Residential air quality near noise barriers strongly affected by wind velocity

Residing within 300-500 m of main roads is linked to specific negative health effects, including reduced lung capacity and increased cardiovascular mortality (Health Effects Institute, 2010). Noise barriers, widely used due to their ability to reduce noise levels, can also have the beneficial side effect of limiting the dispersion of traffic emissions from highways into adjacent areas. We investigated how a high noise barrier influences near-road aerosol concentrations under varying wind conditions. An urban site, which includes a highway, was simulated using observations of traffic emissions, topography data and recorded traffic patterns over 2 h with in-situ observations utilized for validation. We presented continuous spatial fields of aerosol concentrations and wind velocity, which give a more comprehensive view of the situation than localized measurements. We found that noise barriers reduced aerosol concentration behind the barrier under low (typical) wind speed condition but under the high-speed crosswind condition, the noise barrier had an overall adverse effect on nearby air quality, contrary to expectation. This is due to two main reasons: (1) air parcels with high particulate loading from the traffic sources slowdown in the presence of the barrier, leading to a high concentration plume on the windward side of the barrier; and (2) the upward motion of the flow near the noise barrier carries the high concentration plume into the wind flow above the barrier, which then disperses pollutants toward adjacent areas. In the context of providing better air quality near highways, this study helps urban planners to have a deeper understanding of noise barrier's efficacy under different wind conditions to optimize both noise and air pollution control.