Atmospheric pollution as a result of mobile emission sources. OBZhD

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Atmospheric pollution as a result of mobile emission sources. Basics of safe life

Fundamentals of Safe Life Activities (OBZhD)

In recent decades, due to the rapid development of motor transport and aviation, the share of emissions entering the atmosphere from mobile sources has increased significantly: trucks and cars, tractors, diesel locomotives and aircraft. In cities, motor transport is estimated to account for (depending on the city's level of industry and the number of cars) between 30 and 70% of total emissions.

motor transport. The main contributors to air pollution are gasoline-powered vehicles (about 75%), airplanes (about 5%), diesel-powered vehicles (about 4%), tractors and other agricultural vehicles (about 4%), railway and water transport (about 2%).

The largest amount of pollutants is emitted during acceleration of the car, as well as when driving at low speed. The relative share (of the total mass of emissions) of hydrocarbons and carbon monoxide is highest during braking and idling, and the share of nitrogen oxides is highest during acceleration. From these data it follows that cars pollute the air especially strongly during frequent stops and when driving at low speed.

Green wave traffic systems, which significantly reduce the number of traffic stops at intersections, are being created in cities and are designed to reduce air pollution. The mode of operation of the engine, in particular, the ratio between the masses of fuel and air, the moment of ignition, fuel quality, the ratio of the surface of the combustion chamber to its volume, etc., has a great influence on the quality and quantity of emissions of impurities. With an increase in the ratio of the mass of air and fuel entering the chamber combustion, emissions of carbon monoxide and hydrocarbons are reduced, but emissions of nitrogen oxides are increased.

Despite the fact that diesel engines are more economical, and emit no more substances such as CO, NO2 than gasoline engines, they produce significantly more smoke (mainly unburned carbon, which, moreover, has an unpleasant odor created by some unburned hydrocarbons). ). And when you consider that diesel engines produce a lot of noise, it becomes clear that they affect human health much more than gasoline engines.

aircraft engines. Although the total emission of pollutants by aircraft engines is relatively small (for a city, country), in the airport area, these emissions make a decisive contribution to environmental pollution. In addition, turbojet engines (like diesel engines) emit a plume of smoke that is clearly visible to the eye during landing and takeoff.

According to the estimates obtained, a significant part of the fuel is spent on taxiing the aircraft to the runway (RWY) before takeoff and taxiing from the RWY after landing (in terms of time, on average, about 22 minutes). At the same time, the proportion of unburned and released into the atmosphere fuel during taxiing is much larger than in flight. A significant reduction in emissions can be achieved, in addition to improving the operation of engines (fuel atomization, enrichment of the mixture in the combustion zone, the use of fuel additives, water injection, etc.), by reducing the time of operation of engines on the ground and the number of engines operating during taxiing (only due to the latter a 3-8 times reduction in emissions is achieved).

For the past 10-15 years, much attention has been paid to the study of the effects that may arise in connection with the flights of supersonic aircraft and spacecraft. These flights are accompanied by pollution of the stratosphere with nitrogen oxides and sulfuric acid (supersonic aircraft), as well as aluminum oxide particles (transport spacecraft). Since the listed pollutants destroy ozone, it was initially believed (supported by appropriate model calculations) that the planned increase in the number of flights of supersonic aircraft and transport spacecraft would lead to a significant decrease in the ozone content, with all the subsequent detrimental effects of ultraviolet radiation on the Earth's biosphere. However, a thorough analysis of this problem made it possible to conclude that supersonic aircraft emissions have a weak effect on the state of the stratosphere.

Chlorofluoromethanes (CFM), such as Freon-11 and Freon-12, gases released, in particular, during the evaporation of aerosol preparations, can have a stronger impact on the ozone layer and global air temperature. Since CFMs are very inert, they propagate and live for a long time not only in the troposphere, but also in the stratosphere, having rather strong absorption bands in the atmospheric transparency window.

In conclusion, it can be noted that all these anthropogenic effects are offset on a global scale by natural factors - for example, atmospheric pollution by volcanic eruptions.

Authors: Aizman R.I., Krivoshchekov S.G.

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