4%	United States
Environmental Protection
** Agency
Office of Transportation and Air Quality
EPA-420-R-21 -022
October 2021
Best Practices for
Reducing Near-Road Pollution
Exposure at Schools

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Best Practices for
Reducing Near-Road Pollution
Exposure at Schools
vvEPA
U.S. Environmental Protection Agency
Richard Baldauf, Ph.D., P.E.
Office of Transportation and Air Quality
Office of Research and Development
U.S. Environmental Protection Agency
Washington, DC, USA
Ken Davidson and Sarah Sullivant
Region 9
U.S. Environmental Protection Agency
San Francisco, CA USA 94501
Chad Bailey
U.S. Environmental Protection Agency
Office of Transportation and Air Quality
Ann Arbor, Ml 48105
Olivia S. Ryder Ph.D. and Douglas S. Eisinger, Ph.D.
Sonoma Technology
Petaluma, CA 94954
Dahlia Chazan
Arup North America Ltd.
San Francisco, CA 94105

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Contents
Introduction	1
Purpose of This Publication	1
Intended Audience	1
Other EPA Resources for Schools	1
Reducing Near-Road Pollution Exposure at Schools	3
Near-Road Air Pollution and Children's Health	3
How Can Near-Road Pollution Exposure Be Reduced in Schools?	5
Building Design and Operation Strategies for Reducing Near-Road Pollution
Exposure	6
Ventilation, Filtration, and Indoor Air Quality in Schools	6
Actions for Building Occupants	12
Summary	13
Site-Related Strategies for Reducing Near-Road Pollution Exposure	16
Transportation Policies	16
Site Location and Design	17
Roadside Barriers	20
Air Quality Measurements	22
Summary of Recommendations	23
School Ventilation and Filtration System Assessment	25
Related Documents	26
Acknowledgments	27

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Introduction
Purpose of This Publication
The U.S. Environmental Protection Agency (EPA)
created this document to help existing and planned
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 truck traffic,
or near other sources of significant particulate air
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 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
railyards, ports, industrial facilities, and wildfires.
Additionally, many of the best practices targeting
indoor air quality may also be beneficial for reducing
exposure to airborne viruses such as COVID-19 or
other respirable pathogens. Resources regarding
COVID-19 and air quality can be found in the
associated Resources Guide.
For existing schools located near heavily traveled
roads, school officials should contact their state or
local air pollution agency or their EPA regional office
for assistance in evaluating any impacts of traffic-
related air pollution exposure at your school. For
schools that are being constructed in new locations
near major roads, refer to EPA's School Siting
Guidelines. The School Siting Guidelines is a
companion to this publication and includes
information on evaluating impacts of nearby sources
of air pollution, like highways and other transportation
facilities, when siting new schools or examining
existing schools for potential renovations or upgrades.
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 to address traffic-
related air pollution exposure due to a school's
proximity to a heavily traveled roadway or trucking
corridor. This guide aims to outline multiple potential
approaches to reduce exposures. The publication
should also be useful to these same audiences located
near other sources of particulate and gaseous air
pollution, such as railyards, ports, industrial facilities,
and wildfires.
Other audiences that may find this resource applicable
to their work include community-based environmental
and health organizations; heating, ventilation, and air
conditioning (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, tribal, and international agencies.
Other EPA Resources for
Schools
The EPA website 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
1

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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.
2

