Best Practices for Reducing
Near-Road Pollution
Exposure at Schools
November 2015
oEPA
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Best Practices for Reducing
Near-Road Pollution
Exoosure at Schools
SEPA
U.S. Environmental Protection Agency
EPA would like to acknowledge the following organizations
that provided comments on an earlier draft of this document:
South Coast Air Quality Management District
Southern California Green, Clean and Healthy Schools Partnership
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Contents
Introduction 1
Reducing Near-Road Pollution Exposure at Schools 2
Near-Road Air Pollution and Children's Health 2
How Can Near-Road Pollution Exposure Be Reduced in Schools? 3
Building Design and Operation Strategies for Reducing
Near-Road Pollution Exposure 3
Ventilation, Filtration, and Indoor Air Quality in Schools 3
Passive/Natural Ventilation 4
Mechanical Ventilation 4
Filtration 5
Actions for Building Occupants 7
Summary 8
Site-Related Strategies for Reducing Near-Road Pollution Exposure 9
Transportation Policies 9
Establish Anti-Idling and Idle Reduction Policies 9
Upgrade Bus Fleets 9
Encourage Active Transportation 10
Site Location and Design 10
Roadside Barriers 12
Sound Walls 12
Vegetation 13
Summary of Recommendations 14
School Ventilation and Filtration System Assessment 15
Additional Resources.. ,. 16
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Introduction
Purpose of This Publication
This publication can help school communities identify
strategies for reducing traffic-related pollution
exposure at schools located downwind from heavily
traveled roadways (such as highways), along corridors
with significant trucking traffic, or near other traffic or
vehicular pollution sources. Many of these strategies
are already being used by schools across the country
to reduce exposures to traffic-related air pollution.
We hope that this compilation of best practices will
help other schools that want to take steps to address
concerns about traffic-related pollution exposure.
Many of the best practices outlined in this publication
may also be effective in reducing exposure at schools
near other sources of particulate air pollution, such as
rail yards, ports, and industrial facilities.
Contact your state or local air pollution agency
for assistance in evaluating the impacts, if any, that
traffic-related air pollution may have on your school.
EPA's School Siting Guidelines also include information
on evaluating impacts of nearby sources of air
pollution. Evaluating the potential impact of traffic-
related air pollution may be performed as part of an
overall environmental evaluation for your school.
Intended Audience
This publication was designed for school
administrators, facility managers, school staff,
school nurses, school-based health centers, parents,
students, and others in the school community who
are concerned about traffic-related air pollution
exposure due to a school's proximity to a heavily
traveled roadway or trucking corridor and who
want to understand potential approaches to
reduce exposures. Other audiences that may find
this resource applicable to their work include
community-based environmental and health
organizations; HVAC professionals, architects,
design engineers, and construction contractors who
can apply the principles of this document during
facility siting, design, and construction; and other
federal, state, local, and tribal agencies.
Other EPA Resources for
Schools
The EPA website (www.epa.gov/schools) offers many
documents and tools to help states, districts, schools,
teachers, parents, and students create or enhance
productive and healthy learning environments.
These resources address a broad range of issues that
affect children's health in schools, from selecting
appropriate locations for schools to maintaining the
buildings and grounds. Some of these resources
may address strategies that are discussed in this
publication. You can use these comprehensive
resources to assess your school's environmental
health efforts and implement or improve related
programs, policies, and procedures. If you have
questions about EPA's resources for schools, contact
your regional school coordinator.
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Reducing Near-Road Pollution
Exposure at Schools
Exposure to traffic-related air pollution has been linked
to a variety of short- and long-term health effects,
including asthma, reduced lung function, impaired
lung development in children, and cardiovascular
effects in adults. Children's exposure to traffic-related
air pollution while at school is a growing concern
because many schools are located near heavily traveled
roadways. This document briefly introduces the health
risks associated with traffic-related pollution exposure
and offers strategies to reduce students' exposure in
new and existing schools.
Near-Road Air Pollution and
Children's Health
Pollutants directly emitted from cars, trucks, and other
motor vehicles are found in higher concentrations
near major roads. Examples of directly emitted
pollutants include particulate matter (PM), carbon
monoxide, oxides of nitrogen, and benzene, though
hundreds of chemicals are emitted by motor vehicles.
Motor vehicles also emit compounds that lead to
the formation of other pollutants in the atmosphere,
such as nitrogen dioxide, which is found in elevated
concentrations near major roads, and ozone, which
forms further downwind. Beyond vehicles' tailpipe and
evaporative emissions, roadway traffic also emits brake
and tire debris and can throw road dust into the air.
Individually and in combination, many of the pollutants
found near roadways have been associated with
adverse health effects.
Studies show that concentrations of
traffic-related air pollutants can be elevated
inside classrooms, and that traffic is one of the
most significant sources of air pollution in both
the indoor and outdoor school environments.
Motor vehicle pollutant concentrations tend to be
higher closer to the road, with the highest levels
generally within the first 500 feet (about 150 meters)
of a roadway and reaching background levels within
approximately 2,000 feet (about 600 meters) of a
roadway, depending on the pollutant, time of day, and
surrounding terrain.1 Many scientific studies have found
that people who live, work, or attend school near
major roads appear to be more at risk for a variety of
short- and long-term health effects, including asthma,
reduced lung function, impaired lung development in
children, and cardiovascular effects in adults.
Children are particularly susceptible to health
problems resulting from air pollution exposure due to:
Respiratory systems that are not fully
developed. Studies show exposures to air
pollution in childhood can result in decreased
lung function.2
Higher rates of exposure than adults because they
are more active and they breathe more rapidly.
