In cities, the most complex anthropogenic formations, a specific and often unfavourable ecological environment for man’s life has been created. All around we can find only concrete buildings, pavements, cars, crowded streets, therefore air pollution can not be avoided. If we compare the quality of air in cities with those in rural areas, it can be concluded that it has much less oxygen and more bacteria and germs. One of the best assistants in the fight against harmful gases, dust and soot, and a good regulators of gas exchange are green areas, and their most important element – vegetation.
Vegetation has an important role in purifying urban air of dust and gases, which are deposited on the leaves, branches and trunk of trees. The air in green areas in spring and summer contains 42%, and in winter 37% less dust than the air above the open constructed spaces. In the depths of the forests the content of dust in air is reduced by more than 2.5 times. The dust is best retained by coarse leaves, such as elm (Ulmus campestris) and leaves covered with hairs, like lilac (Syringa vulgaris). Green surfaces absorb carbon dioxide from the air and enrich the air with oxygen. One hectare of green plantations absorb 8 litres of carbon dioxide for one hour. One hectare of forest produces the amount of oxygen which is sufficient to maintain life activities of 30 people.
Green areas significantly affect the air temperature in cities, especially in the warm period, when the air temperature is significantly lower in the middle of green areas. Foliage has a great ability to reflect, in addition plants evaporate a certain amount of moisture, increasing the humidity. The level of humidity in parks and green areas is twice as many than in urban areas, particularly on streets.
Plant species in the course of its long evolution have developed such a perfect system of biological protection from microorganisms and other negative impacts to ensure the survival and successful distribution in conditions of modern ecological crisis. Especially important protective substances are phytoncide. They kill or slow the development of certain bacteria that cause disease. Phytoncide from the bark of fir (Abies sp.) kills Diphteria bacteria, leaves of poplar (Populus sp.) – Dysentery. Particularly high level of phytoncide is produced by conifers . l hectare of juniper (Juniperus sp.)creates 30 kg of these substances during 24 hours. A great amount of phytoncide is created by pine (Pinus sp.) and spruce (Picea sp.). The air in parks has 200 times less bacteria than the air on streets.
Green plants are a reliable means of protection against noise, reducing noise levels by 5-10%. The highest percentage of absorption of noise can be achieved by planting different species of trees and shrubbery.The plants which have the best ability to reduce noise are : Norway maple (Acer platanoides L.), Linden (Tilia sp.) Berlin poplar (Populus x Berolinensis DIPP.), Oak (Quercus robur L.), Hornbeam (Carpinus betulus L.), Canadian poplar (Populus canaden-sis Asch.), Birch (Betula verrucosa Ehrh.). Therefore, proper selection of appropriate species and their positions around the source of noise can produce significant effects in the battle with noise pollution.
Above all, the green color of leaves, the quiet ambience, phytoncide presence in the air and increased oxygen content have a positive physiological effect on the nervous system of people, improving their health and ability to work. Therefore we can say that green environment, which have proven a better, healthier and cleaner air microclimate than other urban areas, creates the best conditions for rest and relaxation. The conclusion is simple: planting new trees and saving the green areas are highly recommended methods of preservation the healthy environment of cities.