- The EPA told the
U.S. Court of Appeals for the D.C. Circuit in a court filing
in late October 2021 that it will initiate a rulemaking process
to reassess, by the end of 2023, the Agency's December 2020 decision
to retain the 2015 ozone human health and vegetation standards.
- On April 28, 2022,
the EPA published the draft document "Policy Assessment
for the Reconsideration of the Ozone National Ambient Air Quality
Standards, External Review Draft (Draft PA)." The draft
document was prepared as a part of the current reconsideration
of the 2020 final decision on the national ambient air quality
standards (NAAQS) for ozone (O3). The primary and secondary O3
NAAQS are set to protect the public health and the public welfare
from O3 and other photochemical oxidants in ambient air. The
draft document is available on the EPA's website at https://bit.ly/3vXz2hn. Dr. Lefohn's comments
on the draft document were submitted on May 30, 2022 to the official
Docket and are available by clicking here.
- The EPA Administrator
made the Agency's final ozone rulemaking decision on December
23, 2020. Both the human health and vegetation ozone standards
remained at the levels established in 2015. The EPA's decision
on the ozone standards can be reviewed here. In regard to the secondary ozone standard
used to protect vegetation, the EPA Administrator focused his
comments on Lefohn et al. (1997) and Lefohn and Foley (1992).
Both papers appear to have played an important role in the Administrator's
December 2020 decision for the secondary ozone standard. As the
EPA reconsiders both the human health and vegetation ozone standards,
additional focus will be on the use of the current 8-h ozone
standard as a means to control W126 exposure values for the protection
of vegetation. In his comments on the "Policy Assessment
for the Reconsideration of the Ozone National Ambient Air Quality
Standards, External Review Draft (Draft PA)" document, Dr.
Lefohn focused some of his comments on the EPA's use of the current
primary 8-h standard to control for W126 exposures that affect
vegetation. His May 30, 2022 comments to the Docket can be viewed
Lefohn, AS, Jackson, W, Shadwick, DS and
Knudsen, HP (1997). Effect of surface ozone exposures on vegetation
grown in the southern Appalachian Mountains: Identification of
possible areas of concern. Atmospheric Environment 31(11): 1695-1708.
Lefohn, AS and Foley, JK (1992). NCLAN
Results and their Application to the Standard-Setting Process:
Protecting Vegetation from Surface Ozone Exposures, J Air Waste
Manag Assoc 42(8): 1046-1052.
On October 1, 2020, Dr. Lefohn, President
of A.S.L. & Associates, LLC, responded to EPA's request for
comments on the draft ozone rulemaking proposal. His 222 page
document, filed in the official Docket, can be downloaded here.
In December 2019, his comments on the drafts of the EPA's Integrated
Science Assessment for Ozone (ISA) and Policy Assessment (PA)
documents were filed in the U.S. government's official Docket.
Dr. Lefohn's comments on the Integrated Science Assessment for
Ozone (ISA) report can be downloaded here. His comments on the Policy Assessment
(PA) document can be downloaded here. Some of the points made in the three
- There are two fundamental principles important
in the ozone rulemaking activity.
- Fundamental Principle One: Higher Hourly
Average Ozone Concentrations Should be Weighted More than Middle
and Lower Values when Assessing Human Health and Environmental
Effects. The use of long-term average concentrations is not
supported by human health and vegetation laboratory experiments.
Based on ozone laboratory experiments, Haber's Rule (i.e., concentration
multiplied by time) is not appropriate.
- Fundamental Principle Two: Daily Maximum
Hourly Averaged Ozone Concentrations Will Remain Well above 0
Parts per Billion (ppb) Even if all Anthropogenic Emissions Were
Eliminated Worldwide. In other words, there are natural sources
of ozone that contribute substantially to surface ozone concentrations
that are measured daily around the world.
- As a result of emission reductions, the
highest ozone concentrations are reduced and the lowest concentrations
are increased due to the reduction of NO scavenging.
- Annual average or median concentrations
increase as emissions are reduced at some monitoring sites
in the US. This is a result of the reduction of NO scavenging
on the lower concentrations.
- In 2015, EPA noted in its ozone rulemaking
process that both acute and chronic ozone health effects could
be reduced by reducing the higher hourly average concentrations.
This is an important statement by the Agency because it indicates
that ozone exposure metrics, used in models for estimating long-term
risk to humans, should be focused on the reduction of the higher
ozone values rather than attempting to reduce the entire distribution
of hourly average concentrations. The use of ozone exposure metrics,
based on annual average concentrations which increase at many
sites because of the reduction of NO scavenging associated with
emission reductions, could result in less than accurate human
health ozone risk estimates.
