Determination of real-world emission factors of trace metals, EC, OC, BTEX, and semivolatile organic compounds (PAHs, PCBs and PCNs) in a rural tunnel in Bilecik, Turkey

Characteristics, source analysis, and health risk of PM2.5 in the urban tunnel environment associated with E10 petrol usage

The increase in the number of motor vehicles has intensified the impact of traffic sources on air quality. Our aim was to illustrate the characteristics of PM2.5 emissions from vehicles fueled with E10 (a blend of 10% ethanol and 90% gasoline). A 21-day PM2.5 sampling in a fully enclosed urban tunnel and the component analysis were completed, and the characteristics, sources, and health risks of tunnel PM2.5 were studied. Moreover, the PM2.5 pH and its sensitivity were investigated by the thermodynamic model (ISORROPIA-II). In addition, exposure models were used to assess the health risks of different heavy metals in PM2.5 to humans through respiratory pathways. The two-point Cu/Sb ratio (entrance: 4.0 ± 1.4; exit: 4.4 ± 1.7) was close to the diagnostic criteria indicating a significant impact from brake wear. NO3-, NH4+, and SO42- constituted the main components of water-soluble ions in PM2.5 of the tunnel, accounting for 83.0-84.6% of the total concentration of inorganic ions. The organic carbon/elemental carbon ratio of the tunnel was greater than 2, indicating that the contribution of gasoline vehicle exhaust was significant. The average emission factors of PM2.5 in the fleet was 31.4 ± 16.6 mg/(veh·km). The pH value of PM2.5 in a tunnel environment (4.6 ± 0.3) was more acidic than that in an urban environment (4.9 ± 0.6). The main sensitive factors of PM2.5 pH in the urban atmosphere and tunnel environment were total ammonia (sum of gas and aerosol, NH3) and temperature, respectively. The results of the health risk assessment showed that Pb posed a potential carcinogenic risk, while As and Cd presented unacceptable risks for tunnel workers. The non-carcinogenic risk index of heavy metals of PM2.5 in the tunnel environment exceeded the safety threshold.

Characterization and apportionment of carbonaceous aerosol emission factors from light-duty and heavy-duty vehicle fleets in Maharashtra, India

This study aims to investigate the characteristics of carbonaceous aerosols and estimate emission factor (EF) based on roadway tunnel measurements, from two distinct vehicular fleets: an all light-duty vehicle (LDV) fleet, and a mixed fleet of 80% LDV and 20% heavy-duty vehicle (HDV). Carbonaceous content (organic carbon: OC and elemental carbon: EC) in total fine particles (PM2.5) accounted for 41% ± 6.8% in LDV fleet and 48% ± 7.2% in mixed fleet. While higher volatile OC dominated in the LDV fleet emissions, in mixed fleet, lower volatile OC and EC emissions dominated due to the presence of higher HDV and super-emitter (SE) fractions which led to significantly higher optically active absorbing aerosols. Reconstructed HDV fleet EF was higher than LDV fleet by 36 times (PM2.5), 19 times (OC) and 51 times (EC). Our findings emphasize the significance of implementing vehicle inspection and maintenance programs, coupled with decarbonization of HDVs to mitigate on-road vehicular emissions in India.

Insights into the Electronic Structure Effect of SnMnOx Nanorod Catalysts for Low-Temperature Catalytic Combustion of o-Dichlorobenzene

For the catalytic combustion reaction of chlorinated volatile organic compounds (CVOCs), the redox properties and acid sites of the catalyst surface are key factors in determining the activity, selectivity, and chlorine-resistance stability. Herein, a series of SnMnOx catalysts for the catalytic combustion of CVOCs were prepared by the changing of Sn-doping way to regulate the electron valance state of Mn element, including reflux (R-SnMnOx ), co-precipitation (C-SnMnOx ) and impregnation (I-SnMnOx ). It was discovered that the R-SnMnOx catalyst had better activity and chlorine resistance than the R-MnOx , C-SnMnOx and I-SnMnOx catalyst, and we discovered that the doping ways of Sn in MnOx catalyst could regulate greatly the surface acidity, active oxygen species, the chemical state of Mnn+ species, and redox ability. Especially, the R-SnMnOx catalysts exhibit excellent water resistance, and the reasons were related to the strong interaction of Snn+ and Mnn+ , which could promote obviously the dispersion of active Mn species, form a large number of acid sites, provide the abundant lattice oxygen species, and own the excellent redox ability, which accelerate the rate of charge transfer between Snn+ and Mnn+ (Sn4+ +Mn2+ →Sn2+ +Mn4+ ) to produce the abundant active species and accelerate the rapid conversion of benzene and intermediates conversion.

