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Air Quality Agreement - Progress Report 2006
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Section 3: Scientific and Technical Cooperation
and Research
Emission Inventories and Trends
JOINT EFFORTS
 The United States and Canada have updated and improved their emission
inventories and projections to reflect the latest information available.
These emission inventories were also processed for U.S. and Canadian
air quality models to support the technical assessment of air quality
problems. In the United States, the most recent emission inventory data
are for the year 2002. The 2003 and 2004 emissions data in this report
were developed by interpolating between 2002 emissions and 2010 projections
developed to promulgate the CAIR.
Both countries were active participants in the NARSTO (formerly North
American Research Strategy for Tropospheric Ozone) emission inventory
assessment, which was completed in the summer of 2005. The final report
is titled Improving Emission Inventories for Effective Air Quality
Management across North America. This report includes recommendations
for the long- term improvement of the emission inventory programs in
both Canada and the United States as well as in Mexico, the third participant
in NARSTO.
Emissions data for both countries for 2004 are presented in Figures
26, 27, 28, and 29. Figure
26 shows the distribution of emissions by
source category grouping for SO2, NOx, and VOCs.
The following observations can be made from Figure
26:
- SO2 emissions in the United States stem primarily from
coal-fired combustion in the electric power sector. Canadian SO2 emissions
come mostly from smelters in the industrial sector, with fewer emissions
from the electric power sector, due to the large hydroelectric capacity
in Canada. The distribution of NOx emissions in the two countries
is similar, with nonroad and on-road vehicles accounting for the greatest
portion of NOx emissions in both countries.
- VOC emissions are the most diverse of the emission profiles in
each country. The most significant difference is that most VOCs come
from the industrial sector in Canada. This is the result of the proportionately
higher contribution of oil and gas production in Canada.
Figure 26 U.S. and Canadian National Emissions by Sector for
Selected Pollutants, 2004
Click to enlarge
Source: EPA and Environment Canada
The emission trends, shown in Figures 27, 28,
and 29 for SO2,
NOx, and VOCs, respectively, show the relative contribution
in emissions over the 1990-2004 period. In the United States, the major
reductions in SO2 emissions
came from electric power generation sources. For NOx, the
reductions came from on-road mobile sources and electric power generation
sources. For VOCs, the reductions were from on-road mobile sources and
solvent utilization. For all three pollutants during this time period,
the United States generated substantially more emissions than Canada.
At the same time, while both countries have seen major reductions in
SO2 emissions, the United States has shown greater emission
reductions than Canada for VOCs and NOx.
Figure 27 SO2 Emissions in the United
States and Canada, 1990-2004
Click to enlarge
Source: EPA and Environment Canada
Figure 28 NOx Emissions in the United
States and Canada, 1990-2004
Click to enlarge
Source: EPA and Environment Canada
Figure 29 VOC Emissions in the United States and Canada, 1990-2004
Click to enlarge
Source: EPA and Environment Canada
Air Quality Reporting and Mapping
JOINT EFFORTS
 Each country is responsible for ensuring instrument calibration and
comparability of measurements of ozone and PM. Since 2001, the jurisdictions
in the United States and Canada have collaborated on contributing to
the EPA-led AIRNow program (www.epa.gov/airnow). Since 2004, the website
has been expanded to provide information on PM and ozone measurements
on a continental scale year-round (see Figures 30 and 31).
Canadian efforts continue to improve mapping by combining measurements
with numerical forecasts from the operational air quality forecasting
model. In each country, air quality forecasting services are being improved.
Canada and the United States are collaborating in the continuing development
of national air quality forecast models. Jurisdictions consult in preparing
routine forecasts for border regions and in developing communications
materials for the public.
Figure 30 AIRNow Map Illustrating Real-Time
Concentrations of Ground-Level Ozone (1-Hour Average Peak Concentration)
Source: EPA
Figure 31 AIRNow Map Illustrating Real-Time
PM2.5 Concentrations
(3-Hour Average)
Source: EPA
CANADA
Environment Canada is continuing to expand and refurbish federal and
provincial/territorial networks of monitoring stations across the country.
Canada maintains two national ambient air quality monitoring networks,
the National Air Pollution Surveillance (NAPS) network and CAPMoN. The
NAPS network is a joint federal, provincial, territorial, and municipal
network established in 1969. It is primarily an urban network, with over
260 air monitoring stations located in over 170 communities. The augmented
CAPMoN is a rural network with 30 air monitoring stations in Canada and
one in the United States.
The NAPS network gathers measurements on the components of smog (i.e.,
ozone, PM, SO2, CO, NOx, VOCs). Between 2002 and
2005, Environment Canada invested significantly in new equipment for
the NAPS network, including 58 new and replacement ozone monitors, 36
new and replacement NOx monitors, 11 new VOC samplers, 76
continuous PM2.5 monitors (tapered element oscillating microbalances
(TEOMs) and beta attenuation monitors (BAMs)), and eight new PM filter-based
samplers. In addition, Environment Canada started a chemical speciation
sampling program in December 2002 to characterize PM. Twelve sites are
now operating across Canada. The agency also built two new laboratories
to support this work and equipped them with an inductively coupled plasma-
mass spectrometry instrument for metals analysis and an organic carbon/elemental
carbon analyzer. Overall, since 2004, the network has expanded from 240
to 260 air monitors and now covers over 170 communities.