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Reducing Near-Road Pollution
Exposure at Schools
Primary and secondary school-aged 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 air pollution exposure
and offers strategies to reduce students' exposure in
new and existing schools.
17,000
schools in rural and urban
areas across the U.S. are located within 250 meters
(-820 feet) of a heavily traveled road.
Kingsley, 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 A'l (primaiy road with limited access or
interstate highway) or A2 (primary road without limited access).
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. In some areas, other transportation
sources like trains, ships, and planes, as well as
industrial sources, can add to the local pollution
burden. 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 (NO2), 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.
Studies sho' 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.
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.
Individually and in combination, many ofthe pollutants
found near roadways have been associated with
adverse health effects.
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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. Studies show that certain ethnic
groups and people who are in a low socioeconomic
position often experience an increased burden from
traffic emissions.2'3'4 EPA has concluded that diesel
exhaust is likely to be carcinogenic to humans at
environmental levels of exposure, and the
International Agency for Research on Cancer classifies
diesel exhaust as a known human carcinogen.5'5
Nationally, the overall prevalence of asthma in
children is approximately 8%. Asthma is a particularly
complex respiratory disease with many factors,
genetic and environmental, that interact to influence
its development and severity. Extensive evidence links
four common air pollutants (particulate matter,
ground-level ozone, oxides of nitrogen, and sulfur
oxides) to respiratory diseases in children. The
mixture of pollution from traffic-related sources
appears to pose particular threats to a child's
1	Karner, 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/es100008x
2	Rowangould, G.M. (2013) A census of the near-roadway population:
public health and environmental justice considerations. Trans Res D
25: 59-67. http://dx.doi.ora/10.1016/i.trd.2013.08.003
3	Tian, N.; Xue, J.; Barzyk. T.M. (2013) Evaluating socioeconomic and
racial differences in traffic-related metrics in the United States using
a GIS approach. J Exposure Sci Environ Epidemiol 23: 215-222.
4	Boehmer, T.K.; Foster, S.L.; Henry, J.R.; Woghiren-Akinnifesi, E.L.; Yip,
F.Y. (2013) Residential proxim ity to major highways - United States,
2010. Morbidity and Mortality Weekly Report 62(3): 46-50.
5	https://www.iarc.who.int/pressrelease/iarc-diesel-engine-exhaust-
carcinoaenic/
6	https://www.epa.gov/national-air-toxics-assessment/nata-frequent-
guestions
respiratory system.7 Children can also be exposed to
air pollution inside homes, schools, and other
buildings. Indoor air pollutants from biological
sources (such as mold, dust mites, or pet dander) can
lead to allergic reactions, can exacerbate existing
asthma, and have been associated with the
development of respiratory symptoms. For more
information, see America's Children and the
Environment (ACE).
Children are particularly susceptible to health problems
resulting from air pollution exposure due to:
Having respiratory systems that are not fully
developed. Studies show exposures to air pollution
in childhood can result in decreased lung function.8
Having higher rates of exposure than adults
becausethey are more active and they breathe
more in proportion to their body size.
Typically spending more time outdoors than adults.
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.9 While there is no national
definition or threshold for a heavily traveled road,
several organizations have denoted roads as "high-
volume" when they experience over 50,000 (Federal
Highway Administration and rural California roads),
80,000 (New York), and 100,000 (urban California
roads) vehicles per day.10'11 Smaller volume roads
7	Boothe, V.L. and Baldauf, R.W., 2020. Traffic emission impacts on
child health and well-being. In Transport and Children's Wellbeing
(pp. 119-142). Elsevier.
8	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
https://www.healtheffects.ora/publication/traffic-related-air-
pollution-critical-review-literatu re-em issions-exposure-and-health
9	Kingsley, 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 A1 (primary road with limited access or interstate
highway) or A2 (primary road without limited access).
10	https://ww3.arb.ca.gov/ch/rd technical advisory final.pdf
11	https://www.fhwa.dot.gov/policvinformation/hpms/volumeroutes/
ch5.cfm
4

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with large numbers of trucks, however, may also have
large amounts of air pollution impacting air quality
near the road. In addition, diesel-powered school
buses can be a significant source of pollution near
schools if there are numerous buses staged close to
school buildings during pick-up and drop off or if
excessive idling is permitted.
Exposure to traffic-related pollution is a concern both
indoors and outdoors—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.12'13
How Can Near-Road Pollution
Exposure Be Reduced in
Schools?
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
Elevated PM concentrations
in schools have been linked to:
•	Poor ventilation;
•	Ineffective, poorly maintained, or
nonexistent air filtration;
•	Proximity to major 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.
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design, and the use of roadside barriers. Many of
these strategies may also be effective at reducing
exposure at schools near other sources of outdoor
particulate and gaseous air pollution (e.g., railyards,
industry, wildfires) 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.14
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
12 Mejia, 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.2010.11.009
^ Mullen, N.A., Bhangar. S., Hering, S.V., Kreisberg, N.M., & Nazaroff,
W.VV. (2011). Ultrafine particle concentrations and exposures in six
elementary school classrooms in northern California. Indoor Air, 21(1),
77-87. doi:10.1111/j.1600-0668.2010.00690.x
14 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. At
http://www.epa.aov/iaq/schools/pdfs/Enerav Savings Plus Health G
uideline.pdf
5