Emission factors for a biofuel impacted fleet in south America's largest metropolitan area

The Metropolitan Area of São Paulo (MASP) is among the largest urban areas in the Southern Hemisphere. Vehicular emissions are of great concern in metropolitan areas and MASP is unique due to the use of biofuels on a large scale (sugar-cane ethanol and biodiesel). In this work, tunnel measurements were employed to assess vehicle emissions and to calculate emission factors (EFs) for heavy-duty and light-duty vehicles (HDVs and LDVs). The EFs were determined for particulate matter (PM) and its chemical compounds. The EFs obtained for 2018 were compared with previous tunnel experiments performed in the same area. An overall trend of reduction of fine and coarse PM, organic carbon (OC), and elemental carbon (EC) EFs for both LDVs and HDVs was observed if compared to those observed in past years, suggesting the effectiveness of vehicular emissions control policies implemented in Brazil. A predominance of Fe, Cu, Al, and Ba metals emission was observed for the LDV fleet in the fine fraction. Cu presented higher emissions than two decades ago, which was associated with the increased use of ethanol fuel in the region. For HDVs, Zn and Pb were mostly emitted in the fine mode and were linked with lubricating oil emissions from diesel vehicles. A predominance in the emission of three- and four-ring polycyclic aromatic hydrocarbons (PAHs) for HDVs and five-ring PAHs for LDVs agreed with what was observed in previous studies. The use of biofuels may explain the lower PAH emissions for LDVs (including carcinogenic BaP) compared to those observed in other countries. The tendency observed was that LDVs emit higher amounts of carcinogenic species. The use of these real EFs in air quality modeling resulted in more accurate simulations of PM concentrations, showing the importance of updating data with real-world measurements.

Mechanisms of biostimulant-enhanced biodegradation of PAHs and BTEX mixed contaminants in soil by native microbial consortium

Despite the co-occurrence of polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene, and xylene (BTEX) in the field, to date, knowledge on the bioremediation of benzene and benzo[a]pyrene (BaP) mixed contaminants is limited. In this study, the mechanisms underlying the biodegradation of benzene and BaP under individual and co-contaminated conditions followed by the enhanced biodegradation using methanol, ethanol, and vegetable oil as biostimulants were investigated. The results demonstrated that the benzene biodegradation was highly reduced under the co-contaminated condition compared to the individual benzene contamination, whereas the BaP biodegradation was slightly enhanced with the co-contamination of benzene. Moreover, biostimulation significantly improved the biodegradation of both contaminants under co-contaminated conditions. A trend of significant reduction in the bioavailable BaP contents was observed in all biostimulant-enhanced groups, implying that the bioavailable BaP was the preferred biodegradable BaP fraction. Furthermore, the enzymatic activity analysis revealed a significant increase in lipase and dehydrogenase (DHA) activities, as well as a reduction in the catalase and polyphenol oxidase, suggesting that the increased hydrolysis of fats and proton transfer, as well as the reduced oxidative stress, contributed to the enhanced benzene and BaP biodegradation in the vegetable oil treatment. In addition, the microbial composition analysis results demonstrated that the enriched functional genera contributed to the increased biodegradation efficiency, and the functional genera in the microbial consortium responded differently to different biostimulants, and competitive growth was observed in the biostimulant-enhanced treatments. In addition, the enrichment of Pseudomonas and Rhodococcus species was noticed during the biostimulation of benzene and BaP co-contamination soil, and was positively correlated with the DHA enzyme activities, indicating that these species encode DHA genes which contributed to the higher biodegradation. In conclusion, multiple lines of evidence were provided to shed light on the mechanisms of biostimulant-enhanced biodegradation of PAHs and BTEX co-contamination with native microbial consortiums.

A Review of Gas Measurement Practices and Sensors for Tunnels

The concentration of pollutant gases emitted by traffic in a tunnel affects the indoor air quality and contributes to structural deterioration. Demand control ventilation systems incur high operating costs, so reliable measurement of the gas concentration is essential. Numerous commercial sensor types are available with proven experience, such as optical and first-generation electrochemical sensors, or novel materials in detection methods. However, all of them are subjected to measurement deviations due to environmental conditions. This paper presents the main types of sensors and their application in tunnels. Solutions will also be discussed in order to obtain reliable measurements and improve the efficiency of the extraction systems.

Tunnel measurements reveal significant reduction in traffic-related light-absorbing aerosol emissions in China

Light-absorbing aerosols (LAA), including black carbon (BC) and brown carbon (BrC), profoundly impact regional and global climate. Vehicle emission is an important source of LAA in urban areas, but real-world emission features of LAA from the urban vehicle fleet are not fully understood. This study evaluates traffic-related BC and BrC emission factors (EFs) and their vehicular emission inventories via road tunnel measurements in Tianjin, China, in 2017 and 2021. The distance-based and fuel-based EFs of BC for the mixed fleet were 1.05 ± 1.28 mg km^-1 veh^-1 and 0.057 ± 0.057 g (kg-fuel)^-1, respectively, in 2021, with a dramatic decrease of 80.6 % compared to those in 2017. The BC EFs for gasoline vehicles (GVs, including traditional gasoline and hybrid vehicles) and diesel vehicles (DVs) were 0.55 ± 0.065 mg km^-1 veh^-1 and 10.5 ± 2.52 mg km^-1 veh^-1, respectively, in 2021. Compared to 2017, the BrC EFs also decreased significantly in 2021, by 10.8-53.6 %, with 0.32 ± 0.45 mg km^-1 veh^-1 and 0.018 ± 0.020 g (kg-fuel)^-1 of distance-based and fuel-based EFs for mixed fleet. The BrC EFs for GVs and DVs were 0.091 ± 0.024 mg km^-1 veh^-1 and 3.06 ± 0.91 mg km^-1 veh^-1, respectively, in 2021. Based on the BC and BrC EFs for GVs and DVs and annual mileage for each vehicle category, the annual vehicular LAA emission inventories were estimated. From 2017 to 2021, the annual vehicular LAA emissions in Tianjin have been significantly reduced, by 69 % for BC and 10 % for BrC. DVs account for a small amount of the vehicle population (8.4 %), but contribute to most of the BC (83 %) and BrC (86 %). Our study demonstrates the significant reduction of vehicular light-absorbing aerosols emission due to vehicle pollution prevention and control in China.

