- As of December
14, 2012, the EPA announced that the number of nonattainment
areas are 46 ozone (8-hour 2008 standard), 41 ozone (8-hour 1997
standard), 9 sulfur dioxide, 46 PM-10, 35 PM-2.5 (1997 Standard),
32 PM-2.5 (2006 Standard), 2 lead (original standard), and 21
lead (2008 Standard) in the United States. There are no CO and
NO2 nonattainment areas in the United States. Maps of the ozone,
carbon monoxide, sulfur dioxide, lead (2008), PM-10, and PM-2.5
nonattainment areas are available for review and download.
- On December 14, 2012, the EPA announced
that it was going to change the annual health National Ambient
Air Quality Standard (NAAQS) for fine particles to 12.0 micrograms
per cubic meter (ug/m3) and retain the 24-hour fine particle
standard of 35 ug/m3. The agency also retained the existing standards
for coarse particle pollution (PM10).
- On October 11, 2011, environmental and public health
groups sued the Obama administration for rejecting stronger ozone
standards. The environmental law group, Earthjustice, filed the
lawsuit on behalf of the American Lung Association, Environmental
Defense Fund, Natural Resources Defense Council, and Appalachian
Mountain Club. The suite is associated with the President rejecting
the EPA's recommendation for more restrictive Ozone National
Ambient Air Quality Standards. In July, the Agency had recommended
that the ozone human health standard be reduced to 0.070 ppm
from 0.075 ppm and that a new vegetation standard be set at the
13 ppm-hour level. For more information about the Agency's proposed
changes to the ozone standards, please go to http://www.epa.gov/airquality/ozonepollution/actions.html
- On September 2, 2011, President Obama requested that
the EPA withdraw the Agency's draft Ozone National Ambient Air
Quality Standards, which it had submitted for review to the President's
Office of Management and Budget on July 11. The President cited
the importance of reducing regulatory burdens and regulatory
uncertainty, particularly as the Nation's economy continues to
recover. The President stated "Work is already underway
to update a 2006 review of the science that will result in the
reconsideration of the ozone standard in 2013. Ultimately, I
did not support asking state and local governments to begin implementing
a new standard that will soon be reconsidered." The White
House press release can be found by clicking here.
The letter from the White House's OMB to EPA Administrator Lisa
Jackson provided specific reasons for the President's decision.
The letter can be read by clicking here.
On September 22, 2011, the EPA announced
that it was moving forward to implement the 2008 ozone standard,
starting with the recommendations the states made in 2009 and
updating them with the most current, certified air quality data.
The Agency anticipates issuing proposed changes to the states'
recommendations later this fall. EPA indicates that it will quickly
initiate and complete a rulemaking to establish nonattainment
area classification thresholds so that it can finalize the designations.
Based on initial review of the 2008-2010 ozone air quality data,
52 areas that monitor air quality exceed the 0.075 ppm standard.
EPA expects to finalize the nonattainment designations for the
2008 ozone standard by mid-2012. However, EPA notes that it faces
litigation with respect to the timing of the designations and
expects that the resolution of the litigation may well affect
the precise timing of the schedule for designations.
On January 7, 2010, the EPA announced its proposal
to strengthen the national ambient air quality standards for
ground-level ozone. The EPA's proposal decreased the 8-hour primary
ozone standard level, designed to protect public health, to a
level within the range of 0.060-0.070 parts per million (ppm).
EPA proposed establishing a distinct cumulative, seasonal secondary
standard, referred to as the W126 index, which is designed to protect
sensitive vegetation and ecosystems, including forests, parks,
wildlife refuges, and wilderness areas. Dr. Lefohn, A.S.L. &
Associates' President, developed and proposed the W126 index
almost 25 years ago as a metric that could be used to protect
vegetation from ozone exposure. EPA proposed to set the level
of the W126 secondary standard within the range
of 7-15 ppm-hours. The proposed revisions resulted from a reconsideration
of the identical primary and secondary ozone standards set at
0.075 ppm in March 2008. The Agency's decision was planned to
be made in August 2010. However, on August 20, the Agency announced
that it will delay its announcement to on or around the end of
October. In early November, the EPA announced that it would reach
a final decision on the ozone standards by December 31, 2010.