The ozone monitors at 18 CAPMoN sites continue to gather data in real
time, in support of the Air Quality Prediction Program and for distribution
to the U.S. AIRNow program. Integrated PM2.5 and PM10 mass
measurements, PM2.5 speciation measurements, and VOC measurements
are being made at five CAPMoN sites (within 500 km (310 miles) of the
border). Reactive nitrogen compounds (including nitric oxide (NO), NO2,
and NOy) are being continuously measured at three sites-the
Centre for Atmospheric Research, Egbert, Ontario; Kejimkujik, Nova Scotia;
and Saturna Island, British Columbia.
UNITED STATES
The majority of air quality monitoring performed in the United States
is carried out by state and local agencies in five major categories of
monitoring stations-State and Local Air Monitoring Stations (SLAMS),
National Air Monitoring Stations (NAMS), Photochemical Assessment Monitoring
Stations (PAMS), PM2.5 Speciation Trends Network (STN), and
air toxics monitoring stations. In addition, ambient air monitoring is
performed by the federal government (EPA, National Parks Service, and
the National Oceanic and Atmospheric Administration), Tribes, and industry.
A detailed description of current ambient air monitoring in the United
States, as well as future plans, can be found in the December 2005 draft
National Ambient Air Monitoring Strategy (www.epa.gov/ttn/amtic/monitor.html).
The primary purpose of the SLAMS/NAMS network is to determine compliance
with the NAAQS for ozone, PM2.5, PM10, CO, SO2,
NO2, and lead. Ozone is monitored at approximately 1,200 locations
in the United States. Ambient monitoring for PM2.5 is conducted
at more than 1,100 SLAMS using the filter-based Federal Reference Method
and at over 260 continuous PM2.5 stations.
Measurements of PM10, CO, SO2, NO2,
and lead are currently made at approximately 1,000, 400, 500, 400, and
200 sites, respectively.
Chemically speciated PM2.5 data are collected at 54 urban
trends sites and over 160 supplemental speciation sites as part of the
STN. Speciated PM data are also collected at more than 50 rural sites
and approximately 180 Class I areas as part of the IMPROVE Network (http://vista.cira.colostate.edu/improve).
In addition, five urban sites are operating continuous chemical speciation
technologies for nitrates, sulfates, and carbon. EPA and states will
use the results from these five sites to consider whether these continuous
measurement technologies will be used at additional locations. A new
network of PM10-2.5 monitoring is planned for monitoring compliance with
the recently proposed PM10-2.5 NAAQS. This network is expected to replace
most of the existing PM10 network.
The PAMS network measures ozone and its precursors in the most severe
ozone nonattainment areas. These data are used to aid in control strategy
development, emissions reduction tracking, and improvements to ozone
modeling and forecasting. These sites also provide information on pollutant
transport and local meteorology. In 2005, over 100 PAMS sites were in
operation in five regions of the United States: the Northeast, the Great
Lakes area, Georgia (Atlanta area), five areas in Texas, and seven areas
in California.
Toxic air pollutants are monitored at over 200 sites, including 23 National
Air Toxics Trends Stations (NATTS) sites. The NATTS network is intended
to provide long-term monitoring data for certain priority air toxics,
including organic chemicals and metal toxics, across representative areas
of the country in order to establish overall trends for these pollutants.
The PAMS program also contributes a significant number of data on certain
organic toxics. To complement NADP's Mercury Deposition Network (MDN),
EPA is supporting a planned ambient speciated mercury network that will
provide information on status and trends in mercury concentrations as
well as dry deposition estimates. The effort will utilize the NADP committee
structure as a platform for initiation and continued growth.
The NADP operates three monitoring networks for the purpose of determining
geographical and temporal trends in precipitation chemistry. The largest
and oldest of these is the NADP/NTN, which was established in 1978 and
now operates over 230 precipitation monitoring sites across the nation.
The network is a cooperative effort between the State Agricultural Experiment
Stations, U.S. Geological Survey, U.S. Department of Agriculture, and
numerous other governmental and private entities. The precipitation at
each station is collected and then sent to the NADP Central Analytical
Laboratory, where it is analyzed for hydrogen (acidity as pH), sulfate,
nitrate, ammonium, chloride, and base cations (i.e., calcium, magnesium,
potassium, and sodium). Comprehensive quality assurance programs ensure
that the data remain accurate, precise, and comparable from year to year.
The NADP has also expanded its sampling to two additional networks.
The NADP/MDN, currently with over 90 sites, was formed in 1995 to determine
trends of mercury in precipitation. Weekly samples of precipitation are
collected in specially treated sampling vessels for shipment to the NADP
Mercury Analytical Laboratory. All samples are analyzed for total mercury,
and samples from participating locations are also analyzed for methyl
mercury. Another network, NADP/AIRMoN, was formed for the purpose of
studying precipitation chemistry with greater temporal resolution. Precipitation
samples are collected daily from a network of nine sites and analyzed
for the same constituents as the NADP/NTN samples.
EPA operates CASTNET, a long-term monitoring program established in
1988 to assess the effectiveness of SO2 and NOx emission
reductions (www.epa.gov/castnet). CASTNET's objectives are to detect
and quantify temporal and geographic trends in regional air quality and
deposition for the United States. CASTNET currently comprises 88 regionally
representative sites that measure ground-level ozone and weekly concentrations
of total sulfur- and nitrogen-containing PM and precursor gases SO2 and
nitric acid. In addition, each site measures meteorological parameters
for use in an inferential model to estimate dry deposition rates at the
sites. The CASTNET program is currently evaluating an automated semicontinuous
monitoring instrument that measures both gaseous (SO2, nitric
acid, ammonia) and aerosol components (sulfate, ammonium, nitrate, chloride,
and other base cations).