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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 health implications of children breathing in
PM (and specifically diesel PM, 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.
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, ventilation,
and air conditioning (HVAC) system. 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.15
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
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.
•	Ensure minimum outside air ventilation rates
are maintained throughout occupancy as
required by code.
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 since there is limited ability to manage
some air movement. Strategies for reducing pollution
exposure in naturally ventilated classrooms include
reducing indoor sources of air pollution15 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 below for more
information).
Additionally, there are filtration-related options for
schools with passive systems, which are described in
the sections that follow.
15 Mendell, 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.
16 https://www.epa.aov/indoor-air-aualitv-iag/indoor-pollutants-and-
sources
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Mechanical Ventilation
Recommendations
•	Use mechanical ventilation if possible.
Central l-IVAC 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.
-	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,
buildings, drop-off zones, and other
pollutant sources, such as designated
smoking areas.
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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 improper balance in a building's HVAC
system can result in the building becoming
incorrectly 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
17 ASHRAE Ventilation for Acceptable Indoor Air Quality Standards,
https://www.ashrae.ora/technical-resources/bookstore/standards-62-
1-62-2
moisture into the walls of the building. In cold
climates, moisture can condense in walls and
promote mold growth, posing an environmental
hazard with health consequences, in addition to
structural consequences. Therefore, pressure relief
dampers that allow air to exit the building or exhaust
fans that draw air out are typically recommended.
An additional consideration when sealing building
envelopes is ensuring that proper mechanical
ventilation is maintained such that carbon dioxide
(CO2) concentrations do not exceed the
recommended indoor limit of 1,000 ppm set by the
American Society of Heating, Refrigerating and Air-
Conditioning Engineers (ASHRAE).17 Previous studies
have shown that this may occur if the building is tight
and there is substandard or no mechanical
ventilation.18
EPA recommends19 that central HVAC air handling
units be used when possible, as they are often quieter
(and therefore less likely to be turned off), easierto
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
18	https://www.tandfonline.com/doi/full/10.1080/10962247.2019.1629362
19	https://www.epa.aov/iaa-schools/heating-ventilation-and-air-
conditionina-svstems-part-indoor-air-qualitv-desian-tools
7

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quality, the necessary ducting and registers tend to
increase system cost. For more information regarding
recommended air exchange rates, see the ASHRAE
Ventilation for Acceptable Indoor Air Quality
Standards. Ductwork in central ventilation systems
should be evaluated, cleaned if needed, and tested
regularly for leaks by an HVAC professional.
Regardless of the type of system used, mechanical
ventilation systems are typically more reliable than
natural methods because airflow rates are
controllable.
Filtration
Recommendations
•	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, such
as MERV-13 and above, including the
installation of pre-fiIters, if necessary.
MERV-13 + can trap smaller particles,
including viruses. MERV-16+ is preferred
when possible.
•	Inspect and replace filters regularly
according to manufacturer
recommendations,
•	Where possible, locate air intakes away from
pollution sources.
•	Keep air vents clear of items that may block
airflow.
•	Consider also including an activated
charcoal filter to remove gaseous pollutants.
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.20 Achieving maximum
performance of filtration systems requires:
Proper installation;
Continuous operation;
Atight building envelope (i.e., minimal air leaks);
Effective air distribution;
Careful placement of air inlets and outlets to
face away from major roadways and to avoid
pulling air into the school from parking lots
where buses and cars are idling;
Ensuring vents are free from items that may
block filtered air from reaching the room; 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 exposed to the filtration
system and removed (for instance, particles entering
the classroom through open doors or windows,
through leakage in the building envelope, from
indoor sources, or from dust being kicked up from
floors).
94 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
8

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Portable Classrooms
Due to the structural nature of portable and mobile classroom buildings, they can be susceptible to multiple issues
including poorly functioning HVAC systems, loud ventilation systems, water entry and mold growth, pollution from
nearby parking lots or loading areas where they are often located, and less securely sealed building envelopes.
Recommendations to improve air quality in portable classrooms include:
•	Siting portable classrooms away from major roadways or bus zones where idling may occur
•	Using portable standalone filter units for classrooms that are not equipped with a central filtration system
-	Care should be taken to ensure they are appropriate for the occupancy and room size
•	If window filtration units or HVAC are available, using the highest MERV-rated filter the system will allow
•	Upgrading any existing HVAC or filtration systems to accommodate higher MERV-rated filters
•	Locating HVAC and air handler units away from teaching areas to minimize noise
•	Tightening the building envelope
-	Ensuring sufficient total ventilation to address mold issues and maintain appropriate humidity levels
For more information regarding guidelines for establishing and maintaining indoor air quality in portable classrooms,
see the Portable Classroom section on the Indoor Air Quality Design Tools for Schools website.
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.21
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. It is also important to note that
filters not rated as MERV are often only used to
protect the HVAC equipment and do not provide air
quality benefits.
Schools planning energy
efficiency upgrade projects may
consider simultaneous upgrades to improve
indoor air guality.
U.S. Environmental Protection Agency. (2014). Energy savings
plus health: Indoor air quality guidelines for school building
upgrades. Available at
https://www.epa.qov/iaq-schools/protecting-iaq-durinq-
school-enerqv-efficiencv-retrofit-proiects-enerqy-savinqs-plus
21 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
over time, 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
https://ww2.arb.ca.qov/list-carb-certified-air-cleaninq-devices
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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
23
concentrations by close to 90%.
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.
Studies examining filtration systems in schools have
found that all types of air pollution 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 MERV 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.22 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
efficiencies close to 90%.23 However, performance
depends on the amount of air that can be processed
by the unit and other classroom layout featuresthat
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.23
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
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. For example, the filter rack
size needs to be considered; some higher-MERV-
rated filters are too thick to fit into existing filter
racks, and some HVAC systems may not have enough
power to adequately push air through more efficient
filters. In some systems, the addition of a high MERV-
rated filter can result in 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-
® 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
® 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.l 2013
10

