Atmospheric Environment (1967)最新文献

A hybrid Eulerian-Lagrangian, photochemical model has been developed for the assessment and prediction of the impact of large point sources on air quality. This simple model is based on solving the mass conservation equations which include chemical reaction terms in the cells of a two-dimensional crosswind plane which moves with the air parcel. Testing of the model is done in three ways. First, the chemistry is evaluated using results of smog chamber experiments simulating Melbourne's emissions and meteorological conditions. Second, the accuracy of the emissions inventory is tested using aircraft measurements. Finally the overall performance of the model is evaluated using monitoring station data. In general the model gives good agreement with the measurements, with the predictions for O₃ being somewhat better than those for NO₂. This result was also found in the three-dimensional study of McRae and Seinfeld (1983, Atmospheric Environment17, 501–522) for the Los Angeles area.

The effect of ambient (outdoor) environmental parameters on formaldehyde levels in a temperature controlled urea-formaldehyde foam-insulated (UFFI) house and a mobile home was investigated over a 9-month period (July–March). Strong correlations between formaldehyde levels, solar radiation, ambient temperatures, inside/outside temperature differences and water vapor pressure were observed in the UFFI house and in the mobile home. Stepwise regression revealed a significant independent effect of solar radiation values on indoor formaldehyde levels in the UFFI house but not in the mobile home. Stepwise regression revealed no significant independent effect of the other environmental variables evaluated. The independent effect of solar radiation on formaldehyde levels in the UFFI house indicates that solar radiation can have a significant effect on formaldehyde concentrations, and this effect may explain anomolous results in whole house source interaction studies.

Eight short-term long-range transport models (MESOPUFF, MESOPLUME, MSPUFF, MESOPUFF II, MTDDIS, ARRPA, RADM and RTM-II) have been tested with field data from two data bases involving tracer releases. The Oklahoma data base involved two separate experiments with measurements taken at 100 and 600 km arcs downwind of a 3-h perfluorocarbon release. The Savannah River Plant data base encompassed 15 experiments with measurements taken over 2–5 days at distances of 28–144 km downwind from a 62 m stack release of Kr-85 gas.

Application of the American Meteorological Society statistics to the model/data comparisons showed that six of the eight models predicted within a factor of two of the observed concentrations for all of the following: points paired in space and time, points paired in space only, and for points unpaired in space and time. However, the ratio of the standard deviation of residuals to the average observed value showed improvement as more unpairing was done in the comparison of the models with the data. The statistical comparisons reveal a definite tendency of the models to overpredict plume concentrations. Supplemental graphical comparisons showed that plume concentration overprediction is accompanied with an underprediction of plume spreading, and that a definite time lag is often observed between the time of arrival of the observed plume and the time of arrival of the predicted plume.

The causes of model/data discrepancies can be largely traced to inadequate wind field modeling that leads to an incorrect temporal and spatial positioning of the plume, and the use of the Turner [Workbook of atmospheric dispersion estimates. U.S. Dept of H.E.W. Publication 999-AP-26 (1970)] curves to downwind distances beyond which they can accurately represent the scales of atmospheric turbulence. The use of multilayer wind field models and the use of the Heffter [J. appl. Met.4, 153–156 (1965)] formula for lateral plume dispersion close to the source appear to improve model accuracies.