Ozone air quality over North America: Part II - An analysis of trend detection and attribution techniques

Assessment of regulatory programs aimed at improving ambient O-3 air qualit y is of considerable interest to the scientific community and to policymake rs. Trend detection, the identification of statistically significant long-t erm changes, and attribution, linking change to specific climatological and anthropogenic forcings, are instrumental to this assessment. Detection and attribution are difficult because changes in pollutant concentrations of i nterest to policymakers may be much smaller than natural variations due to weather and climate. In addition, there are considerable differences in rep orted trends seemingly based on similar statistical methods and databases. Differences arise from the variety of techniques used to reduce nontrend va riation in time series, including mitigating the effects of meteorology and the variety of metrics used to track changes. In this paper, we review the trend assessment techniques being used in the air pollution field and disc uss their strengths and limitations in discerning and attributing changes i n O-3 to emission control policies.