- The DC Court of
Appeals on August 23, 2019 rendered its decision on the EPAs
2015 ozone (smog) standards. The Court remanded back to the EPA
for reconsideration the ozone standard to protect vegetation.
The W126 metric, created by A.S. Lefohn, that CASAC recommended
to protect vegetation is involved in this decision. The DC Court
of Appeal's decision will not be appealed in the near future
because the EPA has decided to reconsider EPA's December 2020
decision on the current human health and vegetation ozone standards.
For more information, please read the entire decision by the Court. The year 2022
will be a busy year for the EPA and the new CASAC ozone panel
on reviewing the scientific evidence associated with the reconsideration
of the 2015 human health and vegetation ozone standards, as well
as the Agency's response to the DC Court of Apeals.
- The Working Group
I contribution to the IPCC's Sixth Assessment Report, AR6 Climate
Change 2021: The Physical Science Basis, addresses the latest
physical understanding of the climate system and climate change.
The report is an interesting read. The report can be downloaded
- In a recent published article, Go slow to go fast:
A plea for sustained scientific rigor in air pollution research
during the COVID-19 pandemic, the authors (Heederik, Smit,
and Vermeulen), all associated with the Division of Environmental
Epidemiology, Institute for Risk Assessment Sciences, Utrecht
University, Utrecht, The Netherlands, noted that over a ten-day
period, three papers involving original research associating
COVID-19 mortality and air pollution were published. These publications
attracted considerable attention from international news outlets
and on social media. According to the authors, all three ecological
studies relied on aggregate data, which can suffer from the well-known
problem of ecological fallacy, where a misjudgment in interpretation
occurs as inferences about individuals are reasoned from the
group to which the individual belongs. The authors believe that
this is a major issue, mostly ignored in these studies resides
in the complexity of a potential association between air pollution
and COVID-19 morbidity and mortality. The authors' article was
published in the European Respiratory Journal. The Journal
is the flagship journal of the European Respiratory Society.
The entire article can be downloaded at https://bit.ly/3hHRxO6.
- Design values published
by the EPA provide an opportunity to quantitatively evaluate
for the period 2015-2017 the status of ozone (smog) exposures
in the national parks in the United States. Ozone data from 43
monitors in the US national park system were evaluated for potential
human health risk. Sixty-one percent of the monitoring sites
in the park system received a grade of either "A" or
"B", 12% received a grade of "C", and 28%
received a grade of either "D" or "F".
More information available at https://bit.ly/2MfFuM4.
- Over the years in the United States, we made considerable
progress in reducing ozone (i.e., smog) exposures. The 3-year
average of the annual 4th highest daily 8-h concentration is
the form of the US ozone standard to protect human health and
welfare (i.e., vegetation). In 2015, the US EPA lowered the standard
to 70 parts-per-billion (ppb). More information available at
- The use of different
air quality markers (metrics) for surface ozone calculated from
the same time series can result in different trend patterns.
This outcome is important to researchers, as well as policymakers
and regulators, who use exposure metrics to assess how changes
in ozone levels affect human health, vegetation, and climate.
one conclusion from a metrics assessment based on the Tropospheric
Ozone Assessment Report or TOAR, an effort by the International
Global Atmospheric Chemistry Project to create the world's largest
database of surface ozone observations from all available ozone
monitoring stations around the globe. The TOAR paper, Global
surface ozone metrics identified for climate change, human health,
and crop/ecosystem research, was published in the journal
Elementa: Science of the Anthropocene. The list of metrics
used in the TOAR program can be downloaded here. The paper is available at the Elementa
website at: https://www.elementascience.org/article/10.1525/elementa.279/
24 international researchers who worked on the paper anticipate
that their effort will provide scientists, regulators, and policymakers
with better insight about spatial and temporal variation that
relate to climate change, human health, and crop/ecosystem around
paper provides the following:
description of 25 metrics, which are used for assessing spatial
and temporal trends by environmental agencies and researchers
around the world (4 for model-measurement comparison, 5 for characterization
of ozone in the free troposphere, 11 for human health impacts,
and 5 for vegetation impacts).
The scientific rationale for the selection of each of the 25
A detailed description of the statistical methods based on stringent
scientific principles used in the Tropospheric Ozone Assessment
Report (TOAR) program.
