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Panel: Steve Risotto
Media: Sarah Scruggs

Photochemical Reactivity – Why is this Important to you?

Improving air quality and addressing the formation of ground level ozone, or smog, is a major public policy issue in the United States and around the world. In order to reduce ozone levels, federal and state agencies are implementing programs to reduce NOx and VOC emissions from a variety of sources, and also products that contain solvents such as paints and coatings. An attractive feature of a photochemical reactivity-based approach is that it provides formulators with greater flexibility than traditional mass-based approaches, so that the desired product performance requirements can be maintained as the potential to contribute to ozone levels is reduced

The passage of the Clean Air Act Amendments of 1990 marked the beginning of an aggressive attempt to control solvent VOCs by identifying areas that were not in compliance with the national ambient ozone standard. Those States with ozone nonattainment areas were required to submit a more detailed State Implementation Plan or SIP for tackling their air pollution problems. A necessary ingredient to these plans was the requirement for a 15 percent reduction of VOC release over a 6 year period in those areas in moderate violation of the standard. Although ozone contribution to air pollution is indisputable, the methods used to control VOC release from consumer products have been the subject of considerable debate for many years.

Traditionally, solvent VOCs have been regulated using mass-based controls that limit the mass percentage of VOCs in various products or formulations, such as paint. A mass-based approach treats all non-exempt VOCs alike in their ability to generate ozone. However, solvent VOCs vary significantly in their ability to impact ozone levels.

The following list cites some of the most serious problems with the use of mass-based limits in a control scheme for solvent VOCs. In particular, mass-based controls:

  • do not utilize the latest scientific knowledge and allow the continued use of inaccurate and outmoded chemical "lumping" techniques to group VOCs into a few discrete chemical groups;
  • have become increasingly expensive to implement and comply with as the reservoir of controllable solvent VOCs is diminished;
  • do not provide manufacturers with enough options to reformulate their products in a manner that will preserve performance under all use conditions;
  • are arguably at variance with Section 183e of the Clean Air Act, which requires the use of the "best available control" measures to achieve attainment;
  • stifle innovation and product improvement by needlessly restricting solvent VOC content rather than VOC hazard;
  • promotes the use of an exempt category of VOCs that is mistakenly believed to lack any ozone forming potential;
  • are based on the mistaken belief that they are actually reducing urban ozone levels in all circumstances when recent evidence shows the ozone-forming potential of products is increasing.

Despite the fact that mass-based controls are rapidly becoming ineffective, many State regulatory authorities have adopted the position that reactivity will only be considered as a VOC control option once mass-based opportunities have been exhausted. Although both types of controls have their own advantages and disadvantages, recent events suggest that mass-based controls are becoming ineffective and going forward significant benefits are more realistically achieved with widespread adoption of reactivity-based controls.


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