On December 8, 2010, the EPA announced that it would delay its
final decision on the ozone standards until July 2011. EPA announced
on July 26 that it would not make a decision on the ozone standards
by its previously announced deadline of July 29. On August 12,
EPA indicated to the court that it is "fully committed"
to the ozone standards and it would move forward once the White
House review was complete. Based on several considerations, on
September 2, 2011, the President requested that the EPA withdraw
For those interested in
reviewing the historical reasons for recommending the range of
concentrations for the primary and secondary ozone standards,
information is available. On August 25, 2006, the EPA's Clean
Air Scientific Advisory Committee (CASAC) met in Research Triangle
Park at a public meeting to discuss and recommend to the EPA
the range of ozone concentrations that the Agency should consider
for establishing the human health and vegetation ozone standards.
The EPA taped and then transcribed the meeting's proceedings
and provided an unofficial transcript to the public on CASAC's
discussion. Please click here
to download the transcript.
For identifying violating
counties for the 2006-2008 period for the proposed human health
and vegetation ozone standards, please visit our maps webpage. Please note that for the 8-h ozone standard,
there will be more counties that violate the standard than the
US EPA has estimated due to the selection methodology that the
Agency utilizes in identifying monattainment areas. For more
information, please join A.S.L. & Associates in the Discussion
area on Facebook.
As part of the
proposed changes to the current 8-hour ozone human health standard,
the EPA estimated that the percentage of violating counties with
monitors for the 0.060, 0.065, and 0.070 ppm thresholds would
be 96%, 90%, and 76%, respectively. For the 3-year average of
the annual maximum 3-month cumulative 12-hour W126 secondary
ozone standard, the EPA estimated that the percentage of violating
counties with monitors for the 7 and 15 ppm-hour thresholds would
be 91% and 31%, respectively.
Some of the
background concerning the events that led to the EPA's Administrator's
decision on revising the 8-hour ozone standard helps in better
understanding the process. On
March 12, 2008, the EPA Administrator announced a decision on
the human health and vegetation ozone standards. At that time,
EPA revised the 8-hour "primary" ozone standard, designed
to protect public health, to a level of 0.075 parts per million
(ppm). The previous standard, set in 1997, was 0.08 ppm. EPA
decided not to adopt the cumulative exposure index as the vegetation
standard (i.e., secondary ozone standard). Although the EPA Administrator
recommended the W126 index as the secondary ozone standard,
based on advice from the White
Post, April 8, 2008; Page D02), the EPA Administrator made the
secondary ozone standard the same as the primary 8-hour average
standard (0.075 ppm). On May 27, 2008, health and environmental
organizations filed a lawsuit arguing that the EPA failed to
protect public health and the environment when it issued in March
2008 new ozone standards. On March 10, 2009, the US EPA requested
that the Court vacate the existing briefing schedule and hold
the consolidated cases in abeyance. EPA requested the extension
to allow time for appropriate EPA officials that were appointed
by the new Administration to review the Ozone NAAQS Rule to determine
whether the standards established in the Ozone NAAQS Rule should
be maintained, modified, or otherwise reconsidered. Based on
the September 2, 2011 decision by the President, it appears that
health and environmental organizations may be headed back to
- The range of suggested
values for the W126 standard is mainly based on the recommendations
that were made at a Workshop that took place in Raleigh, North
Carolina in 1996. To better understand what took place at this
workshop, please click here. The EPA recommends an accumulation
over a 12-hour (8 am 8 pm) exposure period over a 3-month
period giving greater weight to exposures at higher levels of
ozone. Our analyses and peer-reviewed published papers indicate
that such a secondary
ozone standard, in the proposed form, would overestimate vegetation
effects. For information about why the use of a 12-hour versus
a 24-hour accumulation period would contribute
to the inconsistency problem of the W126 index, please click here. You can learn more about the subject
of vegetation effects by visiting our Table of Contents web page.