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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.24 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
power 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 integrated air sensor to monitor
ventilation needs, and thereby help optimize ventilation
rates, could offset long-term, higher energy costs due
to over-ventilation. Air sensors for ventilation monitoring
should be installed by a professional.
24	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
25	EPA guidance on air cleaners and air filters:
https:/7www.epa.aov/'indoor-aii -quality-iag/air-cleaners-and-aii -
filters-home
® CADR, as described by ASHRAE, is the rate of particle removal from
air passing through a filter and is approximately equal to the product
of airflow rate and the contaminant removal efficiency. For more
Indoor Air Cleaners
Recommendations
•	Choose a unit that is appropriate for the size
of the room where it will be used.
•	Choose a unit that removes particles and/or
volatile organic compounds based on need.
•	For classrooms relying on passive/natural
ventilation, use quiet, portable, stand-alone
filtration systems to reduce indoor
concentrations.
•	Where possible, locate air cleaner intake
away from pollution sources for maximum
efficacy.
•	Ensure maximum energy efficiency by
choosing a portable unit with an EPA
ENERGY STAR designation.
In addition to minimizing sources of air pollutants
and proper ventilation, air filtration can help to
reduce indoor air pollution. If HVAC air filtration is
not available, or if additional filtration is required,
portable air cleaners might be a suitable option.
Portable air cleaners (also known as air purifiers) are
designed to help reduce indoor air pollution in a
specific area or a single room.25
There are several factors to consider when choosing
an appropriate portable air cleaner for a given space.
These include:
• Ensuring the unit is appropriate for the size of
the room it will be used in by checking its
Clean Air Delivery Rate (CADR).25
Note: To remove PM using portable air
cleaners, choose units that have a high CADR
rating for "smoke."27
information, see the ASHRAE Position Document on Filtration and Air
Cleaning:
https://vwyw.ashrae.ora/file%20librarv/about/position%20documents
/filtration-and-air-cleanina-pd-pdf
https://www.epa.aov/sites/production/files/2019-
09/documents/harriman Stephens brennan -
new guidance for residential air cleaners - ashrae journal sept-
2019. web version.pdf
11

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•	Deciding if the unit needs to remove volatile
organic compounds (VOCs) as well as particles.
If so, choosing one with an activated carbon
charcoal filter might be necessary. VOC filters
are helpful at schools near heavy passenger
vehicle traffic; where indoor cleaning and
maintenance involves solvents, where dry-
erase white board markers emit strong odors;
or where there are other indoor or outdoor
pollution sources involving chemicals or liquid
fuels.
•	Ensuring the lowest noise rated cleaner is used
if noise will be an issue.
•	Careful consideration of the placement of the
portable air cleaner for maximum efficacy.
•	Choosing a portable air cleaner with an EPA
ENERGY STAR designation to conserve energy
and optimize efficiency.
•	For more information about these factors and
other important considerations, see the EPA
Guide to Air Cleaners. Care should be taken to
ensure that regular maintenance is performed,
as directed by the manufacturer, on portable
air cleaners. It is also important to keep in
mind that longer air cleaner operating hours
provide better particle removal, which, in turn,
increases the potential for health benefits.28
Actions for Building Occupants
Recommendations
Train teachers, school staff, and students (where
appropriate) 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.
•	Planning strenuous outdoor activities during
times with lower amounts of traffic.
•	Consider how school buildings are used on
weekends that may require changes to
HVAC operation. This may include:
-	Sporting events in athletic facilities
-	Adult extension education
-	Classes taking place on weekends
•	Adhere to local, school, and health department
recommendations regarding outside ventilation
due to pandemic conditions.
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 peaktraffic (e.g.,
morning and evening rush hours) when near-road
28 EPA guidance on air cleaners and air filters:
https://www.epa.qov/indoor-air-aualitv-iag/air-cleaners-and-air-
filters-home
12

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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
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). Indoor pollution sources should be
reduced as much as possible and should also be
considered when considering ventilation upgrades,
filtration methods, and other mitigation strategies.
Raising awareness about indoor and outdoor air quality
issues and providing training for staff on optimal
building operating practices (including HVAC
operation) are inexpensive strategies that can
supplement upgrades to the ventilation and filtration
system and building and site design. EPA has many
resources to address indoor air quality (IAQ)
management in schools, including the IAQ Tools for
Schools program. This program provides an easy-to-
use framework and set of tools to train staff on IAQ
management and can be found, along with the other
school IAQ resources, on the EPA IAQ school
website. Training is recommended as a complementary
strategy and should not be considered an alternative
to ventilation upgrades.
Outdoor exposure may be reduced by 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-uptimes, and consider
locating activities farther from roads and loading
zones. Resources are available to help teachers plan
when students should stay indoors based on current
air quality.29 In addition, many schools implement the
Air Quality Flag Program to raise awareness of the
daily air quality index (AQI). The school flags,
combined with information on current air quality from
AirNow. can be used to help plan outdooractivities.
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.
23 The Utah Recess Guidance for Schools,
https://health.utah.gOv/asthma/airqualii:v/recess.phD
13

