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For over 36 years, A.S.L. & Associates developed extensive experience and resources for the purpose of assessing the potential impacts of air pollution on the environment. Its clients included major industrial, environmental, and governmental groups. In 2017, A.S.L. & Associates migrated its capability to a new company, A.S.L. & Associates, LLC, which is under the direction of the Company's President and Founder, Dr. Allen S. Lefohn. The new company continues the tradition of focusing on environmental issues that directly link pollutant exposure with both human health and vegetation effects. Combined, individual staff members have over 50 years of experience working in the exposure- and dose-response research area.

A.S.L. & Associates is unique in its approach toward developing solutions to complex issues. The company teams with leading scientists from around the world to focus on complex scientific issues. Because our research is cutting edge, more than 90% of our results are published in major peer-reviewed scientific journals. At times, A.S.L. & Associates is asked to prepare materials that are presented to those responsible for the air pollution standard-setting process.

A.S.L. & Associates is unique in its approach to performing its research. Besides receiving research funding from its clients, A.S.L. & Associates funds its own research. A.S.L. & Associates believes that in economic upswings, as well as economic downswings, it is important to continue to develop the research results that provide important inputs into learning more about the relationship between air pollution exposure and (1) human health and (2) vegetation effects. For the purpose of informing the general public, researchers, and policymakers, research results are placed on A.S.L. & Associates' web site ( The web site is visited by thousands from around the world each month. Some of the most popular pages visited on the web site are those associated with (1) the "piston effect" (i.e., slowing down of reductions of the higher hourly average concentrations) and how it affects the reduction of hourly average surface ozone concentrations as air pollutant emissions are reduced, (2) natural background of surface ozone and its relationship to the "piston effect", (3) the biological importance of the higher hourly average air pollution concentrations more than the mid- and lower-level values for both human health and vegetation effects, (4) our exposure- and dose-response research on vegetation and human health, (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.

The Company's President and Founder, Dr. Allen S. Lefohn, and his research associates have established an outstanding reputation for providing research and analyses in several major areas. Some of these research areas are

Standard-Setting Evaluations

  • The evaluation of the limitations associated with exposure models that relate to risk assessment methodologies.
  • Why specific human health and vegetation exposure metrics behave differently as emissions change.
  • The evaluation of the strengths and weaknesses associated with epidemiological methodology and the standard-setting process.
  • The evaluation and assessment of ambient air quality standards and critical levels/loads.
  • The evaluation and assessment of using the W126 cumulative ozone exposure index as a secondary standard to protect vegetation.
  • Developing the scientific rationale for explaining the "piston" effect, which affects our ability to attain surface ozone standards.
  • The identification of areas in the United States that violate Federal ozone, PM-2.5, and other criteria pollutant standards.
  • Characterizing natural background ozone levels and how they relate to the standard-setting process.
  • Evaluating the occurrences of elevated short-term 5-minute SO2 average concentrations in the U.S.
  • The evaluation of mathematical models that relate short-term 5-minute SO2 concentrations with hourly average concentrations.

Human Health Effects

Vegetation Effects

  • The development of vegetation and human health exposure-response relationships.
  • Explore the efficacy of various defense mechanisms for helping to define "effective" dose.
  • The development of a bridge that allow for the use of exposure-response and dose-response data for predicting vegetation effects.
  • Explore the efficacy of applying the U.S. 8-hour ozone standard to protect forests and agricultural crops.
  • Identify "areas of concern" for areas that may be impacted by ozone exposures for forests in North Carolina, Tennessee, and South Carolina.
  • Summarize ozone exposures that may have an effect on vegetation grown in the Southern Appalachian region of the United States.
  • Summarize the state-of-knowledge for the U.S. EPA of the status of the use of relevant exposure indices for predicting ozone effects on vegetation (Chapter 9 of the EPA's 2006 Ozone Criteria Document).
  • Develop exposure-response relationships for tree seedlings using data from five intensive Southern Commercial Forest Research Cooperatives.
  • The design of vegetation air pollution exposure studies that mimic ambient conditions.
  • Application of geographic information system (GIS) approaches that integrate vegetation effects with exposure information.

Air Quality Characterizations

  • Determine ozone trends analyses on anthropogenically influenced monitoring sites in the United States and on worldwide background ozone "signature" monitoring sites.
  • The application of mathematical interpolation techniques (e.g., kriging) to predict ozone exposures across the United States.
  • The identification of clean sites in the United States and other parts in the world that can serve as indicators of natural background for surface ozone and other pollutants.
  • The identification of clean sites in the United States that can serve as indicators of natural background for particulate matter.
  • Summarize the state-of-science for the National Acid Precipitation Assessment Program (NAPAP) for the air quality characterization of agricultural and forested areas for vegetation effects purposes.
  • Summarize the state-of-knowledge for the U.S. EPA of the air quality characterization of ozone for urban and rural areas for health and vegetation effects purposes (Chapter 4 of the 1996 Ozone Criteria Document and Chapter 3 of the 2006 Ozone Criteria Document).
  • The development of scientifically defensible approaches to predict ozone levels as a function of emission reductions (i.e., rollback methods).
  • The characterization of air pollution co-occurrences under ambient conditions for designing human health and vegetation exposure experiments.
  • Defining air quality characterization in biologically meaningful terms.
  • Develop a global sulfur emissions inventory for purposes of the development of global climate models.

Some of the published research results can be reviewed at our publications web page. We welcome your suggestions on future environmental research efforts as well as your participation in our efforts. For further information, please contact us at

A.S.L. & Associates, LLC
P.O. Box 196
Clancy, Montana 59634

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