One key aspect of the draft National Ambient Air Monitoring Strategy
is the proposed introduction of a new multipollutant monitoring network
referred to as NCore. Monitors at NCore multipollutant sites will measure
particles (PM2.5, speciated PM2.5, PM10-2.5), ozone,
SO2, CO, NOx (NO/NO2/NOy),
and basic meteorology. It is anticipated that ammonia and nitric acid
measurements will also be made at these sites in the future. Sites will
be located in broadly representative urban (about 55 sites) and rural
(about 20 sites) locations throughout the country. In many cases, states
will likely collocate NCore sites with PAMS or NATTS sites to further
promote multipollutant measurements. The objective of this network is
to gather additional information needed to support emissions and air
quality model development, air quality program accountability, and future
health studies. In January 2006, EPA proposed revisions to the ambient
air monitoring regulations to reflect NCore, which are expected to be
finalized in late 2006. Information on the notice of proposed rulemaking
for these revisions can be viewed at www.epa.gov/ttn/amtic/40cfr53.html.
Update to the Transboundary Particulate Matter Science Assessment
 In addition to the work carried out under the Transboundary PM Science
Assessment (published in 2004), additional model scenarios have been
carried out through the Canadian Meteorological Centre in Dorval, Quebec.
For example, the CHRONOS model was applied for the summer of 2003 to
determine the extent of the influence that Canadian emissions have on
ambient PM in the United States.
Using the 0.2 µg/m3 limit as a guide (it is used under
the U.S. CAIR) to determine if one jurisdiction contributes significantly
to another's nonattainment of the average annual PM2.5 standard,
the work demonstrates the influence of Canadian emissions on U.S. PM2.5 levels.
The influence of Canadian emissions on the United States extends significantly
into the entire east coast of the United States as well as the Midwest
and to a lesser extent the west coast (Figure 32).
Figure 32 Composite Map of the Influence of Canadian Emissions
(U.S. Emissions Zeroed Out) on PM2.5 Levels in
the United States during the Summer of 2003
Click to enlarge
Source: Environment Canada
Health Effects
 Health Canada has launched two research programs to characterize air
pollution exposure and human health issues under the Canadian portion
of the Border Air Quality Strategy, coordinated with research in the
United States. Work has also continued on development of air health indicators,
both for real-time reporting (Air Quality Health Index (AQHI)) and for
development of a method for tracking health improvements due to changing
air quality in the border area.
Research in the Great Lakes Basin Airshed
Health-related research activities in the Great Lakes basin airshed
include the following:
- Windsor Children's Respiratory Health Study: This three-phase
study targets a sensitive population in an area with relatively high
air pollution. The first phase (December 2004) was a baseline questionnaire
survey of approximately 20,000 Windsor elementary school students.
The
second phase (June 2005) involved cross- sectional tests of children's
lung function and inflammation, and the third (December 2005) involved
month-long daily lung function tests of 200 asthmatic children for
correlation with outside air pollution. Data analyses are under way.
- Windsor Exposure Assessment Study: This project has two
components. The first is a spatial air pollution assessment study (2004-2007),
which determines community levels of air pollutants such as PM, NO2,
SO2,
ozone, nitrate, elemental carbon/organic carbon, VOCs, polycyclic aromatic
hydrocarbons, and acid vapor. The data from this study are used in
support of the health research being carried out in the area. Methods
for analysis include the geographic information system (GIS), which
maps the area of influence for different pollutants. The second component
of the project is to monitor personal exposure to air pollution, which
matches the protocol of the EPA's Detroit Exposure and Aerosol Research
Study (DEARS) in methodology. Healthy and non-smoking adults (2005)
and school children (2006-2007) have been recruited to monitor air
pollution levels in their indoor and outdoor environments and their
personal exposure levels. The last test is scheduled for summer 2007.
- Long-term Exposure to Air Pollutants and Mortality and Morbidity
Rates including Cancer: Mortality and morbidity rates for Windsor,
Sarnia, and London since the late 1970s have been compared with Ontario
provincial rates; the association with air pollution is now under investigation
using GIS techniques.
- Cardiovascular Effects of Air Pollution on Diabetic Patients: The
Windsor Diabetic Patients Panel study involves following diabetic patients
for seven weeks to monitor their personal exposure to PM10 and
their cardiovascular health markers. The results suggest that an acute
exposure to particulate air pollution may be linked to an impaired
cardiovascular function in diabetic patients.
- Seniors' Health Study: The Windsor Seniors' Health Study
is investigating day-to-day indoor and outdoor exposure to varying
levels of air pollutants and the influence on their cardiovascular
function.
- Pregnant Women and Birth Outcomes Study: This is a feasibility
study of pollution exposure and health and birth outcomes for 10 pregnant
women in the area of Ottawa, Ontario.
- In Vitro Toxicology Study: The cytotoxicity of components
of PM to human epithelial cells is studied, using particle samples
from specific Windsor locations.
Research in the Georgia Basin-Puget Sound International Airshed
The research is being carried out by the University of British Columbia,
the University of Victoria, and the University of Washington. The research
is coordinated through a partnership between Health Canada and the British
Columbia Centre for Disease Control and includes the following studies:
- Establishment of a Childhood Disease Cohort: A birth cohort
of 120,000 children born in the Georgia Basin airshed was established
to evaluate the relationship between air pollution exposure and respiratory
disorders. Preliminary analyses have shown an association between air
pollution and bronchiolitis.
- Birth Outcomes in the GVRD: British Columbia Perinatal Database
Registry and the British Columbia Linked Health Database are being
used to relate maternal air pollution exposure during pregnancy and
adverse birth outcomes.
- Personal Exposures and Activity Patterns of Pregnant
Women and Infants: Data have been collected on personal exposure,
activity information, and exposure to traffic for 20 pregnant women
(with a target of 40) as a function of stage of pregnancy and season.