Emission characteristics and light absorption apportionment of carbonaceous aerosols: A tunnel test conducted in an urban with fully enclosed use of E10 petrol

To reduce the heavy dependence on petroleum, bioethanol has been increasingly employed as an alternative and sustainable transportation fuel. However, the characteristics of black carbon (BC) emissions from E10 petrol vehicles (i.e., ethanol-gasoline containing 10% ethanol) are still unclear, especially under real driving conditions. Here, a tunnel test was conducted during a cold winter. This tunnel was characterized by heavy traffic comprising more than 98% E10-fueled gasoline vehicles (GVs). Real-time BC concentrations, traffic parameters and meteorological conditions were recorded during the sampling campaign. The average BC concentration inside the tunnel (10.94 ± 5.02 μg m^-3) was almost twice the background concentration. Based on aethalometer AE33 in situ measurements and the minimum R-squared (MRS) method, real-time aerosol light absorption was apportioned. The light absorption proportions of BC, primary brown carbon (BrC₁) and secondary brown carbon (BrC₂) were 79.86%, 2.78% and 17.36%, respectively, at 370 nm. The BC emission factor (EF_BC) of the E10-fueled vehicles was 1.09 ± 0.49 mg km^-1·veh^-1 and 15.24 ± 6.85 mg·(kg fuel)^-1, lower than those of traditional gasoline fueled vehicles in previous studies. This study can support the compilation of vehicular BC emission inventories, provide recommendations for biofuel policies and contribute to comprehensively understanding the climatic impact of E10 petrol.

On-road vehicular emission characterization from the road-tunnel measurements in India: Morphology, emission factors, and sources

In India, there is very limited data on vehicular emission characterization in real-world driving conditions and the contribution of non-exhaust vehicular emissions to ambient particulate matter (PM) is still unanswered. Furthermore, there are no real-world emission factors (EFs) for the PM constituents. Thus, this study aims to characterize the trace elements and metals, and black carbon (BC) in PM_2.5 and PM₁₀ from the light-duty vehicles (LDVs) and mixed vehicular fleet with significant contribution of heavy-duty vehicles (HDVs) through road-tunnel measurements. Real-world EFs were estimated for the measured PM chemical constituents. Further, source apportionment was carried out to find the plausible sources and their contribution to total PM_2.5 and PM₁₀ road traffic emissions. Air pollutant and traffic measurements were conducted at two roadway tunnels: Eastern Freeway tunnel (FT; only LDVs) and Kamshet-I tunnel (KT; 80% LDVs & 20% HDVs) in Mumbai, India covering both peak and off-peak traffic hours. Major elements (Al, Ca, Fe, K, Mg, and Na) constitute 90─93% of total measured elemental concentrations in both PM_2.5 and PM₁₀ road traffic emissions. Overall, the elemental concentrations were higher for the HDV-dominant fleet than the LDV-fleet for both PM_2.5 and PM₁₀. Similarly, BC was higher for the HDV-dominant fleet which is corroborated by the morphological analysis. The measured BC, trace elements and metals EFs in this study were higher than those reported than previous road tunnel studies with similar vehicle composition indicating the presence of high-emitting vehicles in this study. The dominant proportion of PM_2.5 road traffic emissions was from the tailpipe (52%) followed by brake wear (30%) and vehicular driven resuspended road dust (18%). Whilst, resuspended road dust (63%) was identified as the major source of PM₁₀ traffic emissions followed by vehicular exhaust (28%) and brake wear (9%). With the potential increase in the share of electric and hybrid vehicles in the vehicular fleet, the relative contribution of non-exhaust emissions to the airborne PM will be more significant. Hence, there is an imminent need to regulate non-exhaust vehicular emissions.

Method Development for Separation and Analysis of Tire and Road Wear Particles from Roadside Soil Samples

A comprehensive understanding of tire and road wear particles (TRWPs) and their detection and quantification in soils is still challenged by the lack of well-set standardized methods, inherent technological inconsistencies, and generalized protocols. Our protocol includes soil sampling, size separation, and organic matter removal by using hydrogen peroxide followed by density separation and analysis. In this context, roadside soil samples from different sites in Kansas and Ohio, USA, were collected and analyzed. Tire cryogrinds analogous to TRWPs were used to evaluate various density separation media, and collected particles more than 1 mm in size were then subjected to infrared spectroscopy (IR), thermogravimetric analysis (TGA), and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX) to confirm TRWP presence. Particles smaller than 1 mm were Soxhlet extracted, followed by gas chromatography-mass spectrometry (GC-MS) to validate the presence of tire-related intermediates. SEM-EDX validated the presence of elemental combinations (S + Zn/Na) ± (Al, Ca, Mg, K, Si) attributed to tires. Ketones, carboxylic acids, epoxies, cyclohexane, and benzothiazole sulfenamide (BTS) intermediates were the most probable tire-related intermediates observed in the roadside soil samples. Thus, this simple, widely applicable, cost-effective sample preparation protocol for TRWP analysis can assist TRWP research advancement in terrestrial environments.

