Personal exposure to UFP from bicycling measurements in Birmingham, UK

Cycling activity has benefits for both health and the environment. However, there are also health risks for cyclists due to their direct exposure to air pollutants from on-road vehicle emissions. Higher breathing rates and the proximity to the emission sources while cycling could also increase the health risk for the cyclist. Airborne particle exposure, particularly ultrafine particles (UFP, Dp smaller than 100nm) has been considered to have a detrimental effect on human health. The assessment of exposure to UFP is essential for UFP management, which is also included in a Good Practice Statement by WHO.

In this study, we estimated the personal exposure to UFP using mobile measurements (bicycling) between 17 October and 18 November 2022, in Birmingham, UK. The measurements were conducted at three (3) different times (morning, afternoon, and evening) on weekdays and weekends. A miniature particle counter (DiscMini) that measures particle number concentration (PNC), and average diameter with 1s resolution was used. Besides, a similar instrument was also deployed at an urban background site which was passed during the bicycling measurements.

A total of 34 trips (~1.5 hours, and ~12km per trip) were completed. Overall, the result revealed that the exposure to PNC varied substantially both spatially and temporally. Relatively higher PNC exposure was found during the morning (MWD) and evening (EWD) trips on weekdays, while the lowest was during morning weekend (MWE) trips. The mean concentration of MWD, EWD, and MWE was 16664#/cm3, 15255 #/cm3, and 4004#/cm3, respectively. A moderate level was observed during the afternoon on weekdays and weekend (AWD, AWE), and evening weekend (EWE) ranging from 8321-9676 #/cm3.

During weekend trips, the average geometric mean diameter was observed to be larger (43-52.3 nm), suggesting a greater relative background contribution during the weekend, especially in the morning. All the average PNC from bicycling measurements were 2.3-2.6x higher than that measured at the background site due to more emission sources being present along the route. However, PNC and average diameter measured at the background site revealed similar behaviour to the mobile measurement with high concentrations during morning and evening on  weekdays.

Spatial analysis indicated some hotspots that were at intersections and traffic lights. A construction area and shopping park area also exhibited high concentrations, especially during afternoon and evening weekend trips. These results may be of value in support of strategies to mitigate UFP personal exposure, particularly for cyclists who commute daily in this area and on similar routes elsewhere.