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

Characterization of PM2.5 emissions from on-road vehicles in the tunnel of a major Middle Eastern city

Traffic emissions are an important source of air pollution worldwide, but in the Middle East, this problem is exacerbated by weak or no enforcement of emission regulations. Comprehensive measurements of fine PM emission factors (EFs) from road transport in the region have not yet been conducted, but such data are necessary for quantitative assessments of the health impact of transport emissions in the region. To address this need, PM2.5 samples collected inside the Salim Slam tunnel in Beirut, Lebanon were analyzed for carbonaceous matter (organic carbon (OC) and elemental carbon (EC)), water-soluble ions, elements, and selected organic compounds. The OC/EC ratio was 1.8 for the total fleet and 2.6 for light-duty vehicles (LDV), in agreement with the dominant proportion of gasoline LDV in the Lebanese fleet. A Cu/Sb ratio of 4.2 ± 0.1 was observed, offering a valuable metric for detecting brake wear emissions in subsequent studies conducted in the region. The EFs of carbonaceous matter, elements and ions generally varied by a factor 0.1 and 10 in comparison to literature values, while those for alkanes and polycyclic aromatic hydrocarbons were similar to the upper values previously reported. The average number size distribution was characterized by a single mode around 35 nm. The particles number EF (for diameters between 10 and 480 nm) was within the range of 1014-1015 particles per kg of fuel. The chemical mass balance model showed an average contribution to EF of 62% from non-exhaust sources. This study highlights the need for more enforceable stringent vehicular regulations because of the local practices (i.e., removal of catalyst) and some EF values are very high compared to other studies/countries.

Organic carbon, elemental carbon and particulate semivolatile organic compound emissions from a common-rail diesel engine: Insight into effect of fuel injection pressure at different loads

Effect of fuel injection pressure on organic carbon (OC), elemental carbon (EC) and particulate semivolatile organic compounds (SVOCs), i.e., n-alkanes and polycyclic aromatic hydrocarbons (PAHs), emissions from a common-rail diesel engine was analyzed comprehensively. EC emission rate evidently decreased with increasing injection pressure at low fuel injection pressure ranges (80-120 MPa), while engine load effect on the EC emission was insignificant at high injection pressure ranges (140-160 MPa). The higher fraction of EC2 in the total EC emission appeared at the highest injection pressure ranges (140-160 MPa) under middle and high loads, suggesting the spontaneous carbonization process from soot precursor to ordered soot during the high temperature process. Low injection pressure provided poor combustion condition and caused unburned diesel fuel to volatilize more 2-3 ring PAHs. The percentage of 4-ring PAHs exhibited a rise-then-fall trend with increasing injection pressure, while the maximum percentage of 5-7 ring PAHs appeared at the highest injection pressure ranges (140-160 MPa) under high load condition, suggesting that higher combustion temperature and larger pyrolysis zone under the high injection pressure promoted the formation of lager and more stable PAHs. The fractions of fuel-derived short chain (C16-C21) and oil-derived long chain (C22-C33) in the total n-alkanes exhibited obvious load and injection pressure dependence.

Optical properties of vehicular brown carbon emissions: Road tunnel and chassis dynamometer tests

Brown carbon (BrC), as an important light-absorbing aerosol, significantly impacts regional and global climate. Vehicle emission is a nonnegligible source of BrC, but the optical properties of BrC emitted from vehicles remain poorly understood. This study evaluates the absorption Ångström exponent (AAE) of traffic-related light-absorbing aerosols (i.e., AAE_Tr) and the absorption emission factor (EF_abs) of vehicular BrC via chassis dynamometer tests and a road tunnel measurement in Tianjin, China. AAE_Tr are estimated as 0.98-1.33 and 1.11 ± 0.001 for tested vehicles and on-road vehicle fleet, respectively. The AAE of vehicular BrC (AAE_BrC) is 3.83 ± 0.092 for on-road vehicle fleet. The vehicle technology updates effectively reduce the EF_abs of vehicular BrC. Among the four tested China 5 and China 6 gasoline vehicles in the chassis dynamometer tests, BrC EF_abs of China 5 gasoline direct injection vehicle is the highest, while China 6 mixing fuel injection vehicle exhibits the lowest EF_abs. The BrC EF_abs of on-road vehicle fleet at 370 nm wavelength are 0.081 ± 0.0058 m² kg^-1 for mixed fleet, 0.074 ± 0.018 m² kg^-1 for gasoline vehicles (GVs), and 1.66 ± 0.71 m² kg^-1 for diesel vehicles (DVs) in the tunnel measurement. EF_abs of GV fleet in the road tunnel is higher than China 5 and China 6 vehicles, as China 1-4 vehicles accounted for 26.8% of the total vehicle fleet in the tunnel. EF_abs of vehicular BrC are lower than those from biomass burning and coal combustion emissions. The light absorption of BrC from GVs and DVs accounts for 7.2 ± 2.1% and 1.5 ± 0.77% of total traffic-related absorption at 370 nm, respectively. Our study provides optical features of BrC from vehicle source and could contribute to estimating the impacts of vehicular aerosol emissions on global and regional climate change.

