Air Toxics: Overview
The air we breathe can become contaminated with pollutants from a variety
of natural and man-made sources. Since federal legislation involving
ambient air quality was enacted in 1970, air pollution control
has focused on criteria air pollutants,
including sulfur dioxide (SO2), carbon monoxide (CO), nitrogen oxides
(NOx), ozone (O3) and particulate matter, which are primarily by-products
of fossil fuel combustion. However, due to increasing scientific
evidence of their effects on human health, the focus of ambient
air quality has begun to shift to include not only "criteria" air pollutants,
but also "toxic" air pollutants. Toxic air pollutants are also
referred to as air toxics or hazardous air pollutants (HAPs) and are
defined as those pollutants that are suspected of causing cancer or
other serious health effects in humans, or of having serious adverse
effects on the environment.
In order to help protect the health of Maine residents and preserve
our environment, the State of Maine Department of Environmental Protection,
Bureau of Air Quality (DEP) developed this web page to help enlighten
Maine's public as to the hazards associated with air toxics. In addition,
the US EPA developed a program to control hazardous air pollutant emissions.
This program is set forth in Section 112 of the 1990 Clean Air Act Amendments
(CAAAs) . It is designed to reduce the emissions and ambient air
impact of a number of toxic air pollutants likely to be used by business
and industry in the state.
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What are toxic air pollutants?
Toxic air pollutants are those pollutants that, at sufficient concentrations
and exposure cause adverse health or environmental impacts, such as
respiratory disease or cancer. In general, the toxic air pollutants
that are of greatest concern are those that are released to the air
in large enough amounts to create a risk to human health and that have
the potential to reach many people.
Title III of the CAAAs has identified 188
hazardous air pollutants (HAPs) . The 188 HAPs consist of toxic
air pollutants identified by EPA which, when their emissions are
not controlled through available technology, are most likely to have
the greatest impact on ambient air quality and human health. The
list of hazardous air pollutants regulated under Maine law (06-096
CMR Ch. 137) is slightly larger as it contains dioxin and other
compounds not found on EPA's list.
Toxic air pollutants may exist as particulate matter or
as vapors. Examples of gaseous toxic air pollutants include benzene,
toluene and xylenes which are found in gasoline; chloroform, which is
released as a byproduct of pulp & paper production, perchloroethylene,
which is used in the dry cleaning industry; and methylene chloride,
which is used as a solvent by a number of industries, just to name a
few. Examples of air toxics typically associated with particulate
matter include heavy metals such as cadmium, mercury, chromium, and
lead compounds; and semivolatile organic compounds such as polycyclic
aromatic hydrocarbons (PAHs) which are generally emitted from the combustion
of wastes and fossil fuels.
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What are the
human and environmental effects of toxic air pollutants?
emission of toxic pollutants into the air can have serious effects to
human health and the environment. Human exposure to these pollutants
can include both short-term (acute) and long-term (chronic) complications.
Many factors can affect how different toxic air pollutants may impact
human health, including the quantity which a person is exposed to, the
development stage of the person, the duration and frequency of the exposure,
the toxicity level of the pollutant, and the person's overall health
and level of resistance or susceptibility. Short-term exposures
can include effects such as eye irritation, nausea or difficulty in
breathing. Long-term exposures to many air toxics may result in
damage to the respiratory or nervous systems, birth defects, and reproductive
In addition, toxic air pollutants can have indirect effects on human
health through deposition onto soil or into lakes and streams, potentially
affecting ecological systems and eventually human health through consumption
of contaminated food.
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What are the sources of air
There are many man-made sources of toxic air pollutants in Maine. These
sources may be divided into three categories.
- point sources
- area sources; and
- mobile sources.
Each of these source categories are described below.
A point source (also known as a major source) is a
stationary source that emits or
has the potential to emit 10 tons or more per year of any one of the
listed HAPs, or 25 tons or more per year of combined HAPs. Examples
of point sources can include chemical plants, paper mills, large printing
and coating operations, power plants and waste incinerators. These sources
can release air toxics through emissions from stacks and vents, fugitive
process emissions, equipment leaks during material transfer and handling,
or accidental releases. EPA estimates that 26% of all man-made
air toxic emissions come from point sources.
