Gasoline Vehicle Exhaust Research Articles

Chemical Characterization of Fine Particulate Matter in Gasoline and Diesel Vehicle Exhaust

ABSTRACT This study investigated the chemical composition (carbonaceous species, water-soluble ions and metal elements) of fine particulate matter (PM2.5) emitted by gasoline and diesel vehicles. The emission factors of PM2.5, total hydrocarbons (THC), carbon monoxide (CO) and oxides of nitrogen (NOx) were also determined. The emission measurements were performed for four gasoline and four diesel vehicles on a dynamometer with a constant volume sampling system. Vehicles having larger engines and higher accumulated mileages had higher emission factors of gaseous pollutants. Moreover, the average emission factor of NOx was about 30 times higher for diesel vehicles than for gasoline vehicles. The average PM2.5 emission factors for gasoline and diesel vehicles were 1.57 mg km–1 and 57.8 mg km–1, respectively. The ratio of organic carbon to elemental carbon (OC/EC) was found to be a good indicator of gasoline vehicle emissions (OC/EC > 1) and diesel vehicle emissions (OC/EC < 1). Among water-soluble ions, Ca2+ and SO42– had the highest contribution to PM2.5 emitted by gasoline vehicles, while NO3–, SO42– and Ca2+ had the highest contribution to PM2.5 emitted by diesel vehicles. Na, Ca, Fe and Zn were the top four metal elements in terms of their contributions to PM2.5 mass for both types of the vehicles, while Cd, Cr, Pb and Sb were some of the toxic metal elements detected in PM2.5.

Assessment of Carbonaceous Aerosols at Mount Tai, North China: Secondary Formation and Regional Source Analysis

ABSTRACT To understand the concentrations, secondary organic aerosols (SOA) formation and source characteristics of carbonaceous aerosols in the regional environment of North China, a total of 48 fine particulate matter (PM2.5) samples were collected at the top of Mount Tai in the summer of 2015. Organic carbon (OC) and element carbon (EC) were analyzed and resolved into eight carbonaceous species using an Organic/Elemental Carbon Analyzer following the IMPROVE thermal-optical reflectance (TOR) protocol. OC and EC mass concentrations were 4.42 ± 3.04 and 1.58 ± 0.92 µg m–3, respectively, which were much higher than that of other domestic or abroad observation sites. Carbonaceous aerosols showed weekday-high trend during sampling period, which can be partly explained by anthropogenic effects. Higher concentrations of secondary organic carbon (SOC) were estimated by EC-tracer method during cloud/fog processing, indicating the fact that aqueous-phase reaction in droplets was an important pathway for SOC formation. Two source analysis approaches, consisting of Potential Source Contribution Function (PSCF) and Positive Matrix Factorization (PMF) were adopted to identify the regional sources and emission sources of carbonaceous species, and the apportion contributed by these sources. PSCF result demonstrated that the potential regional sources in the northwest, southwest and east coastal areas of Mount Tai contributed significantly to carbonaceous species loading in PM2.5. Additionally, three main emission sources were identified according to PMF result: diesel vehicle exhaust, biomass burning and mixed sources of gasoline vehicle exhaust and coal combustion, and each of sources had an average contribution of 26.4%, 19.0% and 54.5% to carbonaceous aerosols, respectively.

Sources and abatement mechanisms of VOCs in southern China

Volatile organic compounds (VOCs) have an important influence on the formation of photochemical smog and secondary organic aerosols in the atmosphere. In this paper, we investigated 104 VOCs in Heshan from 22 October to 22 November 2014 to identify the sources and abatement mechanisms of VOCs in southern China. Weather conditions, species correlations, daytime and nighttime abatement mechanisms, secondary pollutant transformations, air-mass origins and source apportionments were studied. During the observation period, the average concentration of VOCs in the atmosphere of Heshan was 61.0 ± 35.5 ppbv, and the wind speed played a pivotal role in the diffusion and dilution of VOCs. The study on the rates of OH, O3 and NO3 radicals found that alkenes, aromatics, hydrocarbons and carbonyl compounds were the most active volatile organic compounds in Heshan. For alkanes, alkynes, and aromatics, removal is determined by their reactions with OH radicals. For highly reactive alkenes and styrene, nighttime removal via O3 and NO3 radicals was also significant. The backward-trajectory cluster analysis of air masses indicated that pollution mainly derived from the east-northeast. The paint solvent usage, paint solvent usage + liquefied petroleum gas (LPG) usage, biomass burning, coal burning + industrial combustion sources, gasoline vehicle exhaust, diesel vehicle exhaust, industrial sources, and fuel evaporation (gasoline) contributed 11%, 22%, 13%, 17%, 12%, 8%, 11%, and 6% to VOCs during the observation period, respectively.