- As part of the
current review of the ozone standarrds, for the EPA's Clean Air
Scientific Advisory Committee (CASAC) meeting in Chapel Hill,
NC that took place on May 19-20, 2011, we prepared a 55-page
summary of what we believe the research status is of surface
ozone policy-relevant background. There is much controversy on
what the range of background ozone is in the United States. The
EPA, using a model, believes that background ozone is in the
range of 15-35 ppb. However, models tend to poorly estimate the
contribution of natural processes, such as stratospheric intrusions
into the lower troposphere. Our research is indicating that frequent
occurrences greater than or equal to 50 ppb that occur at both
high- and low-elevation monitoring sites across the US are influenced
by transport from the stratosphere to the lower troposphere.
The enhanced ozone concentrations that appear to be related to
stratospheric transport occur during the springtime and sometimes
during the summertime. In addition, long-range transport of Eurasian
biomass burning, as well as wildfires in the US, contribute to
background ozone concentrations. Estimating the range of background
ozone properly is important because the range of background concentrations
is used in the EPA's risk assessment for human health and vegetation,
as well as assessing the amount of emission reductions required
to attain a specific ozone level (i.e., standard). If the actual
background level of ozone is higher than EPA estimates with models,
then the Agency may overestimate human health as well as vegetation
risks and present inaccurate information to the public and policymakers.
If you would like to read the 55-page report by Allen S. Lefohn
and Samuel J. Oltmans on the status of policy-relevant background
(PRB) ozone, please click here.
- For several
years, A.S.L. & Associates has had an on-going effort to
better understand the range and frequency of occurrence of background
ozone levels that may not be affected by emission reduction strategies.
In a paper published
in May 2001, the research team consisting of Allen Lefohn, Samuel
Oltmans, Tom Dann, and Hanwant Singh discussed that background
ozone levels were higher and that the natural short-term variability
was more frequent and greater than previously believed. The authors
are associated with the following institutions: A.S.L. &
Associates, NOAA, Environment Canada, and NASA, respectively.
In our 2001 paper, we concluded that hourly levels greater than or equal to 50 ppb occur
more frequently as a result from natural sources than previously
2006, the US EPA defined Policy-Relevant
Background (PRB) for ozone as those concentrations that would
occur in the United States in the absence of anthropogenic emissions
in continental North America (i.e., the United States, Canada,
and Mexico). PRB concentrations include contributions from (1)
natural sources everywhere in the world and (2) anthropogenic
sources outside the United States, Canada, and Mexico. In 2008,
we published results, using empirical data, confirming that at
some locations in the US, PRB ozone concentrations are greater
than or equal to 50 ppb. In
late September 2009, the National Research Council released the
report, Global Sources of Local Pollution. In the report,
the Committee states that modeling and analysis supports the
finding that Policy-Relevant Background (PRB) is 20-40 ppb for
the United States. Unfortunately, the NRC conclusion does not
agree with the peer-review literature using empirical data that
hourly averaged PRB ozone concentrations are greater than or
equal to 50 ppb. Although
spatially low-resolution models have been exercised and indicated
that conclusions reached by Lefohn et al. (2001) were
incorrect, our current research and the results published by
other research groups support the conclusions reached by Lefohn
et al. (2001) that PRB ozone concentrations are greater
than or equal to 50 ppb at both high- and low-elevation monitoring
sites. Clearly, low-resolution models are unable to adequately
capture the important processes that are important for characterizing
PRB and therefore, underestimate policy relevant background concentrations.
The latest results using GEOS-Chem models continue to underestimate
PRB ozone concentrations. An Internet-based slide presentation is available for purposes
of previewing our paper. Also please be sure to check out the
answer to our quiz that identifies the month
in which the highest 8-hour daily maximum concentration occurred
for the 4 remote ozone monitoring sites. Additional information
on background ozone concentrations can be found in the Air Quality
Analyses section of our Table of Contents. In-depth discussions are
provided on this very important topic.
