Observations The collection of slope values were plotted against time and box plots show the distribution for each of the six daily trips of the vessel.

Since there is more urbanization on the southwestern shore of Lake Michigan, there are higher emissions of ozone precursors compared to the opposite shoreline. Typical trends for ozone concentrations for this region involve elevated levels around Lake Michigan with peak ozone levels expected around 4:00 PM. In this analysis, no clear trend in a gradient across the lake emerges.

Continued Work Ozone concentrations will be compared with data obtained from models of the region previously generated by the National Oceanic and Atmospheric Administration (NOAA). The 2009 data will continue to be filtered and examined for the agreement between modeled concentrations and observations.

New equipment has been installed on the ferry to gather data during the 2013 operating season to continue to compare with the models produced by NOAA.

Data Analysis and Model Comparison of Atmospheric Ozone above Lake Michigan

Nathan Fuhrman Patricia Cleary Chemistry University of Wisconsin-Eau Claire

Abstract Stable atmospheric conditions trap ozone precursors found in smog in a layer above the surface of Lake Michigan. In 2008-2010, hourly measurements of ozone concentration were taken by an ozone analyzer onboard the Lake Express Ferry that traveled from Milwaukee, WI to Muskegon, MI. Although ozone concentration in the atmosphere around Lake Michigan is monitored at sites on land, these data are the first measurements taken over the lake where ozone is predicted to be high. These observed data were filtered based on the presence of the ozone precursor of carbon dioxide to remove concentrations that were unrepresentative of the regional air mass. The observed atmospheric ozone data will be analyzed to look for trends which will be compared to a national model for the purpose of evaluating the accuracy of the model for the region. Data will continue to be studied further to examine the spatial distribution of ozone over the lake.

Introduction This project has examined the data collected by the ozone analyzer onboard the Lake Express Ferry during the 2010 operating season. The vessel crosses the lake weather permitting four or six times a day depending on time of year. Carbon dioxide concentrations were also recorded to be an indicator for the presence of exhaust air plumes which could cause increases in ozone concentrations that are not representative of the regional air mass. Latitude and longitude, tracked by a Global Positioning System, were recorded along with the time for each reading.

4 6 8 10 12 14 16 18 20 22

-60

-40

-20

0

20

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Slo

pe V

alue

Time of Day (hours)

6:00 AM 10:15 AM 12:30 PM 4:45 PM 7:00 PM 11:00 PM

Data Analysis The data was filtered for plumes of exhaust gases, detected in the data as increased levels of CO2 gas, because they are not representative of the regional air mass and NOx/O3 chemistry effectively destroys ozone in these plumes. The filtered data was then sorted by assigning trip indices to mark the data corresponding to single traversals of the vessel across the lake. Using the longitude and time data for each reading, ozone concentrations were isolated into cohorts corresponding to individual traversals of the vessel. A linear fit was found for each collection of ozone concentrations and the slope values were examined for evidence of a concentration gradient over the surface of the lake. Several examples of the ozone data selections are shown below along with a linear fit.

Ozone concentrations plotted against day of year for the 6:00 AM trip from Milwaukee, 10:15 AM trip from Muskegon, and 12:30 PM trip from Milwaukee:

Ozone concentrations plotted against day of year for the 4:45 PM trip from Muskegon, 7:00 PM trip from Milwaukee, and 11:00 PM trip from Muskegon:

Slope values from linear regressions with low R2 values (< 0.6) were disregarded and the data cohorts were not considered when examining the slope values. Slope values with magnitudes greater than 100 were also not considered.

180.52 180.54 180.56 180.58

22

23

24

Ozo

ne C

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tion

(ppb

)

Day of Year

184.44 184.46 184.4835

40

45

50

55

60

65

Ozo

ne C

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tion

(ppb

)

Day of Year

187.93 187.94 187.95 187.96 187.97

40

45

50

55

60

65

70

Ozo

ne C

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tion

(ppb

)

Day of Year

224.84 224.86 224.88

45

50

55

Ozo

ne C

once

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tion

(ppb

)

Day of Year

259.24 259.26 259.28 259.3020

30

40

Ozo

ne C

once

ntra

tion

(ppb

)

Day of Year

230.72 230.74 230.76

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55

60

65

Ozo

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Co

nce

ntr

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n (

pp

b)

Day of Year

AcknowledgementsThis research was possible with collaboration and support from: The Lake Express, Great Lakes Institute, GLOS, UW-Milwaukee, NOAA

Co-authors: John Schafer2, Joseph Fillingham2, Harvey Bootsma2, Eric J. Williams3, Thomas Langel3, Steven Brown3

2. School of Freshwater Science, University of Wisconsin – Milwaukee 3. NOAA Earth System Research Lab

Funding: UW-EC ORSP Student/Faculty Collaboration Grant

Printing: UW-EC Learning and Technology Services

Source: Rethinking the Ozone Problem in Urban and Regional Air Pollution. Washington, D.C.: The National Academies Press 1991.

The meteorological calm over the surface of the lake together with the presence of a large urban region along the shore line provides an interesting environment for the formation of ozone. These data are being examined for correlations as well as agreement with national models which often show increased ozone concentration over this region.

The chemical formation of ozone is influenced by the presence of volatile organic compounds (VOC) and nitrogen oxides (NOx). In the presence of sunlight, hydroxyl radicals react with the VOCs and oxygen to form organic oxides that further react with NOx to produce nitrogen dioxide and radicals. Nitrogen dioxide, in the presence of sunlight, generates elemental oxygen which reacts with oxygen gas to form ozone.

Shown below are typical ozone isopleths which diagram the relationship between concentrations of VOC and NOx.

The usual ratio of VOC/NOx for ozone production with this particular plot is 8/1. NOx-limited regions are common in areas downwind of urban areas. VOC-limited regions are common in highly polluted areas.