Field investigation for ambient wind speed and direction effects exposure of cyclists to PM2.5 and PM10 in urban street environments

Abstract

In China, an increasing number of cyclists commute on urban streets. Cyclists are usually exposed to high traffic-related particulate matter (PM) concentrations. The distribution of cycling exposure concentrations may be affected by meteorological conditions under different street configurations. To investigate these impacts, we collected concentrations of PM 2.5 and PM 10 at the breathing height of cyclists and meteorological data in two differently oriented streets and an open road in Fuzhou. Relative exposure concentrations (RECs) were determined by subtracting the background concentration and monitoring intervals were determined with the minimisation of the coefficient variation of traffic to identify the impacts of meteorology (e.g., wind speed and wind direction) on REC distribution. Wind speed had the most significant impact on REC and explained 26–63% of the variation in REC. Higher RECs (>6 μg/m 3 ) were mainly distributed at lower wind speeds (<2 m/s), while lower RECs (<3 μg/m 3 ) were dominant when the wind speed exceeded 4 m/s. Temperature and relative humidity were not significantly correlated with the REC. Parallel winds can improve the dispersion of particles. In the up-wind condition, RECs on the leeward side were 2 μg/m 3 higher than those on the windward side because of the accumulation of particles caused by the vortex effect, especially in the west-east streets with residential roadside buildings with strip pattern features. More building gaps on both sides of the streets could weaken the vortex effect, and RECs on the leeward side decreased faster with increasing wind speed. These results can be used to propose strategies for reducing cycling exposure. • Relative exposure concentration (REC) improved the identification of meteorological factors. • Wind speed can explain 26–63% of the variation in cycling REC. • Parallel wind can better benefit the dispersion of particles. • Buildings with strip pattern features can increase REC on the leeward side. • More gaps between buildings can benefit the dispersion of pollutants in urban streets.