- EPA released its design value findings on air quality on September 2, 2010 and concluded
for the period 2007-2009:
14 of the 126 areas originally
designated nonattainment for the 8-hour O3 National Ambient Air
Quality Standard (NAAQS) failed to meet the 1997 8-hour O3 NAAQS
for the period 2007-2009 (see Table);
2 of the areas originally designated nonattainment
had incomplete data (see
No additional unclassifiable/attainment areas
failed to meet the O3 NAAQS in 2007-2009 (see Table);
As of September 2, 2010, 79 of the 126 areas
originally designated nonattainment for the 8-hour O3 NAAQS are
classified as maintenance areas, meaning they have been redesignated
to attainment (see
Four of the original 39 areas designated nonattainment
for the PM2.5 NAAQS in April, 2005 (using 2001-2003 data) failed
to meet the annual PM2.5 NAAQS in 2007-2009. Twenty-nine of the
original 39 nonattainment areas met the annual NAAQS in 2007-2009.
Six areas have insufficient data to allow a determination of
compliance with respect to the annual PM2.5 NAAQS in 2007-2009;
in each of these six areas, one or more sites for which compliance
cannot be determined for 2007-2009 clearly violated the NAAQS
in a previous period (e.g., for 2006-2008) (see Table);
Eighteen of the 31 areas originally designated
nonattainment for the 24-hour PM2.5 NAAQS failed to meet the
NAAQS with 2007-2009 data. Nine of the original 31 nonattainment
areas met the 24-hour PM2.5 NAAQS in 2007-2009. The other four
areas are shown to have incomplete data with respect to the 24-hour
PM2.5 NAAQS; in each of these four areas, one or more sites for
which compliance cannot be determined for 2007-2009 clearly violated
the NAAQS in a previous period (e.g., for 2006-2008). (see Table);
For 2007-2009, no counties, outside of existing
nonattainment areas, did not meet the PM2.5 annual NAAQS (see Table).
Five counties, outside of existing nonattainment areas, did not
meet the PM2.5 24-
hour NAAQS for 2007-2009. (see Table);
There were 59 counties not meeting the new
daily maximum 1-hour SO2 average NAAQS (see Table);
There was one county, Cook county Illinois,
that did not meet the new daily maximum 1-hour average NO2 NAAQS
EPA's web site (www.epa.gov/airtrends/ozone.html), the Agency
summarized ozone trends for the periods 1980-2010 and 1990-2010.
Figures 1 and 2 below have been reproduced from the Agency's
current website. Lefohn, Shadwick, and Oltmans (2010) have statistically
quantified in a paper published in the peer-reviewed journal,
Atmospheric Environment, a site-by-site trending analysis
for the period 1980-2008 and 1994-2008. Although the figures
below illustrate a national average change, Lefohn et al. (2010)
point out that many ozone monitoring sites show no statistical
changes over time as well as a small number of sites show increases
in trending. Please see the publications
list for the citation. Table 1 below lists the changes over the
past several years.
Figure 1. National 8-hour Ozone Air Quality Trend, 1980-2010.
Based on annual fourth highest daily maximum 8-hour ozone concentration
trended over the period of time.
Figure 2. National 8-hour Ozone Air Quality Trend, 1990-2010.
Based on annual fourth highest daily maximum 8-hour ozone concentration
trended over the period of time.
Table 1. Comparison
of trending by US EPA for two exposure metrics for several time
2nd Highest 1-Hour Average
4th Highest 8-Hour Average
As indicated above, Lefohn et al. (2010)
published their trending findings for surface ozone monitoring
sites across the United States. Using statistical trending on
a site-by-site basis of the (1) health-based annual 2nd highest
1-hour average concentration and annual 4th highest daily maximum
8-hour average concentration and (2) vegetation-based annual
seasonally corrected 24-hour W126 cumulative exposure index,
they investigated temporal and spatial statistically significant
changes that occurred in surface ozone in the United States for
the periods 1980-2008 and 1994-2008. For more information about
the Lefohn et al. (2010) and Lefohn et al. (2008) (for the period
1980-2005 and 1990-2005) findings, please click
Since 1997, we have
been discussing the "piston" effect in the peer-reviewed
literature (see publications listing).