Area sources are smaller air toxic sources, each releasing
less than 10 tons per year of any individual HAP and less than 25 tons
per year of combined HAPs. Examples of stationary area sources
include sources such as dry cleaners, gas stations, small print shops,
auto body shops, electroplaters and furniture manufacturers. Area
sources also include consumer products used in homes and offices such
as cleaners, pesticides, paints, glues, etc. Even though emissions
from each individual area source may be relatively small, their collective
emissions can create significant health risks particularly where there
are a large number of area sources located in a small area, or when
they are located in populated areas. EPA has estimated that 24% of all
man-made air toxic emissions are attributable to area sources.
Mobile sources include automobiles, trucks, buses
and non-road vehicles such as boats, trains, farm equipment and recreational
vehicles. Despite major improvements in vehicle emissions
over the past two decades, people are driving longer distances today.
EPA estimates that 50% of all man-made air toxic emissions come from
mobile sources. Toxic air pollutants are generated by mobile sources
through the incomplete combustion of fuel as well as through the evaporation
of toxic components of the fuel. The US EPA web site on Air
Toxics from Motor Vehicles is an interesting site to visit. For
additional information on mobile sources in general, check out EPA's mobile
sources web site.
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What is being done to control
toxic air pollutant emissions in Maine?
Several programs have been implemented in Maine to control the emissions
of toxic air pollutants. A summary of each of these programs is
Major Stationary Sources
Major stationary sources of HAPs (and some
area sources that are of particular concern) in Maine are subject
to the National Emissions Standards for Hazardous
Air Pollutants (NESHAPs) found in Title III of the Clean Air
Act Amendments (CAAA) of 1977. Rather than setting ambient air quality
standards for each pollutant, the 1990 CAAA directed EPA to set technology-based
standards. The technology standards use maximum
achievable control technologies (MACT) for 175 source categories
that require reductions of HAP emissions. These MACT standards have
been phased in over the past several years. When fully implemented,
these standards are expected to significantly reduce total annual
HAP emissions to the ambient air.
Motor vehicles are such an integral part of our society that virtually everyone
is exposed to their emissions. EPA estimates that mobile source (car, truck,
and bus) air toxics could cause up to 1,500 cases of cancer each year,
or about half of the cancers caused by all outdoor sources of air toxics. Maine
has several programs in place which help to reduce emissions of air toxic
compounds from mobile sources.
- Vehicle Emissions Control Program - The control
of air toxics emissions from motor vehicles has been addressed at
the federal level through technological controls on motor vehicles
such as catalytic converters. Pre-1975 vehicles without catalytic
converters, and even pre-1981 vehicles with simple catalysts, emit
far more air toxics than newer vehicles. New cars today are capable
of emitting 90% less hydrocarbons over their lifetimes than the uncontrolled
models of the 1960s. Most air toxics are hydrocarbon compounds, so
any hydrocarbon control program indirectly reduces air toxics emissions
- Stage I and Stage II Vapor Recovery Program - Distribution
and marketing of gasoline is one of the largest combined sources
of uncontrolled air toxic emissions in Maine. Gasoline vapors
contain benzene, a known carcinogen, as well as many other toxic
substances. Maine has implemented programs, known as Stage
I and Stage II vapor recovery systems, to control emissions from
these sources. Stage I gasoline vapor recovery systems capture
the vapors released from the underground storage tanks at gas stations
when being refilled by tank trucks. Stage II systems capture gasoline
vapors which would otherwise be vented during individual vehicle
refueling at gas stations. In addition, all gasoline tank trucks
operating in Maine must be equipped with gasoline vapor control equipment.
Virtually all gasoline dispensing facilities statewide were required to
install Stage I vapor recovery equipment by November 1, 1994. Stage II
vapor recovery requirements apply to gasoline dispensing facilities in
the three counties of York, Cumberland, and Sagadahoc with an annual throughput
of 1,000,000 gallons of gasoline or more in a given year.
- Congestion Mitigation and Air Quality Improvement Program -
The Transportation Equity Act for the 21st Century (TEA-21) provides
funding and flexibility for a variety of transportation purposes.
One key component of TEA-21 is a program called the Congestion
Mitigation and Air Quality Improvement program (CMAQ) which was created
specifically to fund projects to improve air quality. The CMAQ program
assures a source of funds for reducing congestion and for developing
transportation alternatives such as public transit, shared-ride programs,
bicycle and pedestrian services, and employer trip reduction programs.