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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 in this document. Once an initial
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. Mitigation strategies for different HVAC/ventilation types. HVAC/ventilation system types are listed from more
effective to generally less effective, and mitigation strategies are listed from the simplest (and least costly) to implement on
the left to those that require a higher level of effort on the right.
H VAC/Venti I ati o n
Type
Mitigation Strategies

Educate
Staff
Air Seal
Building
Adjust Air
Intake
Use Filtration
Upgrade
System
Central HVAC system
serving multiple
classrooms; high-
efficiency filtration
use not limited by
airflow

V
Change air intake
locations if near
pollution source(s)
(e.g., roadway,
drop-off zone,
parking)
Use MERV-16 +
filter
Use pre-filters

More
effective
|
Central HVAC system
serving multiple
classrooms; high-
efficiency filtration
use limited by airflow
V
V
Change air intake
locations if near
pollution source(s)
(e.g., roadway,
drop-off zone,
parking)
Use highest
compatible
MERV-rated
filter
Use pre-filters or
high-performance
panel filters
Modify airflow to
be compatible
with higher
efficiency
filtration
Single-classroom
HVAC unit (e.g., unit
ventilator)
V
V
Avoid airflow
obstructions
Use quiet systems
Use highest
compatible
MERV-rated
filter
Use pre-filters or
high-performance
panel filters
Upgrade to a
central HVAC
system
Passive/natural
ventilation
y
May be an option
if adequate
ventilation to
dilute and remove
pollutants from
indoor sources is a
challenge
Avoid bringing in
air during periods
of high traffic
Use a portable
stand-alone
filtration system
Switch to a
mechanical
ventilation
method
15

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Site-Related Strategies for
Reducing Near-Road
Pollution Exposure
Transportation Policies
Recommendations
•	Limit school bus and passenger vehicle
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
improved bus technologies like electric or
some alternative fuels, including LPG, CNG,
and LNG.
•	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.
Establish Anti-Id ling and Idle Reduction
Policies
Bus and passenger vehicle operation and idling can
produce large amounts of PM and other air pollutants.
Some schools, states, and localities 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. For
more information, see the idle-free schools toolkit.
30 https://www.edf.ora/sites/default/files/cleanbuses 14 screen.pdf
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 1990.30 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. Examples include engines certified to operate on
alternative fuels such as liquid petroleum gas (LPG),
compressed natural gas (CNG), and liquefied natural gas
(LNG). A co-benefit of upgrading older school buses,
for children who use them as transport, is reduced
in vehicle exposure. Discuss potential funding options
for bus fleet upgrades with your state or local
environmental or air quality agency.31
M U.S. Environmental Protection Agency. (2010). Clean school bus.
Available at
https://www.epa.aov/sites/production/files/documents/CleanSchoolBu
s.pdf
16

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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%.32
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.32
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.33
When considering walking and biking routes to
school, impacts on safety, lighting, access, and
maintenance requirements should be considered.
The U.S. Department of Transportation Safe
Routes to School Programs website provides
various links to resources, like the Safe Routes to
School National Partnership, which contains
information about programs that promote walking
and biking to school.
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.
Site Location and Design
Recommendations
•	For new school developments, consider
locations farther from major roads and other
areas with heavy truck traffic, but still within
the community.
•	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.
In response to concerns about the impacts of near-road
air pollution, several agencies, including EPA and several
state agencies, have established siting guidelines for new
schools that recommend reducing traffic-related air
pollution exposure (Table 2).
32 Safe Routes to School National Partnership. (2012). Safe routes	33 National Center for Safe Routes to School. (2013). Starting a walking
to school and traffic pollution: Get children moving and reduce	school bus. Available at http://www.walkinaschoolbus.org
exposure to unhealthy air. Available at
http://www.saferoutespartnership.org/sites/default/files/pdf/Air S
ource Guide web.pdf
17

