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SCHOOL BUSES

 

 

 

 

 

Children’s Exposure to Diesel Exhaust on School Buses

Children’s Exposure

to Diesel Exhaust

on School Buses

 

John Wargo, Ph.D.

YALE UNIVERSITY

STUDY DESIGN AND ANALYSIS:

John Wargo, Ph.D.

David Brown, Sc.D.

Environmental Research Institute,

University of Connecticut

 

EDITED BY:

Mark Cullen, M.D.

Susan Addiss, MPH, Murs

Nancy Alderman, MES

 

ENVIRONMENT AND HUMAN HEALTH, INC.

FEBRUARY 2002

 

Air Quality Monitoring and Analysis Provided by:

ENVIRONMENTAL RESEARCH INSTITUTE

UNIVERSITY OF CONNECTICUT

Kevin Hood, Michael Trahiotis, and Jared Yellen

 

Environment & Human Health, Inc.

1191 Ridge Road • North Haven, CT 06473

Phone: (203) 248-6582 • Fax: (203) 288-7571

www.ehhi.org

Copyright © 2002 Environment & Human Health, Inc.

 

 

 

Abstract

 

In the United States nearly 600,000 school buses transport 24 million students to school

daily. Each year buses travel 4.3 billion miles as children take nearly 10 billion school

bus rides. In Connecticut, 387,000 students ride to school each day on 6,100 buses. If

rides average 30 minutes in each direction, students will spend 180 hours on buses each

year. Collectively, U.S. children spend 3 billion hours on school buses each year.

 

Connecticut children annually spend more than 50 million hours on school buses.1

A vast majority of U.S. school buses are powered by diesel fuel. Diesel exhaust is

comprised of very fine particles of carbon and a mixture of toxic gases. Federal agencies

have classified diesel exhaust as a probable human carcinogen. Benzene, an important

component of the fuel and exhaust, is designated to be a known human carcinogen.

 

Components of diesel exhaust are genotoxic, mutagenic, and can produce symptoms of

allergy, including inflammation and irritation of airways. There is no known safe level

of exposure to diesel exhaust for children, especially those with respiratory illness.

 

The Centers for Disease Control and Prevention (CDC) estimates that 4.5 million U.S.

children have asthma. This figure includes nearly 44,500 school-aged children in

Connecticut diagnosed with the illness. Diesel exhaust can adversely affect children with

underlying respiratory illnesses such as asthma, bronchitis, and infections. Diesel

emissions may enhance the effects of some allergens among sensitive individuals.

Children’s airways are not yet fully developed and have a smaller diameter than those of

adults. If airways are inflamed or constricted by asthma, allergies or infections, diesel

exhaust may make breathing more difficult.

 

Fine particulate concentrations (PM2.5) measured on buses in this study were often

5-10 times higher than ave rage levels measured at the 13 fixed-site PM2.5 m o n i t o r i n g

stations in Connecticut. Levels of fine particles we re often higher under certain circ u m -

stances: when buses we re idling with windows opened, when buses ran through their ro u t e s

with windows closed, when buses moved through intense traffic, and especially when buses

we re queued to load or unload students while idling.

 

Children’s Exposure to Air Pollution on School Buses

This study concludes that the laws intended to control air pollution in the U.S. and

Connecticut must be strengthened to protect the health of children in several import a n t

respects. First, fixed monitoring facilities do not capture the variability in air pollution

experienced by children. Second, air quality indoors and within vehicles is not regulated by

E PA or the State of Connecticut, while Americans spend on average between 80-90% of

their time indoors. T h i rd, tougher diesel regulations adopted by EPA last year are

insufficient to protect health. Under the new provisions, they will be phased in between

2006-2010. This delay means that children may be exposed to increasing levels of diesel

exhaust for nearly a decade, as truck and bus traffic are likely to continue their steady rate

of increase. Fourth, Connecticut is already beyond compliance with federal air quality

standards for ozone, which may exacerbate respiratory illnesses. Given the limited

monitoring facilities and extended averaging periods allowed by current law, state

“c o m p l i a n c e” with federal standards offers little assurance of sufficient health pro t e c t i o n .

Fifth, routine emissions testing for school buses is not re q u i red by federal law, and school

buses are specifically exempted from testing in Connecticut. Sixth, Connecticut adopted

idling regulations, limiting idling time to 3 minutes, however, few know of the re s t r i c t i o n ,

and it is neither monitored nor enforced.