Road tunnel-derived coarse, fine and ultrafine particulate matter: physical and chemical characterization and pro-inflammatory responses in human bronchial epithelial cells

BACKGROUND

Traffic particulate matter (PM) comprises a mixture of particles from fuel combustion and wear of road pavement, tires and brakes. In countries with low winter temperatures the relative contribution of mineral-rich PM from road abrasion may be especially high due to use of studded tires during winter season. The aim of the present study was to sample and characterize size-fractioned PM from two road tunnels paved with different stone materials in the asphalt, and to compare the pro-inflammatory potential of these fractions in human bronchial epithelial cells (HBEC3-KT) in relation to physicochemical characteristics.

METHODS

The road tunnel PM was collected with a vacuum pump and a high-volume cascade impactor sampler. PM was sampled during winter, both during humid and dry road surface conditions, and before and after cleaning the tunnels. Samples were analysed for hydrodynamic size distribution, content of elemental carbon (EC), organic carbon (OC) and endotoxin, and the capacity for acellular generation of reactive oxygen species. Cytotoxicity and pro-inflammatory responses were assessed in HBEC3-KT cells after exposure to coarse (2.5-10 μm), fine (0.18-2.5 μm) and ultrafine PM (≤ 0.18 μm), as well as particles from the respective stone materials used in the pavement.

RESULTS

The pro-inflammatory potency of the PM samples varied between road tunnels and size fractions, but showed more marked responses than for the stone materials used in asphalt of the respective tunnels. In particular, fine samples showed significant increases as low as 25 µg/mL (2.6 µg/cm²) and were more potent than coarse samples, while ultrafine samples showed more variable responses between tunnels, sampling conditions and endpoints. The most marked responses were observed for fine PM sampled during humid road surface conditions. Linear correlation analysis showed that particle-induced cytokine responses were correlated to OC levels, while no correlations were observed for other PM characteristics.

CONCLUSIONS

The pro-inflammatory potential of fine road tunnel PM sampled during winter season was high compared to coarse PM. The differences between the PM-induced cytokine responses were not related to stone materials in the asphalt. However, the ratio of OC to total PM mass was associated with the pro-inflammatory potential.

Tailpipe and Nontailpipe Emission Factors and Source Contributions of PM10 on Major Freeways in the Los Angeles Basin

In this study, the emission factors of PM₁₀ and its chemical constituents from various contributing sources including nontailpipe and tailpipe emissions were estimated on two interstate freeways in the Los Angeles basin. PM₁₀ samples were collected on the I-110 and I-710 freeways as well as at the University of Southern California (USC) campus as the urban background site, while freeway and urban background CO₂ levels were measured simultaneously. PM₁₀ samples were analyzed for their content of chemical species which were used to estimate the emission factors of PM₁₀ and its constituents on both I-110 and I-710 freeways. The estimated values were employed to determine the emission factors for light (LDV) and heavy-duty vehicles (HDV). The quantified species were also processed by the positive matrix factorization (PMF) model to produce PM₁₀ freeway source profiles and their contribution to PM₁₀ mass concentrations. Using the PMF factor profiles and emission factors on the two freeways, we characterized the emission factors for light-duty and heavy-duty vehicles by each nontailpipe source. Our findings indicated higher nontailpipe emission factors of PM₁₀ and metal elements on the I-710 freeway compared to the I-110 freeway, due to the higher fraction of heavy-duty vehicles (HDVs) on that freeway. Furthermore, the generation of nontailpipe PM₁₀ from resuspension of road dust was twice of tire and brake wear. The results of this study provide significant insights into PM₁₀ freeway emissions and particularly the overall contribution of nontailpipe and tailpipe sources in Los Angeles, which can be helpful to modelers and air quality officials in assessing the importance of individual traffic-related emissions on the overall population exposure.