Detailed Speciation of Intermediate Volatility and Semivolatile Organic Compound Emissions from Gasoline Vehicles: Effects of Cold-Starts and Implications for Secondary Organic Aerosol Formation.

Over the past two decades vehicle emission standards in the United States have been dramatically tightened with the goal of reducing urban air pollution. Secondary organic aerosol (SOA) is the dominant contributor to urban organic aerosol. Experiments were conducted at the California Air Resources Board Haagen-Smit Laboratory to characterize exhaust organics from 20 gasoline vehicles recruited from the California in-use fleet. The vehicles spanned a wide range of emission certification standards. We comprehensively characterized intermediate volatility and semivolatile organic compound emissions using thermal desorption two-dimensional gas-chromatography-mass-spectrometry with electron impact (GC × GC-EI-MS) and vacuum-ultraviolet (GC × GC-VUV-MS) ionization. Single-ring aromatic compounds with unsaturated C4 and C5 substituents contribute a large fraction of the intermediate volatility organic compound (IVOC) emissions in gasoline vehicle exhaust. The analyses of quartz filters used in GC × GC-VUV-MS show that primary organic aerosol emissions were dominated by motor oil. We combined our new emissions data with published SOA yield parametrizations to estimate SOA formation potential. After 24 h of oxidation, IVOC emissions contributed 45% of SOA formation; BTEX compounds (benzene, toluene, xylenes, and ethylbenzene),40%; other VOC aromatics, 15%. The composition of IVOC emissions was consistent across the test fleet, suggesting that future reductions in vehicular emissions will continue to reduce SOA formation and ambient particulate mass levels.

Volatile organic compounds in stormwater from a community of Beijing, China

Stormwater samples were collected from six different land use sites with three time-intervals during a precipitation event on August 12, 2016, from a community of Beijing, China. A total of 46 species volatile organic compounds (VOCs) were detected in these stormwater samples, including methyl tertiary-butyl ether (MTBE), aromatic hydrocarbons, halogenated aromatics, Halogenated alkanes, and alkenes. The total VOC concentrations varied in the six sites following order: highway junction > city road > gas station > park > campus > residential area, except for MTBE, which was much higher at gas station compared to other land use sites. ANOVA results indicated both land use and precipitation time intervals could significantly affect the VOC concentrations even in the small area. The Beijing atmospheric VOC concentrations were too low to explain the high concentrations in stormwater, suggesting that land surfaces may be the main sources of VOC other than the ambient atmosphere. MTBE and other VOCs correlation analysis indicated that MTBE mostly came from gasoline emissions, spills or vehicle exhausts, whereas the BTEX (benzene, toluene, ethylbenzene, Xylenes) and the halogenated aromatics were transferred from chemical plants through land surfaces accumulating and the wind blowing atmospheric VOCs. Xylenes/ethylbenzene (X/E) ratios variations indicated that stormwater incorporated larger amount of fresh emitted air during the precipitation event than prior to it. Information of these stormwater VOCs in this study could be used in the community pollution reduction strategies.

Respiratory hazard assessment of combined exposure to complete gasoline exhaust and respirable volcanic ash in a multicellular human lung model at the air-liquid interface