In 1997, we predicted that there would be a leveling off of improvements
in O3 concentrations as O3 emission precursors were reduced at
some monitoring sites Our prediction apparently has been verified
by our most current analysis (Lefohn et al., 2010). The "piston"
effect, as described in the peer-review literature and on this
web site, affects the ability of the
nation to attain the 8-hour ozone standard. As we discussed in
our original paper, the peak hourly average concentrations (i.e.,
hourly average concentrations greater than or equal to 0.10 ppm)
are reduced much faster than the mid-level concentrations (i.e.,
0.06-0.099 ppm). In the most recent EPA Ozone Criteria Document
(2006), the Agency notes "The highest O3 concentrations
have tended to decrease over the past 15 years, while there has
been little change in O3 concentrations near the center of the
distribution." The document notes that this is consistent
with results published in Europe. Interesting, the Agency notes
in the document that there has been an increase in O3 concentrations
at the lower levels throughout the monitoring period, which is
consistent with data obtained in Europe, showing that O3 minima
increased during the 1990s because of reduced titration of O3
by reaction with NO in response to reductions in NOx emissions.
Based on our published findings, the EPA has attempted to take
into consideration the "piston" effect by utilizing
theoretical rollback models that allow the higher hourly average
ozone concentrations to be reduced at a faster rate than the
mid-level values. Clearly the "piston" effect heavily
influences the Nation's ability to attain an 8-hour ozone standard.
We discuss more about the "piston" effect and how it
affects the attainability of the ozone standard in our concerns
EPA's web site (http://www.epa.gov/airtrends/aqtrends.html),
the Agency summarizes emission trends for the period 1980-2008.
The tables below are the most current estimates provided by EPA
on its web page as of October 2009.
National Emissions Estimates
(fires and dust excluded)
For Common Pollutants and their Precursors
Carbon Monoxide (CO)
Nitrogen Oxides (NOx)
Particulate Matter (PM)
Sulfur Dioxide (SO2)
1. In 1985 and 1996 EPA refined its methods for estimating emissions.
Between 1970 and 1975, EPA
revised its methods for estimating PM emissions.
2. The estimates for 2005 and beyond are from the final version
2 of the 2005 NEI.
3. For CO, NOx, SO2 and VOC emissions, fires are excluded because
they are highly variable; for
direct PM emissions both fires and dust are excluded.
4. PM estimates do not include condensable PM.
5. EPA has not estimated PM2.5 emissions prior to 1990.
6. The 1999 estimate for lead is used for 2000, and the 2002
estimate for lead is used for 2005 and
7. PM2.5 emissions are not added when calculating the total because
they are included in the PM10
in Air Quality
1980 versus 2008
1990 versus 2008
1. --- Trend data not available
2. PM2.5 air quality based on data since 2000
3. Negative numbers indicate improvements in air quality
1980 versus 2008
1990 versus 2008
1. --- Trend data not available
2. Direct PM10 emissions for 1980 are based on data since 1985
3. Negative numbers indicate reductions in emissions
- On February
24, 2009, the U.S. Court of Appeals for the D.C. Circuit remanded
the National Ambient Air Quality Standards (NAAQS) for fine particulate
matter (PM2.5) to EPA for reconsideration of the annual level
of the standard (which EPA left at 15 micrograms per cubic meter
(µg/m3)) and reconsideration of the secondary PM2.5 NAAQS.
With respect to the annual PM2.5 NAAQS, the court held that the
agency failed to explain adequately why an annual level
of 15 µg/m3 is requisite to protect the public health,
including the health of vulnerable subpopulations, while providing
an adequate margin of safety. 42 U.S.C.§ 7409(b)(1).