A comparison of the trend behavior for each of the ozone impact
metrics when using the same surface ozone concentration time
components of the Tropospheric Ozone Assessment Report (TOAR)
(http://www.igacproject.org/activities/TOAR) are the use
of metrics that are biologically defensible, as well as the use
of statistical methods that adhere to stringent scientific principles.
This paper provides the background for the selection of the metrics
and the statistical methods used in the international TOAR program.
- Background ozone
is an important part of the challenge to attaining the 0.070
ppm ozone standard. Although the EPA is continuing the ozone
area designation process, the Agency is still concerned about
the effect that background has on attainment of the 2015 ozone
standard. Specifically, the key reasons that the EPA proposed
a delay in 2017 to implementing the new ozone standard were
understanding the role of background ozone levels;
accounting for international transport; and
consideration of exceptional events demonstrations.
is much controversy on what the range of background ozone is
in the United States. 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.
Our published material on background ozone can be found here. Our current
research continues to address how to integrate background ozone
with the attainment process.
- Since A.S.L.
& Associates' founder, Dr. Allen Lefohn, participated like
others in the first Earth Day on April 22, 1970, we have seen
much progress in controlling environmental pollution and improving
the Nation's health and welfare (i.e., vegetation). For example,
the US EPA began to regulate ozone with the promulgation of a
ground-level National Ambient Air Quality Standard (NAAQS) in
1971, with subsequent revisions in 1979, 1997, 2008, and 2015.
Following promulgation of the 1997 ozone standard, the US EPA
issued a NOx State Implementation Plan (SIP) Call, which reduced
regional summertime NOx emissions from power plants and other
large stationary sources by 57% in 22 Eastern US states. In addition,
the US EPA established national rules that substantially reduced
NOx and VOC emissions from on-road mobile sources by 53% and
77% between 1990 and 2014, respectively. Overall, NOx and VOC
have decreased in the US by 52% and 39% from all sources since
in the magnitude of national and regional emissions, as well
as any long-term changes in international emissions, climate,
and inter-annual meteorological variability, can drive shifts
in the distributions of hourly surface ozone (O3) concentrations.
Changes in the distributions of hourly average O3 concentrations
can result in changes in the magnitude of exposure metrics used
for assessing human health and vegetation effects. Surprisingly,
trend patterns in O3 exposure metrics may be in a similar direction
as emissions change (e.g., metrics increase as emissions increase)
or trend patterns of metrics may not be in a similar direction
as emissions change (e.g., metrics increase as emissions decrease)
(Lefohn et al., 2017; Lefohn et al., 2018 - see publications list). Besides
the work by Lefohn et al. (2017, 2018), other researchers have
reported this observation in the literature. This is a very important
observation because if a biologically irrelevant O3 metric is
selected for assessing trends, an incorrect conclusion may be
drawn concerning the relationship between emissions reductions
and the protection of the public's health and welfare. Over the
past 20-30 years, substantial changes in O3 concentrations have
been observed at many sites across the world, likely driven by
a combination of the large emissions changes and potentially
by shifts in various meteorological conditions. The paper by
Lefohn et al. (2017) investigated the relationship between exposure
metrics, hourly O3 concentration distributions, and emission
changes. To achieve this, we analyzed the response of 14 human
health and vegetation O3 metrics to long-term changes in the
hourly O3 concentration distribution, as measured at 481 monitoring
sites in the EU, US, and China. The study provided insight into
the utility of using specific exposure metrics for assessing
emission control strategies. One important aspect of the study
was that trends in mean or median concentrations did not appear
to be well associated with some of the exposure metrics applicable
for assessing human health or vegetation effects. Additional
insights concerning the relationships between emissions reductions,
hourly average concentration distributions, and human health
and vegetation exposure metrics are discussed in Lefohn et al.
(2017) and Lefohn et al. (2018) (please see publications list).
