Development of a land-use regression model for ultrafine particles in Toronto, Canada

Abstract This study applies land-use regression (LUR) to characterize the spatial distribution of ultrafine particles(UFP) in a large city. Particle number(PN) concentrations were measured in residential areasaround Toronto, Canada, between June and August 2008. A combination of fixed and mobile monitoring was used to assess spatial gradients between and within communities. The fixed monitoring locations included a central site, two downtownsites, and four residential sites located 6–15 km from the downtowncore. The mobile data included average PN concentrations collected on 112 road segments from 10 study routes that were repeated on three separate days. The mobile data was used to create the land-use regression model while the fixed sites were used for validation purposes. The predictor variables that best described the spatial variation of PN concentration (R 2 = 0.72, validated R 2 = 0.68) included population density within 300 m, total resource and industrial area within 1000 m, total residential areawithin 3000 m, and major roadway and highway length within 3000 m. The LUR model successfully predicted the afternoon peak PN concentration (slope = 0.96, R 2 = 0.86) but over-predicted the 24-h average PN concentration (slope = 1.28, R 2 = 0.72) measured at seven fixed monitoring sites.