Evidence of non-tailpipe emission contributions to PM2.5 and PM10 near southern California highways

Particulate Matter (PM) concentrations near highways are influenced by vehicle tailpipe and non-tailpipe emissions, other emission sources, and urban background aerosols. This study collected PM_2.5 and PM₁₀ filter samples near two southern California highways (I-5 and I-710) over two weeks in winter 2020. Samples were analyzed for chemical source markers. Mean PM_2.5 and PM₁₀ concentrations were approximately 10-15 and 30 μg/m³, respectively. Organic matter, mineral dust, and elemental carbon (EC) were the most abundant PM components. EC and polycyclic aromatic hydrocarbons at I-710 were 19-26% and 47% higher than those at the I-5 sites, respectively, likely due to a larger proportion of diesel vehicles. High correlations were found for elements with common sources, such as markers for brake wear (e.g., Fe, Ba, Cu, and Zr) and road dust (e.g., Al, Si, Ca, and Mn). Based on rubber abundances, the contributions of tire tread particles to PM_2.5 and PM₁₀ mass were approximately 8.0% at I-5 and 5.5% at I-710. Two different tire brands showed significantly different Si, Zn, carbon, and natural rubber abundances.

Evaluating the inhalation bioaccessibility of traffic-impacted particulate matter-bound PAHs in a road tunnel by simulated lung fluids

Polycyclic aromatic hydrocarbons (PAHs) are the most highly concerned pollutants bound on traffic-impacted particulate matter (TIPM). The inhaled TIPM-bound PAHs risk has attracted much attention, whereas the inhalation bioaccessibility, a method to refine the exposure risk assessment, has not yet been extensively introduced in the exposure risk assessment. Thus, in vitro assays using artificial lung fluids including artificial lysosomal fluid (ALF), Gamble's solution (GS), and modified GS (MGS) were conducted to assess the inhalation bioaccessibility of USEPA 16 PAHs in TIPM collected from an expressway tunnel, the influence factors of PAHs' inhalation bioaccessibility were explored, and the exposure risk of TIPM-bound PAHs was estimated based on inhalation bioaccessibility. Results showed that the average PAHs concentrations were 30.5 ± 12.9 ng/m³, 36.2 ± 5.19 ng/m³, and 39.9 ± 4.31 ng/m³ in the tunnel inlet PM_2.5, TSP, and tunnel center PM_2.5, respectively. Phe, Flt, Pyr, Nap, Chr, BbF, and BkF were found as the dominant species in TSP and PM_2.5, indicating a dominant contribution of PAHs from diesel-fueled vehicular emissions. The bioaccessible fractions measured for different PAH species in tunnel PM_2.5 and TSP were highly variable, which can be attributed to PAHs' physicochemical properties, size, and carbonaceous materials of TIPM. The addition of Tenax into SLF as an "adsorption sink" can greatly increase PAHs' inhalation bioaccessibility, but DPPC has a limited effect on tunnel PM-bound PAHs' bioaccessibility. The incremental lifetime carcinogenic risk (ILCR) of tunnel inlet PM_2.5-bound PAHs evaluated according to their total mass concentration exceeded the threshold (1.0 × 10^-6) set by the USEPA, whereas the ILCRs estimated based on the inhalation bioaccessibility were far below the threshold. Hence, it is vitally important to take into consideration of pollutant's bioaccessibility to refine health risk assessment.