On the reduction of urban particle concentration by vegetation - a review

In order to assess the filtration performance of plants with respect to atmospheric dust, deposition on vegetation has been investigated by a number of different methods (field studies, numerical and physical modelling) over the past few years. The intention of this review is to assess the extent to which a reduction in particle concentration (especially PM10) can be accomplished by existing vegetation or targeted planting on the basis of international publications. The range of this assessment however is limited to the quantitative filtration potential of urban vegetation. Deposition velocity was taken as a measure of filtration performance as, a particle deposited on a plant is in effect taken from the atmosphere. As regarding published deposition velocities, there are differences of an order of magnitude between measured values and the results of model calculations. The average published value (similar to 1 cm s(-1)) corresponds to a reduction in pollutant concentration (PM10) of about 1 % in urban areas. In addition, analyses carried out for a busy arterial road show that very large vegetation areas (in excess of 10,000 m(2)) would be needed to compensate for local emissions of particles (PM10) by vehicles at a deposition velocity of 1 cm s(-1). However, current in-situ measurements indicate deposition velocities considerably higher than 1 cm s(-1) and, for PM1, velocities above 10 cm s(-1). If these results were confirmed by further measurements, local planting campaigns covering small areas could also be beneficial for a reduction of particle concentrations.