Atmospheric Environment. Part B. Urban Atmosphere最新文献

An automatic rain collector was developed with emphasis on simplicity, construction with readily available low-cost materials, inexpensive maintenance and reliable operation at temperatures above freezing point. The rain sensor is of the heated AC conductometric type and the circuit includes electronic protections against false triggering by electrical transients. With this collector, the first studies of chemical characterization of wet only deposition were made in São Paulo over the period of November 1988 to June 1990. Results are presented and compared with previous total deposition studies. For this period the volume-weighted mean values of the pH and conductivity were 4.6 and 19 μS cm⁻¹, respectively.

The concentrationof vehicular pollutants, wind, turbulence and traffic volume were measured in three different typical street canyons in Guangzhou City. Air dispersion in different types of urban canyons was compared. The configuration of a street is an important factor that influences air dispersion. In low wind conditions, it is rare that a stable vortex is formed in a canyon with irregular configuration. The movement of vehicles may dominate the flow near the surface of the narrow street canyon when tee wind at roof-level is weak. Simple operational models have been proposed. They performed well in predicting the air pollution due to vehicular emission in different street canyons in Guangzhou City.

By a multiple series of laboratory simulations of rain runoff on marble tiles it was possible to obtain a semi-quantitative evaluation of pre-industrial recession rates for marble surfaces exposed to weathering. The approximate value of 0.03–0.05 mm per century was established for partially sheltered vertical surfaces. The lower value refers to climatic conditions typical of Rome whereas the higher value relates to more severe climatic conditions (heavier rainfalls and/or lower rain intensities). Even higher values, that is, 0.15–0.25 mm per century (always to be intended as approximate) can be obtained for fully exposed and inclined marble surfaces. These data were compared to the recession rates obtained by other scholars, especially relating to tombstone studies: a certain agreement was found only for the lower values reported. On this basis a revision of the methodologies and an interpretation of the divergencies are proposed.

Simultaneous measurements of ozone and —for the first time in Munich—of PAN were carried out at two sites in the urban area of Munich during two periods (16 June–15 September 1989 and 1 January–30 April 1990). Maximum mixing ratios reached 75 ppbv for ozone (10-min-average) and 5.6 ppbv for PAN (20-min-value), respectively. Ozone showed more pronounced diurnal variations than PAN. In both cases they were related to diurnal variations of the global radiation and the mixing ratios of NO_x. Regarding ozone linear correlation analysis with meteorological parameters revealed distinct dependencies, especially on UV radiation, whereas the results for PAN reflected its more complicated formation. As far as dependencies on wind velocity are concerned, both ozone and PAN exhibited maximum mixing ratios in cases where the wind velocity was below 5 ms⁻¹. With increasing wind velocity both mixing ratios tended towards their natural background concentrations. Investigations concerning the influence of the wind direction did not disclose any particular local effects, but rather a relationship to the general weather situations. On the whole, PAN could be considered as a more characteristics indicator of smog conditions than ozone due to its low background concentrations and its thermal instability.

The precipitation chemistry of Greater Manchester, a Metropolitan County in the northwest of England, has been examined for small scale spatial variability using a network of 18 bulk precipitation collectors. Significant spatial variability was found for concentrations of non-marine SO₄²⁻, NO₃⁻, NH₄⁺, Ca²⁺ and H⁺ ions. The statistical associations between the data were investigated using correlation, partial correlation and principal components analyses. It was found that zero-order correlation coefficients were inadequate for the interpretation of the data and that the computation of first, and higher order partial correlation coefficients was necessary in order to explain the interrelationships between the data and their spatial variability. The statistical associations between the data suggest relationships between Ca²⁺ and non-marine SO₄²⁻, and NO₃⁺ in precipitation which are discussed in terms of their possible precursor species. Potential source effects were examined in conjunction with atmospheric removal processes. The dry deposition of SO₄ particles, rather than the dry deposition of SO₂, may explain the spatial variability of non-marine SO₄²⁻. The erosion of CaSO₄ formed from the reaction of SO₂ with CaCO₃ on urban surfaces with subsequent resuspension is thought to be the basis of the relationship between Ca²⁺ and non-marine SO₄²⁻ concentrations in precipitation. The wet and dry deposition of CaCO₃ particles from local sources may be partially responsible for the spatial variability of H⁺, and dry deposition and scavenging of NH₃, in conjunction with the predominant wind direction may explain the spatial variability of NO₃⁻ and NH₄⁺ ions. Ammonia is thought to originate from sources both outside the study area and within it.

Atmospheric aerosol samples were collected by a low volume sampler in a typical urban site of Thessaloniki city, from March 1989 to December 1990. The concentrations of the components Cl⁻, NO₃⁻, SO₄²⁻, Na⁺, K⁺, Ca²⁺, Mg²⁺ and NH₄⁺ were determined. Data obtained showed a significant correlation of SO₄²⁻ with NH₄⁺, Ca²⁺, Mg²⁺ and NO₃⁻. The contribution of the sea sprays was estimated to be 47% of aerosol chlorides but only 1.5% of aerosol sulfates. Aerosol sulfates are neutralized by atmospheric ammonia to form (NH₄)₂SO₄. Data evaluation considering wind direction led to the conclusion that local urban and industrial emission sources are primarily responsible for aerosol sulfates.

Street level air pollution due to traffic emission is a cause of concern in Guangzhou City. During the winter and summer of 1988, the traffic-related air pollutant concentrations, wind field, traffic volume and vehicle speed were measured extensively in three types of street canyons in Guangzhou City. Various types of motor vehicle emission in idle condition were measured and the composite emission factors of vehicles were derived. The variation of traffic volume and vehicle speed in 223 mainstreets were also investigated. The annual air pollutant concentration levels of traffic source emission were calculated. Using CO as a traffic emission tracer for air pollution on the street, the contributions of traffic emission to street level air pollution were determined by the receptor method. Ground level air pollution in Guangzhou has changed from coal combustion emission type into traffic source emission type. The average contributions of traffic source emission to the concentration of CO and NO_x on the street in 1988 are about 87% and 67%. The most significant pollutant of ambient air quality that traffic source emission influences in NO_x.