CO2 absorption/emission and aerodynamic effects of trees on the concentrations in a street canyon in Guangzhou, China

In this paper, the effects of trees on CO2 concentrations in a street canyon in Guangzhou, China are examined by Computational Fluid Dynamics (CFD) simulations of the concentration distribution, taking into account both the CO2 absorption/emission and aerodynamic effects of trees. Simulation results show that, under a 2 m/s southerly prevailing wind condition, CO2 absorption by trees will reduce the CO2 concentration by around 2.5% in the daytime and at the same time the trees' resistance will increase the difference of CO2 concentrations in the street and at the inflow by 43%. As the traffic density increases to 50 vehicles/min, the effect of trees on the ambient CO2 concentration will change from positive to negative. At night, trees have a negative effect on the concentration in the street canyon mainly because of their resistance to airflow. When environmental wind changes, the effect of trees will be different.

► The trees affect CO2 concentrations in a street canyon.
► Both the CO2 absorption and flow resistance of trees are significant factors by day.
►  As the emissions of CO2 increase, the effect of trees will become negative.
► At night, trees have a negative effect on CO2 concentration due to the resistance.