A CASE-STUDY OF EMISSION CHANGES AND OZONE RESPONSES

The ability to determine the sensitivity of O-3 to NOx and/or VOC is c entral to the development of successful programs to reduce ambient O-3 concentrations. Equally, quantifying trends in surface O-3 time serie s in response to emissions changes is critical to determining the succ ess of those programs. However, whilst both tasks are desirable from a regulatory perspective they are scientifically challenging. Herein da ily maximum O-3 concentrations from sites in the Greater Vancouver reg ion are declimatized to determine the underlying trends, and those tre nds interpreted in the light of information regarding changing precurs or emissions and ambient concentrations. Declimatized daily maximum O- 3 concentrations at sites outside the urban core decreased between 198 4 and 1991. Using ambient data and emission inventories it is determin ed that O-3 concentrations in this region are VOC-sensitive. This find ing coupled with information regarding changing precursor emissions an d ambient NOx concentrations and previously reported changes in the fo rm of the diurnal profile of O-3 concentrations are used to develop th e hypothesis that the decrease in declimatized daily maximum O-3 conce ntrations in this region are a product of enhanced NO scavenging. (C) 1997 Elsevier Science Ltd.