The influence of the vegetation cycle on the mitigation of air pollution by a deciduous roadside hedge

Vegetation barriers along roads can mitigate the effects of air pollution from traffic. Here, we measure a range of air pollutants in front and behind a hedge during the dormancy, greenup and part of the maturity vegetation cycle along with auxiliary variables. This is the first time a long time-series measuring multiple pollutants on both sides of a hedge is presented. This time-series allows assessing the influence of the annual vegetation cycle, wind direction and high versus low concentrations of both gaseous and particulate matter pollutants across a hedge. A marked jump in concentrations of particles happens after the hedge is greening up; this jump was not seen for gases. For example, a concentration difference for CO and PM1 of - 8 %, -1 % for PM2.5 and - 3 % for NO2 and + 10 % for PM10, during dormancy and greenup was measured. At the beginning of the maturity phase, all three PM fractions experience a rapid increase in concentration difference, not seen for gases, to - 52 % for PM1, -44 % for PM2.(5) and -35 % for PM10. The effect of wind direction is shown to be minor. These measurements are a first step towards an accurate assessment of city-scale air pollution mitigation potential of hedge-like vegetation.