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Street canyon vegetation very effectively improves urban air quality

Tom Pugh, Lancaster Environment Centre

Wednesday 11 January 2012, 1300-1345

Street-level concentrations of nitrogen dioxide (NO2) and particulate matter (PM) exceed public health standards in many cities, causing increased mortality and morbidity. Concentrations can be reduced by controlling emissions, increasing dispersion, or increasing deposition rates, but little attention has been paid to the latter as a pollution control method. Both NO2 and PM are deposited onto surfaces at rates that vary according to the nature of the surface; deposition rates to vegetation are much higher than those to hard, built surfaces. Previously, city-scale studies have suggested that deposition to vegetation can make a very modest improvement improvement (<5%) to urban air quality. However, no previous studies take full account of the interplay between urban form and vegetation, specifically the enhanced residence time of air in street canyons. Here we show that increasing deposition by the planting of vegetation in street canyons can reduce street-level concentrations by as much as 40% for NO2 and 60% for PM.

Substantial street-level air quality improvements can be gained through action at the scale of a single street canyon or city-wide. Moreover, vegetation will continue to offer benefits in the reduction of pollution even if the traffic source is removed from city centers. Thus, we show how the judicious use of vegetation can create an efficient urban pollutant filter, yielding rapid and sustained improvements in urban air quality.

Note: This short presentation is in a joint session with Dave Leedal's talk.