The effects of emission control strategies on light-absorbing carbon emissions from a modern heavy-duty diesel engine

<div><p>Control of atmospheric black carbon (BC) and brown carbon (BrC) has been proposed as an important pathway to climate change mitigation, but sources of BC and BrC are still not well understood. In order to better identify the role of modern heavy-duty diesel engines on the production of BC and BrC, emissions from a heavy-duty diesel engine operating with different emission control strategies were examined using a source dilution sampling system. The effect of a diesel oxidation catalyst (DOC) and diesel particulate filter (DPF) on light-absorbing carbon (LAC) was evaluated at three steady-state engine operation modes: idle, 50% speed and load, and 100% speed and load. LAC was measured with four different engine configurations: engine out, DOC out, DPF out, and engine out with an altered combustion calibration. BC and BrC emission rates were measured with the Aethalometer (AE-31). EC and BC emission rates normalized to the mass of CO₂ emitted increased with increasing engine speed and load. Emission rates normalized to brake-specific work did not exhibit similar trends with speed and load, but rather the highest emission rate was measured at idle. EC and OC emissions were reduced by 99% when the DOC and DPF architecture was applied. The application of a DPF was equally effective at removing 99% of the BC fraction of PM, proving to be an important control strategy for both LAC and PM. BC emissions were unexpectedly increased across the DOC, seemingly due to a change aerosol optical properties. Removal of exhaust gas recirculation (EGR) flow due to simulated EGR cooler failure caused a large increase in OC and BrC emission rates at idle, but had limited influence during high load operation. LAC emissions proved to be sensitive to the same control strategies effective at controlling the total mass of diesel PM.</p><p>Implications: <i>In the context of black carbon emissions, very small emission rates of brown carbon were measured over a range of control technologies and engine operating conditions. During specific idle engine operation without EGR and adjusted fueling conditions, brown carbon can be formed in significant amounts, requiring careful management tactics. Control technologies for particulate matter are very effective for light-absorbing carbon, reducing black carbon emissions to near zero for modern engines equipped with a DPF. Efforts to control atmospheric brown carbon need to focus on other sources other than modern diesel engines, such as biomass burning.</i></p></div

Single Exposure to near Roadway Particulate Matter Leads to Confined Inflammatory and Defense Responses: Possible Role of Metals

Inhalation of traffic-associated atmospheric particulate matter (PM2.5) is recognized as a significant health risk. In this study, we focused on a single (“subclinical response”) exposure to water-soluble extracts from PM collected at a roadside site in a major European city to elucidate potential components that drive pulmonary inflammatory, oxidative, and defense mechanisms and their systemic impacts. Intratracheal instillation (IT) of the aqueous extracts induced a 24 h inflammatory response characterized by increased broncho-alveolar lavage fluid (BALF) cells and cytokines (IL-6 and TNF-α), increased reactive oxygen species production, but insignificant lipids and proteins oxidation adducts in mouse lungs. This local response was largely self-resolved by 48 h, suggesting that it could represent a subclinical response to everyday-level exposure. Removal of soluble metals by chelation markedly diminished the pulmonary PM-mediated response. An artificial metal solution (MS) recapitulated the PM extract response. The self-resolving nature of the response is associated with activating defense mechanisms (increased levels of catalase and glutathione peroxidase expression), observed with both PM extract and MS. In conclusion, metals present in PM collected near roadways are largely responsible for the observed transient local pulmonary inflammation and oxidative stress. Simultaneous activation of the antioxidant defense response may protect against oxidative damage

Global Perspective on the Oxidative Potential of Airborne Particulate Matter: A Synthesis of Research Findings