Source identification of exhaust and non-exhaust traffic emissions through the elemental carbon fractions and Positive Matrix Factorization method

Our study implies the importance of exhaust and non-exhaust emissions in a highway road tunnel, which is crucial to assess their impacts on air quality, human health, climate and developing functional methods for controlling. The total suspended particulates (TSP) and road dust (RD) samples were collected by PUF samplers and manually sweeping, respectively. Campaigns were performed in the summer and winter of 2014 in a highway road tunnel in Bolu, Turkey. Chemical analyses were presented to characterize the contents of organic carbon (OC) fractions (OC1,2,3,4), elemental carbon (EC) fractions (EC1,2,3,4,5,6), polycyclic aromatic hydrocarbons (PAHs) and metals (Al, Ba, Ca, Cu, Mg, Mn, Pb, Sr, Cr and Fe) in the collected TSP and RD samples. Positive matrix factorization (PMF) and orthogonal (Deming) regression analysis were applied to find out the exhaust and non-exhaust vehicle emissions of metal and carbonaceous species in the tunnel. The results showed that the identified source profiles included resuspended road dust (43%), non-exhaust emissions (37%), diesel exhaust emissions (13%), and gasoline exhaust emissions (7%). The relationship between emission markers of metal species and EC carbon fractions was supported by correlation studies. Among these EC fractions, EC4 and EC2 were the most abundant fractions in aerosol and RD samples, respectively and so they highly represented the diesel and non-exhaust emissions. Besides, the EC1 fraction was the indicator of gasoline-fueled emissions. Lower EC1 and higher soot-EC contribution obtained in tunnel aerosol (AS) samples showed the dominance of diesel-fueled vehicles in the tunnel. The data represented herein would help to identify the characteristic of vehicle emissions.

Size-fractionated nonpolar organic compounds of traffic aerosol emissions in a highway tunnel

Size-fractionated aerosol samples (PM_0.25, PM_0.25-1, PM_1-2.5, and PM_2.5-10) were collected in a highway tunnel in Shanghai, China. The concentrations of nonpolar organic compounds (NPOCs), i.e., n-alkanes, polycyclic aromatic hydrocarbons (PAHs) and hopanes in the aerosol samples at the tunnel inlet and outlet, emission factors (EFs) of individual NPOCs in PM₁₀, and EFs of size-fractionated individual NPOCs were analyzed comprehensively. NPOC concentrations in this tunnel were lower than the earlier tunnel results, which might be attributed to the tunnel configuration effect on the pollution dilution along the tunnel, in addition to the improvement of engine technology and fuel quality during past decades. n-Alkane homologs for C₁₄-C₃₅ exhibited a smooth hump-like distribution pattern with the most abundance at C₂₂ and 1-2 carbon number shifts of C_max in comparison to those in other tunnels due to different fleet and fuel compositions. The most abundant PAHs from diesel (e.g., Nap, Phe, Flu and Pyr) and gasoline (e.g., BghiF, BbkF, BeP, DBA and BghiP) vehicle emissions presented concentration increases of 1.8-5.8 times from the tunnel inlet to outlet. The individual n-alkane and PAH distributions exhibited obvious size dependence, while it was expected that the relative abundances and homolog distributions of hopanes were very similar for different size stages. Several diagnostic ratios, e.g., fossil/plant n-alkanes and LMW/HMW PAHs, were evidently size dependent, indicating different sources of size-fractionated n-alkanes and PAHs.

Emissions and light absorption of carbonaceous aerosols from on-road vehicles in an urban tunnel in south China

With changing numbers, compositions, emission standards and fuel quality of on-road vehicles, it is imperative to accordingly characterize and update vehicular emissions of carbonaceous aerosols for better understanding their health and climatic effects. In this study, a 7-day field campaign was conducted in 2019 in a busy urban tunnel (>30,000 vehicles day^-1) in south China with filter-based aerosol samples collected every 2 h at both the inlet and the outlet for measuring carbonaceous aerosols and their light absorbing properties. Observed fleet average emission factor (EF) of total carbon (TC) was 13.4 ± 8.3 mg veh^-1 km^-1, and 17.4 ± 11.3 mg veh^-1 km^-1 if electric and LPG-driven vehicles were excluded; and fleet average EF of organic carbon (OC) and elemental carbon (EC) was 8.5 ± 6.6 and 4.9 ± 2.6 mg veh^-1 km^-1 (11.0 ± 8.8 and 6.3 ± 3.6 mg veh^-1 km^-1 if excluding electric and LPG vehicles), respectively. Regression analysis revealed an average TC-EF of 319.8 mg veh^-1 km^-1 for diesel vehicles and 2.1 mg veh^-1 km^-1 for gasoline vehicles, and although diesel vehicles only shared ~4% in the fleet compositions, they still dominate on-road vehicular carbonaceous aerosol emissions due to their over 150 times higher average TC-EF than gasoline vehicles. Filter-based light absorption measurement demonstrated that on average brown carbon (BrC) could account for 19.1% of the total carbonaceous light absorption at 405 nm, and the average mass absorption efficiency of EC at 635 nm and that of OC at 405 nm were 5.2 m² g^-1 C and 1.0 m² g^-1 C, respectively.

