IMPACT OF INERT ORGANIC NITRATE FORMATION ON GROUND-LEVEL OZONE IN A REGIONAL AIR-QUALITY MODEL USING THE CARBON BOND MECHANISM 4

A regional air quality model is used to assess the impact of inert org anic nitrate formation on ground-level ozone in the eastern United Sta tes during summer. The chemical mechanism used is the Carbon Bond Mech anism 4 (CBM4), which is widely used by regulatory agencies in the Uni ted States in air quality modeling applications. Recently, modificatio ns were made to the reaction mechanism involving the organic peroxy ra dicals which form inert organic nitrates without a critical scientific review of the effects of these changes. In this study, we demonstrate for the first time that the simulated large-scale distribution of gro und-level ozone is extremely sensitive to these mechanism changes. Inc lusion of radical-radical reactions involving the organic peroxy radic als suppresses inert organic nitrate formation, and leads to significa nt increases in nitrogen oxide levels over large parts of the model do main. As a consequence of increased rates of ozone photochemical produ ction, ozone mixing ratios are enhanced by as much 10-25 ppbv when the se additional radical termination pathways are considered in the model .