- Cardiovascular Cohort Study: The British Columbia Linked
Health Database is being used to enumerate a cohort of adults over
the age of 45 in the Georgia Basin, to investigate the relationship
between air pollution and cardiovascular disease among age groups independent
of predisposing condition and among high-risk populations.
- Walkability Study: This GIS study will integrate land use
and transportation network information to link walkability and emissions
exposure, for ultimate application to Vancouver and Seattle.
- Data Inventory and Consolidation: A data inventory website
has been developed (www.geog.uvic.ca/AIR) linking existing GIS information
to facilitate estimation of individual exposure to air pollution. Data
gaps and opportunities for improvement of data utilities have been
identified.
- Regional Infiltration Modeling: Building characteristics
from property assessment data are being used to develop a model of
indoor versus ambient PM2.5 levels for exposure assessment,
validated by a monitoring campaign.
- Modeling PM2.5 with MODIS: Satellite
aerosol measures will be used to study temporal and spatial levels
of PM2.5.
- Modeling Population Exposure: A probabilistic model of personal
exposures will be developed using GIS and randomly selected time-activity
patterns, to assess errors in cohort exposures.
- Enhanced Assessment of Exposure to Traffic and Wood Smoke: Related
technologies including GIS and monitoring campaigns were used to develop
modeled and validated exposure estimates to the urban neighborhood
scale for health studies and air quality management.
- Particulate Matter Exposure and Infant Health in Puget Sound: This
study involves monitoring of a birth cohort for traffic and woodsmoke
pollution using individualized geospatial exposure estimates to relate
birth outcomes and air pollution.
Canadian Air Quality Health Index
In 2006, a comprehensive proposal for a new AQHI will be presented for
approval of a multistakeholder steering committee. The AQHI is intended
to replace existing indices for public reporting in use across Canada,
all of which are based on a design from 1976, which does not reflect
the current understanding of short-term health effects of air pollution.
The index employs a linear, no-threshold concentration-response relationship
of short-term health risks from multiple pollutants, expressed in a 0-10+
scale. Work to develop the AQHI started in 2001 in a multistakeholder
context and has involved surveys and focus groups in 2004 and 2005 to
develop communications messaging and more recent pilot testing of the
proposed new index.
Canadian Air Health Indicator
A health indicator was proposed in May 2005, which may be used as a
measure of progress in air quality management over time. The Air Health
Indicator (AHI) is defined as the percentage of the number of daily deaths
attributable to exposure to the pollutant of interest. The AHI is proportional
to the level of risk, estimated using an appropriate statistical model,
and the level of the pollutant of interest. The AHI may be used to evaluate
spatial and temporal trends of air pollution and the related health risk
in Canada since 1981. More analyses are being conducted to refine the
methodology.
U.S. Report on Health Effects of Ozone
The health and welfare effects of ozone are documented and critically
assessed in the EPA Ozone Criteria Document and EPA Ozone Staff Paper.
At the end of February 2006, the final draft of the revised Ozone Criteria
Document was released to the public. The final Ozone Criteria Document
can be found at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=149923.
The purpose of this revised document, titled Air Quality Criteria
for Ozone and Other Photochemical Oxidants, is to critically evaluate
and assess the latest scientific information published since the last
review of the ozone NAAQS, completed in 1996. This new 2006 review
focuses on useful new information that has emerged in the last decade
and is pertinent in evaluating health and environmental effects data
associated with ambient air ozone exposures. A separate EPA Ozone Staff
Paper, prepared by EPA's Office of Air Quality Planning and Standards,
will draw upon key findings/conclusions from this document, together
with other analyses, to develop and present options for consideration
by the EPA Administrator regarding review and possible revision of
the ozone NAAQS.
There has been new research that suggests additional health effects
beyond those that had been known when the 8-hour ozone standard was set
in 1997. Since 1997, more than 1,700 new health and welfare studies relating
to ozone have been published in peer-reviewed journals. Many of these
studies have investigated the impact of ozone exposure on such health
effects as changes in lung structure and biochemistry, inflammation of
the lungs, exacerbation and causation of asthma, respiratory illness-related
school absence, hospital and emergency room visits for asthma and other
respiratory disorders, and premature mortality.
Ozone can irritate the upper and lower respiratory system, causing cough,
throat irritation, and/or discomfort (e.g., pain) in the chest. Ozone
can reduce lung function, cause wheezing, and make it more difficult
to breathe deeply. During exercise, breathing may become more rapid and
shallower than normal, thereby limiting a person's normal activity. Ozone
can also aggravate asthma, leading to more asthma attacks that require
a doctor's attention and/or the use of additional medication. In addition,
ozone can inflame and damage the lining of the lungs, which may lead
to permanent changes in lung tissue, irreversible reductions in lung
function, and a lower quality of life if the inflammation occurs repeatedly
over a long period. People who are particularly vulnerable to ozone exposures
include children, the elderly, and adults who are active outdoors (e.g.,
outdoor workers).
Aggravation of existing asthma resulting from short-term ambient ozone
exposure was reported prior to setting the 1997 ozone standard and has
been observed in studies published subsequently. In addition, a relationship
between long-term ambient ozone concentrations and the incidence of new-onset
asthma in adult males (but not females) was reported. Subsequently, an
additional study suggested that incidence of new diagnoses of asthma
in children is associated with heavy exercise in southern California
communities with high ozone concentrations. This relationship was documented
in children who played three or more sports and thus spent more time
outdoors. It was not documented in those children who played one or two
sports. Previous studies have shown relationships between ozone and hospital
admissions in the general population. A study in Toronto reported a significant
relationship between 1-hour maximum ozone concentrations and respiratory
hospital admissions in children under the age of two. Given the relative
vulnerability of children in this age category, there is particular concern
about these findings. Increased rates of illness-related school absenteeism
have been associated with 1-hour daily maximum and 8-hour average ozone
concentrations in studies conducted in Nevada. These studies suggest
that higher ambient ozone levels may result in increased school absenteeism.