Intermediate volatile organic compounds emissions from vehicles under real world conditions

Real-world vehicle emission factors (EFs) for the total intermediate volatile organic compounds (total-IVOCs) and volatile organic compounds (VOCs) from mixed fleets of vehicles were quantified in the Yangtze tunnel in Shanghai. Relationships of EFs of IVOCs with fleet compositions and vehicle speed as well as secondary organic formation potentials (SOAFPs) from IVOCs and VOCs were studied. Multiple linear regression (MLR) was used to estimate EFs of total-IVOCs for gasoline and diesel vehicles. IVOCs were classified into unresolved complex mixtures (unspeciated cyclic compounds and branched alkanes (b-alkanes)) and speciated targets (11 n-alkanes and ten polycyclic aromatic hydrocarbons (PAHs)). The results showed that the average EF of total-IVOCs was 24.9 ± 7.8 mg/(km·veh), which was comparable to that of VOCs. Unspeciated cyclic compounds and b-alkanes dominated the main composition (~77% and ~19%), followed by n-alkanes (~4%) and PAHs (~1%). EFs of IVOCs showed a significant, positive relationship with diesel vehicle fractions (p < 0.05). EFs of IVOCs dropped notably with the decrease of the diesel vehicle fractions. SOAFP produced by the total organic compounds (IVOCs + VOCs) was 8.9 ± 2.5 mg/(km·veh), in which up to 86% of SOAFP was from IVOCs. Estimated EFs of total-IVOCs for gasoline vehicles and diesel vehicles were 15.3 and 219.8 mg/(km·veh) respectively. Our results demonstrate that IVOCs emitted from diesel vehicles are the main emission sources under real world conditions and significant contributions of IVOCs emissions to SOA formation is evident, which indicates the necessity of making control policies to reduce IVOCs emissions from vehicles.

Volatile organic compounds from a mixed fleet with numerous E10-fuelled vehicles in a tunnel study in China: Emission characteristics, ozone formation and secondary organic aerosol formation

The Chinese government has developed an ambitious project to promote the application of ethanol gasoline (E10) on a national scale since 2017. Given the difference in fuel properties between E10 and traditional gasoline, it is necessary to evaluate the volatile organic compound (VOC) emissions from E10-fuelled vehicles. In this study, a two-week sampling campaign was conducted in an urban tunnel, in which E10-fuelled vehicles were dominant, to evaluate the characteristics of VOC emissions from the mixed fleet. In total, 105 VOC species were identified, and the ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP) were estimated. The results showed that for vehicular VOC concentrations in the tunnel, alkanes, oxygenated VOCs (OVOCs) and alkenes were the most abundant VOC groups, with the average proportion being more than 80% of the total VOCs. The fleet-average VOC emission factor (EF) was 14.8 mg/km/veh, which was much lower than that from traditional gasoline-fuelled vehicle fleets, and alkanes, OVOCs, alkenes and aromatics were the major VOC groups. Because of the large number of E10-fuelled vehicles in the mixed fleet, a high proportion of OVOCs among the vehicular VOC emissions was observed. Ethane, acrolein, ethanol, ethylene and toluene were the top five VOC species with the largest EF in VOC emissions from the fleet. Alkenes were the main contributors with an average contribution of 43.9% of the total OFP, whereas aromatics dominated the total SOAFP by 95.8% on average. These results may provide a reference for the extensive application of ethanol gasoline and the development of vehicular emission models.

Polycyclic aromatic hydrocarbon contamination along roads based on levels on vehicle window films

Vehicular emissions are known to be major contributors of airborne polycyclic aromatic hydrocarbons (PAHs) in cities. In order to assess the long-term contamination of PAHs along roads, we collected organic films from vehicle windows (26 private cars and 4 buses, in Shanghai, China) and used mathematical models to convert the film-bound PAH concentrations to the airborne PAH concentrations. The field measurements of airborne PAHs revealed that the partitioning and Level III fugacity model was suitable to estimate the airborne concentrations of high and low volatile PAHs (expect for naphthalene), respectively. The total airborne PAH concentrations along roads in Shanghai ranged from 0.83 to 3.37 μg m^-3 and the incremental lifetime cancer risks (ILCR_total) by exposure to PAHs along roads were greater than the USEPA lower guideline of 10^-6, indicating non-negligible carcinogenic risks to drivers and passengers, especially via ingestion processes. This study provided a practicable method to investigate long-term air contamination of PAHs in vehicles and along roads based on film-bound PAH on vehicle windows. In addition, it was also possible to investigate the health risk in vehicles as a result of exposure to PAHs. Comparisons of PAHs between roads and shipping lanes also facilitated the delineation of vehicular and shipping PAH inventories. A capsule that summarizes the main finding of the work: Investigating film-bound PAH on vehicle windows is a practicable pathway to investigate the long-term contamination of PAHs in vehicles and along roads. This method can not only simplify the sampling processes, but the model calculations. The results also enabled investigations into ILCR in vehicles and specified source apportionment of traffic PAHs.

The Seasonality Impact of the BTEX Pollution on the Atmosphere of Arad City, Romania

Benzene, toluene, and total BTEX (benzene, toluene, ethylbenzene, and xylene) concentrations registered for one year (2016) have been determined every month for one high-density traffic area. The assessment was performed in Arad City, Romania, to evaluate these pollutants and their influence on the inhabitants’ health. The contaminants were sampled using a static sampling method and analyzed by gas chromatography coupled with mass spectrometry. Benzene was the most dominant among the BTEX compounds—the average concentrations ranged from 18.00 ± 1.32 µg m⁻³ in December to 2.47 ± 0.74 µg m⁻³ in August. The average toluene concentration over the year was 4.36 ± 2.42 µg m⁻³ (with a maximum of 9.60 ± 2.39 µg m⁻³ in November and a minimum of 1.04 ± 0.29 µg m⁻³ in May). The toluene/benzene ratio (T/B) was around 0.5, indicating substantial contributions from mobile sources (vehicles). The emission and accumulation of different aromatic compounds (especially benzene) could deteriorate the urban air quality. The lifetime cancer risk (LTCR) for benzene was found to be more than 10⁻⁵ in winter, including the inhabitants in the “probable cancer risk” category.