Children spend a lot of time at school, and nearly
17,000 schools in rural and urban areas across the
U.S. are located within 250 meters (~820 feet) of a
heavily traveled road.3 Exposure to traffic-related
pollution is a concern both indoors and outdoors
1Karner, A. A., Eisinger, D. S.; & Niemeier, D. A. (2010). Near-roadway air quality: Synthesizing the findings from real-world data. Environmental Science & Technology, 44(14), 5334-5344.
doi:10.1021/es!00008x
2 Health Effects Institute. (2010). Traffic-related air pollution: A critical review of the literature on emissions, exposure, and health effects. Special Report 17. Available at http://pubs.
healtheffects.org/view.php?id=334
3Kingsley, S. L, Eliot, M. N., Carlson, L, Finn, J., Macintosh, D. L, & Suh, H. H. (2014). Proximity of US schools to major roadways: A nationwide assessment. Journal of Exposure Science and
Environmental Epidemiology, 24, 253-259. doi:10.1038/jes.2014.5. This study defines major roadways as those with a Census Feature Class Code classification of Al (primary road with
limited access or interstate highway) or A2 (primary road without limited access).
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concentrations tend to be higher outdoors, yet
numerous studies have found that concentrations of
traffic-related pollutants can also be elevated inside
classrooms, where children spend most of the school
day.4'5 In addition, diesel-powered school buses can
be a significant source of pollution near schools.
How Can Near-Road Pollution
Exposure Be Reduced in
Schools?
Over the past several decades, emission control
technologies and regulations have led to large
decreases in emissions per vehicle. Pollutant
concentrations have also declined, though at a
slower rate, because there has been growth in both
the number of vehicles and vehicle miles traveled.
Government and industry are still working to reduce
the amount of pollutants emitted by motor vehicles.
In the meantime, several strategies are being used
by communities and schools across the country to
reduce traffic-related pollution exposure. Some of
these strategies aim to reduce indoor exposure at
the individual building level, while others target
reductions indoors and outdoors on a larger scale.
Given the importance of PM in general, and diesel
PM specifically as a harmful pollutant, the focus of
this document is on strategies that can be used to
mitigate PM exposure, although some techniques
may be applicable to gaseous pollutants (e.g.,
carbon monoxide, benzene) as well. This document
addresses the following mitigation strategies that
can be implemented by local school authorities:
ventilation, filtration, actions for building occupants,
transportation policies, site location and design, and
the use of roadside barriers. Many of these strategies
may also be effective at reducing exposure at schools
near other sources of particulate air pollution (e.g.,
railyards, industry) and near facilities that have
increased truck and car traffic (e.g., warehouses, ports).
In planning, implementing, and evaluating mitigation
strategies, it may be valuable to assemble a diverse
project team that is committed to ensuring a healthy
environment for children and staff.6
Elevated PM concentrations
in Schools have been linked to:
Poor ventilation;
Ineffective or nonexistent air filtration;
Proximity to roadways;
Open windows and doors allowing entry of
polluted outdoor air during rush hours;
Infrequent and incomplete cleaning of indoor
surfaces; and
High occupancy levels.7-8
Building Design and
Operation Strategies for
Reducing Near-Road
Pollution Exposure
Ventilation, Filtration, and Indoor
Air Quality in Schools
Proper building ventilation is crucial for maintaining
healthy indoor air quality. Ventilation in schools is
achieved passively (e.g., via open windows and doors)
or mechanically by a building's heating, ventilating,
and air conditioning (HVAC) system.
4Mejia, J. F.; Choy, S. L, Mengersen, K.; & Morawska, L. (2011). Methodology for assessing exposure and impacts of air pollutants in school children: Data collection, analysis and health
effects - A literature review. Atmospheric Environment, 45(4), 813-823. doi:10.1016/j.atmosenv.2010.il.009
5 Mullen, N. A., Bhangar, S., Hering, S. V., Kreisberg, N. M., & Nazaroff, W. W. (2011). Ultrafine particle concentrations and exposures in six elementary school classrooms in northern
California. Indoor Air, 21(1), 77-87. doi:10.1111/j.l600-0668.2010.00690.x
5 For more information on developing a project team, see EPA's Energy Savings Plus Health guidelines (Appendix A). U.S. Environmental Protection Agency. (2014). Energy savings plus
health: Indoor air quality guidelines for school building upgrades. Available at http://www.epa.gov/iaq/schools/pdfs/Energy Savings Plus Health Guideline.pdf
7 Stranger, M., Potgieter-Vermaak, S. S., & Van Grieken, R. (2008). Characterization of indoor air quality in primary schools in Antwerp, Belgium. Indoor Air, 18(6), 454-463.
"McCarthy, M. C, Ludwig, J. F., Brown, S. G., Vaughn, D. L., & Roberts, P. T. (2013). Filtration effectiveness of HVAC systems at near-roadway schools. Indoor Air, 23(3), 196-207. doi:10.1111/
ina.12015
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Studies have shown that in addition to reducing
health effects related to air pollution exposure,
proper ventilation contributes to a comfortable
learning environment associated with better test
scores and attendance.9
However, improved ventilation does not always
improve air quality. For example, if filtration is not
used, higher ventilation rates can increase pollutant
levels indoors if outdoor pollutant concentrations are
higher than indoor concentrations.
Passive/Natural Ventilation
In passive or natural ventilation systems, air is supplied
to a classroom through open windows or doors or
by leaks in the building envelope (e.g., gaps around
windows and doors). Passive systems rely on dilution
of indoor air contaminants by mixing indoor air
with outdoor air. This approach is only effective if
the outdoor air is less polluted than the indoor air.
It is often challenging to achieve proper ventilation
using passive methods because assessing ventilation
needs and outdoor air quality, as well as controlling
ventilation rates, can be difficult for building occupants
to carry out. Strategies for reducing pollution exposure
in naturally ventilated classrooms include reducing
indoor sources of air pollution and, at schools near
heavily traveled roads, timing air intake (i.e., opening
and closing doors and windows) to avoid bringing in
outdoor air during peak travel times (see Actions for
Building Occupants section for more information).
Additionally, there are filtration-related options for
schools with passive systems, which are described in
the sections that follow.