The air pollutant most clearly associated with premature mortality is
PM, with dozens of studies reporting such an association. However, repeated
ozone exposure is a possible contributing factor for premature mortality,
causing an inflammatory response in the lungs that may predispose elderly
and other sensitive individuals to become more susceptible to other stressors,
such as PM. The findings of other recent analyses provide evidence that
ozone exposure is associated with increased mortality. Most recently,
new analyses of the 95 cities in the National Morbidity, Mortality, and
Air Pollution Study (NMMAPS) data sets showed associations between daily
mortality and the previous week's ozone concentrations, which were robust
to adjustment for PM, weather, seasonality, and long-term trends. Although
earlier analyses undertaken as part of the NMMAPS did not report an effect
of ozone on total mortality across the full year, the NMMAPS investigators
in those earlier studies did observe an effect after limiting the analysis
to summer, when ozone levels are highest. Another recent study from 23
cities throughout Europe also found an association between ambient ozone
and daily mortality.
Numerous recent epidemiological studies have reported associations between
acute ozone exposure and mortality, as summarized in the Ozone Criteria
Document.
Review of U.S. Ozone and Particulate Matter Air Quality Standards
EPA is currently reviewing the NAAQS for ozone; more information, including
supporting documents, can be found at www.epa.gov/ttn/naaqs/standards/ozone/s_o3_index.html.
EPA reviewed the NAAQS for PM. PM is the generic term for a
broad class of chemically and physically diverse substances that exist
as discrete particles (liquid droplets or solids) over a wide range of
sizes. Particles may be emitted directly or formed in the atmosphere
by transformation of gaseous emissions such as SOx, NOx,
and VOCs. Exposure to PM has been associated with premature morbidity
as well as indices of morbidity, including respiratory hospital admissions
and emergency department visits, school absences, work loss days, restricted
activity days, effects on lung function and symptoms, morphological changes,
and altered host defense mechanisms.
The nation's air quality standards for PM were first established in
1971 and were significantly revised in 1987, when EPA changed the indicator
of the standards to regulate inhalable particles smaller than or equal
to 10 microns in diameter (PM10). In 1997, EPA revised the
PM standards, setting separate standards for fine particles, defined
as PM less than or equal to 2.5 microns (PM2.5).
Recent epidemiological studies have continued to report associations
between short-term exposures to fine particles and effects such as premature
mortality, hospital admissions or emergency department visits for respiratory
disease, and effects on lung function and symptoms. In addition, recent
epidemiological studies have provided some new evidence linking short-term
fine particle exposures to effects on the cardiovascular system, including
cardiovascular hospital admissions and more subtle indicators of cardiovascular
health. Long-term exposure to PM2.5 and sulfates has also
been associated with mortality from cardiopulmonary diseases and lung
cancer and effects on the respiratory system, such as decreased lung
function or the development of chronic respiratory disease.
Epidemiological studies have also continued to support a relationship
between short-term exposure to thoracic coarse particles and respiratory
morbidity, with effects ranging from increased respiratory symptoms to
hospitalization for respiratory diseases. New data also suggest associations
with effects on the cardiovascular system and possibly with mortality.
There are several groups that may be susceptible or vulnerable to PM-related
effects. These include individuals with preexisting heart and lung disease,
older adults, and children.
The final revisions to the NAAQS for PM strengthen the short-term fine
particle standard and retain the 24-hour PM10 standard for coarse particles.
Information on the standards can be found at www.epa.gov/air/particles/standards.html.
U.S. Health Research
Health research in the United States has focused primarily on PM in
recent years. EPA has a well-established health research program, consistent
with the recommendations of the National Research Council's Committee
on Research Priorities for Airborne Particulate Matter. The air health
research program is directed towards two main objectives: reducing uncertainties
in setting standards for protection of human and ecological health, and
linking health effects to specific source types and PM attributes through
an integrated multipollutant program.
Characterizing the hazardous component of PM is critically important
to reducing uncertainties in setting future air quality standards and
implementing those standards. Studies of the health effects associated
with ambient and surrogate PM provide insights into the relative toxicity
and mechanisms that relate to specific sources. Multi-city epidemiological
and toxicological studies coordinated with the National Ambient Air Monitoring
Strategy frame a systematic approach that integrates laboratory and field
data to assess the health impacts of mixed components and sources. Research
focuses on identifying susceptible groups with cardiovascular disease
and diabetes and related animal models to address specific risk attributes
(e.g., gene-environment, debilitation). EPA research efforts include
a new cohort study to evaluate the long-term effects of ambient fine
particles, currently responsible for the largest measurable benefits
of PM regulation. Research to characterize mobile source roadway exposures
and risks and reduce uncertainties associated with complex atmospheres
(e.g., PM hazardous components, source attribution, co-pollutants, etc.)
is under way.
There are several research studies taking place in the Detroit-Windsor
area, coordinated with Canadian research efforts. They include DEARS,
children's health studies focusing on characterizing the effects of environmental
pollutants on asthma, and toxicological particle studies to characterize
PM effects. These efforts are aimed at linking health effects to specific
source types and PM attributes.
