Pict. 8.1. Decay of forests caused by acid rain in the Sudetes

Other plants can also be damaged by acid rain, but the effect on food crops is minimized by the application of lime and fertilizers to replace lost nutrients. In cultivated areas, limestone may also be added to increase the ability of the soil to keep the pH stable, but this tactic is largely unusable in the case of wilderness lands. When calcium is leached from the needles of red spruce, these trees become less cold tolerant and exhibit winter injury and even death (Fig. 8.3.).

8.2.2. 8.2.2. Traffic pollution

The environmental impact of traffic (both positive and negative) include the local effects of highways (public roads) such as on noise, water pollution, habitat destruction/disturbance and local air quality; and the wider effects which may include climate change from vehicle emissions. The design, construction and management of roads, parking and other related facilities as well as the design and regulation of vehicles can change the impacts to varying degrees.

Although road vehicles, which mainly originate from industrialised countries, give off similar emissions when new, as required in the country of origin, they are generally maintained less well due to lack of supervision by the authorities and poor economic conditions. This means that the individual vehicle pollutes the environment more heavily for the same mileage, especially as regards the sharp rise in emissions from a poorly maintained engine (e.g. unburnt fuel, noise etc.) and leakage of water-polluting liquids (oil, fuel etc.). Poor quality fuels likewise produce higher levels of pollutants, and unleaded petrol is unobtainable in many countries.

a, Air pollutants are not only harmful to human beings, they can also present a hazard to animals, the soil, vegetation and the climate. Remote effects (i.e. remote both in time and in space) must be considered; one must also remember that combinations of air pollutants may be more harmful than the individual contaminants (synergetic effects). The principal air pollutants emitted by vehicular traffic are as follows:

- Carbon monoxide is not harmful to bloodless animals and plants, but sustained concentrations, even if small, can have an impact on both humans and other vertebrates. Compounds formed with the haemoglobin in the blood restrict the oxygen supply to the tissues, and in this way can cause disorders of the central nervous system.

- Certain hydrocarbons, resulting from incomplete fuel combustion (such as benzol), are carcinogenic among humans.

- Nitrogen oxides are irritants to human beings, and can damage the organs of respiration. In areas of high population density, nitrogen oxides contribute to smog formation. Plants are not directly damaged by nitrogen oxides at concentrations below 200 g/m³ air.

- Under ultraviolet radiation, ozone is produced from nitrogen oxides and hydrocarbons. High ozone concentrations may cause smog and afflict the respiratory tract and circulation in humans. Moreover, ozone can cause serious damage to woodland and also, if present in sufficiently high concentrations, to crops such as vegetables and tobacco plants. Ethylene can have an unfavourable effect on the growth and ageing of plants. The numerous chemical interactions involved have not yet been fully explained.

- Lead and other heavy metals, which are deposited in the bones, are poisonous to humans and can cause disorders of the central nervous system. Lead aerosols are dispersed mainly over an area up to 30 to 50 metres from the roadway, while traces can be carried as far as 100 to 200 metres, depending on wind conditions. Plants absorb lead from the air by surface contact (dust deposits), or from the soil through their roots. As well as growth damage to the plant itself, follow-on effects through absorption into the food chain should also be noted (e.g. milk produced from pastures near busy roads).