An emerging hypothesis in the field of air pollution is that oxidative stress is one of the important pathways leading to adverse health effects of airborne particulate matter (PM). To advance our understanding of sources and chemical elements contributing to aerosol oxidative potential and provide global comparative data, we report here on the biological oxidative potential associated with size-segregated airborne PM in different urban areas of the world, measured by a biological (cell-based) reactive oxygen species (ROS) assay. Our synthesis indicates a generally greater intrinsic PM oxidative potential as well as higher levels of exposure to redox-active PM in developing areas of the world. Moreover, on the basis of our observations, smaller size fractions are generally associated with higher intrinsic ROS activity compared with larger PM size fractions. Another important outcome of our study is the identification of major species and sources that are associated with ROS activity. Water-soluble transition metals (e.g., Fe, Ni, Cu, Cr, Mn, Zn and V) and water-soluble organic carbon (WSOC) showed consistent correlations with the oxidative potential of airborne PM across different urban areas and size ranges. The major PM sources associated with these chemical species include residual/fuel oil combustion, traffic emissions, and secondary organic aerosol formation, indicating that these sources are major drivers of PM-induced oxidative potential. Moreover, comparison of ROS activity levels across different seasons indicated that photochemical aging increases the intrinsic oxidative potential of airborne PM

Exposure to Atmospheric Particulate Matter Enhances Th17 Polarization through the Aryl Hydrocarbon Receptor

<div><p>Lung diseases, including asthma, COPD, and other autoimmune lung pathologies are aggravated by exposure to particulate matter (PM) found in air pollution. IL-17 has been shown to exacerbate airway disease in animal models. As PM is known to contain aryl hydrocarbon receptor (AHR) ligands and the AHR has recently been shown to play a role in differentiation of Th17 T cells, the aim of this study was to determine whether exposure to PM could impact Th17 polarization in an AHR-dependent manner. This study used both cell culture techniques and <i>in vivo</i> exposure in mice to examine the response of T cells to PM. Initially experiments were conducted with urban dust particles from a standard reference material, and ultimately repeated with freshly collected samples of diesel exhaust and cigarette smoke. The readout for the assays was increased T cell differentiation as indicated by increased generation of IL-17A in culture, and increased populations of IL-17 producing cells by intracellular flow cytometry. The data illustrate that Th17 polarization was significantly enhanced by addition of urban dust in a dose dependent fashion in cultures of wild-type but not AHR^-/- mice. The data further suggest that polycyclic aromatic hydrocarbons played a primary role in this enhancement. There was both an increase of Th17 cell differentiation, and also an increase in the amount of IL-17 secreted by the cells. In summary, this paper identifies a novel mechanism whereby PM can directly act on the AHR in T cells, leading to enhanced Th17 differentiation. Further understanding of the molecular mechanisms responsible for pathologic Th17 differentiation and autoimmunity seen after exposure to pollution will allow direct targeting of proteins involved in AHR activation and function for treatment of PM exposures.</p> </div

Th17 differentiation <i>in</i><i>vitro</i> is enhanced with addition of SRM1649b to culture conditions.

<p>A-B: Naïve CD4⁺ T cells were isolated from the spleens of male C57BL/6 mice (B6) and cultured in Th17 conditions (anti-CD3/CD28 antibody + mIL-6 (20 ng/ml) + huTGF-β (5 ng/ml)) for 4 days in the absence or presence of SRM1649b (10, 20 or 40 μg/ml) or FICZ (200 nM). Triplicate culture supernatant was harvested and ELISA measured the concentration of IL-17A and IL-22 (A). Data presented is representative of 3 experiments. In separate experiments, total RNA was harvested from cells and the relative levels of IL-17A, IL-22 and IL-23R mRNA were determined by qRT-PCR (B). Data is relative to cells treated with anti-CD3/CD28 antibody stimulation but without mIL-6 and huTGF-β. Fold increase results from cultures with (w/) SRM1649b were compared for significance with cultures without (w/o) SRM1649b using the paired student’s t-test. The number in parenthesis indicates the number of individual assays used for that target gene. C-D: Naïve B6 CD4⁺ T cells were cultured in Th17 conditions (anti-CD3/CD28 antibody + mIL-6 (20 ng/ml) and varying concentrations of huTGF-β (0 - 5 ng/ml)) for 4 days in the absence or presence of SRM1649b (40 μg/ml). Cells were harvested from and subjected to intracellular cytokine analysis to determine the percent of IL-17A and IFN-γ expressing CD4⁺ T cells present after culture. Data from 3 separate experiments were pooled and statistical comparison was made between the cultures with versus cultures without SRM1649b at each concentration of huTGF-β. *, p < 0.05; **, p < 0.01; ***, p < 0.001.</p

