Atmospheric Environment. Part A. General Topics最新文献

This paper derives expressions for the maximum cross-wind integrated and ceterline concentrations at ground level for an elevated source in the convective boundary layer. These expressions account for the observation that the probability density function (pdf) of vertical velocities in the convective boundary is positively skewed with a negative mode. The estimates obtained with these formulae compare favorably with observations reported by Briggs (1993; Boundary-layer Met.62, 315–328).

The paper also examines the error associated with using a symmetric Gaussian pdf instead of the skewed pdf to estimate the ground-level concentration. We show that the error is equivalent to an underestimation of a factor of almost 1.5 for the cross-wind integrated concentration and a factor of 1.3 for the ground-level centerline concentration.

This paper considers some of the statistical aspects of estimating specimen emission rate profiles from chamber concentration level measurements, which is a major step in assessing indoor pollution levels. Parametric and nonparametric modeling approaches are applied to the problem, and their relative advantages and disadvantages are discussed. The issue of experimental design is also addressed, and the choice of an optimal set of experimental conditions and sampling times is considered. Some simulation results are presented to contrast the efficiencies of various experimental designs.

In coastal areas featuring industrial plants, air masses rich in photochemical pollutants can be transported offshore and then back inshore as a result of the land-sea breeze circulation system. Precursors of O₃ are transported out to sea in the morning hours and the offshore-formed oxidants blown back to the coast in the early afternoon by the sea breeze, thereby raising the concentration of ozone at ground level. Along the northwestern coast of the Adriatic Sea this phenomenon takes on a marked significance, involving an offshore distance of approximately 30–40 km. The present paper surveys the findings of experimental studies conducted in the Ravenna area over the last decade, and reports the results of an empirical trajectory model developed to provide a dynamic interpretation of the ground-level distribution and concentration of photochemical oxidant concentrations along the area's coastline.

Measurements of indoor radon concentrations in the village Umhausen (2600 inhabitants, Ötztal valley, Tyrol, Austria) revealed unusually high indoor radon concentrations up to 274,000 Bq m⁻³. The medians measured on the basements were 3750 Bq m⁻³ in winter and 361 Bq m⁻³ in summer, those on the ground floors were 1180 Bq m⁻³ and 210 Bq m⁻³, respectively. Seventy-one per cent of the houses showed basement radon concentrations above the Austrian action level of 400 Bq m⁻³ in winter, 33% in summer. There are indications that the high radon concentrations are due to a giant rock slide about 8700 years ago. The unusually high radon concentrations in Umhausen coincide with a statistically significant increase in lung cancer mortality. For the period 1970–1991 the age and sex standardized mortality rate is 3.85 (95% confidence interval: 2.9 to 5.1). The control population is the total population of Tyrol (630,000 inhabitants).

A widely used air quality model performance index, the normalized mean square error, NMSE, is analyzed in detail. It is shown that the main purposes of the index, i.e. avoiding bias towards model overestimate or underestimate and giving an overview of the model performance over the entire data set of sampled concentrations, are not fulfilled. It is also shown that in certain situations, that have not to be considered as limit cases, the “best” condition to get the lowest value of the NMSE is completely different from what one would expect by simple logical considerations. A proposal is then made to obtain the desired results by the use of different indices.

This paper reports seasonal and spatial variations in the ambient air concentration of nitrogen dioxide throughout the State of Bahrain, from February to December 1992. Monitoring sites were chosen to include urban areas with high traffic density, suburban areas with low traffic density, commercial and industrial areas. Correlations between meteorological parameters and mean NO₂ concentrations were analysed, and NO₂ levels were only significantly correlated with temperature (r = 0.63). Only February, a winter month, showed a significantly lower concentration of NO₂ with an overall mean value of 23 μgm⁻³, whereas in August, a summer month, it was 33 μgm⁻³. The results revealed that in a hot region like Bahrain, NO₂ concentrations do not show significant monthly variations. Also summer-averaged NO₂ values exceeded corresponding spring and winter values. In cold regions opposite patterns were observed. Moreover, the results revealed significant spatial variations in NO₂ concentrations. In suburban areas with low traffic density, the overall mean NO₂ level was 15, with a range of 12–17 μg m⁻³, while in urban areas with high traffic density, the overall mean value was 52 with a range of 44–60 μg m⁻³. The mean NO₂ value in industrial sites with low traffic density was 21 with a range of 14–27 μg m⁻³, whereas in the same areas near major roads, it was 32 with a range of 31–32 μg m⁻³. These results indicate that automobiles exhaust are the dominant source of NO₂ in Bahrain. The highest NO₂ levels were found in roads with high traffic density, which are narrow, with several traffic lights and roundabouts, suggesting the effect of road geometry on NO₂ levels.

The results of an audited production and use survey for chlorodifluoromethane (HCFC 22) for the years 1980–1991 are reported. Annual production figures for 1970–1979 have also been collected. The time delays for release to the atmosphere for the various uses of this commercial gas are estimated in order to calculate annual emissions. Calculated atmospheric concentrations and trends are compared with available measurements. Uncertainties in calculated parameters are examined relative to assumptions made in the analysis.