 

It is possible to reduce children’s exposure to diesel emissions immediately. We suggest

prohibition of bus idling, especially while loading and unloading students. Exposures could

also be reduced by limiting the amount of time students spend on buses. The dirtiest buses

should be identified by testing emissions and air quality within passenger compartments .

The cleanest buses could then be assigned to the longest routes.

 

These interventions would provide some relief, but additional steps are needed to protect the

respiratory health of children, and provide the “adequate margin of safety” re q u i red by the

Clean Air Act. The current fleet of diesel-powered buses should soon be retrofitted with

interior air filters, particle traps, catalytic converters, and be powered by ultra low sulfur

fuels. These strategies, if adopted together, would substantially reduce pollution levels in the

air students breathe on their way to and from school.

 

Children’s Exposure to Diesel Exhaust on School Buses

1. Diesel Buses: Each day, nearly 600,000 school buses transport 24 million students to

schools in the U.S. Within Connecticut, nearly 387,000 children ride 6,100 school

buses, and a vast majority are powered by diesel fuel.

 

2. Children’s Time on Buses: The time spent on buses by individual students varies

between 20 minutes and several hours per day. For one child, a half-hour ride to school,

and a half-hour ride home each day amounts to 180 hours per school year—90 full 24-

hour-days over 12 years of school. Annually, U.S. children spend 3 billion hours on

school buses. Connecticut children spend 50 million hours on buses each year.

 

3. Background Particulates: Connecticut background fine particulate matter levels (PM2 . 5)

a re near or above national standards, when averaged over 24 hours. Children’s exposure to

diesel exhaust from school buses constitutes an additional exposure beyond background

levels of particulates reported from current monitoring efforts.

4. Background Ozone: Connecticut is not in compliance with current federal ozone

standards. In 2001, portions of the state exceeded the 8-hour limit on 26 days, and the

1-hour limit was exceeded on 9 days. Ozone is known to exacerbate asthma, and is

normally highest in the afternoon, when children’s exposure to diesel particulates fro m

school bus rides is also likely to be high. NOx precursors to ozone have increased over the

past 10 years. In 2001, nearly 109 million people lived in 272 counties where federal ozo n e

limits we re exceeded.

5. Carcinogenicity of Diesel Exhaust: Diesel exhaust is classified as a probable human

carcinogen by many governmental authorities, including the International Agency

for Research on Cancer (WHO), the U.S. National Toxicology Program, the U.S.

Environmental Protection Agency, and as a known carcinogen by the State of

California. The California South Coast Air Quality Management District recently

estimated that nearly 71% of the cancer risk from air pollutants in the area is associated

with diesel emissions. Diesel exhaust includes benzene, 1,3-butadiene, and soot, all

classified as known human carcinogens. Nearly 33 studies have explored the association

between diesel exhaust exposure and bladder cancer. A recent meta analysis of this

literature found increased risk between 18-76%. These findings are based primarily

upon studies of truck drivers, railroad workers, bus drivers and shipyard workers.

Children’s Exposure to Diesel Exhaust on School Buses

Summary of Findings

 

6. Diesel Exhaust Contains 40 Hazardous Air Pollutants: In addition, diesel exhaust

contains both carbon particulates and 40 chemicals that are classified as “hazardous air

pollutants” under the Clean Air Act.

 

7. Particulates and Respiratory Diseases: Exposure to particulates has been associated

with: increased mortality among those with cardiopulmonary diseases; exacerbation of

symptoms for asthma, bronchitis, and pneumonia; decreased lung function; and

retarded lung development. It has also been correlated with increased hospital

admissions and emergency room visits for respiratory illnesses.

 

8. Children’s Susceptibility: Children may be especially susceptible to adverse respiratory

effects following exposure to fine-diameter particulate matter (PM2.5) emitted from

diesel engines. Nearly 94% of diesel particulates have diameters less than 2.5

micrometers (um).4 The average diameter of diesel particulates is 0.2 micrometers.

Smaller particles are able to penetrate children’s narrower airways reaching deeply

within the lung, where they are more likely to be retained. Higher rates of respiration

among child ren may lead to their higher exposure, when measured per unit of their

b o d y weight.

 

9. No Known Safe Ex p o s u re to Diesel Ex h a u s t : T h e re is no known safe exposure to diesel

exhaust for children, especially those with asthma or other chronic re s p i r a t o ry disease.