Communities resident in urban areas located near active volcanoes can experience volcanic ash exposures during, and following, an eruption, in addition to sustained exposures to high concentrations of anthropogenic air pollutants (e.g., vehicle exhaust emissions). Inhalation of anthropogenic pollution is known to cause the onset of, or exacerbate, respiratory and cardiovascular diseases. It is further postulated similar exposure to volcanic ash can also affect such disease states. Understanding of the impact of combined exposure of volcanic ash and anthropogenic pollution to human health, however, remains limited.The aim of this study was to assess the biological impact of combined exposure to respirable volcanic ash (from Soufrière Hills volcano (SHV), Montserrat and Chaitén volcano (ChV), Chile; representing different magmatic compositions and eruption styles) and freshly-generated complete exhaust from a gasoline vehicle. A multicellular human lung model (an epithelial cell-layer composed of A549 alveolar type II-like cells complemented with human blood monocyte-derived macrophages and dendritic cells cultured at the air-liquid interface) was exposed to diluted exhaust (1:10) continuously for 6 h, followed by immediate exposure to the ash as a dry powder (0.54 ± 0.19 μg/cm2 and 0.39 ± 0.09 μg/cm2 for SHV and ChV ash, respectively). After an 18 h incubation, cells were exposed again for 6 h to diluted exhaust, and a final 18 h incubation (at 37 °C and 5% CO2). Cell cultures were then assessed for cytotoxic, oxidative stress and (pro-)inflammatory responses.Results indicate that, at all tested (sub-lethal) concentrations, co-exposures with both ash samples induced no significant expression of genes associated with oxidative stress (HMOX1, NQO1) or production of (pro-)inflammatory markers (IL-1β, IL-8, TNF-α) at the gene and protein levels. In summary, considering the employed experimental conditions, combined exposure of volcanic ash and gasoline vehicle exhaust has a limited short-term biological impact to an advanced lung cell in vitro model.

Characteristics of VOCs Pollution in the Winter Atmosphere of a Typical Petrochemical Industry Park

Concentrations of volatile organic compounds (VOCs) in ambient air of a typical petrochemical industry park were measured using an on-line monitor (TH-300B) from December 2014 to February 2015. The composition, temporal variations, sources, and photochemical reactivity of VOCs were analyzed. Alkanes were the most abundant VOC species and contributed to 86.73% to total VOC concentrations in winter. Concentrations of TVOCs, alkanes, alkenes, and aromatic hydrocarbons were high at night and low during the day. The changes in alkane and alkene concentrations were consistent with those in TVOC concentrations. Using principal component analysis and multiple linear regression (PCA-MLR) in combination, five sources of VOCs were identified; fuel evaporation, industrial emissions, a mix of gasoline vehicle exhaust and plant emissions, diesel vehicle exhaust emissions, and fuel combustion with contributions of 60.02%, 8.50%, 2.07%, 12.21%, and 17.20%, respectively. Propylene-equivalent concentration (Propy-Equiv) and maximum incremental reactivity (MIR) method were used to calculate the contributions of VOCs measured in the study area to ozone production. Alkanes contributed most to ozone production followed by alkenes and aromatic hydrocarbons. The contribution rate of cyclopentane, n-butane, and 1-pentene were higher owing to their long photochemical age in the study area.

Secondary Organic Aerosol Production from Gasoline Vehicle Exhaust: Effects of Engine Technology, Cold Start, and Emission Certification Standard.

Secondary organic aerosol (SOA) formation from dilute exhaust from 16 gasoline vehicles was investigated using a potential aerosol mass (PAM) oxidation flow reactor during chassis dynamometer testing using the cold-start unified cycle (UC). Ten vehicles were equipped with gasoline direct injection engines (GDI vehicles) and six with port fuel injection engines (PFI vehicles) certified to a wide range of emissions standards. We measured similar SOA production from GDI and PFI vehicles certified to the same emissions standard; less SOA production from vehicles certified to stricter emissions standards; and, after accounting for differences in gas-particle partitioning, similar effective SOA yields across different engine technologies and certification standards. Therefore the ongoing, dramatic shift from PFI to GDI vehicles in the United States should not alter the contribution of gasoline vehicles to ambient SOA and the natural replacement of older vehicles with newer ones certified to stricter emissions standards should reduce atmospheric SOA levels. Compared to hot operations, cold-start exhaust had lower effective SOA yields, but still contributed more SOA overall because of substantially higher organic gas emissions. We demonstrate that the PAM reactor can be used as a screening tool for vehicle SOA production by carefully accounting for the effects of the large variations in emission rates.

