Analysis of Ambient Air Quality Trends at Selected West Central Airshed Society Stations: Tomahawk and Carrot Creek
Nabila Haque1, Mohamed Gamal El-Din1 and Warren B. Kindzierski2
1 Department of Civil & Environmental Engineering, University of Alberta, Edmonton, Alberta, Canada
2 SEACOR Environmental Inc., 6940 Roper Road, Edmonton, Alberta, Canada
Abstract: In recent years concerns are growing about the potential health impacts from coal-fired power generating stations in West Central Airshed Society (WCAS) zone in Alberta. In this respect, detection of temporal trends can potentially provide information on source-receptor relationship and also help evaluating the control programs. The objective of this study was, therefore, to identify whether and to what extent the concentrations of ambient air quality parameters have changed over a span of 7 to 8 years near two selected WCAS stations, Tomahawk (from 1997 to 2004) and Carrot Creek (from 1998 to 2004). The stations are on the eastern side of the airshed with an elevation within 700m to 1000m asl, and characterized by greater anthropogenic activities. The pollutants studied include O3, NO2, SO2 and PM2.5 (PM is not monitored in Carrot Creek).
The methodology adopted in this research consisted of two approaches, in order to provide a thorough means to asses the change in the pollutants concentrations. First approach consisted of trend detection using various percentiles of the hourly concentration data from each year, concentrating on the “mid-to-moderate-range” (from 50th to 98th percentile). The second approach employed frequencies (number of hours) in which various benchmark concentrations were exceeded each year. The benchmark concentrations were determined from the baseline dataset for each pollutant. Assuming the summary statistics to be linear, a hypothesis test (at α = 0.05) was conducted for the best fit lines to check whether the slope was greater or less than zero.
For Tomahawk, statistically significant decreasing trends were observed in cases of SO2 and NO2 at most of the benchmark percentiles. For O3 and PM2.5, on the other hand, none of the observable increasing trend proved to be statistically significant, and consequently indicating no change in air quality with respect to these two criteria pollutants. For Carrot Creek, SO2 once again exhibited a clear and significant decreasing trend in most cases, while O3 and NO2 displayed no change that is statistically significant enough. The results obtained from the second approach strongly supported the observations from the first.