October 2015, the EPA announced that both the human health and
vegetation ozone standards were 70 ppb. Prior to that, on November
26, 2014, the EPA Administrator proposed an ozone human health
(primary) standard in the range of 65 to 70 ppb and indicated
that she would take comment on a standard as low as 60 ppb. The
EPA Administrator noted that she placed the greatest weight on
controlled human exposure studies, citing significant uncertainties
with epidemiologic studies. Reasons for placing less weight on
epidemiologic-based risk estimates were key uncertainties about
(1) which co-pollutants were responsible for health effects observed,
(2) the heterogeneity in effect estimates between locations,
(3) the potential for exposure measurement errors, and (4) uncertainty
in the interpretation of the shape of concentration-response
functions for ozone concentrations in the lower portions of ambient
distributions. The health standard is mainly based on the controlled
human exposure study of Schelegle et al. (2009) that reported
clinical effects at 72 ppb. Dr. Milan Hazucha of UNC Chapel Hill
and Dr. Lefohn, A.S.L. & Associates) designed the ozone hourly
exposure regimes used in the Schelegle et al. (2009) study. To
the 72 ppb threshold of effects resulting from the Schelegle
et al. (2009) study, the Administrator applied a Margin of Safety
that helped her establish the ozone health standard below the
72 ppb level. Although the CASAC recommended a separate exposure
metric for the secondary standard (the W126 vegetation metric),
the EPA adopted the 8-hour standard of 0.070 ppm to protect vegetation.
The Agency believed that the 3-month, 12-h W126 exposure index
used for assessing vegetation effects could be controlled to
a level of 17 ppm-h or less by using the 8-hour standard. Industry
and environmental organizations
are back in court contesting the decision of the 8-hour ozone
standard set at the 0.070 ppm level. On August 23, 2019, the
D.C. Court of Appeals rendered its decision on the various challenges
to the Environmental Protection Agency's 2015 revisions to the
primary and secondary national ambient air quality standards
for ozone. The Court denied the petitions, except with respect
to the secondary ozone standard, which it remanded for reconsideration,
and grandfathering provision, which the Court vacated.The Court
of Appeal's decision makes interesting reading and is available
by clicking here.
Although the EPA attempted to address in December 2020 several
of the Court's concerns about the Agency's 2015 decision on the
ozone vegetation standard, there still remain deficiencies in
the Agency's rationale. Perhaps in the reconsideration process
for the 2015 ozone standards, these deficiences will be addressed
during the 2022-2023 deliberations.
perspective is important in understanding the background concerning
the events that led to the EPA's Administrator's decision on
revising the 8-hour ozone standard in October 2015. 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. After an
extensive review process, the Obama Administration decided to
not revise the 0.075 ppm standard that was set during the Bush
Administration. The reason provided was that the EPA would soon
begin a new review cycle of the science associated with surface
ozone and recommend whether the 0.075 ppm standard needed to
- 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. 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 believed. In 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 (renamed by the EPA as North American Background
(NAB)) 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,
background ozone concentrations were greater than or equal to
50 ppb. In September 2009,
the National Research Council released the report, Global
Sources of Local Pollution. In the report, the Committee
stated that modeling and analysis supports the finding that background
was 20-40 ppb for the United States. Unfortunately, the NRC conclusion
did not agree with the peer-review literature using empirical
data that showed that hourly averaged background ozone concentrations
at times were greater than or equal to 50 ppb. Although spatially low-resolution
models were exercised at the time that 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 backgrund
ozone concentrations are greater than or equal to 50 ppb at both
high- and low-elevation monitoring sites. 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 some 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.
- The range of suggested
values for the W126 ozone vegetation standard is in part
historically 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 workshop's conclusions are very
interesting and are still relevant today (i.e., 26 years later).
Over the years, the EPA and CASAC have focused on an ozone standard
that accumulates over a 12-hour (8 am 8 pm) exposure period
for a 3-month period giving greater weight to exposures at higher
ozone levels. Our analyses and peer-reviewed published papers
indicate that such a secondary
ozone standard, in its proposed form, might overestimate vegetation
effects. For information about the such a standard, please click
here. You can learn
more about the subject of vegetation effects by visiting our
Table of Contents web page.
- 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. 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.
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 the most current trends analysis by the EPA (https://www.epa.gov/air-trends/air-quality-national-summary#air-quality-trends).
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 lower and
lower 8-hour standards are established. As we discussed in our
original paper, the peak hourly average concentrations are reduced
much faster than the mid-level concentrations. This pattern is
discussed in our publication on trends in the EU, US, and China
(Lefohn et al., 2017-see publications
list). Clearly the "piston effect" heavily influences
the Nation's ability to attain an 8-hour ozone standard as standard
levels are reduced. We discuss more about the "piston effect"
and how it affects the attainability of the ozone standard in
our concerns web area.
- 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 in the EPA's PM and Ozone rulemaking
documents indicate a pattern of results that illustrate uncertainties
that have been problematic especially in the setting of the ozone
human health standard. Details about the epidemiological concerns
are discussed in our epidemiological
concerns web page.
- 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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