Source Identification of VOCs In METU Campus Through Factor Analysis

In this study, 55 ozone precursor VOCs, which are routinely measured in PAMS (Photochemical Assessment Monitoring Station) were measured in a suburban station located at Middle East Technical University, Environmental Engineering Department in, Ankara. Daily air samples were collected in evacuated canisters between January – December, 2014. Collected samples were analyzed with GC-FID system and concentrations of 51 VOCs were determined. Mean VOC concentrations ranged between 0.048±0.061 µg m-3 (cis-2-penten) and 10±13 µg m-3 (toluene). Average benzene concentration was 1.49 ± 1.74 μg m-3. Factor Analysis (FA) was applied to determine the major sources of VOCs that contribute to the measured concentrations in the university campus. FA application revealed nine factors that can be grouped under four major components, including (1) transportation: gasoline vehicle exhaust emissions, evaporative losses from gasoline vehicles, gasoline evaporation in gas stations and diesel emissions, (2) industrial emissions: industrial evaporation and industrial application, (3) solvent emissions: surface coatings and solvent use and (4) asphalt application.

Characteristics of Organic Carbon and Elemental Carbon in Atmospheric Aerosols in the Urban Area in Beibei, a Suburb of Chongqing

To investigate the pollutive characteristics of atmospheric carbonaceous aerosols in Beibei District, a suburb of Chongqing Municipal City, graded aerosol samples were continuously collected by cascade impactors over one year, from March 2014 to February 2015. Carbonaceous aerosols, including organic carbon (OC) and elemental carbon (EC), were detected by a DRI 2001A carbon analyzer. The results showed that the average annual concentrations of OC and EC in the PM2.1 were 16.3 ± 7.6 and 1.8 ± 0.7 µg m–3, and in the PM9.0 were 25.0 ± 9.6 and 3.2 ± 1.2 µg m–3, respectively. On the one hand, a more seasonal distribution of OC concentrations appeared in the PM2.1 (winter > spring > summer > autumn) than in the PM9.0 (winter ≈ spring ≈ summer > autumn); furthermore, whereas the OC significantly positively correlated with wind speed for both the PM2.1 (P spring > summer > autumn), and the EC in the PM2.1 significantly negatively correlated with temperature (P < 0.05). Additionally, both the OC and the EC were concentrated mainly in the fine particles (< 2.10 µm), and the size distributions of the OC in all four seasons displayed a bi-modal pattern that peaked in the size ranges of 0.43–0.65 µm (for fine particles) and 4.7–5.8 µm (for coarse particles), whereas the EC displayed a uni-modal pattern that peaked in the size range of 4.7–5.8 µm (for coarse particles). Furthermore, the correlations between the OC and the EC were analyzed, and the SOC (secondary organic carbon) in the PM2.1 was estimated using the primary OC/EC ratio. It was found that the OC highly significantly correlated with the EC (P < 0.01), with the average annual concentration of the SOC being 6.3 ± 5.9 µg m–3, which accounted for 33.5 ± 22.6% of the OC. Analyzing the sources of the pollutive atmospheric aerosol in Beibei further demonstrated that it mainly originated in biomass burning, gasoline-vehicle exhaust, and coal combustion.

Towards Smart Parking Based on Fog Computing

An experience of finding a vacant parking slot can be very stressful in densely populated areas, especially in peak hours. Such parking process takes a long time, wastes significant gasoline, and emits extra vehicle exhaust that harms the environment. Smart parking, aiming to assist drivers in finding desirable parking slots more efficiently through information and communication technologies such as vehicle ad hoc networks (VANETs), has received extensive attention recently. Current VANETs-based parking slot allocations cannot provide a fully satisfactory solution, because vehicle communication devices-onboard units-and roadside units lack computational capabilities to perform humanized and accurate service provisioning, such as real-time parking slots information and probabilistic prediction on future parking slots. Therefore, we, in this paper, propose a fog computing-based smart parking architecture to improve smart parking in real time. Fog nodes deployed at parking lots, cooperating with each other, enable realtime parking slot information provisioning as well as parking requests processing. The cloud center can further enhance smart parking capability by enforcing global optimization on parking requests allocation. The experimental results of our approaches show higher efficiency compared with other parking strategies. The proposed fog computing-based smart parking can lower the average parking cost and minimize gasoline wastes and vehicle exhaust emission.