Acid Deposition Effects
Aquatic Effects Research and Monitoring
 An assessment of the most recent information available on acid deposition
effects on aquatic chemistry and biota in Canada was recently completed
and summarized in the 2004 Canadian Acid Deposition Science Assessment.3 The
assessment reveals a decreasing trend in lake sulfate levels in southeastern
Canada in response to reductions in SO2 emissions; however,
many of these lakes are still acidified, and many do not meet a pH condition
of ≥6, a key threshold for the sustenance of fish and other aquatic
biota. Some of the factors believed to be mitigating changes in surface
water quality include the widespread decline in base cations from watershed
soils, the release of stored sulfur from soils (i.e., drought induced),
and the impairment of within-lake alkalinity generating processes.
Overall improvements in the capacity of many lakes to support aquatic
biota are being observed. For instance, a general increase in the number
of breeding fish-eating waterbirds was observed in lakes in Ontario,
Quebec, and Newfoundland, particularly those in close proximity to reduced
emission sources. At the same time, algae, invertebrates, and waterbird
food chains in many lakes in this region continue to show acidification
impacts (i.e., direct effects of acidification, metal toxicity, loss
of prey species, and reduced nutritional value of remaining prey), particularly
in lakes and rivers where fish communities have been impacted. Atlantic
salmon populations in rivers of the Southern Upland region of Nova Scotia
continue to be severely impacted and will likely become extinct if adult
survival rates remain at current low levels and pH recovery continues
to be delayed.
Biological recovery is very complex; therefore, complete community recovery
will lag behind chemical improvements, possibly by several decades. It
is also likely that lakes will recover to a state that is more dilute
(lower ion concentrations and therefore more sensitive) than their preacidification
state, and biological communities will be permanently altered.4
Terrestrial Effects Research
The effects of acid deposition on soils and forests were also assessed
and summarized in the 2004 Canadian Acid Deposition Assessment.5 The
net loss of base cations from forested catchments in eastern Canada has
slowed down in response to declines in sulfate deposition, yet widespread
net losses are still occurring. Weathering inputs of base cations are
not sufficient to balance leaching losses, particularly for calcium.
Also, there is mounting evidence regarding the relationship between the
size of base cation reservoirs in forested watersheds and the acidification
of surface waters as well as the lack of recovery of pH levels. Also,
the negative effects of decreased fertility on tree vitality are becoming
increasingly supported by recent studies. The threat to the productivity
of eastern Canadian forests that are located in poorly buffered soils
is of concern. Quantifying the relationship between acid deposition,
base cation depletion, and forest health is difficult due to a number
of confounding factors related to site conditions. Further research is
needed to elucidate this relationship.
The assessment also reveals that eastern Canadian watersheds are exhibiting
releases of sulfur from soils in excess of deposition. Two internal catchment
sources, sulfate desorption and release via decomposition of organic
matter, are considered the likely causes for the budget imbalance. The
release of this extra sulfur acts as an additional acid load for soils
and downstream waters and may be partly mitigating the recovery of surface
waters in eastern Canadian forested watersheds.
Nitrogen, on the other hand, is an essential nutrient for tree growth
that is often limiting in eastern Canadian ecosystems; thus, nitrogen
saturation does not appear to be a problem in most eastern Canadian watersheds.
Some signs of nitrogen saturation have been observed in watersheds in
Ontario, which highlights the importance of continuing to monitor changes
in nitrogen concentrations. In eastern Canadian watersheds, sulfate continues
to be the primary acidifying agent.
Critical Loads and Exceedances
The critical load of acid deposition is defined as the maximum deposition
that an ecosystem can assimilate without significant long-term harmful
effects. Deposition of both nitrogen and sulfur compounds can contribute
to a critical load exceedance, which has been used in Canada as the primary
indicator of potential long-term environmental damage. For the first
time in North America, new and combined critical load estimates have
been generated for sulfur and nitrogen acid deposition for both sampled
surface waters and upland forest soils using steady- state models (Figure
33). Since sulfur and nitrogen have different atomic weights, the combined
critical load cannot be expressed in mass units (kilograms per hectare
per year, or kg/ha/yr); instead, it is expressed in terms of ionic charge
balance as "equivalents per hectare per year" (eq/ha/yr). Twenty
kilograms of sulfate per hectare per year is the same as 416 eq/ha/yr.
Figure 33 Critical Loads of Acid Deposition for Canada
Click to enlarge
Note: Critical (maximum) loads of combined total sulfur and nitrogen
acidity for Canada in equivalents/hectare/year calculated using a model
appropriate to the receptor. The value for each grid cell represents
the lowest of either the 5th percentile lake value or the 5th percentile
soil polygon value. The index map (lower left) indicates which model
was used for the grid cell value (red = Expert, yellow = Steady State
Water Chemistry (SSWC), green = Simple Mass Balance (SMB)).
Source: Jeffries, D.S. and Ouimet, R. (2005) Chapter 8: Critical loads:
Are they being exceeded? In: 2004 Canadian Acid Deposition Science
Assessment [CD-ROM]. Available from Environment Canada.
 Exceedance calculations confirm that 21-75 percent of the mapped area
in eastern Canada, corresponding to approximately 0.5-1.8 million square
kilometers, continues to receive levels of acid deposition in excess
of critical loads according to best- and worst-case assumptions of nitrogen-based
acidification, respectively. The optimistic end of the range (Figure
34) estimates the current (minor) level of nitrogen-based acidification,
whereas the pessimistic end of the range (Figure
35) offers a long-term
view by assuming steady-state conditions in which all sulfur and nitrogen
deposition is acidifying; in other words, nitrogen uptake no longer occurs
due to ecosystem saturation.
