Simultaneously reducing CO2 and particulate exposures via fractional recirculation of vehicle cabin air.

Prior studies demonstrate that air recirculation can reduce exposure to nanoparticles in vehicle cabins. However when people occupy confined spaces, air recirculation can lead to carbon dioxide (CO2) accumulation which can potentially lead to deleterious effects on cognitive function. This study proposes a fractional air recirculation system for reducing nanoparticle concentration while simultaneously suppressing CO2 levels in the cabin. Several recirculation scenarios were tested using a custom-programmed HVAC (heat, ventilation, air conditioning) unit that varied the recirculation door angle in the test vehicle. Operating the recirculation system with a standard cabin filter reduced particle concentrations to 1000 particles/cm3, although CO2 levels rose to 3000 ppm. When as little as 25% fresh air was introduced (75% recirculation), CO2 levels dropped to 1000 ppm, while particle concentrations remained below 5000 particles/cm3. We found that nanoparticles were removed selectively during recirculation and demonstrated the trade-off between cabin CO2 concentration and cabin particle concentration using fractional air recirculation. Data showed significant increases in CO2 levels during 100% recirculation. For various fan speeds, recirculation fractions of 50-75% maintained lower CO2 levels in the cabin, while still reducing particulate levels. We recommend fractional recirculation as a simple method to reduce occupants' exposures to particulate matter and CO2 in vehicles. A design with several fractional recirculation settings could allow air exchange adequate for reducing both particulate and CO2 exposures. Developing this technology could lead to reductions in airborne nanoparticle exposure, while also mitigating safety risks from CO2 accumulation.

Measuring Particulate Emissions of Light Duty Passenger Vehicles Using Integrated Particle Size Distribution (IPSD).

The California Air Resources Board (ARB) adopted the low emission vehicle (LEV) III particulate matter (PM) standards in January 2012, which require, among other limits, vehicles to meet 1 mg/mi over the federal test procedure (FTP). One possible alternative measurement approach evaluated to support the implementation of the LEV III standards is integrated particle size distribution (IPSD), which reports real-time PM mass using size distribution and effective density. The IPSD method was evaluated using TSI's engine exhaust particle sizer (EEPS, 5.6-560 nm) and gravimetric filter data from more than 250 tests and 34 vehicles at ARB's Haagen-Smit Laboratory (HSL). IPSD mass was persistently lower than gravimetric mass by 56-75% over the FTP tests and by 81-84% over the supplemental FTP (US06) tests. Strong covariance between the methods suggests test-to-test variability originates from actual vehicle emission differences rather than measurement accuracy, where IPSD offered no statistical improvement over gravimetric measurement variability.

Comparison of particle mass and solid particle number (SPN) emissions from a heavy-duty diesel vehicle under on-road driving conditions and a standard testing cycle.

It is important to understand the differences between emissions from standard laboratory testing cycles and those from actual on-road driving conditions, especially for solid particle number (SPN) emissions now being regulated in Europe. This study compared particle mass and SPN emissions from a heavy-duty diesel vehicle operating over the urban dynamometer driving schedule (UDDS) and actual on-road driving conditions. Particle mass emissions were calculated using the integrated particle size distribution (IPSD) method and called MIPSD. The MIPSD emissions for the UDDS and on-road tests were more than 6 times lower than the U.S. 2007 heavy-duty particulate matter (PM) mass standard. The MIPSD emissions for the UDDS fell between those for the on-road uphill and downhill driving. SPN and MIPSD measurements were dominated by nucleation particles for the UDDS and uphill driving and by accumulation mode particles for cruise and downhill driving. The SPN emissions were ∼ 3 times lower than the Euro 6 heavy-duty SPN limit for the UDDS and downhill driving and ∼ 4-5 times higher than the Euro 6 SPN limit for the more aggressive uphill driving; however, it is likely that most of the "solid" particles measured under these conditions were associated with a combination release of stored sulfates and enhanced sulfate formation associated with high exhaust temperatures, leading to growth of volatile particles into the solid particle counting range above 23 nm. Except for these conditions, a linear relationship was found between SPN and accumulation mode MIPSD. The coefficient of variation (COV) of SPN emissions of particles >23 nm ranged from 8 to 26% for the UDDS and on-road tests.

