Nuisance dust deposition and soiling rate measurements

Changes in soiling rate of clean clear microscope slides have mean measured at four sites in central London and two to the south-west of London. The study was conducted over the course of a year to sample a wide range of weather conditions. The purpose of the study was to investigate the variation in soiling rates over time at busy roadside, sheltered roadside and non-roadside situations. Measurements were made using a Diffusion Systems Ltd Nuisance Dust Meter. Soiling rates in central London, where traffic flows are more dense, were found to be greater than outside London, and roadside sites were found to be dirtier than non-roadside ones. The closer proximity of high density traffic with a greater proportion of diesel engined vehicles in central London is likely to be an important contributory factor to this. Over the course of a year, weekly soiling rates at a particular site could vary by a factor of two. At all sites soiling levels increased approximately lineally with time for the first week, after which the rate of increase tended to fall off with time. These results show that if the soiling characteristics of a site are to be compared, it is necessary to standardise the time over which measurements are made, and that it is necessary to carry out measurements over a number of months in order to experience a typical range of weather conditions. A standard averaging time of one week is proposed for individual soiling measurements.