T h e re is no single standard for acceptable cancer risk from diesel exhaust in the U.S.

 

10. Asthma Prevalence: Nationally, 4.8 million children have asthma. More than 44,500

Connecticut school children have the disease.

 

11. Asthma Costs: Asthma costs an average of $500 per child per year for medications,

physician care, and hospital treatment. Annual direct medical costs are estimated to be

nearly $22 million for Connecticut school students alone. This estimate does not

account for other costs that often include school absenteeism, lost parental work while

caring for ill children, psychological effects, and abnormal social development.

 

12 . C h i l d re n’s Ex p o s u re to Particulates on Bu s e s : Children we re exposed to airborne

particulate concentrations in tested buses that we re sometimes 5-15 times higher than

b a c k g round levels of PM2 

 

Children’s Exposure to Diesel Exhaust on School Buses

13. Variability Within Buses: Particulate and black carbon levels vary within individual buses over

time. The most important influences on variability include: bus idling behavior, queuing

practices, bus ventilation via windows, and outdoor concentrations on bus routes. Particulate

and carbon concentrations did not vary by sampling location within diesel buses, e.g., front vs.

rear. Engine model, age of engine, number of miles since last overhaul, maintenance cycles,

location of bus engine (front, next to driver, or rear), elevation change, passenger load, and

climate may all influence levels of interior pollutants and children’s exposure.

 

14. Exhaust From Other Traffic: The intensity and type of traffic along bus routes significantly

affects air quality on buses. Buses following diesel-powered vehicles, including other buses, h a ve

i n c reased levels of carbon and particulate concentrations within passenger compart m e n t s .

Pa rticulate levels rose rapidly within the passenger cabin when buses pulled behind other diesel

vehicles in traffic. No buses tested had air filtration equipment capable of re m oving the fine

p a rticles detected in the buses.

 

15. Idling Buses: Idling buses tested had higher concentrations of particulates and

carbon than moving buses. Higher concentrations occurred when idling buses had

open windows when compared with buses with closed windows. There is a

current Connecticut Department of Environmental Protection (DEP) regulation,

DEP 22a-174-18 (a)(5), that limits idling time to 3 minutes, yet it is neither monitored nor

enforced.

 

16. Queued Idling Buses: Queued idling buses had the highest levels of particulates and black

carbon measured. Idling buses tend to accumulate diesel exhaust which may be retained during

the ride, depending upon bus ventilation rates. Particulate and carbon concentrations rise

rapidly once idling begins.

 

17. Length of Bus Route: The length of bus routes affects the magnitude of childre n’s exposure to

air pollutants in the interior compartment. Time in transit between home and school spent by

Connecticut students varied between 20-180 minutes per day in the towns sampled. The longest

routes may occur in the rural parts of the state, especially in large regional school districts.

18. Lower Emissions From Natural Gas Buses: Natural gas buses studied emitted 60-98% less

carbon than diesel-powered buses.

 

Children’s Exposure to Diesel Exhaust on School Buses

19. Findings Are Likely to Underestimate Exposure: Exposures to carbon and particulates

found in this study were measured in environments with exceptionally low traffic and

few other sources of pollution. Most children are exposed to additional pollution from

traffic and other residential, commercial and industrial activities. These findings

therefore are likely to underestimate levels of fine particulates and carbon found in

more urban areas and routes with higher traffic intensity.

 

20. Additional Sources of Particulate Exposure Threaten Children: Residential use of

tobacco products, wood stoves, candles, kerosene heaters, and poorly ventilated cooking

stoves are for many children additional sources of exposure to carbon-based particulates

and organic gases that result from combustion. Federal and state monitoring efforts fail

to account for these exposures despite the fact that most people spend more than 80%

of their time indoors. Most epidemiological studies that associate PM10 levels with

adverse respiratory health effects consider particles measured by outdoor stationary

monitoring facilities, neglecting indoor air exposures.

 

21. School Buses Are Exempt From Emissions Testing: School buses are currently exempt

from routine emissions testing in Connecticut.5 There is no federal requirement that all

state governments monitor school bus emissions, although some states require testing.