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Table 2 School siting documents developed by various agencies.
Agency
Guidance
Key Outcomes
U.S. EPA
School Siting
Guidelines (2011)
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.
California Air
Resources Board
Strategies to Reduce
Air Pollution
Exposure Near High-
Volume Roadways
(2017)
Recommends that new schools are located more than 500 feet from
major roadways (>50,000 vehicles/day).
California
Department of
Education
School Site Selection
and Approval Guide
(2000)
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.
South Coast Air
Quality
Management
District
Air Quality Issues in
School Site
Selection: Guidance
Document (2005.
updated 2007)
Recommends a buffer zone of no less than 500 feet, and as much as
1,000 feet, between schools and majorroadways.
Los Angeles
Unified School
District
Distance Criteria for
School Siting (2008)
Recommends that new schools are not built within 500 feet of a
freeway or major transportation corridor (>100,000 vehicles/day).
State of Oregon
School Siting
Handbook (2005)
Recommends locating schools away from major arterial roads and
railroads as these are dangerous to cross and reduce safe walking and
biking access to schools. Ensure good connections between school and
nearby neighborhoods to encourage walking or biking to school.
Ohio Department
of Health
Smart School Siting
(2018)
Recommends considering remote student drop off locations, locating
parking lots farther from school, and creating separate entrances for
motorized and non-motorized modes of transport.
18

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While California guidelines recommend that new
schools should not be located within 500 feet of
major roads (those with >50,000 vehicles per day
in rural areas or > 100,000 vehicles per day in urban
areas),34 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 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.35
Overall, EPA recommends multiple strategies, as
described in this document, to reduce students'
overall exposure.
School sites include a variety of land use types,
such as classrooms, playgrounds, athletic fields,
offices, and maintenance and storage facilities. For
new or remodeled school developments near
roadways, there may be opportunities to reduce
traffic-related pollution exposure through careful
site design. By 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.
Surface Parking
School
Apartments
Parking
Structure
Retai
500' FROM HIGHWAY
500' FROM HIGHWAY
Office
Building
School
Office
Building
Surface Parking
Parking
Structure
Retail
iMHiMvEl
-Limited-Access Highway
¦LimitedAccess Highway
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).
34 https://ww3.aib.ca.aov/ch/rd technical advisory final.pdf
" Wolfe M.K., McDonald, N.C., Arunachalam, S., Baldauf, R. and
Valencia, A., 2020. Impact of school location on children's air pollution
exposure. Journal of Urban Affairs, pp.1 -17
19

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Roadside Barriers
Recommendations
•	Use a solid roadside barrier and/or
vegetation to block traffic-related pollutants
from influencing air quality near the school
along highways or very large local roads.
•	Minimize gaps in solid and vegetative
roadside barriers.
•	For vegetative barriers, use mature, dense
greenery (conifers preferred) and locate the
barrier downwind and close to the roadway.
•	Consult with a specialist or use one of the
resources identified in the text of this
document to choose species that do not
change by season (e.g., conifers) and that
are appropriate for the region and site.
•	Vegetation should be properly maintained
to ensure vegetative health and to prevent
gaps from forming.
Solid Barriers
Pollutant concentrations behind a solid barrier
located downwind of a roadway, such as a sound wall
or fence, 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%.36-37'38
In situations where school authorities
do not have jurisdiction over or
ownership of 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).
concentrations may be higher downwind of a wall if
there are gaps in the wall that allow pollutants to
pass through. Solid barriers can be considered for
schools located adjacent to highways and other busy,
high-traffic roadways.
The effectiveness of solid barriers at mitigating near-
road pollution exposure depends on roadway
configuration, local meteorology, and barrier height,
design, and endpoint location. For example, pollutant
* Baldauf, 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.
37 Baldauf, R.W., Isakov, V., Deshmukh, P., Venkatram, A., Yang, B., and
Zhang, K.M., 2016. Influence of solid noise barriers on near-road and
on-road air quality. Atmospheric Environment, 129, 265-276
Lee, E.S., Ranasinghe, D.R., Ahangar, F.E., Amini, S., Mara, S., Choi,
W., Paulson, S. and Zhu, Y., 2018. Field evaluation of vegetation and
noise barriers for mitigation of near-freeway air pollution under
variable wind conditions. Atmospheric Environment, 175, 92-99
20

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Vegetation
Trees and plants along roadways can reduce particle
and some gaseous pollutant concentrations by acting
as a physical barrier between roadways and schools
(similar, in effect, to solid walls and fences), or by
filtering particles as they pass through and
accumulate on leaf surfaces. The amount of removal
depends on plant species, leaf type and size, and
pollutant type.
The effectiveness of trees and plants as physical
barriers also depends on the density and height of
the greenery. In general, evergreen species are
typically more effective than deciduous species
because they keep their greenery ail year, and the
wax-covered, needle-like greenery of 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 15 feet or more) and
have full leaf and branch coverage from the ground to
m Baldauf. R.. McPherson, G., Wheaton, I... 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.
the top of the canopy along the entire length (i.e., no
gaps 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 types chosen should
also not be emitters of air pollution or high levels of
pollen.
Schools can use the EPA Recommendations along with
the U.S. Department of Agriculture's (USDA's) i-Tree
Species Tool to begin the process of designing and
choosing appropriate vegetation for barriers, in
consultation with other experts from plant nurseries,
local cooperative extensions, city government, and/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.
The combined use of vegetation
and solid barriers has shown promise in
reducing vehicle pollution downwindof
roadways by up to 60%.
Bowker, 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.
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.39
21

