Atmospheric Environment. Part B. Urban Atmosphere最新文献

The paper describes the climatic characteristics relevant to urban and building design in hot-humid and in hot-dry tropical regions, respectively. It then discusses the different human comfort issues, the design objectives and the urban design elements which affect and can modify the urban microclimate. The design elements discussed in the paper are: location of towns in a region, density of the built-up area and building's configurations, orientation and width of streets, building design details affecting the comfort of people outdoors, and the design details of “green” areas.

The appropriate (from the climatic aspect) design details of the above urban design elements, and some comments on building design in tropical regions, are discussed with respect to each climate type. Subjects of needed research on issues concerning comfort and design problems in tropical cities, on which more knowledge is needed, are suggested.

The paper is based on a recent WMO Document (Givoni, 1989, WCAP-10, WMO/TD, No. 346).

Air quality due to the release of sulphur dioxide from the thermal power plant within the city limits of Ahmedabad has been computed employing a point, area and line dispersion model. To estimate probable air quality, the meteorological data for 3 consecutive days in the middle of each month of 1983 is used. The concentration of sulphur dioxide is computed at a distance of every 500 m in 16 directions up to the city limit. The air quality in the worst case is estimated in downwind distances under unfavourable meteorological conditions.

The probable zones of high concentrations of sulphur dioxide over residential, commercial and industrial areas of the city are below the ambient air quality standards set by the U.S. EPA in 1971 almost throughout the year. However, in the months of April and October the zone of high concentration (500 μg m⁻³) exceeds the EPA standard. Also, under the most unfavourable meteorological conditions, the estimated high ground-level concentration of sulphur dioxide can reach up to 1000 μg m⁻³ at a distance of 1.25 km from the thermal power plant. This may be attributed to the effect of fumigation.

This paper summarizes three decades of urban climate studies in Johannesburg, South Africa, which is situated on a series of ridges, at an altitude of 1700 m. The first research phase, Near-ground data collection, started with an intensive mobile unit survey measuring wet- and dry-bulb temperatures at midday and near dawn. The results showed that during strong-inversion winter (dry season) nights, the strong heat island and humidity island situated in the city center is more than 11°C warmer than northern suburban valleys. With multiple regression methods the heat island magnitude was estimated to be about 5 K and the relative humidity was 43% lower than the rural areas (but the humidity mixing ratio island was 0.33 g kg⁻¹ higher than the rural areas).

The second phase, Upper air studies, included helicopter, pibal and tethered balloons. Near-ground observations (temperature and wind) were constricted to valleys where anomalies were previously found. The main findings at this stage relate to the interaction between mountain/valley winds with country breezes their connection with cold and warm plumes over the ridges which are dominated by the vertical nocturnal wind shear.

In the third phase, Remote sensing, in situ and mobile acoustic soundings were combined with the other upper air measurement. In addition, ground temperature variations in Johannesburg were estimated from airborne infrared scanner images. The spatial structure of the ground heat-island core shows a steep thermal gradient of about 600–700 m from the city center, comparable to the screen level temperature distribution obtained previously using a meteorological mobile unit.

Measurements of ozone in the urban environment of Delhi were carried out synoptically at four different sites during 1989–1990. The amount of ozone in the ambient air varied from 9.4 to 128.31 ppbv exhibiting wide temporal and seasonal variation. The ozone concentration invariably peaked at noontime and remained high during early summer and spring periods. On many occasions 1-h ozone concentration was more than 113 ppbv, which represents the maximum 1-h limit of ozone in ambient air as prescribed by the U.S. EPA. The results of the study show that there is a significant build up of tropospheric ozone in the urban environment of Delhi.

A comparison of the action on Pentelic marble of nitrates and sulphates with that of NO_x and SO₂ was achieved by passing the polluted ambient air through a filter pack before it entered the reactor chamber holding the marble grains. As a consequence the air reaching the marble was free of nitrates and sulphates, while it contained all the NO_x and SO₂. The effects on the marble grains were quantified and compared with those from a reactor through which unfiltered ambient air was passed simultaneously and under the same conditions. It was found that the action of the acids was much greater than that of the oxides, despite the fact that the concentrations of the latter were much greater.

The first known articles on acid rain appeared when atmospheric pollution reached high levels in the industrial towns of England. Research was carried out to ascertain and interpret earlier documentation, mainly written or printed in Italy, that could throw new light on both the environmental history and the relationship between present-day pollution and weathering of monuments. Very important discussions on dispersion and transport of airborne pollutants, atmospheric scavenging, acid rain, as well as descriptions of effects on fruit, monuments and people, were found in scientific treatises of the 1600s and 1700s. The cause of acidification can be found in volcanic activity, especially that of Stromboli, Vulcano, Vesuvius and Etna, which increased in the 17th and 18th century. Although in the past some pollutants may have reached higher concentrations locally than at present, nowadays air pollution has become a global problem; there are many new species of pollutants and catalysts, and their combined action has increased impressively the environmental risk and the deterioration rate of historic buildings and monuments.

The deterioration of sandstone, marble and granite has been studied under ambient atmospheric conditions. Specially constructed sampling devices, called “micro catchment units”, were installed to sample the run-off water, i.e. the rain water that flows over the stones. Several analysis techniques were invoked for the analysis of the bulk run-off water, as well as electron probe X-ray microanalysis for individual particles in the run-off. An overview of the work is given and preliminary results are discussed.

The NMEP programme consists of 29 sites at which samples of stone and metals are being exposed for a minimum of 4 years to determine rates of decay in the current pollution climate. The sites were chosen to cover a wide range of environmental conditions, climate and topography. Information on meteorological conditions and atmospheric pollutants is being collected from all the sites. Four of the sites also form part of an international programme that is operating concurrently for the United Nations Economic Commission for Europe (UNECE).

The stone tablets are 50 × 50 × 8 mm and are exposed on freely rotating carousels in sheltered and unsheltered positions which represent the washed and unwashed areas of buildings. Tablets of Portland limestone and White Mansfield dolomitic sandstone are exposed at all sites and in addition Monks Park limestone is exposed at the nine sites. Prior to exposure the tablets were cleaned and weighed, and in some cases the surface roughness was measured using an oblique light source and image analysis system.

Tablets have been retrieved after 1 and 2 years of exposure and re-weighed following drying. Samples of powder have been removed from the surface of pristine, sheltered and unsheltered tablets and analysed using ion-chromatography for soluble ionic species (Ca²⁺, Mg²⁺, Na⁺, NH₄⁺, SO₄⁻⁴, NO₃⁻, Cl⁻). The results showed the expected increases in acid species and soluble calcium in the sheltered tablets and increases in chlorides in tablets exposed near to the coast. Tablet surfaces have also been studied to obtain further diagnostic detail.

The results from the analysis of the stone tablets and from the monitoring of pollutant concentrations and meteorological variables have been used to identify empirical relationships and as a basis for mathematical modelling. Preliminary findings from these studies are presented in this paper.