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Timothy S. Dye, Paul T. Roberts, and Marcelo E. Korc

Abstract

The Lake Michigan Air Quality Region (LMAQR) continues to experience ozone concentrations in urban and rural areas above the federal standard of 125 ppb. During the summer of 1991, the LMAQR states sponsored the Lake Michigan Ozone Study, which included a comprehensive field measurement program to gather data to understand the complex meteorology and air quality of that region and to verify predictions from air quality models. Air quality and meteorological data were collected by aircraft, surface monitors, rawinsondes, and radar wind profilers to characterize pollutant distributions and understand transport regimes.

The unique meteorology of the LMAQR and the stable conditions over the lake produce several transport regimes. This paper presents observations of these transport regimes on two days with maximum surface ozone concentrations above 160 ppb in Wisconsin and Michigan. Transport of air with the highest ozone concentrations occurred in a conduction layer, which is a shallow layer of cool air over Lake Michigan. The conduction layer provided a stable environment where morning emissions remained concentrated and allowed reaction at high precursor concentrations. Southerly and southwesterly winds transported pollutants in this layer northward. Eventually this air flowed onshore and produced many nearshore ozone exceedances along the Wisconsin and Michigan shorelines. To successfully model ozone in the LMAQR, meteorological and air quality models must simulate these transport processes and stable conditions over the lake.

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H.H. Jonsson, J.C. Wilson, C.A. Brock, R.G. Knollenberg, T.R. Newton, J.E. Dye, D. Baumgardner, S. Borrmann, G.V. Ferry, R. Pueschel, Dave C. Woods, and Mike C. Pitts

Abstract

A focused cavity aerosol spectrometer aboard a NASA ER-2 high-altitude aircraft provided high-resolution measurements of the size of the stratospheric particles in the 0.06–2.0-µm-diameter range in flights following the eruption of Mount Pinatubo in 1991. Effects of anisokinetic sampling and evaporation in the sampling system were accounted for by means adapted and specifically developed for this instrument. Calibrations with monodisperse aerosol particles provided the instrument's response matrix, which upon inversion during data reduction yielded the particle size distributions. The resultant dataset is internally consistent and generally shows agreement to within a factor of 2 with comparable measurements simultaneously obtained by a condensation nuclei counter, a forward-scattering spectrometer probe, and aerosol particle impactors, as well as with nearby extinction profiles obtained by satellite measurements and with lidar measurements of backscatter.

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J. M. Wilczak, R. G. Strauch, F. M. Ralph, B. L. Weber, D. A. Merritt, J. R. Jordan, D. E. Wolfe, L. K. Lewis, D. B. Wuertz, J. E. Gaynor, S. A. McLaughlin, R. R. Rogers, A. C. Riddle, and T. S. Dye

Abstract

Winds measured with 915- and 404-MHz wind profilers are frequently found to have nonrandom errors as large as 15 m s−1 when compared to simultaneously measured rawinsonde winds. Detailed studies of these errors which occur only at night below about 4 km in altitude and have a pronounced seasonal pattern, indicate that they are due to the wind profilers' detection of migrating songbirds (passerines). Characteristics of contaminated data at various stages of data processing are described, including raw time series, individual spectra, averaged spectra, 30- or 60-s moments, 3- or 6-min winds, and hourly averaged winds. An automated technique for the rejection of contaminated data in historical datasets, based on thresholding high values of rnoment-level reflectivity and spectral width, is shown to be effective. Techniques designed for future wind profiter data acquisition systems are described that show promise for rejecting bird echoes, with the additional capability of being able to retrieve the true wind velocity in many instances. Finally, characteristics of bird migration revealed by wind profilers are described, including statistics of the spring (March–May) 1993 migration season determined from the 404-MHz Wind Profiler Demonstration Network (WPDN). During that time, contamination of moment data occurred on 43% of the nights monitored.

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