A CAPTIVE-AIR IRRADIATION STUDY OF THE RESPONSE OF NITRIC-ACID AND PEROXYACETYL NITRATE TO OZONE CONTROL STRATEGIES IN LOS-ANGELES

Outdoor smog chamber experiments were used to study the sensitivity of the yields of two important nitrogen-containing pollutants, nitric acid (HNO3) and peroxyacetyl nitrate (PAN) to changes in nonmethane hydrocarbon (HC) and nitrogen oxide (NOx) concentrations in Los Angeles. The experiments were conducted at two sites in the Los Angeles Basin using eight chambers filled with morning Los Angeles air on 33 days. At least one chamber was unchanged and served as a control, while the initial HC and/or NOx concentrations were changed by 25-50% in up to seven chambers to simulate O3 control strategies and to broaden the range of HC-NOx conditions studied. Empirical models that predict the maximum yields of HNO3 and PAN were used to determine the response of these pollutants to three possible ozone control strategies. All three strategies (reductions in HC, NOx or both HC and NOx) reduced PAN while only NOx reductions decreased HNO3. However, reducing NOx increased the HC reductions required to attain lower O3 levels. Thus, there is a conflict between the O3 and HNO3 control strategies.