Measurements of Ozone During the Heat Wave of 2012

Here at Eastern Michigan University, undergraduates form the backbone of our research teams. I have been lucky enough to have some great undergraduates working with me over the years and this Lab Note will highlight such group, Sarah Dolan, Aaron Trierweiler and Katelyn Cichon. These students have been specifically looking at ozone data from the calendar year 2012.

During 2012, one of the most intense heat waves in U.S. history enveloped portions of the western plains and Midwest. A persistent high pressure system, also called a "heat ridge" or "heat dome", was trapped by weather systems over the north Atlantic in June and July 2012. This caused many States to experience record temperatures . Although not unusual in the summer, the pattern of hot air covered a broader area than usual and the total amount of hot air was greater. In addition to enabling the basic chemical reactions that create ground-level ozone, high temperatures often create stagnant air conditions that cause ozone pollution to settle over an area and remain for a longer time, which in turn increases the potential for human exposure to harmful ozone concentrations. Clearly the persistent heat dome of 2012 fell into this category and offered a unique opportunity to investigate ozone on the EMU campus during this event.

Effect of heat dome on national temperatures in 2012

 

Data were analyzed in two ways. First, the data were broken down into 24-hour cycles and the average ozone for these data calculated from March to October. Then, the maximum ozone for that day also determined. Data were then worked up to monthly averages and compared to similar averages from 2008-2011. Finally, master 5 year averages were determined. 24-hour averaged ozone concentrations for 2012 were found to be consistently higher than those measured as a 5 year average, both overall and especially during the summer months.

Average monthly ozone concentration in 2012 compared to 5-year average

 

The 2012 data appear to be similar to 5-year averages for the month of March, but show a steady increase in summer where the deviation between 2012 data and the 5-year average is seen in May-September the times associated with peak in situ ozone production. Comparing these deviations with the standard deviation of the 5 year average, it appears that the 2012 concentrations differences are statistically significantly with June and July 2012 (times associate with the largest impact of the heat wave) showing around 10ppbv differences. Similarly, the maximum ozone concentration measured in month shows 2012 to be larger (by a statistically significant amount) when compared to the 5-year average. Again, the deviation begins in early Spring and peak in Midsummer.

Peak monthly ozone in 2012 compared to the 5-year average

 

A record ozone concentrations measured in June 2012 was also seen as this month. The peak ozone value of ozone was 110.3ppb, compared to a 5 year average of has average of ca. 80ppbv during June.