 

22. Federal Particulate Standards Exceeded: EPA estimates that in 2000, 11 million U.S.

children lived in areas that exceeded one or more federal air quality standard. Nearly

3.5 million children lived in areas where the particulate standards were exceeded in

1998. Within Connecticut, bus exposures when combined with background outdoor

particulate levels may elevate children’s average daily exposure beyond the current

federal 24-hour PM2.5 standard.

 

23. Absence of Passenger Cabin Air Quality Standards: Current law does not regulate air

quality within buses.

 

24. Federal Monitoring vs. Personal Monitoring: Federal law and regulation permit the

testing of air quality by means of fixed monitors. In Connecticut, 13 fixed monitors

measure PM2.5. This sampling design fails to capture the local variability and severity

of air pollution in the state. National standards permit averaging particulates over 24-

hour periods. These practices ensure that shorter episodes of intense pollution—such as

those experienced in bus rides—are neither recognized nor regulated by the state or

federal government.

 

Children’s Exposure to Diesel Exhaust on School Buses

25. Tougher Federal Diesel Standards Delayed Until 2006: Tougher new diesel emissions

standards will not be phased in until 2006. This delay poses respiratory health threats to

Connecticut citizens, who now experience air pollution at levels above acceptable

federal standards for ozone. Compliance with current standards does not ensure health

protection. EPA estimated that the new standards would result in 8,300 fewer

premature deaths, 17,600 fewer cases of childhood acute bronchitis, and 360,000 fewer

asthma attacks. These estimates demonstrate the scale of respiratory health threat EPA

believes exist under current conditions.

 

26. Federal Particulate Standards: The exposures identified in this study will not be

affected by the tougher federal PM standards adopted in 1997 (which are different from

the diesel standards described in 26 above), since monitoring to determine compliance

with the PM standards is done outdoors.

 

27. Bus Parking Yards: Bus parking and maintenance facilities have the potential to create

localized particulate air pollution that far exceeds ambient outdoor levels reported from

State monitoring efforts. Pollution may routinely migrate to adjacent properties, as

buses are left idling, or during periods of peak use—early mornings and afternoons. If

vehicles are parked near schools, both outdoor and indoor school air quality may be

diminished.

 

28. Bus Drivers: Bus drivers’ exposure to motor vehicle and diesel exhaust is significantly

higher than children’s, due to longer periods of time spent on buses.

Children’s Exposure to Diesel Exhaust on School Buses

Children’s Exposure to Diesel Exhaust on School Buses

 

 

RECOMMENDATIONS FOR THE FEDERAL GOVERNMENT

1. Retrofit Diesel Buses To Lower Emissions: The federal government should require the retrofit

of existing school buses with particle traps and catalytic converters designed to reduce

emissions. Retrofit of the existing fleet should be completed by 2003.

 

2. Require Buses to Use Ultra Low Sulfur Fuels: The federal government should require the use

of ultra low sulfur diesel fuel (<15 ppm) on school buses. The effect would be to substantially

reduce acid aerosols, ozone precursors, and fine particulate emissions in the immediate vicinity

of children.

 

3. Replace Bus Fleet With Low Emission Vehicles: The federal government should require and

provide financial support for eventual replacement of existing diesel fleets with low emission

vehicles, especially in areas of the country beyond compliance with current federal pollution

standards.

 

4. Test Tailpipe Emissions: The federal government should require periodic tailpipe emissions

testing of all school buses, unless they have been retrofitted with particulate traps and

converters, and use ultra low sulfur fuels.

 

5. Set Passenger Cabin Air Quality Standards: The federal government should establish health

protective standards for air quality within vehicles. Standards should provide an ample margin

of safety for children.

 

6. Re q u i re School Bus Air Fi l t ration Equipment: The federal government should re q u i re the design

and installation of air filtration equipment capable of re m oving vehicle exhaust from air entering

bus passenger cabins. This is especially important when buses travel in areas with high traffic

i n t e n s i t y, or high outdoor background concentrations of pollutants such as urban environments.

 

7. Federal Standards Should Assume Indoor and Vehicular Exposures: EPA should adjust

outdoor air quality standards to account for probable indoor and within-vehicle exposures to

air pollution. The Clean Air Act demands that standards be set to provide “an adequate margin

of safety,” yet governments’ neglect of particulate levels within homes, schools, and vehicles

makes it impossible to conclude that current standards protect health.

 

8. Expand Air Quality Monitoring Network: The federal government should require states to

develop air quality monitoring programs that capture variability in regulated air pollutants.

