OZONE CONTROL STRATEGIES BASED ON THE RATIO OF VOLATILE ORGANIC-COMPOUNDS TO NITROGEN-OXIDES

The 1990 Clean Air Act Amendments require states with O3 nonattainment areas to adopt regulations to enforce reasonable available control technologies (RACT) for NOx stationary sources by November 1992. However, if the states can demonstrate that such measures will have an adverse effect on air quality, NOx requirements may be waived. To assist the states in making this decision, the U.S. EPA is attempting to develop guidelines for the states to use in deciding whether NOx reductions will have a positive or negatiVe impact on O3 air quality. Although NOx is a precursor of O3, at low VOC/NOx ratios, the reduction of NOx can result in increased peak O3. EPA is examining existing information on VOC/NOx ratios to develop "rules of thumb" to guide the states in their decision-making process. An examination of 6 a.m. to 9 a.m. VOC/NOx ratios at a number of sites in the eastern U.S. indicates that the ratio is highly variable from day-to-day and there is no apparent relationship between ratios measured at different sites within the same area. In addition, statistical analysis failed to identify significant relationships between the 6 a.m. to 9 a.m. VOC/NOx ratio and the maximum 1-hr. O3 within a given area. Since we know from smog chamber and modeling studies that such a relationship exists, this further invalidates the assumption that a ratio measured at a single site is representative of the ratio for the entire region. Based on this information, we conclude that having the 6 a.m. to 9 a.m. ambient VOC/NOx ratio for a given area is insufficient information, by itself, to decide whether a VOC-alone, a NOx-alone, or a combined VOC-NOx reduction strategy is a viable or optimum O3-reduction strategy.