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Optimizing Control Strategy Development to Maximize Yield of Co-benefits Across Various Air Pollutants – Criteria Pollutants, Hazardous Air Pollutants, and Greenhouse Gases


The Environmental Protection Agency's (EPA’s) approach to regulating and controlling air pollution since the passage of the Clean Air Act (CAA, and its subsequent amendments) has been to address each pollutant separately. Although that has had success over the past few decades, it success may have limits. Since the last set of amendments in 1990, two classes of pollutants have become large concerns to the transportation and air quality communities. Those two groups of pollutants are hazardous air pollutants (also referred to as toxic air pollutants) and greenhouse gases. These two categories of air pollutants have different characteristics then the criteria pollutants first focused on by the CAA and metrics to measure its impacts and reductions are more elusive. Over the past couple of decades, EPA has also found it increasingly difficult to meet the requirements of the CAA regarding timely review and revising the National Ambient Air Quality Standards (NAAQS) enacted for the criteria pollutants. The NAAQS are required by the CAA to be reviewed every five years but often EPA has missed that schedule. Thus, meeting the current requirements for criteria pollutant review as well as potential requirements for setting and review of some metric for the two new categories of air pollutants will make the current regulation of air pollutants extremely difficult if not impossible. Recently, EPA and other organizations have considered new approaches to regulating air pollutants. Underlying new methods for regulating all pollutants utilizes a “multi-pollutant” approach where the goal is to improve air quality by focusing on the combined benefits of reducing all pollutants. This is important since strategies to reduce the concentration of one pollutant in the atmosphere may actually create a condition increasing another pollutant. Thus, the logically way to proceed for future regulation would be to design regulation with the goal of controlling all pollutants at the same time recognizing the interrelationships that may exist between individual pollutants. Therefore controlling the emissions from each source (vehicle, refinery, power plant, etc…) which typically emits a variety of pollutants requires utilizing a multi-pollutant reduction approach to continue to reduce overall pollution in the ambient air. Strictly focusing on a single pollutant (such as PM), or even a single category of pollutants (such as criteria pollutants) at the expense of all emitted pollutants may limit long term reduction strategies and hamper further air quality improvements. As an example of EPA’s pursuit of the multi-pollutant emission reduction Strategy, EPA has a program, the Advance Program ( http://www.epa.gov/ozoneadvance/) intended to address at least two common air pollutants – ozone and PM. Thus, the emerging multi-pollutant strategies to control emissions require research into how effective these strategies are as they relate to vehicle emissions. This may be particularly true as the Federal government contemplates controlling greenhouse gas emissions using Executive Orders rather than through environmental laws as has been under consideration.


The objective of the research is to focus on how a multi-pollutant strategy could impact the emissions, emission controls, emission reductions strategies and implementation of strategies and control measures on mobile source emissions. It could also serve as supporting material to influence EPA’s efforts to improve the process for air quality regulation of mobile source emissions.


The benefits of the multi-pollutant strategy are many fold:

  1. Eliminate the need to study the impacts of each pollutant separately since none of the pollutants exist in the atmosphere separately
  2. Recognizing inter-reactions of pollutant, pollutant precursors, and pollutant control strategies can further the design of more accurate and possibly more cost effective control strategies.
  3. A more “streamlined” approach may help reduce costs of implementing the strategies. Streamlining environmental reviews has been of increasing interest recently as a method to help support the economic recovery.
Related Research:

There have been several studies undertaken investigating the multi-pollutant regulation approach. Most of these have been non-sector (mobile, stationary, area) specific. This study would be specific to the transportation community. It should be noted that one study did investigate several strategies and their impact on the transportation, but this study did not include hazardous air pollutants or greenhouse gases.

  1. Managing Air Quality in the United States, NRC report, 2004
  2. Multi-Pollutant Emission Benefits of Transportation Strategies, FHWA, 2006
  3. Improving Emission Inventories for Effective Air Quality Management Across North America, NARSTO-05-01, 2009
  4. Multi-Pollutant Air Quality Management, JAWMA, 2010
  5. A Risk-based Assessment And Management Framework For Multipollutant Air Quality, AWMA Proceedings, Frey, et al, 2009
  6. Protecting Human Health From Air Pollution Shifting From a Single-pollutant to a Multipollutant Approach, Epidemiology, 2010
  7. Vision for Clean Air: A Framework for Air Quality and Climate Planning, California Air Resources Board, 2012
  1. Review the reports and papers cited in the “Related Research”
  2. Develop a new report with updated strategies addressing all pollutant categories
  3. Develop a “test plan” for evaluation the effectiveness of implementing the strategies
  4. Conduct a pilot study (note this step could take many years)

These are included in the “Tasks” Section above.


State DOTs, Regional MPOs

Sponsoring Committee:AMS10, Air Quality and Greenhouse Gas Mitigation
RNS Developer:Kevin Black, Federal Highway Administration; Charles Baber, Baltimore Regional Council (MPO); and Doug Eisinger, Sonoma Technology, Inc.
Source Info:2013 TRB Annual Meeting
Workshop 128
Date Posted:12/18/2013
Date Modified:01/03/2014
Index Terms:Air pollution, Air quality management, Greenhouse gases, Regulations, Pollutants, Poisons, Clean Air Act, National Ambient Air Quality Standard, U.S. Environmental Protection Agency,
Cosponsoring Committees: 

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