- Alternative Fuels - A switch to fuels that are
cleaner than today's gasolines offers another
promising strategy for reducing air toxics. There are several choices,
including alcohols, natural gas, propane, and electricity. These
fuels are inherently cleaner than conventional gasoline because they
do not contain toxics such as benzene, and because they are simpler
compounds that do not yield complex combustion by-products. Clean
fuels could reduce by 50% to 90% or more the number of cancers currently
caused by vehicle air toxics emissions.
- Clean Government Initiative – The Maine State
Legislature and Governor have directed state agencies to, whenever
possible, purchase alternative use vehicles, highly fuel-efficient
vehicles, and vehicles with the lowest emissions possible. The clean
government initiative also promotes alternatives to travel, such
as teleconferencing. More information on Maine’s Clean Government
Initiative is available from http://www.maineenergyinfo.com/
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What is Maine's Mercury Reduction
Maine's Mercury Reduction Strategy is a multi-disciplinary approach
to reduce mercury releases from sources in Maine. Visit
the Air Toxics Program's Mercury page for more information about the
reduction strategy and mercury emission trends in Maine.
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Are Maine's toxic
air pollutant control strategies working?
Toxic Release Inventory (TRI)
EPA maintains a program for reporting releases and transfers of toxic chemicals
to the environment known as the Toxic
Release Inventory (TRI). The TRI is a database of information about
releases of more than 650 toxic chemicals from manufacturing facilities
throughout the US. TRI data from affected Maine facilities using, manufacturing,
treating or releasing any of the listed toxic chemicals are reported to
EPA on an annual basis. Although the TRI database represents only
a subset of total toxic emissions, the information can be used to identify
trends in the release of air toxics emissions on an annual basis. Based
upon reported TRI data, Maine has reduced its air toxics emissions over
251% since 1988.
US EPA National scale Assessment
One tool that helps us evaluate potential human exposure to air toxics is
the USEPA's National
Scale Assessment (NSA). The backbone of the NSA is EPA's National
Emissions Inventory (NEI) for HAPs. For documentation on the development
of the 1996 and later NEI emissions estimates refer to the NEI web
page. Since the NSA utilizes 1996 emissions data, it is not representative
of current conditions in Maine, especially in light of the fact that the
TRI data for Maine indicates an overall reduction in HAP emissions of over
251% between 1988 and 2001. However, EPA is currently working on the 2002
version of the NEI, and that will be released in early 2005.
Emissions Inventory Program
DEP has also developed an enhanced air toxics emissions inventory for all
of the 188 HAPs identified in the CAAA, as well as an additional 29 pollutants
that were not included in the CAAA. The purpose of this program is to establish
a comprehensive database of speciated HAP emissions from stationary sources.
The database is used in evaluating the effectiveness of emissions reduction
programs as well as assessing the impact on human health, in Maine. More
information about the Maine Hazardous Air Pollutant emission inventory
program is available here.
Ambient Air Toxics Measurement Program
TRI data and Maine's air toxics inventory indicate that toxic emissions have
decreased significantly in recent years. HAP emissions from mobile sources
and area sources have remained relatively stable, with some modest decreases
(less than 15%). The NSA data (modeled) indicate that ambient concentrations
of at least 10 HAPs exceeded health based benchmark concentrations in Maine
in 1990. Maine's air toxics monitoring program in 1990 confirmed that basic
conclusion (although Maine could not monitor all of the HAPs that the NSA
identifies). Almost all of these HAPs are emitted by the transportation
sector, or small commercial sources, or came to the state via long range
transport. Data collected in the Rumford/Mexico area in 1991, 1993, 1995,
1996, 1998, 1999, 2000, 2001, and 2003 and Portland monitoring from 1999,
2000, 2001 and 2002 indicate that benzene and 1,3-butadiene (transportation
sector pollutants) still remain at levels exceeding 1 in 100,000 cancer
risk levels. More information about
Maine's ambient air toxics monitoring is availabe here.
Current Evaluation and Next Steps
In light of the NSA data suggesting the Air Toxics still pose unacceptable
risk to Maine Citizens, in 2003 Maine DEP launched a new initiative to:
- evaluate the accuracy of the NSA data,
- find out which Air Toxics currently pose a risk to Maine Citizens;
- and develop an action plan to reduce the risk.
This Maine Air Toxics Initiative (MATI) is a facilitated, stakeholder
process. By working with all affected parties, Maine DEP hopes to develop
the most effective reduction program at the least cost. More
information on the Maine Air Toxics Initiative is available here.
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Who do I contact for more information?
For more information on Maine's programs to control toxic air pollutants,
T. Greves at 207(287-7030).
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