Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

More exhaust inhaled by kids inside school buses than by others in the area, says study

05.04.2005


Children on school buses collectively inhale as much or more exhaust emitted from those buses as does the rest of the city’s population, according to a new analysis by researchers at the University of California.

The results highlight the problem of "self-pollution," or exhaust from the vehicle leaking into the cabin, particularly among older buses. This also is the first study to specifically look at how much exhaust is breathed in on school buses. "Although environmental regulators focus on controlling the amount of exhaust emitted by vehicles and other sources, knowing how much of a pollutant is inhaled is a better indicator for related health impacts," said Julian Marshall, a Ph.D. student at the University of California, Berkeley’s Energy and Resources Group and lead author of the study, which is scheduled to appear in the April 15 issue of the journal Environmental Science and Technology, but is available now online. "Diesel is the last big source of air pollution that has yet to be reigned in," said Marshall. "As a policy matter, it seems clear from this analysis that reducing emissions from school buses should be a very high priority."

The researchers noted that children are especially vulnerable to air pollution because, compared with adults, their immune systems are less mature and, per body weight, they inhale more air per day. "For every metric ton of pollution emitted by a school bus, the cumulative mass of pollution inhaled by the 40 or so kids on that bus is comparable to, or in many cases larger than, the cumulative mass inhaled by all the other people in an urban area," said Marshall. "That the values were even close was shocking."



The researchers analyzed results from tracer-gas experiments conducted by scientists at UCLA and UC Riverside. They measured the air in six empty school buses traveling through established routes in south-central and suburban Los Angeles, all areas within the Los Angeles Unified School District. Nine runs were made with windows open and seven runs with windows closed in April, May and June 2002.

Five of the buses were powered by diesel fuel and built between 1975 and 1998. One of the diesel buses, a 1998 model, was equipped with a particle trap to reduce emissions. The sixth bus, built in 2002, ran on compressed natural gas.

Sensitive detectors on the buses tested for sulfur hexafluoride, a gas used as a tracer because it can be picked up at levels as low as 10 parts per trillion and is not present in background air. Sulfur hexafluoride was released into the engine exhaust manifold of the buses so researchers knew that any traces of the gas must have come through the exhaust system of the bus.

Eduardo Behrentz, a post-doctoral researcher at the Environmental Science and Engineering Program and the School of Public Health at UCLA, participated in the experiments and co-authored the new analysis. "We determined that concentrations of key air pollutants were higher inside the bus cabins than outside the cabins," said Behrentz. "While the conditions inside the cabin were affected by the emissions of other vehicles on the road, our tracer gas measurements revealed that a significant amount of the pollutants found inside the buses originated from the buses’ own exhaust systems, especially when the windows were closed."

The experiments included measures of exhaust from neighboring vehicles, but this new analysis focuses on the amount of emissions inhaled from the school bus exhaust system.

The analysis assumed a typical ridership of 40 children per school bus with an average breathing rate of 15 liters of air per minute. The researchers calculated the collective amount of bus emissions inhaled for all riders, called the self-pollution intake fraction, as well as the average intake fraction for individuals.

The researchers found that for every million grams of pollutants emitted by the bus, 27 grams would be inhaled by all 40 riders, or 0.67 grams per child. "In comparison, a city of 1 million people will inhale about 12 grams per million grams of exhaust emitted," said Marshall. "In a single day, a child riding a school bus will breathe in anywhere from 7 to 70 times more exhaust from that bus than a typical L.A. resident will inhale from all school bus emissions in the area."

Not surprisingly, the highest levels of self-pollution were found with the two older buses, particularly when the windows were closed. The intake fraction for a 1975 model diesel bus measured 94 grams of pollution inhaled per million grams emitted, a level 3.4 times greater than average.

The newer model diesel buses are more representative of those found in current school bus fleets. But notably, a survey by School Bus Fleet magazine, a trade publication that tracks statistics in school transportation, finds that California has the highest percentage of pre-1977 school buses in the country. Ten percent of California’s fleet consists of pre-1977 buses, while second-place Missouri reports six percent of its fleet made up of pre-1977 buses. In comparison, 35 other states have no buses built before 1977 in use, and nine states have 1 percent or fewer pre-1977 buses in use.

Interestingly, the differences among the newer buses, including the one with the particle trap on the exhaust pipe and the one running on compressed natural gas, were inconsistent. A 1993 bus with windows closed had an intake fraction level of 10 per million, equivalent to the value for a trap-equipped bus with windows open.

The researchers said this may be because the exhaust is leaking into the cabin of the bus further up the system than the tailpipe, which is where the particle trap is located. Exactly how that exhaust is entering into the cabin is a subject of further study. "The broader message from this study is that there are many exposures to air pollution that are flying below the radar because they are not being picked up by our current air monitoring system," said William Nazaroff, a UC Berkeley professor of civil and environmental engineering who was not part of the study.

Diesel exhaust particulates are considered by public health officials to be a toxic air contaminant and a major source of cancer risk from outdoor air pollution. "Because so many children ride school buses, reducing the emissions of a school bus would give policymakers more bang for their buck than the same reduction of emissions from other diesel vehicles, such as an 18-wheeler or a construction truck," said Marshall.

Yet despite the findings, the researchers said that riding school buses is still safer than being driven to school in passenger vehicles and that parents shouldn’t yank their kids from bus ridership. "School buses are built like a tank, and the chances of children getting killed or seriously injured from a traffic accident in a private passenger vehicle are significantly greater than if they are on a bus," said Marshall.

This work was supported in part by the University of California Toxic Substances Research and Teaching Program and the University of California Transportation Center.

Sarah Yang | EurekAlert!
Further information:
http://www.berkeley.edu

More articles from Studies and Analyses:

nachricht Antarctic Ice Sheet mass loss has increased
14.06.2018 | Technische Universität Dresden

nachricht WAKE-UP provides new treatment option for stroke patients | International study led by UKE
17.05.2018 | Universitätsklinikum Hamburg-Eppendorf

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Temperature-controlled fiber-optic light source with liquid core

In a recent publication in the renowned journal Optica, scientists of Leibniz-Institute of Photonic Technology (Leibniz IPHT) in Jena showed that they can accurately control the optical properties of liquid-core fiber lasers and therefore their spectral band width by temperature and pressure tuning.

Already last year, the researchers provided experimental proof of a new dynamic of hybrid solitons– temporally and spectrally stationary light waves resulting...

Im Focus: Overdosing on Calcium

Nano crystals impact stem cell fate during bone formation

Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...

Im Focus: AchemAsia 2019 will take place in Shanghai

Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.

Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...

Im Focus: First real-time test of Li-Fi utilization for the industrial Internet of Things

The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.

Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.

Im Focus: Sharp images with flexible fibers

An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.

Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Munich conference on asteroid detection, tracking and defense

13.06.2018 | Event News

2nd International Baltic Earth Conference in Denmark: “The Baltic Sea region in Transition”

08.06.2018 | Event News

ISEKI_Food 2018: Conference with Holistic View of Food Production

05.06.2018 | Event News

 
Latest News

Graphene assembled film shows higher thermal conductivity than graphite film

22.06.2018 | Materials Sciences

Fast rising bedrock below West Antarctica reveals an extremely fluid Earth mantle

22.06.2018 | Earth Sciences

Zebrafish's near 360 degree UV-vision knocks stripes off Google Street View

22.06.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>