Characterization of fine particle and gaseous emissions during school bus idling

Air Quality and Behavioral Impacts of Anti-Idling Campaigns in School Drop-Off Zones

Vehicle emissions are a major source of pollution in urban communities and idling may contribute up to 34% or more to local air pollution levels. Reduced idling has been found to be an effective policy tool for improving air quality, especially around schools, where it may also improve outcomes for asthmatic children. We studied two anti-idling campaigns in Salt Lake County, Utah to understand if reduced engine idling leads to behavioral change and subsequent reduction in traffic-related air pollution exposure of the related school. We found a 38% decrease in idling time following an anti-idling campaign and an 11% decrease in the number of vehicles idling at the school drop-off zones. The air quality measurements showed improvement in the middle of the campaign, but seasonal variability as well as atmospheric inversion events had substantial effects on overall ambient pollutant concentrations. This study provides an encouraging starting point to develop more effective anti-idling campaigns to protect the health of children, school staff, and the surrounding community.

Effectiveness of Using Enhanced Filters in Schools and Homes to Reduce Indoor Exposures to PM2.5 from Outdoor Sources and Subsequent Health Benefits for Children with Asthma

Filters can reduce indoor concentrations of particulate matter (PM_2.5), but their benefits have not been well-characterized. This study investigates exposure, health, and cost impacts of high efficiency filters in homes and schools, focusing on the asthma-related outcomes. Reductions in indoor exposures to PM_2.5 from outdoor sources with enhanced filters (e.g., MERV 12) are estimated using probabilistic indoor air quality models, and avoided health impacts are quantified using health impact assessment. These methods are applied using data from Detroit, Michigan, an urban region with elevated asthma rates. Replacing inefficient filters with enhanced filters in schools would reduce the PM_2.5-attributable asthma burden by 13% annually, with higher benefits for more efficient filters. Marginal costs average $63 per classroom or $32 per child with asthma per year. In homes, using efficient furnace filters or air cleaners yields 11 to 16% reductions in the asthma burden with an annualized marginal costs of $151-494 per household. Additional benefits include reductions in health risk for adults and lower exposures to other contaminants such as PM from indoor sources. On the basis of the included health outcomes, efficient filters in schools in particular is a potentially cost-efficient way to reduce the asthma-related health burden for children.

Characteristics of particle coagulation in an underground parking lot

Particles in vehicle exhaust plumes in underground parking lots have adverse health effects due to the enclosed environment in which they are released and the temperature difference between the tailpipe and ambient environment; at the same time, particle coagulation might be obvious near the tailpipe in an underground parking lot. In the present study, airflow and temperature fields were calculated using the Realizable k-ε model, and the Eulerian particle transport model was selected in the numerical simulation of particle concentration dispersion. Polydisperse thermal coagulation due to Brownian collisions was employed to calculate the particle coagulation. The results show that particle coagulation rate and half-time were significant within 1 m from the tailpipe. The variations in the particle coagulation rate and half-time were similar, but their directions were opposite. Air exhaust time was nearly four times longer than averaged half-time and 40 times longer than minimum half-time. The peak particle diameter increased approximately 1.43 times due to coagulation. A double particle concentration at the tailpipe caused the fourfold rise in the particle coagulation rate in the distance ranging less than 1 m from the tailpipe. An increase in exhaust velocity at the tailpipe could shorten the obvious range of particle coagulation along the centerline of the tailpipe from 1 to 0.8 m in the study.

The impact of an anti-idling campaign on outdoor air quality at four urban schools