The existing stationary monitoring network should be supplemented with both additional

s t a t i o n a ry sources, and with personal monitoring data collection to better understand va r i a b i l i t y

in exposure, especially among susceptible populations.

 

Children’s Exposure to Diesel Exhaust on School Buses

RECOMMENDATIONS FOR STATE GOVERNMENTS

1. Prohibit School Bus Idling: Idling should be restricted by State law. Bus drivers should

be required to turn off bus engines immediately upon reaching their destinations. Buses

should not be turned on until fully loaded. This is especially important when buses are

queued while loading and unloading at schools and transfer stations. Exceptions should

include conditions that would compromise passenger safety—e.g., extreme weather

conditions, idling in traffic. In cases where engine operation is necessary to activate safety

equipment such as flashing lights, buses should be retrofitted to permit battery operation.

Idling restrictions should be defined by state statute and include enforcement power, rather

than by the present DEP regulation 22a-174-18 (a)(5).

 

2. Retrofit Diesel Buses To Lower Emissions: The State should plan and implement a

school bus retrofit program to ensure that buses are refitted with particle traps and

catalytic converters designed to reduce emissions. Retrofit of the existing fleet should be

completed by 2003.

 

3 . Re q u i re School Buses to Use Ul t ra Low Sulfur Fuels: The state should facilitate and monitor

the suggested federal requirement that school buses use low sulfur diesel fuel ( < 1 5

ppm).

 

4. Replace Bus Fleet With Low Emission Vehicles: The state should work with federal

agencies (EPA, DOE, DOT) to plan for the replacement of the existing diesel fleet with

new low-emission and alternative-fueled vehicles.

 

5. Set Priorities to Reduce Emissions and Exposure: The State should plan for, guide,

and set priorities to retrofit buses and convert to ultra low sulfur fuels. Priority should

be assigned to communities with the poorest outdoor air quality. Within communities,

priority should be assigned to the routes that have highest traffic intensity.

 

6. Require Routine Maintenance: The State should require that routine maintenance be

conducted to ensure that emissions remain at their lowest possible level. Special care

should be taken to be certain that exhaust systems are fully intact and secure, and that

engine compartments are completely sealed from interior passenger space.

 

7. Test Tailpipe Emissions: The State should be responsible for periodic tailpipe emissions

testing of all school buses.

 

8. Expand PM2.5 Monitoring Network: The State should substantially expand its

monitoring network to more fully capture local variability of air pollutants.

Children’s Exposure to Diesel Exhaust on School Buses

 

1. Prohibit Bus Idling: Local governments and school districts should immediately

adopt policies that require drivers to turn off bus engines upon reaching their

destinations. Buses should not be turned on until fully loaded. This is especially

important when buses are queued while loading and unloading at schools and transfer

stations. Exceptions should include conditions that would compromise passenger

safety—e.g., extreme weather conditions, idling in traffic. In cases where engine

operation is necessary to activate safety equipment such as flashing lights, buses

should be retrofitted to permit battery operation. School districts should inform

drivers about the effects of idling on both indoor and outdoor air quality. This idling

restriction will improve air quality within buses, and in the vicinity of schools.

 

2. Adjust Contract Provisions to Lease Retrofitted Vehicles and Require Clean Fuels:

School districts should adjust their contracts with bus service companies and fuel

providers to require the use of ultra low sulfur fuels, particle traps and catalytic

converters, without waiting for federal or state requirements to take effect.

 

3. Set Priorities: School districts and local governments should allocate buses with the

lowest emissions to the longest routes.

 

4. Limit Ride Duration: School districts should reduce students’ exposure to air

pollution by limiting time spent on buses. This is already regulated by some town

policies. Limiting ride duration would reduce exposure to pollution generated by

diesel buses, and by other traffic.

 

5. Require Routine Maintenance: Local governments should ensure that buses are

monitored and maintained so that emissions remain at their lowest possible level.

Special care should be taken to be certain that exhaust systems are fully intact and

secure, and that engine compartments are completely sealed from interior passenger

space. Maintenance requirements to ensure health protective air quality should

become a routine contract provision between bus companies and local governments.

 

6. Reconsider Location of Bus Parking Lots: Local governments should consider

whether the location of bus parking facilities contribute to routine air pollution in the

vicinity of schools, playgrounds, and residential areas. Some relief may be provided by

setting limits on bus idling within parking lots.

 

 

 

 

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