Relationships between air quality and thermal structure of the lower atmosphere at Salem, Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/dj52w777v

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  • The examination in some detail of the relationships between air quality and the thermal structure of the lowest layers of the atmosphere constituted the primary objective of this thesis. Data for the study were assembled during April-June 1965 at the U.S. Weather Bureau Station, McNary Field, Salem, Oregon. The measures of air quality employed were the estimated mean concentrations of suspended particulate material collected on standard high volume filters near the surface during two six-hour periods each day : early morning (0000 to 0600 L.S.T.) and afternoon (1200 to 1800 L.S.T.). To represent thermal structure, lapse rates of temperature were computed twice daily for each 150-meter-thick layer of air between the surface and 1500 meters above the surface. The information for these computations was taken from the original records of the U.S. Weather Bureau radiosonde flights conducted daily at 0300 and 1500 L.S.T. Graphical and statistical analysis of the relationships between lapse rate and air quality for each of the 150-meter-thick layers and each of the cumulative layers (by 150 meter increments) originating at the surface produced results that were quite different for the morning and afternoon sampling periods. The relationships for the morning period were determined graphically to be continuous and determined statistically to be linear. For this period the stability of the lowest 450 meters appeared to affect most directly the air quality while the thermal structure above about 1000 meters appeared unrelated to air quality. The afternoon relationships, on the other hand, were poorly defined. In fact, the air quality of the afternoon period was better related to the thermal structure of the early morning period than to the contemporaneous thermal structure. On the premise that for a given lapse rate, air quality may fluctuate because of variations in pollutant emission rates and/or because of changes in meteorological variables, supplementary studies were conducted. The test procedure was the same for each variable, and consisted of dividing the data for each sampling period into classes of the parameter, then comparing the resulting relationships both graphically and statistically with the combined relationships. Surface wind velocities, average upper air wind speeds, prominent synoptic features and air mass types, and the stability of the lowest layers of the atmosphere prior to the beginning of the sampling periods were the meteorological parameters considered. Division of data by weekend and work week, and then by day of the week was also considered to assess possible variations of pollutant emission rates over these periods. In no case did subdivision of data by additional parameters produce any apparent increased information. Since pilot balloon data are more numerous and less expensive than corresponding radiosonde data, and since theory indicates that wind shear may be a reasonable estimate of stability, the vertical shears of the horizontal wind profiles of the lower atmosphere were also compared with concurrent estimates of air quality. The relationships between shear and air quality for both sampling periods were judged both graphically and statistically to be poorly defined. Although the development of relationships for the purposes of estimating and predicting air quality was not an objective of this study, many of the developed relationships between lapse rate and air quality might be used for one of these purposes. In particular, selected combinations of lapse rate of the morning period may be used as an estimator of air quality for this period. Similarly, lapse rate of the morning period might be utilized as a predictor of air quality of the afternoon period.
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