Tracer-Gas-Integrated Measurements of Brake-Wear Particulate Matter Emissions from Heavy-Duty Vehicles.

Automotive brake-wear emissions are increasingly important in on-road particulate matter (PM) emission inventory. Previous studies reported a high level of PM emissions from the friction materials of light/medium-duty vehicles, but there are few data available from heavy-duty (HD) vehicles equipped with drum brakes despite their popularity (∼85% in HD vehicle fleet). This study developed a novel tracer-gas-integrated method for brake-wear PM emission measurements and evaluated four HD vehicles on a chassis dynamometer that complied with regulatory exhaust emission testing requirements. Three class-6 vehicles with a similar test weight demonstrated repeatability, with the coefficient of variation in the range of 9-36%. Braking events increased PM concentrations by 3 orders of magnitude above the background level. Resuspension of brake-wear PM also occurred during acceleration and contributed to 8-31% of the total PM2.5 mass. The class-6 vehicles had PM2.5 emissions from a single brake (0.7-1.5 mg/km/brake), generally similar to the level of tail-pipe exhaust PM emissions (0.7-1.5 mg/km/vehicle) of each vehicle. A class-8 vehicle exhibited brake-wear PM2.5 emissions (2.4-3.4 mg/km/brake) significantly higher than the tail-pipe exhaust PM emissions (∼1.3 mg/km/vehicle). This article reports an exceptionally high level of brake-wear PM emissions measured directly from the drum brakes of HD vehicles.

Black carbon emissions in gasoline vehicle exhaust: a measurement and instrument comparison.

UNLABELLED: A pilot study was conducted to evaluate the performance and agreement of several commercially available black carbon (BC) measurement instruments, when applied to the quantification of BC in light-duty vehicle (LDV) exhaust. Samples from six vehicles, three fuels, and three driving cycles were used. The pilot study included determinations of the method detection limit (MDL) and repeatability. With respect to the MDL, the real-time instruments outperformed the time-integrated instruments, with MDL = 0.12 mg/mi for the AE51 Aethalometer, and 0.15 mg/mi for the Micro Soot Sensor (MSS), versus 0.38 mg/mi for the IMPROVE_A thermal/ optical method, and 0.35 mg/mi for the OT21_T Optical Transmissometer. The real-time instruments had repeatability values ranging from 30% to 35%, which are somewhat better than those of the time-integrated instruments (40-41%). These results suggest that, despite being less resource intensive, real-time methods can be equivalent or superior to time-integrated methods in terms of sensitivity and repeatability. BC mass data, from the photoacoustic and light attenuation instruments, were compared against same-test EC data, determined using the IMPROVE_A method. The MSS BC data was well correlated with EC, with R2 = 0.85 for the composite results and R2 = 0.86 for the phase-by-phase (PBP) results. The correlation of BC, by the AE51, AE22, and OT21_T with EC was moderate to weak. The weaker correlation was driven by the inclusion of US06 test data in the linear regression analysis. We hypothesize that test-cycle-dependent BC:EC ratios are due to the different physicochemical properties of particulate matter (PM) in US06 and Federal Test Procedure (FTP) tests. Correlation amongst the real-time MSS, PASS-1, AE51, and AE22 instruments was excellent (R2 = 0.83-0.95), below 1 mg/mi levels. In the process of investigating these BC instruments, we learned that BC emissions at sub-1 mg/mi levels can be measured and are achievable by current-generation gasoline engines. IMPLICATIONS: Most comparison studies of black carbon (BC) measurement methods were carried out in the ambient air. This study assesses the agreement among various BC measurement instrument in emissions from light-duty gasoline vehicles (LDGVs) on standard test cycles, and evaluates applicability of these methods under various fuel types, driving cycles, and engine combustion technologies. This research helps to fill in the knowledge gap of BC method standardization as stated in the U.S. Environmental Protection Agency (EPA) 2011 Report to Congress on Black Carbon, and these results demonstrate the feasibility of quantification of BC at the 1 mg/mi PM standard in California Low Emission Vehicle III regulations.

Emissions of polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs from heavy-duty diesel vehicles with DPF and SCR.