Effect of low-density polyethylene on smoke emissions from burning of simulated debris piles.

UNLABELLED: Low-density polyethylene (LDPE) plastic is used to keep piled debris from silvicultural activities--activities associated with development and care of forests--dry to enable efficient disposal by burning. The effects of inclusion of LDPE in this manner on smoke emissions are not well known. In a combustion laboratory experiment, 2-kg mixtures of LDPE and manzanita (Arctostaphylos sp.) wood containing 0, 0.25, and 2.5% LDPE by mass were burned. Gaseous and particulate emissions were sampled in real time during the entire flaming, mixed combustion phase--when the flaming and smoldering phases are present at the same time--and during a portion of the smoldering phase. Analysis of variance was used to test significance of modified combustion efficiency (MCE)--the ratio of concentrations of fire-integrated excess CO2 to CO2 plus CO--and LDPE content on measured individual compounds. MCE ranged between 0.983 and 0.993, indicating that combustion was primarily flaming; MCE was seldom significant as a covariate. Of the 195 compounds identified in the smoke emissions, only the emission factor (EF) of 3M-octane showed an increase with increasing LDPE content. Inclusion of LDPE had an effect on EFs of pyrene and fluoranthene, but no statistical evidence of a linear trend was found. Particulate emission factors showed a marginally significant linear relationship with MCE (0.05 < P-value < 0.10). Based on the results of the current and previous studies and literature reviews, the inclusion of small mass proportions of LDPE in piled silvicultural debris does not appear to change the emissions produced when low-moisture-content wood is burned. In general, combustion of wet piles results in lower MCEs and consequently higher levels of emissions. IMPLICATIONS: Current air quality regulations permit the use of burning to dispose of silvicultural piles; however, inclusion of low-density polyethyelene (LDPE) plastic in silvicultural piles can result in a designation of the pile as waste. Waste burning is not permitted in many areas, and there is also concern that inclusion of LDPE leads to toxic air emissions.

Carbon nanotubes among diesel exhaust particles: real samples or contaminants?

During three separate studies involving characterization of diesel particulate matter carbon nanotubes (CNTs) were found among diesel exhaust particles sampled onto transmission electron microscopy (TEM) grids. During these studies, samples were collected from three different diesel engines at normal operating conditions with or without an iron catalyst (introduced as ferrocene) in the fuel. This paper is to report the authors' observation of CNTs among diesel exhaust particles, with the intent to stimulate awareness and further discussion regarding the formation mechanisms of CNTs during diesel combustion.

Real-world particle and NOx emissions from hybrid electric vehicles under cold weather conditions.

Hybrid electric vehicle (HEV) technology is critical to reduce the impact of the internal combustion engines on air pollution and greenhouse gases. HEVs have an advantage in market penetration due to their lower cost and higher driving range compared to battery electric vehicles (BEVs). On the other hand, HEVs use an internal combustion engine and still emit air pollutants. It is hypothesized that HEV performance is impacted by the weather conditions as a result of many factors. It was beyond the scope of this work to systematically evaluate all factors so instead we measured emissions from two vehicles driving city and highway routes in Minneapolis, Minnesota in the winter (-5 °C) and looked for major differences in emissions relative to each vehicle and relative to results that would be obtained from a chassis dynamometer in a controlled laboratory setting at a higher temperature approximately 20 °C). The study then looked to associate differences in emissions with the prevailing conditions to gain new insights. Emissions of interest included the total particle number (TPN), solid particle number (SPN), particulate matter mass (PM), and NOx. One key difference in vehicle engine technology was PFI (port fuel injection) versus GDI (gasoline direct injection). We found the frequency at which the Prius hybrid engine reignited was much higher than the Sonata for city and highway driving, although for both vehicles the catalyst temperature remained high and appeared to be unaffected by the reignitions, despite the cold weather. For most conditions, the Prius emitted more NOx but fewer particles than the Sonata. In some cases, NOx and particle emissions exceeded the most comparable laboratory-based emissions standards.

