Urban smoke concentrations at Kew, London, 1898-2004

Historical smoke concentrations at monthly resolution for the early twentieth century are found for Kew Observatory, London, using the atmospheric electricity proxy technique. Smoke particles modify the electrical properties of urban air: an increase in smoke concentration reduces air's electrical conductivity and increases the Potential Gradient (PG). Calibrated PG data are available from Kew since 1898, and air conductivity was measured routinely between 1909 and 1979 using the technique developed by C.T.R. Wilson. Automated smoke observations at the same site overlap with the atmospheric electrical measurements from 1921, providing an absolute calibration to smoke concentration. This shows that the late nineteenth century winter smoke concentrations at Kew were approximately 100 times greater than contemporary winter smoke concentrations. Following smoke emission regulations reducing the smoke concentration, the electrical parameters of the urban air did not change dramatically. This is suggested to be due to a composition change, with an increase in the abundance of small aerosol compensating for the decrease in smoke. (c) 2006 Elsevier Ltd. All rights reserved.

Olfactory attractiveness of mixtures of some host plant and conspecific semiochemicals to the banana weevil Cosmopolites sordidus (Germar, 1824)

A simple "Y" shaped olfactometer was used in laboratory studies on the olfactory attractiveness of mixtures in various proportions of industrial analogues of some host plant and conspecific-based semiochemicals, or their combinations with banana rhizome, to the banana weevil. The aim was to identify factors that influence their attractiveness to the weevil, and consider the possibility for their use as lures for trapping the weevil in the field. Cosmopolites sordidus was attracted to the mixtures at specific concentrations and proportions of constituent chemicals. 6-methylhept-5-en-2-one was only attractive on its own at 1 µl/100 ml and in mixture with 4- mercaptophenol, but not at 10 µl, 0.01 µl, or in combination with banana rhizome. 4-mercaptohpenol and 2-n-butylfuran, which were compatible with most host plant-based chemicals and were attractive as a mixture, were perceived to be key elements in the composition of attractants to the weevil. It was concluded that in addition to the composition, other factors that may determine the attractiveness or otherwise of a mixture to C. sordidus are the proportions and concentrations of the constituent chemicals.