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Air Quality Measurements
Air Sensors
Both indoor and outdoor air quality can be measured
using air sensors. In comparison to regulatory-grade
monitors, non-regulatory air sensors typically require
a lower capital cost, are portable, and are easier to
operate. There are many air sensors available for
purchase, which might lead to confusion over the
benefits and accuracy of each option.40 To assist
those interested in using sensors as part of air
monitoring projects, EPA, the Air Quality Sensor
Performance Evaluation Center (AQ-SPEC), and other
organizations conduct performance evaluations of
select air sensors on the market either under ambient,
fixed-site conditions and/or in a controlled laboratory
exposure chamber.41'42 In these assessments, sensors
are evaluated for how well they measure air
pollutants in terms of accuracy and reliability as well
as how easy they are to use. Additionally, EPA has
recommended Air Sensor Performance Targets and
Testing Protocol to help users consistently test air
sensor devices, calculate performance metrics,
consistently report test results, and evaluate sensor
performance using recommended target values. For
more information on sensor evaluation and
performance, see the EPA Sensor Evaluation Results
page and AQ-SPEC. For more information on sensor
operation and data interpretation, see the EPA Air
Sensor Toolbox.
One application for which air sensors could be used is
to monitor inside school buildings. While the
performance of individual sensors may vary and
studies on the accuracy of the measurement in
indoor environments is still being evaluated, results
can be used to understand potential presence or
trends of certain pollutants. For example, air sensors
can be used in schools to assist in understanding
pollutants inside classrooms, hallways, or other areas.
Broadly, there are two types of air sensors: stationary
40	https://www.epa.aov/aii-sensoi-toolbox
41	https://www.epa.aov/air-sensor-toolbox/evaluation-emeraing-air-
sensor-performance
air sensors (fixed in one location), and portable or
hand-held sensors. Stationary sensors may help a
user understand how pollution levels change in one
location over the school day. Portable air sensors may
help users identify indoor hotspots. Another use for
portable air sensors is to investigate personal
pollution exposure on the way to school or work and
use the information to devise a lower-pollution route.
Both types of air sensors can be used for educational
projects and can help build awareness about indoor
or outdoor air quality.
It is important to keep in mind that air sensors are
not regulatory-grade air quality monitors, and thus
should be used for non-regulatory supplemental and
informational monitoring (NSIM) applications only.
They may need periodic calibration or maintenance.
Refer to the manufacturer's manual and/or the EPA
Air Sensor Toolbox for instructions on proper
maintenance and calibration procedures to ensure
your air sensor data remains of high quality.
42 http://www.aqmd.aov/aq-spec
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Summary of Recommendations
Table 3 summarizes 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., PM) but not others (e.g., volatile organic compounds). These
mitigation strategies reduce risks, but do not eliminate them. Mitigation benefits are estimates and actual costs may
vary based on location, existing filtration infrastructure, and other factors.
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Table 3 Summary of mitigation strategies.
Strategy
Ventilation/
HVAC
System
Type
Benefits
Drawbacks
Mitigation
Benefit

