Measurement of PAN in the Polluted Boundary Layer and Free Troposphere Using a Luminol-NO2 Detector Combined with a Thermal Converter

Peroxyacetyl nitrate (PAN,CH³C(O)O₂NO₂) has been measured inthe polluted boundary layer and free troposphere by thermal conversion tonitrogen dioxide (NO₂) followed by detection of thedecomposition product with a Scintrex LMA-3 NO₂-luminolinstrument. Following laboratory tests of the efficiency of PAN conversionand investigations of possible interferences, the technique was evaluated atthe West Beckham TOR (Tropospheric Ozone Research) Station near the northNorfolk coast in Eastern England between September 1989 and August 1990. PANmeasured by the new technique was reasonably well correlated with PANrecorded using electron capture gas chromatography (EC/GC). PAN was alsowell correlated with ozone (O³) in the summer months. Springand autumn episodes of simultaneously high concentrations of PAN andO³ were examined in conjunction with air parcelback-trajectories and synoptic- and local-scale meteorology in a study ofthe sources of photooxidants on the east coast of England. Spring-timemeasurements of PAN made in the free troposphere in a light aircraft ataltitudes up to 3.1 km showed the presence of 0.54 and 0.26 ppbv PAN inpolar maritime and mid-latitude oceanic air masses, respectively. Thetechnique is particularly suited to airborne applications because potentialinterferences are minimised and the frequency of measurements is higher thangenerally achieved with EC/GC methods.     

Site-specific spectral response of seismic movement due to geometrical and geotechnical characteristics of sites

It is well-known that the response of a site to a seismic solicitation depends on local topographical and geotechnical characteristics. Many aspects of seismic site effect still need to be studied in more detail and they can be incorporated in the seismic norms after quantification. The purpose of this paper is to contribute to establishment of a simple method to include complex site effects in a building code. Horizontal ground movements in various points of two-dimensional (2D) irregular configurations subjected to synthetic SV waves of vertical incidence are calculated. The parametric studies are achieved by means of HYBRID program combining finite elements in the near field and boundary elements in the far field (FEM/BEM). The results are shown in the form of pseudo-acceleration response spectra. For the empty valleys, we can classify the spectral response according to a unique geometric criterion: the “surface/angle” ratio, where surface is the area of the valley opening, and angle denotes the angle between the slope and horizontal line in the above corner. To assess the influence of the 2D effect on the spectral response of filled valleys, the response of alluvial basins are compared with the response of one-dimensional columns of soil. Finally, an offset criterion is proposed to choose a relevant computation method for the spectral acceleration at the surface of alluvial basins.     

The spatial and temporal distribution of heavy metals in sediments of Victoria Harbour, Hong Kong

Victoria Harbour has received substantial loadings of pollutants from industrial and municipal wastewater discharged since the 1950s. Inputs of contaminants have declined dramatically during the last two decades as a result of better controls at the source and improved wastewater treatment facilities. To assess the spatial and temporal changes of metal contaminants in sediments in Victoria Harbour, core and grab sediments were collected. The central harbour areas were generally contaminated with heavy metals. The spatial distribution of trace metals can probably be attributed to the proximity of major urban and industrial discharge points, and to the effect of tidal flushing in the harbour. In the sediment cores, the highest concentrations of trace metals were observed to have accumulated during the 1950s-1980s, corresponding with the period of rapid urban and industrial development in Hong Kong. From the late 1980s, there has been a major decline in the concentrations of trace metals, due to a reduction in industrial activities and to the enactment of wastewater pollution controls in the territory. The Pb isotopic compositions of the sediments revealed the anthropogenic inputs of Pb to the harbour. The (206)Pb/(207)Pb ratios varied from 1.154 to 1.190, which were lower than those of background geological materials in Hong Kong ((206)Pb/(207)Pb: 1.201-1.279). The data also indicated that the Pb in the harbour sediments most likely originated from mixed sources, including the leaded gasoline used in the past and other anthropogenic sources.