Hotspots, daily cycles and average daily dose of [PM.sub.2.5] in a cycling route in Medellin/Puntoscriticos, ciclosdiariosy dosis diaria de [PM.sub.2.5] para una cicloruta en Medellin

Bicycle sharing systems are an alternative to promote sustainable transportation and active living. Bicycle users are exposed to traffic and to pollutants in their trips; therefore, the analysis of pollutant concentrations and user exposure is of utmost importance for planning the expansion of creation of these transportation systems. In order to evaluate the concentrations and exposure of cyclists to [PM.sub.2.5], we designed a route within the bicycle sharing system of Medellin and implemented a sensor-based monitoring protocol. Measurements were carried out with a low-cost sensor validated with local information. Potential average daily dose of [PM.sub.2.5] was calculated based on the average time of exposure and the level of effort made by the user while riding. Hotspots were identified as the zones on the route with concentrations three standard deviations above the average for each route. [PM.sub.2.5] concentrations were found to be highly variable in terms of hour of the day and season of the year. When the concentrations are higher, the potential average daily dose is doubled. There are two types of hotspot according to the built environment configuration on the route, and the concentrations in these hotspots are reaching values considered as harmful for sensitive population groups. The present results are key for the discussion leading to the implementation of measures that will improve the welfare of cyclists in Medellin, that may span from infrastructure intervention to early warning systems.