Trees help to clean the air we breathe. Through their leaves and bark, they absorb harmful pollutants and release clean oxygen for us to breathe. In urban environments, trees absorb pollutant gases like nitrogen oxides, ozone, and carbon monoxide, and sweep up particles like dust and smoke. Increasing levels of carbon dioxide caused by deforestation and fossil fuel combustion trap heat in the atmosphere. Healthy, strong trees act as carbon sinks, offset carbon and reducing the effects of climate change.