Recommendations
Keep windows and doors closed during peak
traffic times (e.g., morning and evening rush
hours).
Minimize indoor sources of air pollution.
Use a stand-alone filtration unit or upgrade to
a mechanical ventilation system.
Mechanical Ventilation
In mechanical ventilation systems, air is circulated
through a building by air intake and/or exhaust
fans. Mechanical systems used in schools can be
grouped into two categories: units that serve a single
room without air ducts (such as a unit ventilator
or individual heat pump) and central air handling
units that serve multiple rooms via ductwork. The
effectiveness of mechanical ventilation depends
on HVAC system type, design, maintenance, and
operation. An imbalance in a building's HVAC system
can result in the building becoming pressurized.
Negative pressure can allow outdoor contaminants
to enter the building through the building envelope,
while positive pressure prevents infiltration of
outdoor air but can force moisture into the walls
of the building. In cold climates, moisture can
condense in walls and promote mold growth.
Therefore, pressure relief dampers that allow air to
exit the building or exhaust fans that draw air out are
typically recommended.
The U.S. Environmental Protection Agency (EPA)
recommends10 that central HVAC air handling units
be used when possible, as they are often quieter (and
therefore less likely to be turned off), easier to maintain
because of the reduced number of individual units, and
compatible with higher efficiency filtration.
While central units typically achieve higher air
exchange rates and therefore better indoor air
9Mendell, M. J.; & Heath, G. A. (2005). Do indoor pollutants and thermal conditions in schools influence student performance? A critical review of the literature. Indoor Air, 15(1), 27-52.
10 U.S. Environmental Protection Agency. (2012). Heating, ventilation and air-conditioning (HVAC) systems. Available at www.epa.gov/iaq/schooldesign/hvac.html
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quality, the necessary ducting and registers tend to
increase system cost. Ductwork in central ventilation
systems should be kept clean and tested regularly
for leaks. Regardless of the type of system used,
mechanical ventilation systems are typically more
reliable than natural methods because airflow rates
are controllable.
Recommendations
Use mechanical ventilation if possible. Central HVAC
units that serve multiple classrooms are typically
more effective than single-room unit systems.
In classrooms where sufficient mechanical
ventilation can be ensured, seal the building
envelope to prevent infiltration of polluted air
through cracks around windows, doors, and
HVAC ducts.
With a properly performing mechanical
ventilation system, keep windows and
doors closed to avoid bringing in polluted
outdoor air.
Ensure that HVAC systems are properly
maintained and operated.
Locate air intakes away from roadways, bus idling,
drop-off zones, and other pollutant sources, such
as designated smoking areas.11
Effective air distribution;
Careful placement of air inlet and outlet
locations; and
Regular maintenance, including replacement
of filters.
Filtration has some practical limitations. Filtration is
only effective at removing particles that enter the
system through an outside air intake and particles
that enter through the return air ducts usually
located at ceiling level. Particles entering the school
through other pathways may not be removed (for
instance, particles entering the classroom through
open doors or windows, through leakage in the
building envelope, from indoor sources, or from
re-suspension from floors). In addition, removal
of gaseous pollutants by filtration is typically less
effective than particle removal; filters that are able
to remove gaseous pollutants are costly and are not
commonly used in schools.
Indoor air filtration is typically incorporated into a
building's HVAC system, although portable, stand-
alone air cleaners are also available. Both system
types typically employ filters that remove air
contaminants based on particle size.13
Schools undertaking energy
efficiency upgrade projects may wish to
consider concurrent opportunities to improve
indoor air quality.14
Filtration
Although diluting air contaminants through ventilation is
sometimes adequate, many buildings (including schools)
require additional air treatment to achieve suitable
indoor air quality. Studies have shown that filtration
in schools can improve indoor air quality by reducing
particle concentrations by as much as 97% relative to
outdoor levels.12 Achieving maximum performance of
filtration systems requires:
Proper installation;
Continuous operation;
A tight building envelope (i.e., minimal air leaks);
uThe Centers for Disease Control and Prevention recommends that schools prohibit all tobacco use at all school facilities and events at all times. See http://www.cdc.gov/healthyschools/
tobacco for more recommendations on tobacco use prevention through schools.
"McCarthy, M. C, Ludwig, J. F., Brown, S. G., Vaughn, D. L, & Roberts, P. T. (2013). Filtration effectiveness of HVAC systems at near-roadway schools. Indoor Air, 23(3), 196-207. doi:10.1111/
ina.12015
13 Some portable, stand-alone air cleaners use alternate technologies to remove contaminants, such as electrostatic precipitators. While effective at removing particles, electrostatic
precipitators tend to be more expensive than traditional filters, require more maintenance overtime, and can generate small amounts of ozone as a by-product of air purification. In
addition, some air cleaners are designed to intentionally generate ozone and are not recommended. The California Air Resources Board maintains a list of air cleaning devices tested and
certified by the State of California to meet California's electrical safety and ozone emission requirements. See http://www.arb.ca.gov/research/indoor/aircleaners/certified.htm
14 U.S. Environmental Protection Agency. (2014). Energy savings plus health: Indoor air quality guidelines for school building upgrades. Available at http://www.epa.gov/iaq/schools/energy_
savings plus health.html
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The degree of indoor air quality improvement from
filtration depends on the filter's Minimum Efficiency
Reporting Value (MERV) rating. Filters with MERV
ratings from 1 to 4 are effective at removing large
particles (e.g., pollen, dust mites, paint dust), but
are less effective at removing small, traffic-related
particles that can enter the respiratory system and
cause adverse health effects. Filters with higher MERV
ratings are increasingly more effective at removing
very small particles.