For the secondary standards, the court held that EPA unreasonably
concluded that the NAAQS are adequate to protect the public welfare
from adverse effects on visibility. The court denied petitions
for review of the primary daily standard for coarse PM and the
petition for review of EPAs revocation of the primary annual
standard for coarse PM. The Court opinion can be read by clicking
21, 2006, EPA announced with regard to primary standards for
fine particles (generally referring to particles less than or
equal to 2.5 micrometers (µm) in diameter, PM2.5) that
it revised the level of the 24-hour PM2.5 standard to 35 micrograms
per cubic meter (µg/m3) and retained the level of the annual
PM2.5 standard at 15 µg/m3. With regard to primary standards
for particles generally less than or equal to 10 µm in
diameter (PM10), EPA retained the 24-hour PM10 and revoking the
annual PM10 standard. With regard to secondary PM standards,
EPA made them identical in all respects to the primary PM standards,
as revised. The issue of reliability of the epidemiological time-series
methodologies continued to be of concern to the Administrator.
The Administrator noted in his decision that there were many
sources of uncertainty and variability inherent in the inputs
to the assessment and that there was a high degree of uncertainty
in the resulting PM2.5 risk estimates. Such uncertainties generally
related to a lack of clear understanding of a number of important
factors, including, for example, the shape of concentration-response
functions, particularly when, as here, effect thresholds can
neither be discerned nor determined not to exist; issues related
to selection of appropriate statistical models for the analysis
of the epidemiologic data; and the role of potentially confounding
and modifying factors in the concentration-response relationships.
For those interested in the possible violation areas for the
revised 24-hour PM-2.5 standard based on 2004-2005 data, please
- On December
22, 2008, EPA designated areas throughout the United States as
"nonattainment" and "unclassifiable/attainment"
for the 24-hour national air quality standard (35 ug/m3) for
fine particulate matter (PM2.5). The EPA designated 211 counties
or parts of counties as nonattainment. These nonattainment areas
include counties with monitors violating the standards and nearby
areas that contribute to that violation. A map of the EPA's PM2.5
designations for nonattainment can be reviewed by clicking
For a comparison of the violators for the PM2.5 annual standard
(2005-2007) and the PM2.5 24-hour average standard (35 ug/m3),
- In December 2008, we presented at the AGU Fall Conference
in San Francisco a summary of one of our several research efforts
dealing with changes in tropospheric ozone levels. The talk was
presented at the Tropospheric Gaseous Composition in the Regional
and Global Perspective 1 - A11F-03 session. The title of
our presentation was: "Tropospheric Ozone Changes from Surface
and Ozonesonde Observations." The research was presented
by the lead author, Samuel Oltmans, NOAA Earth System Research
Laboratory Global Monitoring Division, Boulder, Colorado. The
talk explored the following:
- What are the implications
from this record of observations?
- Are the records consistent
in regions with multiple records?
- At what geographic scale
can conclusions about trends be drawn (global, hemispheric, regional)?
- Are changes related to
precursor emissions, transport variability, stratospheric input?
Based on our analyses,
our conclusions are
- In the Northern Hemisphere,
there is a different pattern of long-term changes between North
America, Europe, and Japan;
- Over North America there
does not appear to be a significant increase over the 30 years
of measurements, although there have been shorter term fluctuations;
- Western Europe saw the
largest increases prior to 1990 but a significant decrease in
growth rates (and in some cases declines) over the past 15 years
over continental Europe;
- In Japan, increases were
primarily prior to the mid 1980s, but with recent increases in
- In the Southern Hemisphere
mid latitudes, at Cape Point, Cape Grim, and Lauder, ozone has
increased significantly with the increases coming primarily in
the austral spring;
- In Hawaii (North Pacific
tropics), increases appear to be associated with decadal transport
- The tropical south Pacific
(Samoa) has not shown significant changes in tropospheric ozone;
- At the South Pole, earlier
declines have reversed so that overall there has been almost
Some possible implications
of recent (i.e., 30 year) observed changes are
- The relationship between
emission changes and longer term hemispheric and global tropospheric
ozone changes is not adequately understood;
- The climate forcing of
tropospheric ozone changes over the recent past is still very
- It will be difficult to
assess the climate forcing reductions that can be gained by reducing
tropospheric ozone with the current network of observations.
Co-authors of the research
study are A. Lefohn, J. Harris, H.-E. Scheel, E. Brunke, H. Claude,
D. Tarasick, I. Galbally, G. Bodeker, J. Davies, T. Koide, B.
Johnson, C. Meyer, F. Schmidlin, E. Cuevas, A. Redondas, P. Simmonds,
and B. Buchman.