Chemical mapping of tire and road wear particles for single particle analysis

Tire and road wear particles (TRWP), which are comprised of polymer-containing tread with pavement encrustations, are generated from friction between the tire and the road. Similar to environmentally dispersed microplastic particles (MP), the fate of TRWP depends on both the mass concentration as well as individual particle characteristics, such as particle diameter and density. The identification of an individual TRWP in environmental samples has been limited by inherent characteristics of black particles, which interfere with the spectroscopic techniques most often used in MP research. The purpose of this research was to apply suitable analytical techniques, including scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDX) mapping and time-of-flight secondary ion mass spectrometry (ToF-SIMS) mapping, to characterize the specific physical and chemical properties of individual TRWP. Detailed elemental and organic surface maps were generated for numerous samples including bulk tread material, cryogenically milled tire tread particles, and TRWP generated from two separate road simulator methods. Key physical and chemical characteristics of TRWP for single particle identification included (1) elongated/round shape with variable amounts of mineral encrustation, (2) elemental surface characteristics including co-localization of (S + Zn/Na) ± (Si, K, Mg, Ca, and Al), and (3) co-localization of organic surface markers, such as C₆H₅⁺ and C₇H₇⁺. Comparisons of TRWP with other polymeric (polystyrene) and non-polymeric (carbon black) particle types demonstrated that a combination of physical and chemical markers is necessary to identify TRWP. Addition of a density separation step to the single particle analysis techniques allowed for the determination of average primary TRWP particle size (34 μm by number distribution and 49 μm by volume distribution) and aspect ratio (65% of TRWP with an aspect ratio > 1.5). The use of chemical mapping techniques, such as SEM/EDX and/or ToF-SIMS mapping as demonstrated herein, can support future research efforts that aim to identify complex MP.

Quantifying metal emissions from vehicular traffic using real world emission factors

Road traffic emissions are an increasingly important source of particulate matter in urban and non-road environments, where non-tailpipe emissions can contribute substantially to elevated levels of metals associated with adverse health effects. Thus, better characterization and quantification of traffic-emitted metals is warranted. In this study, real-world emission factors for fine particulate metals were determined from hourly x-ray fluorescence measurements over a three-year period (2015-2018) at an urban roadway and busy highway. Inter-site differences and temporal trends in real-world emission factors for metals were explored. The emission factors at both sites were within the range of past studies, and it was found that Ti, Fe, Cu, and Ba emissions were 2.2-3.0 times higher at the highway site, consistent with the higher proportion of heavy-duty vehicles. Weekday emission factors for some metals were also higher by 2.0-3.5 times relative to Sundays for Mn, Zn, Ca, and Fe, illustrating a dependence on fleet composition and roadway activity. Metal emission factors were also inversely related to relative humidity and precipitation, due to reduced road dust resuspension under wetter conditions. Correlation analysis revealed groups of metals that were co-emitted by different traffic activities and sources. Determining emission factors enabled the isolation of traffic-related metal emissions and also revealed that human exposure to metals in ambient air can vary substantially both temporally and spatially depending on fleet composition and traffic volume.

Characteristics of volatile organic compounds from vehicle emissions through on-road test in Wuhan, China

VOCs emissions from motor vehicles have become a main source of air pollution in many cities. However, the characteristics of VOCs emissions have not been fully elucidated. Ten representative vehicles were selected in Wuhan, China, and the VOCs emitted by these vehicles under actual working conditions were collected and analyzed through on-road tests. Results showed that the average concentrations of total VOCs emitted by gasoline and diesel vehicles were 5.9 ± 2.4 mg/m³ and 6.8 ± 3.0 mg/m³, while the average emission factors were 5.3 ± 2.2 mg/km and 33.9 ± 22.7 mg/km, respectively. The five compounds emitted at the highest levels by gasoline and diesel vehicles were hexanal, acetone, toluene, p-xylene and iso-pentane. Emission concentration of diesel vehicles was slightly higher than that of gasoline vehicles. Emission factor of diesel vehicles was much higher, because they consumed more fuel and produced more power than gasoline vehicles. The average concentrations of total VOCs emitted by China III, IV and V vehicles were 8.4 ± 1.4 mg/m³, 5.8 ± 3.4 mg/m³ and 5.3 ± 1.9 mg/m³, and their average emission factors were 21.7 ± 18.6 mg/km, 19.4 ± 28.9 mg/km and 9.1 ± 7.2 mg/km, respectively. Vehicle emissions decreased obviously as the emission standards increased. The average concentrations of total VOCs emitted under low-speed and high-speed conditions were 9.4 ± 3.5 mg/m³ and 5.5 ± 1.8 mg/m³. Concentrations of acetone, hexanal, toluene and p-xylene were the highest four VOCs under both conditions. The average emission factor of VOCs under high-speed conditions (24.0 ± 13.6 mg/km) was substantially lower than under low-speed conditions (54.0 ± 41.5 mg/km). Thus, tightening emission standards and reducing traffic congestion would help reduce VOCs emissions.