Studies examining filtration systems in schools have
found that all types of filtration systems improve
air quality conditions inside classrooms and can be
used to reduce exposure to traffic-related pollutants
indoors. Central HVAC systems equipped with
filters tend to be more effective than unit systems
(e.g., window units) with filters. In schools with
central HVAC systems, medium-efficiency filters
(MERV 6-7) tend to reduce particle concentrations
by approximately 20% to 65%, while higher
performance filters (MERV 11-16) can reduce particle
concentrations from 74% to 97% relative to outdoor
concentrations.15 Higher MERV ratings are generally
associated with higher particle removal rates. Stand-
alone systems, although slightly less effective, are
well-suited for classrooms that are not equipped
with a central HVAC system and can achieve removal
In a pilot study of high-
performance filtration in schools,
the South Coast Air Quality Management
District found that the combined use of
register-based and high-performance panel
filters was most effective at reducing particle
concentrations, with reductions of 87-96%,
while the use of the high-performance panel
filter alone reduced particle concentrations
by close to 90%.15
efficiencies close to 90%.17 However, performance
depends on the amount of air that can be processed
by the unit and other classroom layout features
that influence airflow to the system. A downside of
some stand-alone units is that they can be noisier
than HVAC-based filtration. However, quieter stand-
alone units are available that meet the noise level
requirements for new classroom equipment.18
It is important to maintain HVAC filtration
performance through regular maintenance
and proper HVAC system operation. Excessive
depressurization can be avoided by routine cleaning
and filter replacement as necessary. Monitoring
the system pressure can help identify when
filter replacement is needed and can maximize
performance, minimize energy costs, and prevent
early disposal of useful filters. Inexpensive pre-filters
can be used to remove a majority of particle mass
and extend the life of the more expensive main filter.
Filter performance and lifetime can also be improved
by locating outdoor air intakes away from potential
pollution sources so that cleaner air is drawn into
the system.
Some schools may be able to incorporate high-
efficiency filtration into their existing HVAC system.
However, not all HVAC systems are compatible
with high MERV-rated filters. In some systems, the
addition of a high MERV-rated filter can result in
"McCarthy, M. C, Ludwig, J. F., Brown, S. G., Vaughn, D. L, & Roberts, P. T. (2013). Filtration effectiveness of HVAC systems at near-roadway schools. Indoor Air, 23(3), 196-207. dor.10.llll/
ina.12015
"Polidori, A., Fine, P. M., White, V, & Kwon, P. S. (2013). Pilot study of high-performance air filtration for classroom applications. Indoor Air, 23(3), 185-195. doi:10.1111/ina.12013
17Polidori, A., Fine, P. M., White, V, & Kwon, P. S. (2013). Pilot study of high-performance air filtration for classroom applications. Indoor Air, 23(3), 185-195. doi:10.1111/ina.12013
18 Polidori, A., Fine, P. M., White, V, & Kwon, P. S. (2013). Pilot study of high-performance air filtration for classroom applications. Indoor Air, 23(3), 185-195. doi:10.1111/ina.12013
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a large drop in system pressure. The magnitude
of the pressure drop varies by filter type and not
all high-efficiency filters result in a large drop in
pressure. For example, the South Coast Air Quality
Management District's school air filtration program
uses high-performance panel filters that have air
resistance properties similar to conventional filters,
do not require the use of a pre-filter, and do not
reduce airflow through the HVAC system. In addition,
these filters have longer lifespans than the medium-
efficiency MERV filters typically in use, requiring
replacement approximately once per year rather than
every four months.19 Depending on the HVAC system,
installing the highest MERV-rated filter that the
current system can handle may be a cost-effective
way to improve indoor air quality. In other cases,
improving or replacing the existing HVAC system
may be required to achieve the pumping capacity
necessary to accommodate high-efficiency filtration
because of limited airflow.
Capital and/or increased operating costs may pose
limitations to these improvements; however, potential
savings associated with any system upgrades should
also be considered. For example, the cost of purchasing
an air sensor to monitor ventilation needs, and thereby
help optimize ventilation rates, could offset long-term,
higher energy costs due to over-ventilation.
Recommendations
For classrooms relying on passive/natural
ventilation, use quiet, portable, stand-
alone filtration systems to reduce indoor
concentrations.
For schools with mechanical ventilation
systems, use high-efficiency filtration to
reduce particle pollution exposure inside
classrooms.
Upgrade filtration to the highest MERV-rated
filters that the HVAC system can handle.
Consider HVAC system upgrades to
accommodate high-efficiency filtration, including
the installation of pre-filters, if necessary.
Inspect and replace filters regularly according
to manufacturer recommendations.
Where possible, locate air intakes away from
pollution sources.
Actions for Building Occupants
The actions of building occupants can greatly affect
near-road pollution exposure indoors. For instance,
opening windows or doors for ventilation in classrooms
can allow polluted air to enter into the classroom
and overwhelm the air quality benefits of an HVAC
filtration system. Keeping windows and doors closed
is especially important during periods of peak traffic
(e.g., morning and evening rush hours) when near-road
pollutant concentrations are typically highest. Although
the classroom is a noise-sensitive environment, it
is important that HVAC systems are not turned off
during the day.
For naturally ventilated classrooms, there may be
opportunities to time air intake to avoid bringing in
outdoor air during peak concentration times.
Although the focus of this document is traffic-related
pollution exposure, it is important to note that indoor
sources can largely impact (or even dominate) indoor
concentrations of PM and gaseous pollutants. Indoor
"Polidori, A., Fine, P. M., White, V., & Kwon, P. S. (2013). Pilot study of high-performance air filtration for classroom applications. Indoor Air, 23(1), 185-195. doi:10.1111/ina. 12013
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sources include combustion sources, secondhand
smoke, dust from student activity (PM), and (gaseous)
emissions, such as from building materials, furniture,
carpets, air fresheners, personal care products,
biologically derived emissions from mold and bacteria,
and classroom supplies (e.g., dry erase markers and
some cleaners).
Exposure outdoors may be reduced by carefully timing
outdoor activities to avoid times of peak pollution.
Ozone pollution is often worse on hot, sunny days,
especially during the afternoon and early evening.
