Research Projects

Project at a Glance

Project Status: complete

Title: Chemical consequences of air quality standards and of control implementation programs: Roles of hydrocarbons, oxides of nitrogen, and aged smog in the production of photochemical oxidant

Principal Investigator / Author(s): Pitts, James N., Jr.

Contractor: UC Riverside

Contract Number: 2-377

Research Program Area: Atmospheric Processes


Although a great deal of data relating oxidant levels in chambers to initial concentrations of hydrocarbons (HC) and oxides of nitrogen (NOx) has been accumulated during the past two decades, considerable uncertainty continues to exist concerning the roles and relative contributions of HC and NOx in the formation of photochemical smog. The lack of knowledge concerning the precise functional dependence of oxidant formation on HC and NOx levels has led to conflicting positions by regulatory agencies as to the most efficient emission control strategy that would lead to achievement of federal and state ambient air quality standards. This situation has serious technical, social, and economic implications.

For example, the EPA implementation plan for the California South Coast Air Basin presented on January 15, 1973, proposes imposition of drastic levels of gasoline rationing during the months of heavy smog. This control strategy is based upon the assumption that the yearly high one - hour ambient oxidant reading for a given day is directly proportional to the amount of "high reactive hydrocarbon emissions" for that day. It is significant that this assumed straight line proportionality between ambient oxidant reading and reactive hydrocarbon inventory fails to include any consideration of the role of oxides of nitrogen in determining ambient oxidant levels. Serious objections can be raised to this approach since a considerable body of relevant smog chamber data (see Background Section which follows) supports the conclusion that oxidant formation is dependent in part not only on reactive hydrocarbons but also on the concentration of oxides of nitrogen.

Clearly, there is an urgent need to clarify the issue of whether reduction of only reactive HC, or both reactive HC and NOx, is required in order to achieve the ambient air quality standard for oxidant. Further, the problem requires quantification of the degree of reduction(s) necessary to reach the air quality standard.


For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893

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