Do Trees Really Help Clean the Air in Our Cities? Rob MacKenzie – “…First things first; it is not trees that pollute the air of cities in the developed world. As car manufacturers are all too guiltily aware, it is mainly road vehicles that cause pollution. And their impacts are compounded by the choices we make about how and what we drive. Many features of the urban landscape influence how air moves around a city. Impervious objects like buildings, and permeable ones like trees, deflect air from the path imposed by weather patterns, such as high and low pressure systems. The urban landscape turns freshening breezes into whorls of air, which can either contain pollution near its source – where it affects vulnerable hearts and lungs – or lift it away from ground level. Whether the landscape traps or lifts air will depend very sensitively on the exact positioning of roads, buildings, gardens, street trees, intersections, even billboards and other street furniture…”