The influence of urban green space upon air pollutant concentrations

Greenspace has an essential role in influencing the concentration of pollutants in urban areas. The processes for improving air quality are dispersion and deposition, but their relative contributions to reducing air pollution are unclear. Temporal and spatial variability of pollutant concentrations from a roadside into a park were generated using diffusion tubes measurements. Sampling was carried out in urban park areas in Birmingham and London, UK, specifically in Cannon Hill Park, Tile Cross Park, University of Birmingham (UoB), and Hyde Park. The difference in NO_2 concentrations between the roadside and the park was 32% at Cannon Hill Park, 30% at Hyde Park and 38% at the UoB site, and was statistically significant (p < 0.01). Dispersion and dry deposition modelling were performed using the ADMS-Roads model. The set-up and evaluation of dispersion modelling are presented, incorporating the meteorological data, background concentration, emissions set-up, and the ratio of NO₂:NOₓ in the emissions. The evaluation of the model was performed using observational data from two different sites (BROS and EROS) measured by automatic analysers, and by comparison with the diffusion tube spatial profiles. NOₓ deposition velocities were estimated by the gradient method in a grassed quadrangle area of the Biosciences building at UoB, using an analogy with carbon particles which were used to estimate the eddy diffusivity. Although the method showed major weaknesses, the average value of NOₓ deposition velocity (0.0014 ± 0.0024 m s⁻¹) was in the range of literature values, which is from 0.0010 m s⁻¹ to 0.0067 m s⁻¹. The results of NO₂ measurements and the modelling of the dispersion and dry deposition processes provide an understanding that dispersion plays a dominant role in reducing pollutant concentrations in urban parks. The methods developed in this research have a useful potential role in the urban planning process with respect to the location of urban greenspace and parks. Special consideration needs to be given to the distance from major roads and the location with respect to prevailing wind direction.