Figure 34 Current Critical Load Exceedances for Canada
Click to enlarge
Note: Exceedance of critical loads of acidic deposition (eq/ha/yr of
sulfur and nitrogen combined) based on current levels of nitrogen-based
acidification. A negative exceedance indicates that the estimate of current
deposition is less than the grid cell critical load. A positive critical
load is indicative of ongoing environmental damage. Details as in Figure
33.
Source: Jeffries, D.S. and Ouimet, R. (2005) Chapter 8: Critical loads:
Are they being exceeded? In: 2004 Canadian Acid Deposition Science
Assessment [CD-ROM]. Available from Environment Canada.
 The Acid Deposition and Oxidant Model (ADOM) modeling results6 show
that a further 75 percent reduction in SO2 emissions is required
to meet sulfur critical loads for aquatic ecosystems, as published in
the 1997 Acid Rain Assessment. Similar results are not yet available
in terms of reductions needed to achieve new critical load values (Figure
33); however, given that new critical load estimates are lower than 1997
estimates in many areas and higher in a few areas, a reduction of 50-75
percent could be required to meet the newer critical loads.
Since the development of the above maps, new critical load and exceedance
estimates have become available for forests in the provinces of Manitoba
and Saskatchewan, funded by the CCME Acid Rain Task Group. Similar calculations
for the Georgia Basin (British Columbia) and Alberta are in progress.
Figure 35 Long-term View of Critical Load Exceedances for
Canada
Click to enlarge
Note: Exceedance of critical loads of acidic deposition (eq/ha/yr of
sulfur and nitrogen combined) calculated using estimated current deposition
and grid cell critical loads recomputed using the steady-state assumption
of nitrogen saturation. In most areas, the environmental capacity to
absorb nitrogen is not yet exhausted. A positive exceedance indicates
that current deposition either is causing environmental harm or will
do so eventually if it continues at the same level. Details as in Figure
33.
Source: Environment Canada
Recovery of Acidified Lakes and Streams
Acid rain is only one of many large-scale anthropogenic effects that
are affecting lakes and streams in the United States. Climate variability,
forest maturation, biological disturbances (e.g., pest outbreaks), and
land use change can have an impact on ecosystems that are also affected
by acid deposition. Nonetheless, scientists have demonstrated measurable
improvements in some lakes and streams resulting from the Acid Rain Program.
Scientists studied lakes and streams in four regions-New England,
the Adirondack Mountains, the northern Appalachians (including the Catskill
Mountains), and the southern Appalachians (including the Blue Ridge)-and
found signs of recovery in many, but not all, of those areas (see Figure
36). These signs of recovery include reductions in sulfate and aluminum
concentrations (see Table 2) and decreases in acidity. For example, 48
out of 49 monitored Adirondack lakes showed reductions in sulfate concentrations
that correlate with reductions in atmospheric concentrations of sulfur.
These reductions in sulfate, as well as reductions in nitrate concentrations
that do not appear to be due to changes in atmospheric deposition, have
resulted in increased pH and acid neutralizing capacity (ANC, an indicator
of aquatic ecosystem recovery) as well as reductions in the amount of
toxic inorganic aluminum in Adirondack lakes.
Figure 36 Regional Trends in Lake and Stream Acidification,
1990-2004
Click to enlarge
Note: Bars show the magnitude of the regional trend for each variable
in each region.
Table 2 Results of Regional Trend Analyses on Lakes
and Streams, 1990-2004
| |
Concentrations (µeq/L per Year)* |
| Sulfate |
Nitrate |
ANC |
Base Cation |
Hydrogen |
Organic Acids |
Aluminum |
| –1.4 |
–0.02 |
+0.18 |
–1.35 |
–0.02 |
+0.02 |
insufficient data |
| –2.0 |
–0.45 |
+1.08 |
–1.24 |
–0.26 |
+0.15 |
–4.72 |
| –2.3 |
–0.31 |
+0.76 |
–3.73 |
–0.01 |
–0.03 |
insufficient data |
| +1.7 |
–0.55 |
–4.44 |
–4.56 |
–0.01 |
insufficient data |
insufficient data |
*Except for aluminum (µg/L per year).
Note: Values show the slope of the regional trend (the median value
for the trends in all of the sites in the region). Regional trends that
are statistically significant are shown in bold.
Increasing ANC was evident in two of the regions studied (Adirondacks
and northern Appalachians). One-quarter to one-third of lakes and streams
in these regions previously affected by acid rain are no longer acidic
at base flow conditions, although they are still highly sensitive to
future changes in deposition.
Improvements in Surface Water
Long-term monitoring networks provide information on the chemistry of
lakes and streams, which allow us to look at how water bodies are responding
to changes in emissions. The data presented here show regional trends
in acidification from 1990 to 2004 in areas of the eastern United States.
For each lake or stream in the network, measurements of various indicators
of recovery from acidification were taken. These measurements were plotted
against time, and trends for the given lake or stream during the 15-year
period were then calculated as the change in each of the measurements
per year (e.g., change in concentration of sulfate per year). Using the
trends calculated for each water body, median regional changes were determined
for each of the measures of recovery. A negative value of the "slope
of the regional trend" means
that the measure has been declining in the region, whereas a positive
value means it has been increasing. The greater the value of the trend,
the greater the yearly change in the measurement. Movement towards recovery
is indicated by positive trends in ANC and negative trends in sulfate,
nitrate, hydrogen ion, and aluminum. Negative trends in base cations
and positive trends in organic acids can balance out the decreasing trends
in sulfate and nitrate and prevent ANC from increasing.