Particle pollution can be high anytime of day, but higher
levels can be found near idling cars, trucks, and buses
and near busy roads, especially during rush hour. If
possible, plan strenuous outdoor activities outside of
rush hour and drop-off/pick-up times, and consider
locating activities farther from roads and loading zones.
In addition, many schools implement the Air Quality
Flag program to raise awareness of the daily air quality
forecast. The school flags, combined with information
on current air quality from www.airnow.gov, can be
used to help plan outdoor activities.
Raising awareness about indoor and outdoor air quality
issues and providing training for staff on optimal
building operating practices (including HVAC operation)
specific to the design of their school are inexpensive
strategies that can supplement upgrades to the
ventilation and filtration system and building and site
design. EPA's IAQ Tools for Schools program provides
an easy-to-use framework and set of tools to train
staff on indoor air quality (IAQ) management (www.
epa.gov/iaq/schools). Training is recommended as a
complementary strategy and should not be considered
an alternative to ventilation upgrades.
Recommendations
Train teachers and school staff on best ventilation
practices, including:
Keeping windows and doors closed in
mechanically ventilated classrooms to prevent
entry of polluted outdoor air.
Keeping windows and doors closed in
naturally ventilated classrooms during peak
commute times.
Keeping HVAC systems turned on throughout
the day.
Keeping air vents clear of items that may
block airflow.
Understanding the importance of indoor
pollutant sources and how to reduce
emissions from indoor sources.
Plan strenuous outdoor activities during times
with lower amounts of traffic.
Summary
Ventilation and filtration needs vary by school
according to occupancy, proximity to roadways or
other pollutant sources, and the prevalence of indoor
sources. School administrators can improve indoor air
quality by modifying ventilation and filtration systems,
yet it can be difficult to identify which strategies will
yield the most significant improvements for the level
of effort and cost required.
To evaluate which (if any) actions may be needed
to help reduce exposure to traffic-related pollution,
school staff can begin by making a preliminary
assessment. A brief guide to assist in the assessment
of a school ventilation and filtration system is
provided on page 15. Once a baseline assessment of
the current ventilation system is complete, mitigation
strategies suitable for the system can be evaluated.
Table 1 offers mitigation strategies for different types
of ventilation systems typically found in classrooms.
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Table 1. Ventilation systems versus mitigation strategies. HVAC/ventilation system types are listed from
generally less effective to more effective, and mitigation strategies are listed from the simplest (and least
costly) to implement to those that require a higher level of effort.
HVAC/Ventilation
Type Educate
Mitigation Strategies
Passive/natural
Single-classroom
HVAC unit (e.g.,
window unit)
Central HVAC system
serving multiple
classroomshigh-
efficiency filtration
use limited by airflow
Central HVAC system
serving multiple
classroomshigh-
efficiency filtration
use not limited by
airflow
c+ tt Air-Seal Building Improve Air Intake Use Filtration Upgrade System
jtdTT II II
May be an option if
adequate ventilation
to dilute and
remove pollutants
from indoor sources
Avoid bringing in air
during periods of high
traffic
Avoid airflow
obstructions
Use quiet systems
Change air intake
locations if near
pollution source(s)
(e.g., roadway, drop-off
zone, parking)
Change air intake
locations if near
pollution source(s)
(e.g., roadway, drop-off
zone, parking)
Use a portable
stand-alone
filtration system
Use highest
compatible
MERV-rated filter
Use pre-filters or
high-performance
panel filters
Use highest
compatible
MERV-rated filter
Use pre-filters or
high-performance
panel filters
UseMERV16+
filter
Use pre-filters
Switch to a
mechanical
ventilation method
Upgrade to a
central HVAC
system
Modify airflow to
be compatible with
higher efficiency
filtration
N/A
Site-Related Strategies for
Reducing Near-Road Pollution
Exposure
Transportation Policies
Establish Anti-Idling and Idle Reduction Policies
Bus operation and idling can produce large amounts
of PM and other air pollutants. Some schools have
instituted anti-idling or idle reduction policies
to reduce the impact of pollution from buses
and passenger vehicles near schools. Anti-idling
policies can result in large decreases in particle
concentrations, particularly at schools operating
multiple diesel school buses.
Upgrade Bus Fleets
Pollution from school buses can also be reduced by
upgrading bus fleets. Fleet turnover for diesel school
buses is low, with buses typically operating for 20 to 30
years. Older buses emit high levels of PM and other air
pollutants. However, technological advances and tighter
PM emissions standards for new buses, set by EPA, have
resulted in new buses (manufactured during or after
2007) that are 60 times cleaner than buses produced
prior to 1990. Emissions can be reduced by retrofitting
older school buses with PM filters or oxidation catalysts,
or by replacing older buses with newer models.
Emissions may be reduced by using certain alternative
fuels, including biodiesel blends. Engines certified to
operate on alternative fuels such as liquid petroleum
gas (LPG), compressed natural gas (CNG), and liquefied
natural gas (LNG) can also reduce emissions. Discuss
potential funding options for bus fleet upgrades with
your state or local environmental or air quality agency20
20 U.S. Environmental Protection Agency. (2010). Clean school bus. Available at http://www.epa.gov/cleandiesel/sector-programs/csb-overview.htm
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Encourage Active Transportation
Promoting active transportation, such as walking and
bicycling to and from schools, can help reduce traffic-
related pollution by reducing the number of buses
and passenger vehicles nearby. For example, the
addition of walking/biking paths at Roosevelt Middle
School in Eugene, Oregon, reduced traffic volumes
near the school by 24%.21
While active transportation may contribute to
improved air quality near schools, students walking
or biking to school may be exposed to roadway
pollution and other traffic hazards because of
their proximity to motor vehicle traffic. When safe
alternatives exist, biking and walking to school along
routes with lower traffic volumes may help reduce
exposure to pollution and safety hazards.22
Parallel and off-street walking/biking paths through
parks or other off-road areas can also provide a
good alternative to traveling along a road with many
motor vehicles. Pursuing pedestrian and bicycle
infrastructure improvements can help provide safer
routes for students to walk and bike to school. This
could include installing or improving sidewalks,
crosswalks, signs, markings, and countdown timers,
as well as encouraging "walking" school buses.23
When considering walking and biking routes to
school, impacts on safety, lighting, access, and
maintenance requirements should be considered. The
Safe Routes to School National Partnership provides
many resources on promoting safe walking and
biking (www.saferoutespartnership.org).