Effect of cerium oxide nanoparticles on inflammation in vascular endothelial cells.

Because vascular endothelial cell inflammation is critical in the development of cardiovascular pathology, we hypothesized that direct exposure of human aortic endothelial cells (HAECs) to ultrafine particles induces an inflammatory response. To test the hypothesis, we incubated HAECs for 4 h with different concentrations (0.001-50 microg/ml) of CeO(2) nanoparticles and subsequently measured mRNA levels of the three inflammatory markers intercellular adhesion molecule 1 (ICAM-1), interleukin (IL)-8, and monocyte chemotactic protein (MCP-1) using real-time polymerase chain reaction (PCR). Ceria nanoparticles caused very little inflammatory response in HAECs, even at the highest dose. This material is apparently rather benign in comparison with Y(2)O(3) and ZnO nanoparticles that we have studied previously. These results suggest that inflammation in HAECs following acute exposure to metal oxide nanoparticles depends strongly on particle composition.

How do particle number, surface area, and mass correlate with toxicity of diesel particle emissions as measured in chemical and cellular assays?

Increasingly stringent particulate matter (PM) emission standards have brought forth engine design improvements, cleaner-burning fuels, and aftertreatment technologies. Reductions in tailpipe PM mass have concomitantly reduced accumulation-mode particle emissions. However, some strategies promote the emission of nucleation-mode particles, which are typically quantified on a number (PN) basis. We previously demonstrated that PN emissions from heavy-duty diesel vehicles equipped with various aftertreatment systems were inversely correlated, and gravimetric PM mass was positively correlated, with two in vitro assays. This present work expands on the analysis of PM mass and PN with in vitro assays to also include four additional PM metrics: suspended PM mass, active particle surface area, aggregate particle surface area, and accumulation-mode particle number. This new analysis shows that like gravimetric PM mass, suspended particle mass and accumulation mode particle number are well correlated with dithiothreitol consumption rate (DTT) and macrophage reactive oxygen species consumption rate (ROS) assays (R2 = 0.61-0.96). Data suggest that PM mass emissions dominated by nucleation-mode particles induce equal or slightly greater toxicity compared to PM mass dominated by accumulation-mode particles. Data also show that among all PM metrics, those used for regulating PM in the United States and Europe, namely gravimetric mass and solid PN are overall most correlated with in vitro toxicity. Moreover, continued exploration of alternative, low-cost, and more appropriate PM metrics is warranted to better understand the reproducibility of these findings on other engine applications, fuel types, and aftertreatment platforms.

Kinetics of soot oxidation by NO2.

Modern technologies use NO(2) to promote low-temperature soot oxidation for diesel particulate filter regeneration. In this study, the online aerosol technique of high-temperature oxidation tandem differential mobility analysis is used to study kinetics of soot oxidation by NO(2). Soot particles are exposed to varying temperature and NO(2) mixing ratio inside the furnace resulting from thermal decomposition of NO(2) to NO. This causes soot oxidation rates to vary throughout the furnace. Variations in temperatures and NO(2) mixing ratio are thoroughly accounted for the first time. Soot oxidation rates are calculated as a function of frequency factor A(soot), activation energy E(soot), and concentration of NO(2) within the furnace at temperatures ranging from 500 to 950 degrees C. Results suggest A(soot) and E(soot) values for soot oxidation of 2.4 x 10(-14) (nm K(-0.5) s(-1) cm(3) molecule(-1)) and 47.1 kJ mol(-1), respectively, when reaction order to NO(2) is assumed as unity. The activation energy for soot oxidation with NO(2) is significantly lower than oxidation with air. However, parts per million levels of NO(2) cause soot oxidation at low temperatures suggesting NO(2) is a stronger oxidant than O(2).