Introduction
For over 50 years, members of our staff
have performed scientific research on the effects of air pollutants
on the environment. There are hundreds of pages on this website
that focus on the various aspects associated with air pollution
research. In order to assist you in identifying which pages might
be of interest to you, this introduction provides insight into
some of the more important scientific issues. At anytime, please
feel free to visit our Table of Contents.
Using the most current research information,
we continuously assess the scientific rationale for air pollution
standards promulgated nationally and internationally. Our research
sponsors are government, industry, and environmental groups.
Both national and international institutions have supported our
research efforts. Thousands of individuals around the world visit
our web pages daily. Some of the most popular web pages visited
are those associated with (1)
natural background of surface ozone, (2) the biological importance
of the higher hourly average air pollution concentrations more
than the mid- and lower-level values, (3) our exposure- and dose-response
research on vegetation and human health, (4) the "piston
effect" and how it affects the reduction of hourly average
surface ozone concentrations as air pollutant emissions are reduced,
(5) our global sulfur emissions database from 1850-1990, (6)
spatial interpolation of surface ozone (i.e., kriging), (7) concerns
about assumptions associated with epidemiological modeling, (8)
our peer-review publications list, and (9) our Albert Einstein
quotations with references.
For ozone, the following two key fundamental
principles are important in the standards 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. This principle is supported by human clinical laboratory
studies and vegetation chamber experiments performed in the 1980s
and 1990s. The implication of this principle is that the use
of long-term average concentrations for assessing human health
and vegetation risk is not appropriate. In addition, based
on ozone human clinical laboratory studies, Haber's Rule (i.e., the product of concentration
multiplied by time is a constant) is not appropriate for use
in an ozone exposure or dose mathematical relationship. Concentration
is more important than time of exposure and should be weighted
more than duration. For assessing human health and vegetation
effects, Fundamental Principle One plays an important role in
the selection of exposure or dose metrics used in biological
effects models.
- 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 (e.g., stratospheric) that contribute to surface ozone
concentrations measured daily around the world.
An important observation reported in the
peer-review literature is that as a result of emission reductions,
at many ozone monitoring sites, the highest hourly average concentrations
are reduced and the lowest concentrations are increased
due to the reduction of NOx scavenging (Lefohn et al., 2017;
Lefohn et al., 2018). As a result, annual average or median concentrations
consisting of hourly average concentrations increase as
emissions are reduced. The increase in annual or seasonal average
concentrations is also associated with the reduction of NOx scavenging
on the lower concentrations. During the COVID-19 lockdown that
occurred worldwide in 2020, many peer-viewed papers were written
that described the increase of weekly average ozone concentrations
during the lockdown period in comparison to previous years. Many
of the authors of these papers attributed the ozone increase
to the reduction of NOx scavenging resulting from decreases in
NOx emissions (Lefohn, 2020).
For ozone, an important phenomenon is the
"piston  effect".
The EPA has confirmed the existence of the effect that was first
described by A.S.L. & Associates in November 1996
and published in the peer-review literature in 1997 and 1998.
As emissions are reduced, larger reductions occur in the higher
ozone concentrations than the middle values. To attain the 8-hour
ozone standard of 0.070 ppm standard, the high and upper middle
concentration values must be reduced. As emissions are reduced
to attain the 8-hour standard, at many monitoring sites the lower
hourly average concentrations shift upward toward the middle
concentration values (see Lefohn et al., 2017; Lefohn et al.,
2018). The result of emission reductions to attain the ozone
standard is a compression of the high and low hourly average
concentrations toward the middle values. Emission reduction modeling
performed by the EPA in 2014 illustrated the importance of the
"piston effect" in attaining the 8-hour standard. In
the EPA's published trends report for ozone (http://www.epa.gov/airtrends/ozone.html),
the Agency indicated that
while O3 levels are still decreasing nationwide, the rate of
decrease for both the 1-hour and 8-hour levels has continued
to slow down over time. If the limitations
associated with the"piston effect" are ignored, the
EPA and others who recommend lower and lower ozone standards
may find that there is a limit to how low the standard can be
set. Fundamental Principle Two mentioned above limits how low
the ozone standard can be set. For more information on this important
subject, please click here.
Many years ago at a meeting that took place
on August 24-25, 2006
in Durham, NC, the EPA's Clean Air Scientific Advisory Committee
(CASAC) recommended a more stringent human health standard than
the 8-hour 0.08 ppm ozone standard. For the secondary ozone standard
which protects vegetation, CASAC recommended the W126 cumulative exposure index integrated over a 3-month growing
season period measured daily from 0800 to 1959 hr. In June 2007,
the EPA Administrator proposed the W126 index as the secondary
ozone standard. Both the primary and secondary standard recommendations
by CASAC were reflected in the final version of the EPA Ozone
Staff Paper. On March 12, 2008, the EPA Administrator made the
final decision on the human health and vegetation ozone standards.
