Capturing the urban canyon effect on particle number concentrations across a large road network using spatial analysis tools

Publication date: October 2015
Source:Building and Environment, Volume 92
Author(s): William J. Farrell , Laure Deville Cavellin , Scott Weichenthal , Mark Goldberg , Marianne Hatzopoulou
Urban canyons increase overall air pollution concentrations at the street level. Yet, due to the difficulty in characterizing such geometric features over a regional area, they are rarely included in the evaluation of population exposures. This study combines measurements of ultrafine particles (UFP) with land-use regression techniques in order to capture the determinants of near-road concentrations of UFP while specifically accounting for urban canyon effects. Using the mean UFP concentration measured within a set of urban canyons (over 1000 road segments) as the dependent variable, we investigated the effects of a number of urban canyon descriptors (width, height, contiguity, vegetation, and road class) through a multivariate linear regression. Our models are adjusted for the effects of meteorology. The signs and values of the regression coefficients are qualitatively consistent with what is already known about urban canyons: increased building height (bheight = 0.004; 95% CI: 0.001, 0.007) along with decreased canyon width (bwidth = −0.007; 95% CI: −0.012, −0.002) serve to worsen the air quality therein, while increased tree cover (btrees = −1.762; 95% CI: −2.236, −1.289) improves air quality. We also observed that the difference in UFP levels on both sides of the canyon increased with increasing street width (bwidth = 0.113; 95% CI: 0.061, 0.165), and with wind direction more perpendicular to the street. We conclude that it is possible to include urban canyon effects in the development of air pollution exposure surfaces thus refining the assessment of population exposure to air pollution in urban microenvironments.

Graphical abstract