Formation mechanism of secondary organic aerosol from ozonolysis of gasoline vehicle exhaust.

Gasoline vehicles are a major source of anthropogenic secondary organic aerosols (SOAs). However, current models based on known precursors fail to explain the substantial SOAs from vehicle emissions due to the inadequate understanding of the formation mechanism. To provide more information on this issue, the formation of SOAs from ozonolysis of four light-duty gasoline vehicle exhaust systems was investigated with a vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS). Remarkable SOAs formation was observed and the SOAs were primarily aliphatic alkenes. PI mass spectra of the SOAs from all vehicles exhibited similar spectral patterns (a regular mass group with m/z at 98, 112, 126 …). Interestingly, most carbonyl products of aliphatic alkenes observed as major gaseous products have specific molecular weights, and the main formation pathway of SOAs can be explained well using aldol condensation reactions of these carbonyls. This is a direct observation of the aldol condensation as a dominated pathway for SOAs formation, and the first report on the composition and formation mechanism of the SOAs from the ozonolysis of gasoline vehicle exhaust is given. The study reveals that low molecular weight alkenes may play a more significant role in vehicle-induced SOAs formation than previously believed. More importantly, the PI mass spectra of SOAs from vehicles show similarities to the field aerosol sample mass spectra, suggesting the possible significance of the aldol condensation reactions in ambient aerosol formation. Since carbonyls are a major degradation product of biogenic and anthropogenic VOCs through atmospheric oxidation processes, the mechanism proposed in this study can be applied more generally to explain aerosol formation from the oxidation of atmospheric hydrocarbons.

Gasoline aromatics: a critical determinant of urban secondary organic aerosol formation

Abstract. Gasoline vehicle exhaust is an important contributor to secondary organic aerosol (SOA) formation in urban atmosphere. Fuel composition has a potentially considerable impact on gasoline SOA production, but the link between fuel components and SOA production is still poorly understood. Here, we present chamber experiments to investigate the impacts of gasoline aromatic content on SOA production through chamber oxidation approach. A significant amplification factor of 3–6 for SOA productions from gasoline exhausts is observed as gasoline aromatic content rose from 29 to 37 %. Considerably higher emission of aromatic volatile organic compounds (VOCs) using high-aromatic fuel plays an essential role in the enhancement of SOA production, while semi-volatile organic compounds (e.g., gas-phase PAHs) may also contribute to the higher SOA production. Our findings indicate that gasoline aromatics significantly influence ambient PM2. 5 concentration in urban areas and emphasize that more stringent regulation of gasoline aromatic content will lead to considerable benefits for urban air quality.

Distribution and source of rare earth elements in PM2.5 in Xiamen, China.

Particulate matter with diameter ≤2.5 µm (PM2.5 ) is a serious atmospheric pollutant. Composition and source analyses are essential for controlling PM2.5 . Rare earth elements (REEs) have received little attention as a component of PM2.5 . In the present study, PM2.5 samples were collected in urban and suburban areas in Xiamen and analyzed for REEs. The concentration range of total REEs (∑REE) is 12.07 to 98.45 mg/kg, with a mean of 38.53 mg/kg, in urban PM2.5 and 16.44 to 160.62 mg/kg, with a mean of 42.94 mg/kg, in suburban PM2.5 . Light REE concentrations are higher in suburban PM2.5 , whereas heavy REE concentrations are higher in urban PM2.5 , implying distinct sources of REEs in urban and suburban PM2.5 . The scatter plots of δEu-∑REE and La-Ce-Sm suggest that REEs in urban PM2.5 originate from gasoline- and diesel-vehicle exhaust, whereas those in suburban PM2.5 are mainly influenced by gasoline-vehicle exhaust. Environ Toxicol Chem 2017;36:3217-3222. © 2017 SETAC.

