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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 web site 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.

From our years of experience, we have learned that it is what we know about pollutant exposure and its effects on humans and the ecosystem that are the most important aspects of selecting appropriate standards to protect the public. 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 support our research efforts. Thousands of individuals from around the world visit our web pages weekly. 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, 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. The Agency, after reviewing 25 years of air quality data, reported that there were larger reductions in the higher ozone concentrations than the middle values. To attain the 8-hour ozone standard of 0.070 ppm standard, the high to upper middle concentration values must be reduced. The "piston effect" defines whether the 8-hour ozone standard is achievable or just a bureaucratic goal. Most recent emission reduction modeling by the EPA and research groups is illustrating the importance of the "piston effect" in attaining the 8-hour standard. Based on scientific evidence that has been published in the peer-review literature, there is concern among some scientists and engineers that the 8-hour ozone standard may become an elusive goal that will continue to be violated in many locations in the United States long after control strategies are implemented. In the EPA's published trends report for ozone (, the Agency indicated that O3 levels are still decreasing nationwide, but the rate of decrease for both the 1-hour and 8-hour levels slowed during the 1990s. The findings show that the "piston effect" may be affecting the ability of the Nation to attain the 8-hour ozone standard everywhere. If the limitations associated with the"piston effect" are ignored, the EPA and others will continue to push for greater emission reductions that will not necessarily result in improvement to surface ozone levels. For more information on this important subject, please click here.

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 standard than the 8-hour 0.08 ppm ozone standard. The majority of CASAC's members recommended an 8-hour ozone standard of 0.070 ppm. The selection of 0.070 ppm implies that a design value of 0.071 ppm would violate a 0.070 ppm standard. There is considerable uncertainty associated with the (1) epidemiological evidence and (2) data points at the 0.04 and 0.06 ppm levels in the EPA's dose-response function derived from the controlled human exposure experiments. For the secondary ozone standard, 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. Such a secondary ozone standard, in its current form, would overestimate vegetation effects. 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, 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 web site 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, 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 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.

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. 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 seasonal W126 exposures to 17 ppm-hrs or lower. The 70 ppb 8-h ozone standard as per the US EPA's 2015 decision currently serves as a surrogate to achieve ozone levels at or below a 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 38 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 discusses 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

Based on a review of actual ozone concentration information and our own research results, actual background ozone levels are more of a problem than researchers and policymakers believe. Background ozone plays a very important role in attaining the 8-h ozone standard across the U.S.

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 result of this effect is that the 8-hour ozone standard of 0.070 ppm may actually be a "target" at some sites that may never be achieved in the United States. 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 new standard have been published in peer-reviewed journals. For a review of some of these articles, please visit our publications page. The "piston effect" will limit our ability at some sites to consistently attain the 8-hour ozone standard of 0.070 ppm. What causes the "piston effect"? Our most current research results are providing the answers to what causes the effect.

What is the result of EPA using chemistry transport models to generate highly uncertain estimates for background? Actual levels of background ozone are higher than the models suggest and therefore, inadequate estimates of background ozone concentrations will 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 proposed standard levels. We have combined modeling results with estimates of the importance of the contributions from the natural sources such as stratospheric ozone. These results can be found in our publications listed in our publications page.

The EPA has indicated a pattern of inconsistent results in epidemiological time-series studies that is troubling. The epidemiological evidence has played a disproportionately large role in the policy making process. Time-series findings indicate associations of mortality with not only PM and ozone, but with all of the criteria pollutants. Because results of time-series studies implicate all of the criteria pollutants, findings of mortality time-series studies do not seem to allow us to confidently attribute observed effects specifically to individual pollutants. 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 ozone standard. We have commented on the limitations associated with the use of epidemiological results in the current NAAQS-setting process.

Scientists, engineers, and policy makers are focusing their attention on assessing how attainable a 0.070 ppm 8-hour ozone standard is without agency exemptions for naturally occurring violations. 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 will affect our ability to meet the 0.070 ppm 8-hour ozone standard. 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. In June 2000, Canada joined the experiment by passing an 8-hour ozone standard of 0.065 ppm. California has passed an 8-hour, 0.070 ppm ozone standard. The "piston effect", a natural controller of ozone concentrations, will probably dominate the ability of states to attain the 8-hour ozone standard. We continue to perform our research and report, both in the peer-review literature and on this web page, our results. If you are interested in becoming a sponsor of our on-going research, we welcome the opportunity to work with you. We hope you will return to our web page again and again to continue to learn more about this most fascinating topic.

Besides our focus on surface ozone on our web page, we also perform research on particulate matter, epidemiological methodologies, risk assessment, and other important scientific topics. Our most current research on the epidemiological methodologies is showing serious concerns about the statistical approaches used in assessing the effects of both particulate matter and ozone on human health. We have provided a Multimedia Center web page that provides material that will help you understand the important scientific issues that we have been addressing over the past several years. Thank you for taking the time to visit our web page and we hope that the material provided on these pages is helpful to you.

Science is both interesting and fun. It is when policy makers attempt to work with the current state of science that things really get exciting. Science is the search for truth. Sometimes we have answers and sometimes we do not. However, scientists have an obligation to provide guidance to policy makers whether requested or not to assure that scientific facts are presented in such a manner that they are accurate and not obfuscated for political purposes. The purpose of this web page is provide the general public, scientists, policy makers, 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, every week thousands of visitors from 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!

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