A summary of the findings of this analysis follows:
- Sulfate concentrations are declining substantially in all but one
of the regions. Lakes and streams in the southern Appalachians show
increasing concentrations of sulfate. This area is unusual, because
its soils can store large amounts of the sulfate that is delivered
by deposition. After large amounts of sulfate have accumulated in the
soils, stream water sulfate concentrations begin to increase. The southern
Appalachians is the only region where atmospheric deposition chemistry
and the chemistry of lakes and streams are "decoupled."
- Nitrate concentrations are decreasing significantly in all of the
regions, although the magnitude of these changes is small, especially
in New England. It should be noted, however, that this does not appear
to reflect changes in emissions or deposition in these areas and is
likely a result of ecosystem adjustments that are not yet fully understood.
- As a result of declining sulfate (and to some extent nitrate),
the acidity of lake and stream water is decreasing in three of the
four regions. In the Adirondacks and northern Appalachians, ANC is
increasing. In New England, ANC appears to be increasing only slightly
and is not significant, but hydrogen ion concentrations are declining.
Declining hydrogen ion concentrations represent an increase in pH,
which is increasing significantly in the Adirondacks.
- Base cations are important, because they buffer the impact of sulfur
and nitrogen deposition.
Base cation concentrations in lakes and streams
are expected to decrease when rates of atmospheric deposition decline;
if they decrease too much, however, they limit recovery in pH and ANC.
The high rates of base cation decline in the northern Appalachians
may be of concern but do not currently seem to be preventing recovery.
However, this indicator will bear watching in the future.
- Organic acids are natural forms of acidity. Lakes and streams vary
widely in how much natural acidity they have, and increases in organic
acids over time, like declining base cations, can limit the amount
of recovery we observe. Organic acid concentrations are currently increasing
in many parts of the world, but the cause is still being debated. Of
the regions monitored by EPA, only the Adirondacks is showing significant
increases in organic acids, and their increase may be responsible for
10-15 percent less recovery (in ANC) than expected.
- Most of the regions do not have sufficient aluminum data to estimate
trends. Aluminum is a critical element, because it increases when lakes
and streams acidify and is very toxic to fish and other wildlife. The
one region where good aluminum data exist, the Adirondacks, is showing
strong declines in the most toxic form of aluminum (inorganic monomeric
aluminum).
- As mentioned above, the southern Appalachians is unusual, in both
its physiography and its response to changing atmospheric deposition.
Because sulfate is increasing strongly in this region, many of the
other chemical variables (e.g., ANC and pH) show trends typical of
acidifying conditions, rather than recovery.
Long-Term Environmental Monitoring at EPA
EPA's Temporally Integrated Monitoring of Ecosystems (TIME) and Long-Term
Monitoring (LTM) programs are designed to detect trends in the chemistry
of regional populations of lakes or streams and to determine whether
emission reductions have had the intended effect of reducing acidification.
TIME/LTM monitor a total of 145 lakes and 147 streams, representing all
of the major acid-sensitive regions of the northern and eastern United
States (New England, Adirondack Mountains, northern Appalachian Plateau
(including the Catskill Mountains), and the Ridge/Blue Ridge Provinces
of Virginia). TIME/LTM measure a variety of important chemical characteristics,
including ANC, pH, sulfate, nitrate, major cations (e.g., calcium and
magnesium), and aluminum. While the representativeness of the TIME/LTM
network is somewhat limited, the TIME program is the most coherent individual
regional data set for this kind of analysis. In addition, the U.S. Geological
Survey has been measuring surface water quality at several research watersheds
throughout the United States, where sample collection during hydrologic
events and ancillary data on other watershed characteristics have been
used to assess the watershed processes controlling acidification of surface
waters.
As described elsewhere in this report, implementation of the Acid Rain
Program has successfully and substantially reduced emissions of SO2 and
NOx from power generation sources in the United States. As
described in the National Acid Precipitation Assessment Program (NAPAP)
2005 Report to Congress (www.al.noaa.gov/AQRS/reports/napapreport05.pdf),
however, recent modeling and many published articles indicate that SO2 and
NOx emission reductions achieved under Title IV are now recognized
as insufficient to achieve full recovery or to prevent further acidification
in some regions. The studies described above support that conclusion,
showing that environmental improvements have been slow in many sensitive
areas and that signs of recovery still are not evident in some areas.
The NAPAP Report to Congress concluded that additional SO2 and
NOx emission reductions from power plants and other sources
are necessary to decrease deposition and further reduce the number of
acidic lakes and streams in many regions of the United States. Additional
emission reductions will be achieved through implementation of existing
and future regulations to address transport of ozone and fine particles
and mercury deposition, including the NOx SIP Call in the
eastern United States; Tier 2, Tier 3, and diesel rules affecting
mobile sources; SIPs to achieve the ozone and fine particle NAAQS; and
the recent Clean Air rules to reduce interstate transport of fine particles
and ozone, mercury, and regional haze from power plants.
3 Jeffries, D.S., McNicol, D.K., and Weeber, R.C. (2005)
Chapter 6: Effects on aquatic chemistry and biology. In: 2004 Canadian
Acid Deposition Science Assessment [CD-ROM]. Available from
Environment Canada.
4 Weeber, R.C., Jeffries, D.S., and McNicol, D.K. (2005)
Chapter 7: Recovery of aquatic ecosystems. In: 2004 Canadian Acid
Deposition Science Assessment [CD-ROM]. Available from Environment
Canada.
5 Houle, D. (2005) Chapter 5: Effects on forests and soils.
In: 2004 Canadian Acid Deposition Science Assessment [CD-ROM].
Available from Environment Canada.
6 Moran, M.D. (2005) Chapter 4: Current and proposed emission
controls: How will acid deposition be affected? In: 2004 Canadian
Acid Deposition Science Assessment [CD-ROM]. Available from
Environment Canada.
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