Over the past several years,
there have been several articles quoting other sources indicating
that surface ozone concentrations are increasing everywhere.
Our most current research results do not support this claim.
Our research continues to monitor the status of worldwide ozone
levels by performing sophisticated analyses using surface ozone
and ozonesonde data. Previous peer-reviewed papers on background
ozone trends that we have published are
Oltmans S. J., Lefohn A.
S., Scheel H. E., Harris J. M., Levy H. II, Galbally I. E. ,
Brunke E. G., Meyer C. P., Lathrop J. A., Johnson B. J., Shadwick
D. S., Cuevas E., Schmidlin F. J., Tarasick D. W., Claude H.,
Kerr J. B., Uchino O., and Mohnen V. (1998) Trends of ozone in
the troposphere. Geophysical Research Letters. 25:139-142.
Oltmans S. J., Lefohn A.
S., Harris J. M., Galbally I., Scheel H. E., Bodeker G., Brunke
E., Claude H., Tarasick D., Johnson B.J., Simmonds P., Shadwick
D., Anlauf K., Hayden K., Schmidlin F., Fujimoto T., Akagi K.,
Meyer C., Nichol S., Davies J., Redondas A., and Cuevas E. (2006)
Long-term changes in tropospheric ozone. Atmospheric Environment.
- Canada has identified the ozone concentrations for
the 4th highest 8-hour levels across the U.S. and Canada. Maps are available that compare the U.S. and Canada for
- Sometimes policymakers
do not pay careful attention to the technical details associated
with important scientific topics. For example, EPA indicated
in April 2004 in its report, The Ozone Report - Measuring
Progress Through 2003, that for the period 1990 - 2003, six
locations experienced statistically significant increases in
ozone: Great Smoky Mountains (Tennessee) in the eastern United
States and Mesa Verde (Colorado), Rocky Mountain (Colorado),
Craters of the Moon (Idaho), Canyonlands (Utah), and Yellowstone
(Wyoming) in the West.
Park is a relatively remote site for ozone monitoring in the
United States. The greatest frequency of ozone concentrations
greater than or equal to 0.05 ppm occurs in the spring, which
we believe implies a natural stratospheric contribution to the
site. We have not observed trends in ozone in the park since
the beginning of monitoring. Our ozone trending analysis includes
data through 2005. Our review of the latest data for 2006 indicate
that no statistically significant ozone trends would be identified
for Yellowstone National Park if the additional year were included
in our analysis. We pointed out several years ago that EPA's
trending results were due to a change in the physical location
of the actual ozone monitor. In 1996, the monitoring site was
changed and this resulted in two distinct sets of data being
generated. Based on our analysis, EPA should not have combined
the two sets of data for trends analysis in its April 2004 report.
EPA, in its latest estimates of trending at national parks, did
not attempt to identify a trend for the Yellowstone National
Park site for the period 1990 - 2004 because of the change in
physical location (EPA, 2006 - see page AX3-113). The
scientific information showing the changes in the monitoring
site and the effects on trends from 1987 through 2001 is available
In May 2006, the
U.S. National Park Service provided on its web site (http://www2.nature.nps.gov/air/) the results
of its 2005 Annual Performance and Progress Report: Air Quality
in National Parks report. Based on air quality data covering
the period 1995-2004, the National Park Service announced that
both Yellowstone National Park and Glacier National Park are
experiencing statistically significant increases in ozone concentrations.
This finding contradicts our own peer-reviewed published analyses
(Oltmans et al. 2006) and the information provided in
EPA's Ozone Criteria Document published in 2006. Although EPA
did not attempt to determine an ozone trending for Yellowstone
National Park for the scientific reasons detailed above, the
Agency did report that no statistically significant trend was
observed at Glacier National Park for the period 1990-2004. Thus,
our most recent trending analyses (Oltmans et al., 2006)
and EPA's analysis agree that no trend appears to exist at Glacier
National Park. In addition, our most recent analysis (Oltmans
et al., 2006) also shows no trending at Yellowstone National
Park. We believe there are clear reasons for the discrepancy
between the results presented by the National Park Service and
those by EPA and A.S.L. & Associates. Based on our review
of the National Park Service analysis of ozone data, we believe
that at this time, no trends in surface ozone are occurring at
either Yellowstone National Park or Glacier National Park. For
additional information, please
review our technical comments.
