Using small sensors to measure the effect of mobility policies on urban air pollution

Small sensors have the potential to provide valuable complementary measurements to established air quality monitoring stations in urban areas. The flexible deployment options of small sensors also allow for short- or longer-term deployment to e.g., accompany policy implementations. Here we present the results from a number of case studies in Berlin where we used a combination of small sensors and reference instrumentation to assess individual policys impacts on local air quality, a metric important to policymakers assessments of their success. These measurement campaigns included both the stationary and mobile deployment of small sensors, in collaboration with the city. Data generated by the small sensors were calibrated using co-locations and the open-source 7-step methodology developed in our group (Schmitz, et al. 2021, ACP). Measurements deployed alongside the implementation of several policies captured before-after measurements of nitrogen oxides (NOx) and particulate matter (PM). Data from the urban monitoring network was used to account for changes in meteorology and city-wide changes to assist in isolation of the signal from the policy implementations. Through the implementation of a new bike lane, cyclists exposure to NO2 was reduced by 20%; in another case, the closure of a street to vehicle traffic reduced local air pollution to the levels of the urban background. These results were subsequently accounted for by policymakers when determining the success of each measure, considering the implications for human health.