The impact of an 8 h ozone air quality standard on ROG and NOx controls inSouthern California

The new National Ambient Air Quality Standard for ozone in the US uses 8 h averaging for the concentration. Based on the 1993 ambient data for Souther n California, 8 h averaging has a moderate tendency to move the location of the peak ozone concentration east of the location of the peak 1 h ozone co ncentration. Reducing the area-wide peak 8 h ozone concentration to 80 ppb would require an effective reduction of the area-wide peak 1 h ozone concen tration to around 90 ppb. The Urban Airshed Model with improved numerical s olvers, meteorological input based on a mesoscale model and an adjusted emi ssions inventory was used to study the effect of reactive organic gases (RO G) and NOx controls on daily-maximum and peak 8 h ozone concentrations unde r the 26-28 August 1987 ozone episodic conditions in Southern California. T he NOx disbenefit remains prominent for the case of 8 h ozone concentration but is somewhat less prominent, especially when areal ozone exposure is co nsidered, than the case for 1 h ozone concentration. The role of two indica tors - O-3/NOy and H2O2/HNO3 - for NOx- and ROG-sensitivity for 1 and 8 h o zone concentrations were also studied. In general, the indicator trends are consistent with model predictions, but the discriminating power of the ind icators is rather limited. (C) 1999 Elsevier Science Ltd. All rights reserv ed.