A case study of emission changes and ozone responses

The ability to determine the sensitivity of 03 to NO, and/or VOC is central to the development of successful programs to reduce ambient 03 concentrations. Equally, quantifying trends in surface 03 time series in response to emissions changes is critical to determining the success of those programs. However, whilst both tasks are desirable from a regulatory perspective they are scientifically challenging. Herein daily maximum 03 concentrations from sites in the Greater Vancouver region are declimatized to determine the underlying trends, and those trends interpreted in the light of information regarding changing precursor emissions and ambient concentrations. Declimatized daily maximum 03 concentrations at sites outside the urban core decreased between 1984 and 1991. Using ambient data and emission inventories it is determined that O3 concentrations in this region are VOC-sensitive. This finding coupled with information regarding changing precursor emissions and ambient NO, concentrations and previously reported changes in the form of the diurnal profile of 03 concentrations are used to develop the hypothesis that the decrease in declimatized daily maximum 03 concentrations in this region are a product of enhanced NO scavenging.