Ongoing
Cost
Teachers are less likely to turn mechanical
^ t ff systems off; air vents remain unobstructed; Effectiveness may decrease over time;
... ... doors/windows are kept closed durinq peak results depend on traininq quality and
ventilation and indoor „.. ... .... , „ . ,, . , ,
air ualitv best pollution periods; indoor sources of air pollution staff cooperation; teachers or students may
. are reduced; potential to prolong life of perceive classroom air quality is lowered
practices mechanical filters; can be implemented at when windows and doors are closed
new or existing schools
medium-
low
$ 0 - $
Air-seal around
windows, doors,
HVAC ducts, etc.
Mechanical
ventilation
systems
Reduces the amount of unfiltered air entering
the building; can be implemented at new or
existing schools
Indoor pollutant cones, may build over time
if ventilation is insufficient, especially if
indoor pollutant generation is high
medium-
low
$
0
Relocate air intake or Central or Reduces particle and gaseous concentrations
source if roadway/ single in incoming air; can increase lifespan of
pollution source is classroom filters; can be implemented at new or existing
near intake vent HVAC units schools
medium
$$ - $$$ 0
Use portable filtration
units
Naturally
ventilated
classrooms
Reduces particle concentrations from both
outdoor and indoor sources; can be
implemented at new or existing schools
Maintenance and replacement required;
may require system upgrades
medium
$-$$
0-$
Central Larger reductions in particle concentrations
desiqntobe , , , Cost; reduced filtration if HVAC system or
. , , HVAC are possible; can be implemented at new or ..... , ...
compatible with hiqh- . . . buildinq envelope is leakv
... ! ... . systems existinq schools
efficiency filtration
high
$$$ $
Implement anti-
idling/idle reduction
policies
All
Reduces emissions of particles and gases; can
be implemented at new or existing schools
Lack of vehicle climate control during
hot/cold weather
medium
$
$
„ , . , , Purchase cost; may require traininq for bus
Reduces emissions of particles and qases;
Upqrade school bus „.. ... , maintenance and upkeep; potential route
' All potential lonq-term cost reduction; can be .... . ..
fleet ! , . . , , limitations dependinq on lenqth of routes
implemented at new or existinq schools
and range of buses selected
medium
$$$a $
Encourage active
transportation (e.g.,
walking and biking)
to school
All
Reduces emissions of particles and gases;
improved health with exercise; can be
implemented at new or existing schools
Walkers/bicyclists may be exposed to
traffic-related pollution or other hazards
during trips
medium
0 to $
0
If alternative sites are limited, there may not
Locate school site May reduce student exposure to particles be opportunities to locate the school farther
away from pollution and gases at the school, although overall from the road; unintended consequences
sources All exposures may increase if an alternative site from locating sites far from the community NAb NAb 0
(Mainly applicable for requires long commutes by older buses or may include a decreased opportunity for
new schools) cars walking and biking, increased traffic, and/or
increased exposures during commuting
Design school site to
minimize exposure to
pollutant sources
All
Reduces student exposure to particles and
gases; can be implemented at new or existing
schools if there is flexibility to relocate child-
based activities
Effectiveness is site-specific; may be costly
or infeasible for existing schools
medium
$$$
$
Cost; optimal design may be site-specific;
„ , . , maintenance and water needs for
Reduces concentrations of particles and . . .
. ... veqetative barriers; reduced visibility from
Use solid and . „ qases near schools; veqetative barriers may , ...
All , , ,. , . street may be security issue or limit access
veqetative barriers increase shade and improve aesthetics; can . . . .
... , . . , , and connectivity; may need support from
be implemented at new or existinq schools . .... , ,
other stakeholders such as the state
department of transportation
a Local, state, and federal grants or assistance may be available b Consideration for new construction only
medium
$$ - $$$ 0 - $$
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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 (at least 500 ft. away from the road is preferred)?
-	Is the school downwind of the road?
-	Is it at grade, above or below the road (at-grade tends to maximize exposure to roadway pollution)?
•	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. For a more detailed checklist concerning this topic, see the Tools
for Schools Ventilation Checklist
•	Is ventilation achieved passively or mechanically?
•	If mechanical:
-	Is a central HVAC system used or a single-classroom unit?
-	What is the blower capacity?
-	Is filtration being used? If so, what is the MERV rating of the filter(s)?
3.	Assess ventilation operation. For a more detailed checklist concerning this topic, see the Tools for Schools
Ventilation Checklist
•	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?
•	Is the entire ventilation operation following a preventive maintenance system or plan?
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.
•	Are any air intakes located near a roadway, loading zone, or other pollutant source, such as designated
smoking areas?43 Are supply and exhaust vents unobstructed?
•	Can the air intake be relocated to an area that is less influenced by pollutant sources?
43 The Centers for Disease Control and Prevention recommends that schools prohibit all tobacco use at all school facilities and events at all times. See
https://www.cdc.qov/healthvschools/health and academics/tobacco product use.htm for more recommendations on tobacco use prevention
through schools.
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Related Documents
For an overview infographic that summarizes some of the important mitigation strategies and suggestions from
this Best Practices Guide, see the Summary Infographic.
To access a list of resources that provide more information about various topics covered in this Best Practices
Guide, see the Resources Guide.
For case studies concerning implementation of various strategies at schools, see the Case Studies at Schools
Document.
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Acknowledgments
EPA would like to acknowledge the following organizations that provided comments on this document:
U.S. Environmental Protection Agency Offices:
Office of Children's Health Protection
Office of Indoor Air & Radiation
Office of Research & Development
Office of Community Revitalization
Region 5
EPA would like to acknowledge the following organizations that provided comments on an earlier version of this
document:
•	South Coast Air Quality Management District
•	Southern California Green, Clean and Healthy Schools Partnership
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Office of Children's Health Protection (1107A)
and
Office of Transportation and Air Quality
EPA-420-R-21 -022
October 2021
www.epa.gov
United States
JVutMli Environmental Protectio
^1 ** Agency
Recycled/Recyclable
Printed on paper that contains at least 50% post-consumer fiber.

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