Abstract

Mobile platforms are increasingly used to acquire air quality data at a high spatial and temporal resolution in complex urban environments. As such, mobile measurements provide a solution for short-term studies to acquire a spatially spread data set that would not be feasible if using stationary measurements. Mobile monitoring campaigns were carried out with a bicycle platform at two different urban locations, consisting of 20 and 24 repeated runs along a fixed route over a three-week period. The measurement runs were carried out on different days and at different times of the day, without systematical temporal coverage. Significant differences in UFP concentration were found within the day and between days, and also between several streets along the measurement route. These differences were related to traffic intensity and street characteristics. In contrast, PM10 concentrations differed between measurement days, but the within-day variability of PM10 was mostly non-significant. Additionally, the spatial variability was limited and the PM10 concentrations were only significantly different between busy streets, with high concentrations, and quiet background streets, with low ones. The results indicate that for most streets the number of runs was sufficient to give a good approximation of median daytime UFP concentration levels for the measurement period, and for some streets this number could even be reduced to less than 10. However, for PM10 a higher number of runs is needed, and this may be attributed to the significant background contribution to the roadside PM10 concentration, and the high variability of this. We conclude that a limited set of mobile measurements makes it possible to map locations with systematically higher or lower UFP and PM10 concentrations in urban environments.

Highlights

  • Particulate air pollution is a mixture of particles that vary in number, size, shape, surface area, chemical composition, solubility and origin, where the size distribution is typically trimodal, including coarse particles, fine particles and ultra-fine particles (UFP, aerodynamic diameter < 0.1 μm) (Pope and Dockery, 2006)

  • In this study we investigated to what extent a limited set of mobile measurements allows to draw conclusions on urban air pollution and its spatio-temporal variation by using two datasets of mobile measurements

  • The results suggest that the added value of mobile measurements for mapping spatial variability of air quality is more important for UFP than for PM10

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Summary

Introduction

Particulate air pollution is a mixture of particles that vary in number, size, shape, surface area, chemical composition, solubility and origin, where the size distribution is typically trimodal, including coarse particles (aerodynamic diameter > 2.5 μm), fine particles (aerodynamic diameter between 0.1 and 2.5 μm) and ultra-fine particles (UFP, aerodynamic diameter < 0.1 μm) (Pope and Dockery, 2006). This study focuses on the ultra-fine fraction and the coarse fraction with an aerodynamic diameter of < 10 μm (PM10). PM10 is primarily derived from suspension and resuspension of solid material, and contributes greatly to the mass of the total suspended particles in urban environments. UFP contribute little to the mass of the total suspended particles but they are highly abundant. The urban particulate cloud is constantly receiving UFP from primary emissions from combustion sources in transportation, industries and. Temporal patterns of PM10 have been observed over seasons (Monn et al, 1997; Liu et al, 2003), weeks (Monkkonen et al, 2004), days (Roosli et al, 2001) and hours of the day

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