Atmospheric Environment. Part A. General Topics最新文献

The uptake of NO, NO₂ and O₃ by sunflowers (Helianthus annuus L. var. giganteus) and tobacco plants (Nicotiana tabacum L. var. Bel W3), using concentrations representative for moderately polluted air, has been determined by gas exchange experiments. Conductivities for these trace gases were measured at different light fluxes ranging from 820 μEm⁻²s⁻¹ to darkness. The conductivities to water vapor and the trace gases are highly correlated. It is concluded that the uptake of NO, NO₂ and O₃ by sunflowers and tobacco plants is linearly dependent on stomatal opening. While the uptake of NO is limited by the mesophyll resistance, the uptake of NO₂ is only by diffusion through the stomata. Loss processes by deposition to the leaf surfaces are more pronounced for O₃ than for NO and NO₂.

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.

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.