The structure of the Earth's atmosphere and sources of air pollution

Structural composition of the atmosphere and gas balance

The total mass of the Earth's gaseous envelope is approximately 5.9⋅10¹⁵ tons. The gas composition of the atmosphere in its lower layers is practically constant and maintains an oxygen-nitrogen balance up to an altitude of approximately 400–600 km. Above 600 km and up to 1600 km, helium prevails in the atmosphere, and in the uppermost layers — hydrogen. With increasing altitude, atmospheric pressure continuously decreases.

• Atmospheric mass — 5.9⋅10¹⁵ t
• Air share in the troposphere — up to 80 %
• CO₂ growth since 1880 — from 0.027 % to 0.033 %
• Annual CO₂ emission — over 20 billion t
• Space dust — 2–5 million t/year

Depending on the temperature regime, several key zones are distinguished in the atmosphere. The lowest layer — the troposphere — extends from 7 km above the poles to 18 km above the equator. Major meteorological processes occur here: clouds form, precipitation falls, and thunderstorms and storms arise. As altitude increases, the temperature in the troposphere drops to -50 °C.

Above the troposphere is the stratosphere, which is about 50 km long. The temperature in it is initially constant and then rises to values close to 0 °C due to the absorption of ultraviolet radiation by ozone. The mesosphere and thermosphere are located above the stratosphere. In the thermosphere, at an altitude of 400 km, the air temperature can reach 700–1500 °C.

Sources of pollution and the greenhouse effect

The development of industry, energy, and transport since the 19th century has significantly disrupted the natural gas exchange of the biosphere. Atmospheric air pollution is divided into natural and anthropogenic. Natural factors usually do not pose a threat to ecosystems, whereas human economic activity creates a large-scale man-made burden on the environment.

Natural pollution is formed by the following sources:

• Extraterrestrial: space dust from burnt-up meteorites (from 2 to 5 million tons annually).
• Marine: microcrystals of magnesium, sodium, potassium, and calcium salts formed by the drying of sea spray.
• Continental inorganic: dust from arid deserts and steppes, products of rock and soil weathering, and volcanic emissions.
• Continental organic: smoke from forest, steppe, and peat fires, plant spores, aeroplankton, fungal formations, as well as products of biomass decay and decomposition.

Anthropogenic pollution comes from heat power facilities, transport, nuclear fuel cycle enterprises, industrial production, and agriculture. Radioactive contamination is associated with uranium ore mining and transportation, reactor operation, thermal power plant waste, and nuclear testing. Technogenic emissions suppress flora and fauna, and also damage structures.

The annual volume of anthropogenic substances entering the atmosphere is:

• Carbon dioxide — over 20 billion t;
• Dust — over 250 million t;
• Carbon monoxide — 200 million t;
• Sulfur dioxide — 150 million t;
• Ash — 120 million t;
• Nitrogen oxides — 53 million t;
• Hydrocarbons — over 50 million t.

Since 1880, the concentration of carbon dioxide in the air has increased from 0.027 % to 0.033 %, and according to scientists' calculations, this figure will double every 23 years. The accumulation of CO₂ leads to the development of the greenhouse effect. The air envelope with an increased content of carbon dioxide transmits solar radiation but traps the reflected long-wave infrared radiation of the Earth.

The World Environmental Forum held in Kyoto in 1997 stated that in twenty years, the Earth will be 3 degrees warmer. This has not been observed in the entire previous history of humanity. Nights will be warmer, there will be more hot days in summer, and colder ones in winter. Torrential rains will be replaced by prolonged drought.

The most rapid rise in the average temperature on Earth over the last 50 years is observed in the Antarctic region. It has warmed up by 2.5 degrees here, which has caused the collapse of glaciers covering several thousand square kilometers and a rise in the World Ocean level.

This will lead to the flooding of the coastline and the need to evacuate hundreds of millions of people. An increase in air temperature may lead to an increase in mortality among people over 65.

However, the Earth is threatened not only by a great flood. According to American ecologist Wallace Broecker from Columbia University, an increase in the concentration of industrial gases could change ocean currents. For example, the Gulf Stream that warms Europe. And then the temperature in Dublin will drop by 10 degrees.

The final protocol of the Kyoto forum recorded the commitments of the European Union countries to reduce atmospheric pollution by 8% by 2010 compared to 1990 levels.