Differences in airborne particle and gaseous concentrations in urban air between weekdays and weekends. Atmospheric Environment

Airborne particle number concentrations and size distributions as well as CO and NOx concentrations monitored at a site within the central business district of Brisbane, Australia, were correlated with the traffic flow rate on a nearby freeway with the aim of investigating differences between weekday and weekend pollutant characteristics. Observations over a five-year monitoring period showed that the mean number particle concentration on weekdays was (8.8 ± 0.1) x 103 cm-3 and on weekends (5.9 ± 0.2) x 103 cm-3 – a difference of 47%. The corresponding mean particle number median diameters during weekdays and weekends were 44.2 ± 0.3 nm and 50.2 ± 0.2 nm respectively. The differences in mean particle number concentration and size between weekdays and weekends were found to be statistically significant at confidence levels of over 99%. During a one-year period of observation, the mean traffic flow rate on the freeway was 14.2 x104 and 9.6x104 vehicles per weekday and weekend day respectively – a difference of 48%. The mean diurnal variations of the particle number and the gaseous concentrations closely