EPA revised the 8-hour "primary" ozone standard, designed
to protect public health, to a level of 0.075 parts per million
(ppm). EPA decided not to adopt the W126
exposure index. Although the EPA Administrator recommended the
W126 as the secondary ozone standard,
based on advice from the White
House (Washington
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). In 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 as the new Administration
began to review the ozone standard situation, 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. EPA further
requested that it be directed to notify the Court and the Parties
within 180 days of the Court's order vacating the briefing schedule
of the actions the Agency has taken or intends to take, if any,
with regard to the Ozone NAAQS Rule, and the anticipated time
frame for any such actions.
On September 16, 2009,
the EPA announced it would reconsider the 2008 national ambient
air quality standards (NAAQS) for ground-level ozone for both
human health and environmental effects. The Agency planned to
propose any needed revisions to the ozone standards by December
2009 and issue a final decision by August 2010. On January 7,
2010, the EPA announced on its website 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
also proposed to establish a distinct cumulative, seasonal “secondary”
standard, referred to as the W126 index, which was designed to protect
sensitive vegetation and ecosystems, including forests, parks,
wildlife refuges, and wilderness areas. 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. On August 20, 2010, the Agency announced
that it would delay its final 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, the EPA announced that it would delay
its final decision on the ozone standards until July 2011. EPA
announced on July 26, 2011 that it would not make a decision
on the ozone standards by its previously announced deadline of
July 29. On September 2, 2011, President Obama requested that
the EPA withdraw its proposal to revise the ozone standards and
deferred to the normal cycle of evaluating the current state
of science associated with ozone and its effects on human health
and vegetation.
After
performing its evaluation of the science associated with ozone
and its effects, on November 26, 2014, the EPA Administrator
announced that she was proposing an ozone human health (primary)
standard in the range of 65 to 70 ppb and would take comment
on a standard as low as 60 ppb. For the welfare (secondary) ozone
standard, she proposed that the standard be the same as the health
standard IF the final health standard were set in the range of
65 to 70 ppb. The Administrator believed that a health standard
in this range would protect vegetation from ozone exposures of
W126 values within the range of 13-17 ppm-h, which was a different
range (7-15 ppm-h) proposed in 2010. She also took comment on
setting a W126 value in the range of 7-13 ppm-h, which implied
that she was still considering establishing a secondary standard
separate in form from the human health 8-h standard. Prior to
the November 2014 recommendation, in August 2014, the EPA Staff
recommended to the Administrator that she select the ozone primary
standard at a specific level between 60-to-70-parts-per-billion.
For the secondary standard, the EPA Staff recommended that the
Administrator establish a 3-month, 12-h W126 secondary
standard, which would have a specific value within the range
of 7 to 17 ppm-h. On October 1, 2015, the EPA Administrator announced
that both the human health and vegetation ozone standards were
to be 70 ppb.
The
Administrator concluded that protection of vegetation from adverse
effects could be provided by an 8-h ozone standard of 70 ppb
that limits cumulative 3-month, 12-h W126 exposures to 17 ppm-hrs
or lower. The 70 ppb 8-h ozone standard as per the US EPA's 2015
decision and more recent 2020 decision currently serves as a
surrogate to achieve ozone levels at or below a 3-month, 12-h
W126 value of 17 ppm-hrs.
There are still many uncertainties associated
with the science that was used to support the development of
the 8-hour ozone standard. For over 40 years, environmental groups,
industry, and government officials have worked with A.S.L. &
Associates to provide them with the latest scientific information
on ozone and particulate matter. We have carefully noted the
limitations of the science involved in the decision-making process. The June 1997
Feature Article in Environmental
Science & Technology, the September 1997 New Directions
Column in Atmospheric Environment, the June 1998 Policy
Analysis article in Environmental Science & Technology,
the May 2001 peer-reviewed paper in the Journal of Geophysical
Research, and the comments submitted by Lefohn (2020) on the most current ozone rulemaking
proposal discuss several of the important issues described on
the various web pages associated with this site and the uncertainties
associated with the underlying science. Four important issues
that we address in these web pages are
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Based on a review of empirical ozone concentration
information and our own research results, actual background ozone
levels are more of a problem than researchers and policymakers
believe. As the ozone standards are lowered, background
ozone will play a very important role in attaining the lower
8-h ozone standard across the U.S. Background ozone plays an
important role in the margin of safety determinations that establish
the ozone standards proposed by the EPA Administrator. |
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Is there a way to get around the "piston
effect"? Probably not. The "piston
effect" apparently controls the ability of a specific
violating area reaching attainment in a reasonable time frame.