Despite the potential for increased exposure
associated with active transportation, walking and
biking have been shown to improve health, and
people who live in highly walkable neighborhoods
are generally more physically active than those who
live in less walkable neighborhoods. Promoting
walking and biking to school along routes or paths
with lower traffic volumes (relative to other roads)
will increase the likelihood that the health benefits
of exercise outweigh the health risks associated with
increased air pollutant exposures.
Recommendations
Limit school bus idling by instituting anti-
idling or idle reduction policies.
Upgrade school bus fleets by:
- Retrofitting buses with PM filters or
oxidation catalysts; and
Replacing older buses with newer models.
Emissions may be reduced by using certain
alternative fuels, including biodiesel blends.
Engines certified to operate on alternative fuel
such as LPG, CNG, and LNG can also reduce
emissions.
Discuss funding opportunities for bus
fleet upgrades with your local or state
environmental or air quality agency.
Provide walking and biking paths to promote
active transportation and reduce the number of
buses and passenger vehicles near the school.
Site Location and Design
In response to concerns about the impacts of near-road
air pollution, several agencies, including EPA
and several state agencies in California, have established
siting guidelines for new schools that recommend
reducing traffic-related air pollution exposure (Table 2).
While California guidelines recommend that new schools
should not be located within 500 feet or more of major
roads, EPA's School Siting Guidelines note the need to
consider multiple issues associated with exposure and
health. For example, a school sited far from a major road
21Safe Routes to School National Partnership. (2012). Safe routes to school and traffic pollution: Get children moving and reduce exposure to unhealthy air.
Available at http://www.saferoutespartnership.org/sites/default/files/pdf/Air Source Guide web.pdf
22 Safe Routes to School National Partnership. (2012). Safe routes to school and traffic pollution: Get children moving and reduce exposure to unhealthy air.
Available at http://www.saferoutespartnership.org/sites/default/files/pdf/Air Source Guide web.pdf
23 National Center for Safe Routes to School. (2013). Starting a walking school bus. Available at http://www.walkingschoolbus.org
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that requires long commutes by bus or car may result
in higher overall exposure for students, compared to
a school site near a major road that does not require
long commutes. Overall, EPA recommends multiple
strategies, as described in this document, to reduce
students' overall exposure.
School sites include of a variety of land use types,
such as classrooms, playgrounds, athletic fields,
offices, and maintenance and storage facilities. For
new school developments near roadways, there
may be opportunities to reduce traffic-related
pollution exposure through careful site design. By
Table 2. School siting documents developed by various agencies.
Agency
Guidance
Key Outcomes
U.S. EPA
California Air
Resources Board
California
Department of
Education
South Coast
Air Quality
Management
District
Los Angeles
Unified School
District
School Siting
Guidelines (2011)
Air Quality and
Land Use Handbook
(2005)
School Site Selection
and Approval Guide
(2000)
Air Quality Issues
in School Site
Selection: Guidance
Document (2005,
updated 2007)
Distance Criteria for
School Siting (2008)
Recommends considering many factors in evaluating locations for new schools,
including proximity to the community (including community amenities and
infrastructure), distance from major transportation facilities, exposure to air
pollutants during student commutes, feasible mitigation on site, and accessibility by
walking or biking.
Recommends that new schools are not located within 500 feet of major roadways
(>50,000 vehicles/day).
Recommends distancing schools 2,500 feet from major roadways where explosives
are carried and at least 1,500 feet from roads where gasoline, diesel, propane,
chlorine, oxygen, pesticides, or other combustible or poisonous gases are
transported.
Recommends a buffer zone of no less than 500 feet, and as much as 1,000 feet,
between schools and major roadways.
Recommends that new schools are not built within 500 feet of a freeway or major
transportation corridor (>100,000 vehicles/day).
L
Sample layouts for a large land parcel with a school and other land uses. A less desirable layout (left) with the school located close to
the highway is compared to an improved layout (right) with the school more than 500 feet from the highway (red dotted line).
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locating land uses such as maintenance, storage,
parking, and office facilities in the area closest to the
roadway, classroom and play areas can be located
farther from the roadway in areas where air pollutant
concentrations tend to be lower. Some of these
strategies may also be applicable to existing school
sites near roadways, or to sites located near other
sources of diesel particulate air pollution such as
warehouses, truck routes, railyards, and ports.
Exposure to traffic-related pollution can also be
reduced by locating onsite transportation-related
sources, especially school bus drop-off and pick-up
locations, as far from classrooms, play areas, and
building air intakes as possible. Optimal placement of
offices, playgrounds, athletic fields, and classrooms
within a school site depend on a variety of factors,
including typical wind patterns, the amount of time
spent and activities performed outdoors versus
indoors, and indoor ventilation conditions.
Recommendations
For new school developments, consider
locations farther from major roads and other
areas with heavy truck traffic, but still within
the community.
- A quantified evaluation of post-mitigation
air quality impacts may be appropriate
and/or required.
Consider unintended consequences of
any location, such as increased commute
distances and decreased opportunity for
walking and biking.
Consider opportunities to locate playgrounds,
athletic fields, and classrooms farther from
the roadway, or other areas with heavy truck
traffic, by locating maintenance, storage,
parking, and office facilities in the area closest
to the roadway.
Locate bus and passenger vehicle loading
zones away from classrooms, play areas, and
building air intakes.