Idling school buses may increase concentrations of air pollutants including fine particulate matter (PM2.5) and elemental carbon (EC) near schools. Efforts to reduce vehicle idling near schools have rarely included air sampling to objectively assess changes in concentrations of air pollutants. The objective was to determine the impact of an anti-idling campaign on outdoor air quality at four schools with varying exposure to bus and automobile traffic. Outdoor air sampling for PM2.5, EC and particle number concentration (PNC) was conducted at four schools for five days before and after an anti-idling campaign. Sampling began before the morning arrival of buses and concluded after their afternoon departure. Sampling was simultaneously conducted at four corresponding community sites. Differences in PM2.5, EC, and PNC measured at school and community sites for each sampling day were calculated before and after the campaign. Before the campaign, the average outdoor concentration of PM2.5 during the school day at three of the four schools exceeded community background levels and the difference was greatest (4.11 μg m(-3), p < 0.01) at the school with the most buses (n = 39). The largest difference in EC between school and community sites was also observed at the school with the greatest number of buses (0.40 μg m(-3), p < 0.01). Following the anti-idling campaign, the average difference in PM2.5 at the school with the most buses decreased from 4.11 μg m(-3) to 0.99 μg m(-3) (p < 0.05). Similarly, at this school, the difference in the EC level decreased from 0.40 μg m(-3) to 0.15 μg m(-3) and PNC decreased from 11,560 to 1690 particles per cm(3) (p < 0.05). The outdoor concentrations of pollutants at schools with fewer buses (n = 5-11) were not significantly reduced. The concentration of air pollutants near schools may significantly exceed community background levels, particularly in the presence of idling school buses. Anti-idling campaigns are effective in reducing PM2.5, EC and PNC at schools with significant amounts of buses and passenger cars.

Gaseous and Particulate Emissions from Diesel Engines at Idle and under Load: Comparison of Biodiesel Blend and Ultralow Sulfur Diesel Fuels

Diesel exhaust emissions have been reported for a number of engine operating strategies, after-treatment technologies, and fuels. However, information is limited regarding emissions of many pollutants during idling and when biodiesel fuels are used. This study investigates regulated and unregulated emissions from both light-duty passenger car (1.7 L) and medium-duty (6.4 L) diesel engines at idle and load and compares a biodiesel blend (B20) to conventional ultralow sulfur diesel (ULSD) fuel. Exhaust aftertreatment devices included a diesel oxidation catalyst (DOC) and a diesel particle filter (DPF). For the 1.7 L engine under load without a DOC, B20 reduced brake-specific emissions of particulate matter (PM), elemental carbon (EC), nonmethane hydrocarbons (NMHCs), and most volatile organic compounds (VOCs) compared to ULSD; however, formaldehyde brake-specific emissions increased. With a DOC and high load, B20 increased brake-specific emissions of NMHC, nitrogen oxides (NOx), formaldehyde, naphthalene, and several other VOCs. For the 6.4 L engine under load, B20 reduced brake-specific emissions of PM2.5, EC, formaldehyde, and most VOCs; however, NOx brake-specific emissions increased. When idling, the effects of fuel type were different: B20 increased NMHC, PM2.5, EC, formaldehyde, benzene, and other VOC emission rates from both engines, and changes were sometimes large, e.g., PM2.5 increased by 60% for the 6.4 L/2004 calibration engine, and benzene by 40% for the 1.7 L engine with the DOC, possibly reflecting incomplete combustion and unburned fuel. Diesel exhaust emissions depended on the fuel type and engine load (idle versus loaded). The higher emissions found when using B20 are especially important given the recent attention to exposures from idling vehicles and the health significance of PM2.5. The emission profiles demonstrate the effects of fuel type, engine calibration, and emission control system, and they can be used as source profiles for apportionment, inventory, and exposure purposes.

Comparing gravimetric and real-time sampling of PM(2.5) concentrations inside truck cabins

As part of a study on truck drivers' exposure and health risk, pickup and delivery (P&D) truck drivers' on-road exposure patterns to PM(2.5) were assessed in five, weeklong sampling trips in metropolitan areas of five U.S. cities from April to August of 2006. Drivers were sampled with real-time (DustTrak) and gravimetric samplers to measure average in-cabin PM(2.5) concentrations and to compare their correspondence in moving trucks. In addition, GPS measurements of truck locations, meteorological data, and driver behavioral data were collected throughout the day to determine which factors influence the relationship between real-time and gravimetric samplers. Results indicate that the association between average real-time and gravimetric PM(2.5) measurements on moving trucks was fairly consistent (Spearman rank correlation of 0.63), with DustTrak measurements exceeding gravimetric measurements by approximately a factor of 2. This ratio differed significantly only between the industrial Midwest cities and the other three sampled cities scattered in the South and West. There was also limited evidence of an effect of truck age. Filter samples collected concurrently with DustTrak measurements can be used to calibrate average mass concentration responses for the DustTrak, allowing for real-time measurements to be integrated into longer-term studies of inter-city and intra-urban exposure patterns for truck drivers.