The June 1998 policy analysis article in the peer-reviewed journal,
Environmental Science & Technology, discusses this
effect in detail. Additional articles dealing with the difficulty
in achieving the ozone standard have been published in peer-reviewed
journals. For a review of some of these articles, please visit
our publications page. What causes the
"piston effect"? Our most current research results
are providing the answers to what causes the effect. |
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What is the result of EPA using chemistry
transport models to generate highly uncertain estimates for background?
Inadequate estimates of background ozone concentrations may result
in an overestimate by the EPA of the
human health risks associated with 8-hour ozone levels, as well
as the ability to attain lower ozone standard levels that may
be proposed. In our research, we have combined modeling results
with estimates of the importance of the contributions from the
natural sources, such as stratospheric ozone. In its most recent
modeling efforts (2020), the EPA noted that it did not include
stratospheric considerations in its modeled background estimates.
Our results on background modeling can be found in the list of
papers provided in our publications page. |
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The EPA has indicated a pattern
of inconsistent results in epidemiological time-series studies.
This raises concern about the utility of these types of studies
in the current NAAQS-setting process. The EPA Administrator in
October 2015 agreed that the epidemiological risk results did
not provide strong evidence for reducing the current level of
the 8-hour ozone standard below 0.070 ppm. Similar conclusions
were reached by the EPA Administrator in his December 2020 decision.
We have commented on the limitations associated with the use
of epidemiological
results in the NAAQS-setting
process. |
A.S.L. & Associates hopes you will take the time
to carefully read the scientific material provided here and learn
more about the science that affects our ability to meet proposed
lower and lower ozone standards. Much of our attention in the
last few years has been focused on background, the frequency
distribution (i.e., rollback) scenarios that result from emission
reductions in NOx and VOCs, human health and vegetation dose-response
modeling, and the shortcomings associated with epidemiological
modeling. We appreciate having the opportunity to provide you
with our research information. If you desire further information,
please contact A.S.L. & Associates.
By introducing the 8-hour ozone standard
in 1997, the U.S. EPA began an unintentional experiment to quantify
how important anthropogenic emissions are in comparison with
natural emissions and processes. The "piston effect",
a natural controller of ozone concentrations, will probably dominate
the ability of states to attain the 8-hour standard as ozone
standards are proposed to be reduced. We continue to perform
our research and report, both in the peer-review literature and
on this website, our results. We hope you will return to our
website again and again to continue to learn more about this
most fascinating topic.
Science is both interesting and fun. It
is when policymakers attempt to work with the current state of
science that things really get fascinating. Science is the search
for truth. Sometimes we have answers and sometimes we do not.
However, scientists have an obligation to provide guidance to
policymakers, whether requested or not, to assure that the scientific
facts presented are accurate and are not obfuscated for political
purposes. The purpose of this website is to provide to the general
public, scientists, policymakers, and decision makers the opportunity
to review the science that helps make the decisions that influence
the direction in which our environmental policies are directed.
As indicated above, each day thousands of visitors around the
world read the materials contained within our web pages. To start
your visit on our web pages, please visit our Table
of Contents or News sections. Welcome
aboard!
References
Lefohn, A.S., Malley, C.S., Simon, H.,
Wells. B., Xu, X., Zhang, L., Wang, T., 2017. Responses of human
health and vegetation exposure metrics to changes in ozone concentration
distributions in the European Union, United States, and China.
Atmospheric Environment 152: 123-145. doi:10.1016/j.atmosenv.2016.12.025.
Lefohn, A.S., Malley, C.S., Smith, L.,
Wells, B., Hazucha, M., Simon, H., Naik, V., Mills, G., Schultz,
M.G., Paoletti, E., De Marco, A., Xu, X., Zhang, L., Wang, T.,
Neufeld, H.S., Musselman, R.C., Tarasick, T., Brauer, M., Feng,
Z., Tang, T., Kobayashi, K., Sicard, P., Solberg, S., and Gerosa.
G. 2018. Tropospheric ozone assessment report: global ozone metrics
for climate change, human health, and crop/ecosystem research.
Elem Sci Anth. 2018;6(1):28. DOI:
http://doi.org/10.1525/elementa.279.
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