Size-segregated carbonaceous aerosols emission from typical vehicles and potential depositions in the human respiratory system

Particles emitted from five typical types of vehicles (including light-duty gasoline vehicles, LDG; heavy-duty gasoline vehicles, HDG; diesel buses, BUS; light-duty diesel vehicles, LDD and heavy-duty diesel vehicles, HDD) were collected with a dilution sampling system and an electrical low-pressure impactor (ELPI+, with particle sizes covering fourteen stages from 6 nm to 10 μm) on dynamometer benches. The mass concentrations and emission factors (EF) for organic carbon (OC) and elemental carbon (EC) were obtained with a DRI Model 2001 thermal/optical carbon analyzer. A respiratory deposition model was used to calculate the deposition fluxes of size-segregated carbonaceous aerosols in human respiratory system. Results indicated that the OC produced from LDG mainly existed in the size range of 2.5-10 μm, while EC from HDG enriched in 0.94-2.5 μm. For diesel vehicles, both OC and EC concentrations peaked at 0.094-0.25 μm. The OC/EC ratios for PM_2.5 varied from different types of vehicles, from 0.61 to 8.35. The primary emissions from LDD and HDD exhibited high OC/EC ratios (>3), suggesting that using OC/EC higher than 2 to indicate the formation of secondary organic aerosol (SOA) was not universal. The emission factors for OC and EC of LDG (HDG) in PM₁₀ were 1.78 (3.14) mg km^-1 and 0.88 (4.32) mg km^-1, respectively. The OC2 and OC3 were the main section (over 60%) of OC emitted from all the five types of vehicles. EC1 was the most abundant EC fraction of LDG (76.9%), while EC2 dominated for other types of vehicles (more than 62%). About 60% of the OC in ultrafine particles could be deposited in the alveoli. Diesel EC mainly could be deposited in the alveolar region. It is necessary to control the emission of ultrafine particles and diesel EC.

PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) and nitrated-PAHs (NPAHs) emitted by gasoline vehicles: Characterization and health risk assessment

Seventeen polycyclic aromatic hydrocarbons (PAHs) and eight nitrated PAHs (NPAHs) in PM_2.5 and conventional gaseous pollutants exhausted from 54 in-use gasoline vehicles encompassing different emission standards (China 1 to China 5) were tested on the chassis and engine dynamometric test bench. With the increase of emission standards, a decrease in the emissions of PM_2.5-bound PAHs and NPAHs was detected. The emission factors (EFs) of total PAHs and NPAHs in PM_2.5 emitted by the vehicles with a mileage of >100,000 km were greater than that emitted by the vehicles with driving mileage of <100,000 km under all the five emission standards. The EFs of PM_2.5-bound PAHs and NPAHs emitted from port fuel injection engines were larger than that from gasoline direct injection engines. The emissions of PM_2.5-bound PAHs and NPAHs were less correlated with the exhaust of CO, while the hydrocarbon (HC) emissions were strongly correlated with the PM_2.5-bound PAHs emissions. The emissions of NPAHs and NOx had an inverse correlation. The toxic (TEQs) of total PAHs and NPAHs in China 3, China 4 and China 5 were significantly reduced compared to China 1 and China 2, which may be related to exhaust technology improvements. Although the EFs of NPAHs were significantly lower than those of PAHs, the TEQs of NPAHs were higher, which indicates that the toxic effect of NPAHs emitted by gasoline vehicles were stronger than PAHs.

Polychlorinated Naphthalene Congener Profiles in Common Vegetation on the Tibetan Plateau as Biomonitors of Their Sources and Transportation

Polychlorinated naphthalenes (PCNs) are globally transported, carcinogenic, persistent organic pollutants (POPs) that were recently added to the Stockholm Convention with 184 parties. The Tibetan Plateau plays an important role in the global transportation and distribution of POPs. Knowledge of PCN sources and transportation on the Tibetan Plateau is important for their control globally. In this study, we quantified the congener-specific concentrations of PCNs in lichen, moss, soil, and air samples collected on the Tibetan plateau and found that common lichens were effective biomonitors for predicting atmospheric PCNs in this area. The physiochemical properties of the PCNs, the temperatures, and the lichen lipid contents were identified as important factors influencing PCN partitioning between lichens and air. Lichen-air partitioning equations were established and used to predict PCN concentrations in air in Southeast Tibet. The lichens could be used as PCN biomonitors to clarify their spatial variations, sources, and transportation in the southeast of the plateau. PCN concentrations in lichens increased with altitude, suggesting that high-mountain cold-trapping influenced the PCN transportation behavior. Principal component analysis and linear discriminant analysis showed that the major source of PCNs in this region was long-range atmospheric transportation via the Indian monsoon in summer and wind from Southwest Asia in winter. This study provides a novel method using PCN congener profiles as fingerprints and statistical models for studying the geochemical effects of conditions in high-mountain regions on the contamination behaviors of 75 congeners of the notorious PCNs.