Air quality on the Lake Michigan shoreline has been a target area of concern with an urban corridor of Gary, IN-Chicago, IL-Milwaukee, WI extending over the southern and southwestern portion of the lake, many neighboring counties of which are in non-attainment of federal ozone standards. While each state bordering Lake Michigan has dedicated monitoring systems, offshore measurements have been sparse, mainly executed through specific short-term campaigns. From 2008-2010 measurements of ambient ozone were routinely conducted on the Lake Express, a high-speed ferry that travels from Milwaukee, WI to Muskegon, MI up to 6 times daily from spring to fall. Concurrent ozone forecast images from National Weather System's National Air Quality Forecast System (AQFS) in the upper Midwestern region surrounding Lake Michigan were saved from June 18-Nov. 3, 2009 for the hours of 08:00-22:00 CDT. The forecast images are produced from the Community Multi-scale Air Quality (ETA-CMAQ) model. The bias of the ETA-CMAQ O3 forecast was computed and evaluated with respect to ferry position, time of day, 8-hour ozone average and month. The bias is consistently high with a median of 10 ppb overprediction of ozone and complex trends in the bias emerge with respect to ferry location and time of day or month. The extent to which the trends in the bias can pinpoint difficulties in parameterizing the changing photochemical and meteorological conditions over Lake Michigan in a region not previously monitored routinely will be discussed.

Bias of CMAQ model forecast O<sub>3</sub> output over Lake Michigan by comparison with routine ferry-based O<sub>3</sub> observations

247th National Meeting (2014)

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Bias of CMAQ model forecast O3 output over Lake Michigan by comparison with routine ferry-based O3 observations

Bias of CMAQ model forecast O₃ output over Lake Michigan by comparison with routine ferry-based O₃ observations