Surface Ozone Measurements:
Exciting Science for All Seasons All the Time

The most robust set of measurements leading to the hypothesis that humankind is changing the environment in which we live is the long-term record of carbon dioxide from the Mauna Loa Observatory dating back to the 1950s. These and other records show that CO₂ concentrations have increased by more than 30% since the onset of the Industrial Revolution. This data set illustrates how the concept of Global Change was initially brought to light through a set of trace gas measurements. Similarly, and even more dramatically, surface ozone measurements have also increased considerably over the same period of time, possibly by as much as 100-200% over the past century at some locations. Using the SMOG measurement protocol, students from all around the world will have the opportunity to make their own measurements of this important atmospheric trace constituent that is both indicative of human activity and insightful for understanding natural processes. Participating GLOBE students will learn much by being cognizant of the time dependence and spatial variability of their measurements.

For the most part, surface ozone measurements should be made near local noon since surface ozone does exhibit a diurnal cycle with higher concentrations normally slightly after local noon and lower concentrations early in the morning. If a long-term record is to be kept by the students, it is important that measurements be made consistently at the same time of the day. Surface ozone also exhibits interesting seasonality trends. At northern middle latitudes, the highest concentrations are found in the summer. At southern middle latitudes, the highest concentrations are often in the winter and the difference in the concentration between the seasons is relatively small. In the tropics, most long-term records show the highest concentrations in the months of September and October.

Spatial variability also offers exciting science. In and around an urban area, relatively large gradients of ozone can be observed. Highest concentrations are most often found downwind of a city. Thus, on a scale of tens of kilometers, regional observing networks established by a group of SMOG teams can provide the data from which the patterns of ozone can be examined. In addition, observing sites separated by hundreds of kilometers can also be used to examine the differences between urban and rural settings. These data sets are also amenable to the use of other ancillary data sets such as temperature and cloud cover to provide students with additional insights of the processes affecting atmospheric chemistry. On the grandest scale, students can learn much by looking at data from the Northern and Southern Hemispheres and comparing the seasonality of the two data sets. Thus, we envision numerous exciting potential studies that can be performed from the analysis of the surface ozone measurements obtained from our GLOBE students.