AHR is required for upregulation of Th17 cells in response to SRM1649b.

<p>A-B: Naïve B6 CD4⁺ T cells were cultured in Th17 conditions (anti-CD3/CD28 antibody + mIL-6 (20 ng/ml) and varying concentrations of huTGF-β (5 ng/ml) for 4 days in the absence or presence of SRM1649b (40 μg/ml) after which total RNA was harvested. Relative levels of AHR and cyp 1a1 mRNA were determined by qRT-PCR. Data are relative to cells treated with anti-CD3/CD28 antibody stimulation but without mIL-6 and huTGF-β. Fold increase results from cultures with (w/) SRM1649b were compared for significance with cultures without (w/o) SRM1649b using the paired student’s t-test. B: Cells were harvested after 4 days and stained with anti-AHR antibody during intracellular cytokine analysis to determine the percent of AHR-expressing CD4⁺ T cells cultured with (solid line) or without (shaded) huTGF-β. C: Naïve CD4⁺ T cells were isolated from the spleens of male B6 or AHR^-/- mice and cultured in Th17 conditions (anti-CD3/CD28 antibody + mIL-6 (20 ng/ml) +/- huTGF-β (5 ng/ml) for 4 days in the varying concentrations SRM1649b. Supernatants were analyzed by ELISA. D - E: Naïve CD4⁺ T cells were isolated from the spleens of AHR^-/- (D) or DREC^-/- (E) mice and cultured in Th17 conditions (anti-CD3/CD28 antibody + mIL-6 (20 ng/ml) +/- huTGF-β (5 ng/ml) for 4 days +/- SRM1649b. Total RNA was harvested and, the relative levels of IL-17A, and IL-22 mRNA were determined by qRT-PCR. Data is relative to cell treated with anti-CD3/CD28 antibody stimulation but without added mIL-6 and huTGF-β. Fold increase results from cultures with (w/) SRM1649b were compared for significance with cultures without (w/o) SRM1649b using the paired student’s t-test. The number in parenthesis indicates the number of individual assays used for that target gene. *, p < 0.05; **, p < 0.01; ***, p < 0.001.</p

Th17 polarization enhancing activity is found in other PAH containing environmental samples.

<p>A - B: Naïve CD4⁺ T cells were isolated from the spleens of male B6 and cultured in Th17 conditions for 4 days in the presence of varying concentrations of diesel (A) and cigarette (B) extract. Culture media was harvested and the concentration of IL-17A was measured by ELISA. The percent of live/dead stain low CD4⁺ T cells is indicated below the appropriate extract concentration. C - D: Naïve B6 or AHR^-/- CD4⁺ T cells in Th17 conditions in the absence or presence of 8 μg/ml diesel or cigarette extract. Cells were harvested and subjected to intracellular cytokine analysis to determine the percent of IL-17A-expressing CD4⁺ T cells present after culture. For both ELISA and intracellular IL-17A results, data from 3 separate experiments was pooled and statistical comparison was made between the cultures with versus cultures without extract. *, p < 0.05.</p

Investigation of the specific components of SRM1649b that contain Th17 enhancing activity.

