Lindsey Kuettner and Dr. Patricia Cleary  Department of Chemistry  University of Wisconsin-Eau Claire Back Trajectory Analysis and Measurement of Ozone in Air Masses over Lake Michigan Back Trajectory Analysis and Measurement of Ozone in Air Masses over Lake Michigan Abstract The non-attainment status of federal ozone standards in the region surrounding Lake Michigan demonstrates the efficient ozone production in urban and off-shore air masses. The measurement of ozone in air masses over Lake Michigan have been conducted from via routine ferry routes from Milwaukee, WI to Muskegon, MI, which is the most exhaustive data set of off-shore observations at the lake level where exposure is most likely. The measurement of ozone, sulfur dioxide, and nitrogen dioxide levels of shoreline Lake Michigan had been conducted in 2009 via Differential Optical Absorption Spectroscopy (DOAS) in Kenosha, WI. A series of HYSPLIT back trajectory models showing the dispersion of pollutants from those transects will be compared to the observational data in an effort to show a correlation between high ozone and the lake-breeze meteorological effects on trace gases O 3 and NO 2. Ozone is formed photochemically in urban plumes when favorable meteorological conditions are present and has an atmospheric lifetime longer than NO 2. NO 2 contributes to ozone formation but also indicates fresh emissions from fossil fuel combustion, thus HYSPLIT trajectories of 24 hours or less will be used to analyze the paths of air-masses containing both NO 2 and O 3. Introduction Air quality on the Lake Michigan shoreline has been a target of concern as urban counties along the southern and southwestern portion of the lake are in non-attainment areas of federal ozone standards. Through a series of photochemical reactions involving NO 2 species, ozone is formed during favorable meteorological conditions. Sources of NO 2 include automobile and power plant emissions which contributes to the formation of ozone and is linked with a number of adverse effects on the respiratory system. Pollutants such NO x species can be captured and transported through circulation due to a lake breeze effect. Ozone formation is initiated by two major precursors: VOCs and NO x species. When hydroxyl radicals react with VOCs and oxygen, organic oxides are formed which then react with NO x to produce NO 2. All reactions occur in the gas phase. Figure 1. The relation between ozone, VOCs, and NO x species is illustrated. Figure 3. The distribution of ozone was investigated during the highest ozone observations for a select period in August 2009 over Lake Michigan from the ferry and shoreline DOAS measurements. Figure 4. The air masses are described as coming from opposing directions and converging near Lake Michigan. Though these display changes in direction, they primarily travel from the south. Figure 5. In correspondence with Figure 3, a path of air masses traveling from the south/southwest is observed indicating a widespread influence of Chicago area pollution up into WI. Figure 6. Air masses appear to be coming from the south as indicated in Figure 3. The blue path of particles at the Kenosha point appear to travel almost directly with the shoreline. Analysis To better understand the ozone and NO 2 measurements, it is necessary to understand the history of these air masses. Back trajectory HYSPLIT models 1 of the days in Figure 3 were used to further analyze the data and obtain some insight on the paths of pollutants during specific time periods. Back trajectories displaying a 12 hour time period, 12:00 pm CDT to 12:00 am CDT, over 4 consecutive days are compared. The paths of the pollutants was consistently from the south, where more urban regions, Chicago, IL and Gary, IN, are located. Acknowledgments We thank the UWEC ORSP student/faculty collaboration grant for funding this research and UWEC Learning & Technology Services for printing this poster. Conclusion Figure 2. Map of experiment. Path of ferry from Milwaukee, Wisconsin to Muskegon, Michigan is shown. The DOAS instrument was placed at the Kenosha, Wisconsin harbor. Figure 7. Again, the air masses appear to be travelling from the south and the path to Muskegon, MI shows a flow of chemicals from the Gary, IN region. Studying the history of the air masses in which ozone and NO 2 measurements were taken, has shown us the plumes traveled from urban areas like Chicago, IL and Gary, IN where automobile traffic and pollution is high. Back trajectories allow us to make sense of the titration events of O 3 where NO 2 concentrations are high mid-morning, at a time when NO 2 should be rapidly photolyzed in the atmosphere. August 14 displays these high NO 2 concentrations and correspondingly Figure 5 shows the pollution from urban Chicago area. The Lake Express ferry traveled from Milwaukee, WI to Muskegon, MI with an ozone analyzer onboard taking 1-minute off- shore measurements from A shoreline set of O 3, NO 2, and SO 2 data was also collected in Kenosha, WI via Differential Optical Absorption Spectroscopy (DOAS). Wind direction and temperature, meteorological conditions that influence the formation of ozone, were also recorded at the Kenosha harbor. 1 HYSPLIT models made via VOCs are necessary to produce high concentrations of ozone but NO x emissions can be used to determine peak concentrations of ozone in urban areas and areas downwind of major urban areas. Both ozone and NO x are short-lived species as they reside in a steady state of rapid cycling. NO + O 3  NO 2 + O 2 NO 2 then generates NO and O. NO 2  NO + O The elemental oxygen is extremely reactive and readily attaches to a molecule of O 2 forming ozone. O + O 2  O 3 Rapid cycling occurs between NO and NO 2 as it is stuck in a steady state of NO and ozone to NO 2 and oxygen gas in the presence of sunlight.