Continuous measurements of aerosol physical properties in the urban atmosphere

Simultaneous continuous measurements have been made at an urban background site of PM,, mass by Tapered Element Oscillating Microbalance, particle number density by condensation nucleus counter and Fuchs surface area using an epiphaniometer. Concurrent measurements of gaseous NO, and CO have been used to indicate road traffic emissions, and data from a nearby meteorological station have been used for relative humidity, temperature and windspeed. The data indicate that particle number density is a far better indicator of traffic activity than PM,, mass which is strongly influenced by a high background, and also tends to peak rather later than the gaseous pollutants and particle number, presumably as a result of advection of accumulation mode aerosol. PM,, mass and Fuchs surface area generally show a very similar temporal trend, although there is a tendency for the ratio of surface area to dry particle mass to increase with relative humidity. The sampling period included bonfire night celebrations which caused substantial increases in all particle parameters, although the ratio of particle mass to number was considerably higher than for the morning rush hour road traffic-influenced peak. (C) 1999 Elsevier Science Ltd. All rights reserved.