UNLABELLED: In total, 24 polycyclic aromatic hydrocarbons (PAHs) in both gas and particle phases and 35 nitro-PAHs in particle phase were analyzed in the exhaust from heavy-duty diesel vehicles equipped with after-treatment for particulate matter (PM) and NO(x) control. The test vehicles were carried out using a chassis dynamometer under highway cruise, transient Urban Dynamometer Driving Schedule (UDDS), and idle operation. The after-treatment efficiently abated more than 90% of the total PAHs. Indeed, the particle-bound PAHs were reduced by > 99%, and the gaseous PAHs were removed at various extents depending on the type of after-treatment and the test cycles. The PAHs in gas phase dominated the total PAH (gas + particle phases) emissions for all the test vehicles and for all cycles; that is, 99% of the two-ring and 98% of the three-ring and 97% of the four-ring and 95% of the carcinogenic PAHs were in the gas-phase after a diesel particle filter (DPF) and not bound to the very small amount of particulate matter left after a DPF. Consequently, an evaluation of the toxicity of DPF exhaust must include this volatile fraction and cannot be based on the particle fraction only. The selective catalytic reduction (SCR) did not appear to promote nitration of the PAHs in general, although there might be some selective nitration of phenanthrene. Importantly the after-treatment reduced the equivalent B[a]P (B[a]Peq) emissions by > 95%, suggesting a substantial health benefit. IMPLICATIONS: This study demonstrated that after-treatments, including diesel particulate filters (DPF), diesel oxidation catalysts (DOC), and selective catalytic reduction (SCR), significantly reduce the emissions of PAHs from heavy-duty diesel engines. The gas-phase PAHs dominate the total PAH (gas + particle phases) emissions from heavy-duty diesel vehicles retrofitted with various DPFs and not bound to the very small amount of particulate matter left after a DPF. Consequently, an evaluation of the toxicity of DPF exhaust must also include this volatile fraction and cannot be based on the particle fraction only.

Hepatobiliary excretion and enterohepatic circulation of colchicine in rats.

This study investigated the pharmacokinetics of unbound colchicine in rat blood, liver and bile, and its interaction with cyclosporin A (CsA; P-glycoprotein inhibitor) and proadifen (non-specific cytochrome P450 inhibitor) by using a microdialysis and liquid chromatographic system. The pharmacokinetics of colchicine in rat blood showed elimination in a nonlinear manner within the dosage ranges of 1-10mg/kg. Twenty minutes after administration, colchicine reached maximum concentration in the liver and bile. The liver-to-blood distribution ratios (AUC(liver)/AUC(blood)) were 1.8+/-0.6, 1.0+/-0.2 and 0.8+/-0.1, and the bile-to-blood distribution ratios (AUC(bile)/AUC(blood)) were 121.6+/-24.7, 102.2+/-13.4 and 116.5+/-18.4 at dosages of 1, 3 and 10mg/kg, respectively. The high hepatobiliary excretion of colchicine may lead to increased toxicity in normal tissues and indicates that colchicine undergoes hepatobiliary excretion against the concentration gradient from bile-to-blood. The area under the curse (AUC) of colchicine in the liver increased in the proadifen-treated groups, suggesting that metabolism of colchicine may involve cytochrome P450. CsA pretreatment caused an increase in the AUC of colchicine in the blood, a decreased AUC in the bile, and a profound decline in the bile-to-blood distribution ratio. Furthermore, the acute diarrhea and body weight loss caused by colchicine were delayed by pretreatment with CsA. These results indicate that the hepatobiliary excretion of colchicine was regulated by P-glycoprotein (P-gp) and the related acute diarrhea could be modulated by CsA. By using a paired rats model, the enterohepatic circulation of colchicine was also observed.

Measurement of unbound ranitidine in blood and bile of anesthetized rats using microdialysis coupled to liquid chromatography and its pharmacokinetic application.

To investigate the pharmacokinetics of unbound ranitidine in rat blood and bile, multiple microdialysis probes coupled to a liquid chromatographic system were developed. This study design was parallel in the following groups: the control-group of six rats received ranitidine alone (10 and 30 mg/kg, i.v.), the treated-group rats were co-administered with ranitidine and cyclosporine (P-glycoprotein (P-gp) inhibitor) or quinidine (both organic cation transport (OCT) and P-gp inhibitors) in six individual rats. Microdialysis probes were inserted into the jugular vein and the bile duct for blood and bile fluids sampling, respectively. Ranitidine in the dialysate was separated by a reversed-phase C18 column (Zorbax, 150 mm x 4.6 mm i.d.; 5 microm) maintained at ambient temperature. Samples were eluted with a mobile phase containing acetonitrile-methanol-tetrahydrofuran-20 mM K2HPO4 (pH 7.0) (24:20:10:946, v/v), and the flow rate of the mobile phase was 1 ml/min. The optimal UV detection for ranitidine was set at wavelength 315 nm. Between 20 and 30 min after drug administration (10 or 30mg/kg), the ranitidine reached the maximum concentration in the bile. The bile-to-blood distribution ratio (AUC(bile)/AUC(blood)) was 9.8 +/- 1.9 and 13.9 +/- 3.8 at the dosages of 10 and 30 mg/kg, respectively. These studies indicate that ranitidine undergoes hepatobiliary excretion which against concentration gradient from bile-to-blood. In addition, the AUC of ranitidine in bile decreased in the treatment of cyclosporine or quinidine, which suggests that the hepatobiliary excretion of ranitidine was partially regulated by P-glycoprotein or organic cation transporter.