Measured and modelled air quality related effects of a noise barrier near a busy highway

Abstract. A three-month air quality measurement campaign was conducted in spring 2023 near a busy highway in Espoo, Finland. The measurement site featured a high (6.5 m) noise barrier built adjacent to the highway. Additionally, there was a gap in the noise barrier at the selected measurement site, providing an opportunity to study the air quality impacts of the noise barrier. Several air quality measurement devices were installed behind the noise barrier and in the gap at distances of 10, 20 and 40 m from the side of the highway. Additionally, 15 passive samplers were deployed to monitor NO2 concentrations across the study area, mobile measurements were conducted using the ATMo-Lab mobile laboratory on the highway, and concurrent flights with drones equipped with AQ monitors were performed along the highway. The effects of the noise barrier on PM10, PM2.5, lung deposited surface area (LDSA), particle number concentration (PNC), NO2, and black carbon (BC) were quantified based on the analysed measurement data. Furthermore, the measurements were compared with simulated pollutant concentrations from a local-scale Gaussian air quality model (Enfuser) with a nearby obstacle detection and concentration reduction method incorporated in the model to address the effects of the noise barrier in the study. The noise barrier was found to effectively reduce pollutant concentrations behind the barrier. The most notable reductions were observed closest to the highway. The greatest reductions were observed for PM10 (mostly road dust) while gaseous concentrations, such as NO2, exhibited less pronounced decreases.