Air pollution in a microclimate; the impact of different green barriers on the dispersion

[Display omitted] •NO2 is one of the main causes of pollution related mortality in the UK;•The dispersion of NO2 in a microclimate in Manchester was studied;•Air temperature and NO2 concentration showed a negative correlation;•Hedges and trees with different heights were adopted in the neighbourhood;•Trees facilitated the dispersion, while hedges trapped and increased the pollution. This paper studies the impact of different green barriers on the dispersion of air pollution in a neighbourhood. The study was performed with reference to air quality conditions in Manchester, UK. Manchester experiences a high level of NO2. Measured results showed that the average annual concentration level in 2018 was very close to the limit defined by European Union legislation. Maximum and minimum NO2 concentrations occurred during the winter and summer, respectively. Simulations of the dispersion of air pollution in a hypothetical neighbourhood showed that NO2 level was decreased by the increase of air temperature during the simulated day. In four perturbation scenarios, hedges and trees with different heights were added to the neighbourhood as green barriers. Hedges increased the pollution level near the street at the pedestrian level as a result of the reduced wind speed. The simulations demonstrated that using the trees facilitated the dispersion of pollution.