The Impact of an 8 h Ozone Air Quality Standard on ROG and NO sub(x) Controls in Southern California

In 1997, EPA promulgated a new ozone air-quality standard stipulating that the average annual fourth highest daily maximum 8-h O sub(3) concentration of an area should not exceed 80 ppb. To assess the impact of this standard on reactive organic gas (ROG) and nitrogen oxides controls in southern California, the relationship between the daily maximum 1-h and the daily maximum 8-h O sub(3) concentrations was studied. Data from 1993 were used. The Urban Airshed Model was also used to evaluate an O sub(3) episode that occurred in August 1987 during the Southern California Air Quality Study. Results show that using the 8-h averaging moved the location of the area-wide peak O sub(3) concentration east of the location of the peak 1-h O sub(3) concentration. Modeling results indicated that similar emission reduction is needed to achieve a peak 1-h O sub(3) of 140 ppb or a peak 8-h O sub(3) of 100 ppb from their respective base-case O sub(3) concentrations. The indicator trends of O sub(3)/NO sub(y) and hydrogen peroxide/nitric acid for NO sub(x) and ROG sensitivity were consistent with model predictions.