Reducing secondary organic aerosol formation from gasoline vehicle exhaust

On-road gasoline vehicles are a major source of secondary organic aerosol (SOA) in urban areas. We investigated SOA formation by oxidizing dilute, ambient-level exhaust concentrations from a fleet of on-road gasoline vehicles in a smog chamber. We measured less SOA formation from newer vehicles meeting more stringent emissions standards. This suggests that the natural replacement of older vehicles with newer ones that meet more stringent emissions standards should reduce SOA levels in urban environments. However, SOA production depends on both precursor concentrations (emissions) and atmospheric chemistry (SOA yields). We found a strongly nonlinear relationship between SOA formation and the ratio of nonmethane organic gas to oxides of nitrogen (NOx) (NMOG:NOx), which affects the fate of peroxy radicals. For example, changing the NMOG:NOx from 4 to 10 ppbC/ppbNOx increased the SOA yield from dilute gasoline vehicle exhaust by a factor of 8. We investigated the implications of this relationship for the Los Angeles area. Although organic gas emissions from gasoline vehicles in Los Angeles are expected to fall by almost 80% over the next two decades, we predict no reduction in SOA production from these emissions due to the effects of rising NMOG:NOx on SOA yields. This highlights the importance of integrated emission control policies for NOx and organic gases.

Application of VUV-PIMS coupled with GC-MS in chemical characterization, identification and comparative analysis of organic components in both vehicular-derived SOA and haze particles

Gasoline vehicle exhaust is a significant source of volatile organic compounds (VOCs) in megacities. In this study, chemical characterization of secondary aerosol particles from the oxidation of gasoline vehicular exhaust by O3, OH, and NO3 radicals and the airborne aerosol particles collected during a heavy haze episode (23–25 December 2015) in Beijing were elaborately investigated. The secondary organic aerosols (SOAs) collected from the exhaust and airborne aerosol particles were characterized with a newly built vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS) after thermal desorption, and identified by gas chromatography mass spectrometry (GC-MS). The obtained photoionization mass spectra revealed that the SOAs from the oxidation of gasoline vehicular exhaust and airborne aerosol particles possess a series of common characteristic mass peaks at m/z 98, 112, 126, and 140. The components at m/z 98, 112, 126, 140 were further identified to be carbonyl species after PFBHA derivatization followed by GC-MS analyses. The carbonyl species from exhaust SOAs were found to be responsible for 51.7%, 57.5%, 36.3%, and 27.9% of the chemical components in haze particles at m/z 98, 112, 126, and 140, respectively, which indicates that these SOA components from the oxidation of gasoline vehicular exhaust are a major factor that affects the air quality in Beijing. Among the exhaust SOAs, the carbonyl species detected simultaneously in two (P(O3/OH)) or three kinds of exhaust oxidation reactions (P(O3/NO3/OH)) make a significant contributions to these carbonyl species in haze particles (10.6% for m/z 98, 18.3% for m/z 112, 23.4% for m/z 126, and 20.5% for m/z 140). These results implies that the unsaturated VOCs (i.e. alkenes) from exhaust may be one kind of important SOA precursor and that their chemical degradation in the atmosphere may have an important impact on urban air quality in heavy polluted cities such as Beijing, especially during severe winter haze weather.

Primary particulate emissions and secondary organic aerosol (SOA) formation from idling diesel vehicle exhaust in China

In China diesel vehicles dominate the primary emission of particulate matters from on-road vehicles, and they might also contribute substantially to the formation of secondary organic aerosols (SOA). In this study tailpipe exhaust of three typical in-use diesel vehicles under warm idling conditions was introduced directly into an indoor smog chamber with a 30m3 Teflon reactor to characterize primary emissions and SOA formation during photo-oxidation. The emission factors of primary organic aerosol (POA) and black carbon (BC) for the three types of Chinese diesel vehicles ranged 0.18–0.91 and 0.15–0.51gkg-fuel−1, respectively; and the SOA production factors ranged 0.50–1.8gkg-fuel−1 and SOA/POA ratios ranged 0.7–3.7 with an average of 2.2. The fuel-based POA emission factors and SOA production factors from this study for idling diesel vehicle exhaust were 1–3 orders of magnitude higher than those reported in previous studies for idling gasoline vehicle exhaust. The emission factors for total particle numbers were 0.65–4.0×1015particleskg-fuel−1, and particles with diameters less than 50nm dominated in total particle numbers. Traditional C2-C12 precursor non-methane hydrocarbons (NMHCs) could only explain less than 3% of the SOA formed during aging and contribution from other precursors including intermediate volatile organic compounds (IVOC) needs further investigation.