<p>A: Mouse Hepa1 cells that were transfected with luciferase reporter gene fused to the dioxin-responsive elements (DRE) were seeded at 0.6x10⁶ cells per well. Cells were then exposed to media (Control), media + SRM1649b suspended in PBS (SRM/PBS), media + DMSO (DMSO), media + SRM1649b suspended in DMSO (SRM/DMSO) or the organic fraction of SRM1649b suspended in DMSO (fSRM/DMSO) for 4 hours. Luciferase activity was measured on a luminometer. B: Naïve B6 CD4⁺ T cells in Th17 conditions in the presence of fractioned SRM1649b and controls. After 4 days, total RNA was harvested. Using qRT-PCR, the relative levels of IL-17A and Cyp1a1 mRNA were determined. Data presented are the mean and standard deviation of 2 separate experiments and is relative to cells treated with anti-CD3/CD28 antibody stimulation but without mIL-6 and huTGF-β. C: Naïve B6 CD4⁺ T cells in Th17 conditions in the presence varying concentrations of the PAHs benzo[a]pyrene (BaP), benzo[e]pyrene (BeP) and benzo[k]fluoranthene (BkF). Culture supernatant was harvested and ELISA measured the concentration of IL-17A. The line indicates the level of IL-17A expression in cultures exposed to DMSO vehicle only. D: Naïve B6 or AHR^-/- CD4⁺ T cells in Th17 conditions in the presence of BkF. Cells were harvested and subjected to intracellular cytokine analysis to determine the percent of IL-17A-expressing CD4⁺ T cells present after culture. Data from 3 separate experiments was pooled and statistical comparison was made between the cultures with versus cultures without BkF.</p

Exposure to SRM1649b augments IL-17 expression <i>in</i><i>vivo</i> and <i>in</i><i>vitro</i>.

<p>A: Male C57BL/6 mice (B6) were exposed every 3 days to SRM1649b or control PBS (400 μg/20μl PBS) by intranasal administration. 24 hours after the final treatment, mice were euthanized and total RNA was isolated from the right lung. qRT-PCR was performed to measure changes in the steady state expression of IL-17A and Cyp1a1 mRNA. B-C: Splenocytes from male B6 mice were stimulated <i>in </i><i>vitro</i> with dendritic cells isolated from B6 or Balb/c splenocytes in the presence or absence (Control) of either FICZ (200 nM) or SRM1649b (40 μg/ml). After 4 days, supernatants were harvested and the concentration of IL-17A and IFN-γ was measured by cytometric bead array. Total RNA was also isolated from the cultured cells and the relative changes in IL-22 and Cyp1b1 mRNA expression was measured by qRT-PCR. Data from 3 separate experiments were pooled and statistical comparison was made between controls and experimental cultures. *, p < 0.05; **, p < 0.01;.</p

On-Roadway In-Cabin Exposure to Particulate Matter: Measurement Results Using Both Continuous and Time-Integrated Sampling Approaches

<div><p>The Atlanta Commuters Exposure (ACE) Study was designed to measure in-cabin exposure to roadway particulate pollution and acute health response in a panel of adults with and without asthma following a 2-h scripted route along major highways in Atlanta. This article focuses on methods and results of both continuous and integrated approaches used to measure the concentration of PM_2.5 mass, particle number concentration (PNC), black carbon (BC) mass, and particle-bound PAHs, in-cabin noise, PM elemental composition, elemental carbon, organic carbon, water-soluble organic carbon (WSOC) content, and speciation of a broad range of organic compounds including alkanes, hopanes, and PAHs. Speciated PM data indicates that in-cabin particles derive from three non-co-varying processes: the resuspension of road dust containing crustal elements and previously-deposited brake pad residue with a contribution of normal fuel combustion, incomplete combustion processes producing PAHs and carbon particles, and particles ablated from brake pads that have not previously deposited to the roadside environment. Most in-cabin pollutants were elevated during the warm season with the notable exception of PNC. PNC was not found to be correlated with most other pollutants. In-cabin concentrations were marginally higher when windows were open.</p><p>Copyright 2014 American Association for Aerosol Research</p></div