What is air pollution?

Air pollution is often associated with the deposit of black particles seen on windows, leaves and buildings in urban areas. However, much of the air pollution in Britain today is largely invisible and so more difficult to detect, although you may be able to smell the pollutents from car exhausts, farmyards and heavy industry.  Some pollutents contain ammonia and oxides of nitrogen (nitric oxide and nitrogen dioxide). Although nitrogen is essential for the growth of all living organisms, too much nitrogen can cause problems. Ammonia and oxides of nitrogen can stimulate the growth of some plants and fungi but stop others from developing, thereby changing the natural around us. Lichens do not like excessive nitrogen in any form, but may grow particularly well when they are growing close to sources of ammonia. There is also a fungus, commonly known as tar spot that is found on sycamore trees, that we believe is sensitive to air pollution including nitrogen dioxide.