Characteristics of Reactive VOCs Species During High Haze-Pollution Events in Suburban Area of Shanghai in Winter

Based on the online measurements of VOCs of high pollution process at the university site in winter, VOCs' characteristics and species at different levels of haze pollution were analyzed. Fifty-five VOCs were detected during sampling. ∑55VOCs concentrations ranged between 25.5×10-9-1320.3×10-9(avg±SD,240×10-9±181×10-9). Toluene and xylene were the major pollutants during high pollution process, the concentrations of which were higher than those of industrial area. The university site shared a similar VOC composition with that of industrial area, which suggested that it might be influenced by the surrounding industries. VOCs species exhibited high concentrations in nighttime while low concentrations in daytime. The ozone concentrations were on the contrary. Aromatic hydrocarbons were predominant with a high percentage of contribution (70.0%) to OFP (ozone formation potential). Alkenes and alkynes were the second highest group (16.7%). The OFP of VOCs was 2078.2×10-9 under the west-south wind direction, about 4 times higher than the value under other wind directions (505.8×10-9). Aromatic hydrocarbons exhibited a predominant contribution to OFP at different levels of haze pollution in this area, among which, Toluene and xylene contributed more than 50% to OFP. The newest version of EPA PMF model was used to identify the major source of VOCs and evaluate their contributions. Gasoline sources and vehicle exhaust, refinery and petroleum products, solvent use and organic synthetic materials were the identified VOC sources in the study area, contributing 33.1%, 31.5%, 30.5%, and 4.9%, respectively to the ∑55VOCs concentrations.

Stable hydrogen isotope composition of n-alkanes in urban atmospheric aerosols in Taiyuan, China

The hydrogen isotope compositions (δD) of n-alkanes associated with particulate matter with a diameter of ≤10 μm from Taiyuan, China, during heating and non-heating periods were measured via gas chromatography–isotope ratio mass spectrometry to reveal the spatial and temporal characteristics of five functional zones and to provide another constraint on atmospheric pollutants. The δD values of n-C16 to n-C31 during the heating and non-heating periods ranged from −235.9‰ to −119.8‰ and from −231.3‰ to −129.2‰, respectively, but these similar spans had different distribution features. During the heating period, the δD distributions between non–central heating and commercial districts were consistent, as were those between residential and industrial districts; the n-alkanes came from two or more types of emission sources. Coal soot might be the primary local emission source, but not the only source. During the non-heating period, the n-alkanes of n-C16 to n-C20 were more depleted in D with the increasing carbon number in all functional zones, but there was no rule for n-C21 to n-C31. Specifically, coal soot and vehicle exhaust might be the primary sources of n-alkanes for non–central heating districts in the heating and non-heating periods, respectively, according to the δD distribution of n-C18 to n-C22; gasoline vehicle exhaust might be an n-alkane source, and the hydrogen isotope fractionation effect during the condensation process should be a pollution mechanism for the commercial district during the heating period; the δD distribution difference of n-C16 to n-C18 between the two periods in the residential and industrial districts was consistent, which indicates a similar source of fossil fuel combustion and a similar isotope fractionation effect during the non-heating period.

Determination of nitrous acid emission factors from a gasoline vehicle using a chassis dynamometer combined with incoherent broadband cavity-enhanced absorption spectroscopy

Nitrous acid (HONO) is a well-known source of hydroxyl radicals in the troposphere. Vehicle exhaust is considered to be one of the primary emission sources of HONO. In this study, measurements of HONO in gasoline vehicle exhaust were carried out using a chassis dynamometer combined with incoherent broadband cavity-enhanced absorption spectroscopy. When catalysts were warm, concentrations of HONO were higher than those prior to catalysts warming. Other species, such as CO, and total hydrocarbons (THCs), showed the opposite pattern. There were no correlations evident between HONO and other trace species concentrations immediately after emission. The HONO/NOx ratio, a good proxy for the formation of HONO in atmosphere, ranged from 1.1 to 6.8×10−3, which was consistent with previous studies. HONO emission factors (EFs) were calculated to be 0.01–3.6mgkg−1 fuel, which was different from the vehicle's specifications and those reported under different driving cycles. Annual HONO emissions in Japan were estimated using the calculated EFs and other statistical data.