Roadside Barriers
Sound Waits
Pollutant concentrations behind a barrier located
downwind of a roadway are typically lower than
concentrations in the absence of a barrier. Studies
show that reductions in downwind pollutant
concentrations within approximately 500 feet of a
highway in the presence of a well-designed sound
wall can be on the order of 15% to 50%.24
The effectiveness of sound walls at mitigating
near-road pollution exposure depends on roadway
configuration, local meteorology, and barrier height,
design, and endpoint location. For example, pollutant
concentrations may be higher downwind of a wall
if there are gaps in the wall that allow pollutants to
pass through. Sound walls can be considered for
schools located adjacent to highways and other busy,
high-traffic roadways.
In situations where school authorities
do not have jurisdiction or ownership
over the immediate roadside environment,
consider discussing the use of roadside
barriers to reduce traffic-related pollution
exposure with the relevant authority (e.g.,
state department of transportation, city
planning department).
24Baldauf, R. W.; Khlystov, A., Isakov, V., Thoma, E.; Bowker, G. E.; Long, I, & Snow, R. (2008). Impacts of noise barriers on near-road air quality. Atmospheric Environment, 42, 7502-7507.
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The combined use of vegetation
and sound walls has shown promise in
reducing vehicle pollution downwind of
roadways by up to 60%.25
Vegetation
Trees and plants along roadways can reduce
particle concentrations by acting as a physical
barrier between roadways and schools (similar, in
effect, to sound walls), or by filtering particles as
they pass through and accumulate on leaf surfaces.
The amount of removal depends on season, plant
species, leaf size and density, and pollutant type.
The effectiveness of trees and plants as physical
barriers also depends on the density and height of
the greenery. Mature vegetation tends to be more
effective than young vegetation, evergreen species
are typically more effective than deciduous species,
and vegetation with needle-like greenery (e.g.,
conifers) tends to be more effective than broad-
leaved trees. Particle removal rates tend to be higher
when vegetation is located close to the pollutant
source and when wind speeds are low.
The vegetation types chosen for roadside barriers
should be appropriate for the location of interest,
including water requirements, non-invasive species,
and aesthetics. In general, the vegetation barrier should
be thick (approximately 20 feet or more) and have full
leaf and branch coverage from the ground to the top
of the canopy along the entire length (i.e., no gaps
in-between or underneath the vegetation). In some
instances, this type of barrier may require the use of
multiple vegetation types such as a combination of
bushes and trees. The vegetation chosen should also
maintain its structure during all seasons; thus, coniferous
trees would be preferable to hardwood species. The
vegetation types chosen should also not be emitters of
air pollution or high levels of pollen. Schools can use the
U.S. Department of Agriculture's (USDA's) i-Tree Species
tool26 to begin the process of choosing appropriate
vegetation, in consultation with other experts from plant
nurseries, local cooperative extensions, city government,
or the U.S. Forest Service. All vegetation that will be
located near a road should be sited consistent with state
and local safety guidelines.
Recommendations
Use a solid roadside barrier (only along
highways) and/or vegetation to block traffic-
related pollutants from influencing air quality
near the school.
Minimize gaps in solid and vegetative
roadside barriers.
For vegetative barriers, use an evergreen
species with mature, dense greenery and
locate the barrier downwind and close to the
roadway.
Choose species appropriate for region and
site, consulting with plant nurseries, local
cooperative extensions, city governments, or
the U.S. Forest Service.
Similar to sound walls, concentrations may be higher
behind a vegetative barrier that is located downwind of
the roadway if there are gaps in the vegetation such as
missing or dead trees, or lack of cover from the ground
to the top of the vegetation. In any case, vegetation can
be used as a buffer to distance people from the roadway
while creating a more attractive and shaded space that
encourages active transportation (such as walking and
bicycling) as an alternative to vehicle use.27
25Bowker, G. E.; Baldauf, R.; Isakov, V., Khylstov, A., & Petersen, W. (2007). The effects of roadside structures on the transport and dispersion of ultrafine particles from highways.
Atmospheric Environment, 41, 8128-8139.
25 USDA's i-Tree Species is designed to aid users in selecting proper species given the tree functions they desire. The tool is available at www.itreetools.org/species.
27 Baldauf, R.; McPherson, G.; Wheaton, L, Zhang, M.; Cahill, T. Hemphill Fuller, C.; Withycombe, E.; & Titus, K. (2013). Integrating vegetation and green infrastructure into sustainable
transportation planning. Transportation Research News, September-October, 14-18.
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Summary of Recommendations
Table 3 outlines mitigation strategies that can be used to reduce traffic-related pollution exposure in schools,
including ventilation/HVAC system requirements, benefits, drawbacks, and relevance for new and/or existing
schools. Note that some of these mitigation strategies will only serve to reduce pollution exposures indoors
(e.g., filtration), or will only effectively reduce some pollutants (e.g., PM25) but not others (e.g., volatile organic
compoundss). These mitigation strategies reduce risks, but do not eliminate them.
Strategy
Ventilation/
HVAC System
Type
Benefits
Drawbacks
New/
Existing
Schools
Educate staff on
ventilation and
indoor air quality
best practices
All
Teachers are less likely to turn
mechanical systems off; air vents
remain unobstructed; doors/windows
are kept closed during peak pollution
periods; indoor sources of air pollution
are reduced
Effectiveness may decrease over time;
results depend on training quality and staff Both
cooperation
Air-seal around
windows, doors,
HVAC ducts, etc.
