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Exploring the processes governing roadside pollutant concentrations in an urban street canyon

Lookup NU author(s): Professor Margaret Carol Bell CBE, Dr Fabio Galatioto


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This paper describes an in-depth analysis of data made available by the City Authority of Palermo, Sicily, to investigate the huge variation in the measured roadside air pollutant concentrations of carbon monoxide and nitrogen dioxide in terms of the traffic flow levels, the orientation of the street to the prevailing wind, the wind speed, temperature and barometric pressure. The work has attempted to develop generic parameters that can be applied to other urban areas. The methodological approach used the simultaneous noise measurements, in units of dB(B), to help parameterise the traffic flow and adopted a statistical analysis method based on previous work of Grant and Bell (1983). The measurement of ozone was used to accommodate the secondary formation of nitrogen dioxide from nitric oxide. By applying the same explanatory variables derived in Palermo to the data from a site in Marylebone Road, London (UK) the potential transferability of the approach was demonstrated. The rather different meteorological conditions in Sicily compared with the UK, enhanced the fundamental understanding of the physical and chemical processes that govern the levels of roadside pollutants. The results demonstrate that, within the range of data available, the pollutant concentrations and noise levels can be explained in terms of the logarithm of total traffic flow, the ratio of the traffic flows in opposite directions on a two way road and a term that reflects the effective capacity of the road. Whilst the wind speed and direction strongly influence the levels of pollutants, humidity and ambient temperature are found to have a smaller effect. An additional analysis, using the logarithmic function of ozone improved the prediction of nitrogen dioxide concentration levels in both Palermo and London. Finally, whilst the research demonstrates that the explanatory variables are transferable and the coefficients of the regression are highly statistically significant. The magnitude of the coefficients for Palermo, London and both the sites together are quite different. Whilst this is an expected result the differences both in terms magnitude and direction were difficult to understand.

Publication metadata

Author(s): Bell MC, Galatioto F

Publication type: Conference Proceedings (inc. Abstract)

Publication status: Published

Conference Name: XIV Pan-american conference

Year of Conference: 2006