The influence of roadside vegetation barriers on airborne nanoparticles and pedestrians exposure under varying wind conditions

Roadside vegetation barriers are used in many urban areas to restrict air and noise pollution from reaching roadside pedestrians, but their effectiveness in limiting the movement of nanoparticles is not yet known. This study investigates the influence of a roadside vegetation barrier on particle number distribution (PND) and concentration (PNC) and associated exposure under different wind directions. Size-resolved particles in the 5-560 nm size range were measured along a busy roadside in Guildford (Surrey, UK) using a fast response differential mobility spectrometer (DMS50). A custom-built solenoid switching system, together with the DMS50, was used to make sequential measurements at the front (L2), middle (L3) and back (L4) of the vegetation barrier; L1 was in parallel to L2 at a vegetationfree location. Measured data were divided into the three predominant wind directions: crossroad (NW-SW), cross-footpath (NE-SE) and along-road (NW-NE). The consistency in the shape of PNDs and the corresponding geometric mean diameters at the three sites (L2, L3, L4) indicate an identical removal effect of vegetation barrier for all size of particles. Comparison of the PNCs at two parallel locations (with and without the vegetation barrier) showed ~11% higher PNCs (1.99±1.77 ×10 5 cm -3 ) at L2 than those at L1 during cross-road winds, showing the impeding effect of the vegetation barrier. Such differences were insignificant during the remaining wind directions. Cross-road winds indicate the effect of vegetation barrier; the PNCs were decreased by 14 and 37% at L3 and L4, respectively, compared with L2. During cross-footpath winds, particles were carried away by the wind from the sampling location. Significant decrease in PNCs were consequently seen at L3 (1.80±1.01 ×10 4 cm -3 ) and L4 Corresponding author: Address as above; Tel. +44 1483 682762; Fax: +44 1483 682135; Email addresses: [email protected], [email protected]