Oltmans S. J., Lefohn A. S., Harris
J. M., Galbally I., Scheel H. E., Bodeker G., Brunke E., Claude
H., Tarasick D., Johnson B.J., Simmonds P., Shadwick D., Anlauf
K., Hayden K., Schmidlin F., Fujimoto T., Akagi K., Meyer C.,
Nichol S., Davies J., Redondas A., and Cuevas E. (2006) Long-term
changes in tropospheric ozone. Atmospheric Environment. 40:3156-3173.
U.S. Environmental Protection
Agency (2006) Air Quality Criteria for Ozone and Related Photochemical
Oxidants. Research Triangle Park, NC: Office of Research and
Development; report no. EPA/600/R-05/004af.
- Our research team has used ordinary kriging
to develop surface ozone models for the years 1982 to 2009. Our
most recent work has included the kriging of the W126 integrated
and the N100 exposure indices. To read more about our Team's
use of kriging to spatially characterize surface ozone, please
visit our kriging web page.
- Over the past years, A.S.L. & Associates and its
consultants have commented on the strengths and weaknesses associated
with the mathematical and statistical methodologies used in epidemiological
studies to link exposure with human health effects. Many of the
statistical caveats raised throughout the PM and Ozone Criteria
Documents and the PM and Ozone Staff Papers indicate a pattern
of inconsistent results that is troubling. Examples of the growing
pattern of inconsistent and inconclusive findings include the
- Instability of PM mortality
effect estimates resulting from different model specifications
of weather effects and time trends.
- Instability of PM effect
estimates resulting from different selections of monitoring sites
- Increased heterogeneity
of PM effect estimates across cities.
- Greater diversity of findings
among studies and across study areas.
- Contradictory results
from mortality displacement studies.
- PM effect lags that are
inconsistent across cities and across studies.
- Exposure-response relationships
that are inconsistent across cities and across studies.
- Inconsistencies between
short-term and long-term effect studies, such as respiratory
effects of fine particles.
- Contradictory findings
among long-term studies.
Additional details about
the Team's epidemiological concerns are discussed on our epidemiological
concerns web page. The
Team's comments on the first draft of the PM Staff Paper were
submitted to EPA in October 2003. To read more about our concerns
about the first draft, please visit our web page.
EPA announced on April 15, 2004 that
it has designated 474 counties as nonattainment for the 8-hour
ozone standard. There were 126 nonattainment areas. The most
recent update shows an adjustment to these numbers. A map is available to view the locations of nonattainment
counties. We do have concern that while the number of violation
areas of the ozone standard is great, the public may not be at
as much risk as the EPA estimates. In addition, the standard
will be difficult and in many cases impossible to attain due
to the "piston" effect. An Internet-based slide presentation is available that explains the effect.
Additional information about the effect can be found in the Table of Contents section of this web site.
- Sometimes science
and politics mixed together become science fiction. Such is the
case that occurred, when in September 2002, many newspapers across
the United States printed a story summarizing the report, Code
Red: America's Five Most Polluted National Parks, which described
The Great Smoky Mountains as the nation's most polluted national
park, with air quality rivaling that of Los Angeles. For the
period 1997-2001, the report claims that the annual ozone exposure
was higher at Great Smoky Mountains National Park than at Los
Angeles, California. There is a serious technical problem associated
with the report and the report's conclusions are flawed. Please
read "The Rest of the Story."
- In 2000, Haywood County, NC experienced its 4th highest
8-hour ozone concentration at 0.085 ppm.
On May 1, a daily maximum 8-hour average concentration of 0.089
ppm was experienced. A detailed meteorological
that stratospheric ozone played an important role in this ozone
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