Relocate air
intake or source if
roadway/pollution
source is near intake
vent
Mechanical
ventilation
systems
Central HVAC
systems;
single
classroom
HVAC units
Use filtration
Im prove HVAC
system design to
be compatible with
high-efficiency
filtration
All
Central HVAC
systems
Reduces the amount of unfiltered air
entering the building
Reduces particle and gaseous
concentrations in incoming air;
can increase lifespan of filters
Reduces particle concentrations from
both outdoor and indoor sources
Larger reductions in particle
concentrations are possible
Indoor pollutant concentrations may build
over time if ventilation is insufficient, especially Both
if indoor pollutant generation is high
Cost
Maintenance and replacement required; may
require system upgrades
Cost
Both
Both
Both
Implement anti-
idling/idle reduction
policies
Upgrade school bus
fleet
Encourage active
transportation (e.g.,
walking and biking)
to school
All
All
All
Reduces em issions of particles and
gases
Reduces em issions of particles and
gases
Reduces em issions of particles and
gases; improved health with exercise
Lack of vehicle climate control during hot/cold R ,
weather
Cost
Walkers/bicyclists may be exposed to traffic-
related pollution or other hazards during trips
Both
Both
Locate school site
away from pollution
sources
Design school site to
minimize exposure
to pollutant sources
Use solid and
vegetative barriers
All
All
All
May reduce student exposure to
particles and gases at the school,
although overall exposures may
increase if an alternative site requires
long commutes by bus or car
Reduces student exposure to particles
and gases
Reduces concentrations of particles
and gases near schools; vegetative
barriers may increase shade and
improve aesthetics
If alternative sites are limited, there may not
be opportunities to locate the school farther
from the road; unintended consequences from
locating sites far from the community may
include a decreased opportunity for walking
and biking, increased traffic, and/or increased
exposures during commuting
Effectiveness is site-specific; may be costly for
existing schools
Cost; optimal design may be site-specific;
maintenance and water needs for vegetative
barriers
New
Both
Both
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School Ventilation and
Filtration System Assessment
1. Assess whether near-road pollution may be a problem.
Is there a major roadway near the school? If so:
- How far away is it?
Is the school downwind of the road?
Where does school bus pick-up and drop-off occur?
Are there opportunities to reduce bus idling or relocate loading zones away from classrooms and
outdoor recreation areas?
2. Assess the current ventilation and filtration system.
Is ventilation achieved passively or mechanically?
If mechanical:
Is a central HVAC system used or a single-classroom unit?
- Are filters being used?
What is the blower capacity?
- Is filtration being used? If so, what is the MERV rating of the filter(s)?
3. Assess ventilation operation.
Are teachers leaving windows and/or doors open during the day?
Are there opportunities to bring in air during off-peak emission times?
Are teachers turning systems off due to noise issues?
Are filters being inspected, cleaned, and replaced according to the schedule recommended by the
manufacturer?
4. Assess air-sealing needs to limit infiltration of unconditioned air.
Can infiltration of polluted air be reduced by sealing around any of the following:
Windows?
- Doors?
HVAC ducting?
5. Evaluate air intake location(s) relative to roadways or other pollutant sources such as school bus drop-off and
pick-up locations.
Is air intake located near a roadway, loading zone, or other pollutant source, such as designated
smoking areas?28 Are supply and exhaust vents unobstructed?
Can the air intake be relocated to an area that is less influenced by pollutant sources?
28The Centers for Disease Control and Prevention recommends that schools prohibit all tobacco use at all school facilities and events at all times. See http://www.cdc.gov/healthyschools/
tobacco for more recommendations on tobacco use prevention through schools.
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Additional Resources
Information regarding air quality and pollution mitigation in schools is available on the EPA website:
General information about indoor air quality: www.epa.gov/iaq
Creating healthy indoor environments in schools: www.epa.gov/iaq/schools
Energy Savings Plus Health: Indoor Air Quality Guidelines for School Building Upgrades:
www.epa.gov/iaq/schools/energy_savings_plus_health.html
EPA School Siting Guidelines: www.epa.gov/schools/guidelinestools/siting/download.html
Exhibit 5: Factors Influencing Exposures and Potential Risks: www.epa.gov/schools/guidelinestools/siting/
downloads/Exhibit_5_Factors_Infl encing_Exposures_and_Potential_Risks.pdf
Exhibit 6: Screening Potential Environmental, Public Health and Safety Hazards: www.epa.gov/schools/
guidelinestools/siting/downloads/Exhibit_6_Screening_Potential_Environmental_Public_Health_and_
Safety_Hazards.pdf
HVAC systems in schools: www.epa.gov/iaq/schooldesign/hvac.html
EPA Clean School Bus Program: www.epa.gov/cleanschoolbus/csb-overview.htm
The Role of Vegetation in Mitigating Air Quality Impacts from Traffic Emissions: http://archive.epa.gov/nrmrl/
archive-appcd/web/pdf/baldauf.pdf
EPA School Flag Program: http://cfpub.epa.gov/airnow/index.cfm?action=fl g_program.index
Other useful resources include:
California Air Resources Board, Air Quality and Land Use Handbook: www.arb.ca.gov/ch/handbook.pdf
South Coast Air Quality Management District, Air Quality Issues in School Site Selection: Guidance
Document: www.aqmd.gov/docs/default-source/planning/air-quality-guidance/schooLguidance.pdf
South Coast Air Quality Management District, Near-Road Mitigation Measures and Technology Forum
Materials: www.aqmd.gov/home/library/technology-research/technology-forums
California Department of Education, School Site Selection and Approval Guide:
www.cde.ca.gov/ls/fa/sf/schoolsiteguide.asp
Los Angeles Unified School District, Distance Criteria for School Siting:
www.lausd-oehs.org/docs/Misc/DistanceCriteriaTable%20Revl2_10_08.pdf
ASHRAE Standard 62.1-2013, Ventilation for Acceptable Indoor Air Quality, 2013:
www.techstreet.com/ashrae/products/1865968
ASHRAE Indoor Air Quality Guide: Best Practices for Design, Construction, and Commissioning, 2009:
www.ashrae.org/resources--publications/bookstore/indoor-air-quality-guide
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Office of Children's Health Protection (1107A)
EPA-100-R-15-001
www.epa.gov
November 2015
@ Recycled/Recyclable
Printed on paper that contains at least 50% post consumer fiber.
&EPA
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