/or photosensitization. The persistent organic phase suggests the potential to contribute to SOA formation in ambient fine particles. This study highlights that glyoxal photooxidation mediated by nitrate photolysis and photosensitization can significantly enhance the atmospheric sink of glyoxal, which may partially narrow the gap between model predictions and field measurements of ambient glyoxal concentrations.

Characteristics of VOCs and Formation Potentials of O3 and SOA in Autumn and Winter in Tongchuan, China

Volatile organic compounds (VOCs) are the main precursors of tropospheric O3 and secondary organic aerosol (SOA), which can enhance atmospheric oxidation, promote the formation of secondary pollutants, and affect regional air quality and human health. In order to gain insights on VOCs characteristics and their potentials for O3 and SOA formation, the volume fraction of 102 VOCs in autumn and winter in the urban area of Tongchuan were monitored using the TH-300B online monitoring system. The maximum incremental reactivity (MIR) coefficient and the fractional aerosol coefficient (FAC) were used to estimate the ozone formation potential (OFP) and SOA formation potential (SOAFP), respectively. The φ(TVOC, total VOCs) were (50.52±16.81)×10-9 in autumn and (63.21±35.24)×10-9 in winter. The OFPs were 138.43×10-9 in autumn and 137.123×10-9 in winter, and the SOAFPs were 3.098 μg·m-3 and 0.612 μg·m-3, respectively. Alkanes (26.19%) and aromatics (26.04%) were the most abundant species in autumn, and alkanes (48.88%) were the most abundant species in winter. Trans-2-pentene, toluene, and m/p-xylene were the most reactive species in terms of OFPs in autumn, and ethylene, acetylene, and propylene were the top three species contributing to the total OFPs in winter. Toluene, m/p-xylene, and ethylbenzene contributed the most to the total SOAFPs in both of autumn and winter. Traffic emissions were considered as the major source of VOCs in both seasons. VOCs from biomass/coal combustion emissions showed seasonal differences, which were more prominent in winter. The results can provide references for the "one city, one policy" to mitigate regional VOCs pollution and improve ambient air quality.

Water binding to the atmospheric oxidation product methyl vinyl ketone

Methyl vinyl ketone is one of the major oxidation products of isoprene, and therefore, an important precursor of secondary organic aerosol. Understanding its interactions with water is relevant to gain insight into aerosol formation and improve the predictive power of atmospheric chemistry models. The molecular complex formed between methyl vinyl ketone and water has been generated in a supersonic jet and characterized using high-resolution microwave spectroscopy in combination with quantum chemistry calculations. In this study, we show that methyl vinyl ketone interacts with water forming four 1:1 isomers connected by O − H···O and C − H···O hydrogen bond interactions. Water has been found to preferentially bind to the antiperiplanar conformation of methyl vinyl ketone. Evidence of a large amplitude motion arising from the methyl internal rotation has been found in the rotational spectra of the dimer. The threefold methyl internal rotation barrier heights have been further determined and discussed for all the species.

Characteristics of Volatile Organic Compounds in the Pearl River Delta Region, China: Chemical Reactivity, Source, and Emission Regions

Volatile organic compounds (VOCs) are important precursors of photochemical ozone and secondary organic aerosol (SOA). Here, hourly variations of ambient VOCs were monitored with an online system at an urban site (Panyu, PY) in the Pearl River Delta region during August–September of 2020 in order to identify reactive VOC species and major sources of VOCs, OH loss rate (LOH), SOA formation potential (SOAFP), and corresponding emission source regions. The average concentration of VOCs at PY was 31.80 ± 20.82 ppbv during the campaign. The C2–C5 alkanes, aromatics, and ≥C6 alkanes contributed for the majority of VOC, alkenes and aromatics showed the highest contribution to LOH and SOAFP. Further, m/p-xylene, propene, and toluene were found to be the top three most reactive anthropogenic VOC species, with respective contributions of 11.6%, 6.1%, and 5.8% to total LOH. Toluene, m/p-xylene, and o-xylene constituted a large fraction of calculated SOAFP. Seven major sources were identified by using positive matrix factorization model. Vehicle exhaust made the most significant contribution to VOCs, followed by liquefied petroleum gas and combustion sources. However, industrial-related sources (including industrial solvent use and industrial process emission) had the largest contribution to LOH and SOAFP. By combining source contribution with wind direction and wind speed, the regions of different sources were further identified. Based on high-resolution observation data during ozone pollution, this study clearly exhibits key reactive VOC species and the major emission regions of different VOC sources, and thus benefits the accurate emission control of VOCs in the near future.

Modeling secondary organic aerosol formation from volatile chemical products.

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.

IVOC/SVOC and size distribution characteristics of particulate matter emissions from a modern aero-engine combustor in different operational modes

The particulate matter (PM) of Intermediate-Volatile Organic Compounds (IVOC) / Semi-Volatile Organic Compound (SVOC) from aircraft engine emissions, despite being significant precursors of secondary organic aerosols deteriorating air quality in the vicinity of airports, have not been fully investigated at molecular level. In this study, the particulate IVOC/SVOC emissions from a rig test on a Technology of Low Emission Stirred Swirl aero-engine combustor, being operated with dual diffusion and premixed-dominant combustion modes, have been characterized via a two-dimensional gas chromatography-time of flight mass spectrometer (GC × GC-ToFMS). The IVOC/SVOC compounds, including 25n-alkanes, 15 cyclic alkanes and 13 polycyclic aromatic hydrocarbons were analyzed in this study. We found that including the premixed-dominant combustion mode at climb/takeoff conditions reduced the particulate IVOC/SVOC emissions significantly by nearly 80%, compared to using the diffusion combustion mode alone at idle/approach condition. Meanwhile, the measurements on organic PM obtained from a scanning mobility particle sizer spectrometer with a catalytic stripper demonstrated a consistent trend with the the IVOC/SVOC emissions, which were also suppressed by over 85% at climb/takeoff compared to idle/approach. The inter-relationship between the size-resolved organic PM and the speciated IVOC/SVOC emissions has been further explored, showing that the nucleation mode PM is dominated in organic PM by over 50%, in which IVOCs/SVOCs may be a significant contributor. This study expands the understanding of aviation-emitted organic particles, and suggests a path for future aero-engine development to mitigate the IVOC/SVOC emissions particularly at low power conditions. However, compared to the real aero-engine emissions, the results from rig combustor tests should be interpreted with great care, since there are still some work to be done to establish the quantitative relationship between emissions from rig combustors andthose from real engines.