Identification for Locally Generated Ozone Transport Days in Urbanized Areas in Shasta County, California

The California Clean Air Act requires the Air Resources Board (ARB), in cooperation with local air pollution control districts, to assess the relative contribution of upwind emissions to downwind ozone concentrations and determine if the contribution level of transported air pollutants is overwhelming, significant, inconsequential, or some combination thereof. Urbanized areas that are often impacted by transported emissions can be responsible for their own ozone problem when on a few days transported ozone concentrations do not occur. The determination of these local days, inconsequential transport, can be difficult to identify. This paper will describe the procedures used to determine a local day in areas that are impacted by transport using the greater Redding urbanized area in Shasta County as an example.