Exercise 2. Read and translate the text

Air is considered safe when it contains no harmful chemicals and only low levels of other chemicals that become harmful in higher concentrations to humans, other animals, plants, or their ecosystems.

Severe air pollution incidents in cities such as London have shown that breathing dirty air can be dangerous and, at times, deadly. In 1880, 2,200 Londoners died in one such incident when coal smoke from home heating and industry combined to form toxic smog of sulfur dioxide gas and airborne combustion particles

Many nations have adopted ambient air quality standards to safeguard the public against damaging pollutants. These include sulfur dioxide, suspended particulate matter, ground-level ozone, nitrogen dioxide, carbon monoxide, and lead all of which are tied directly or indirectly to the combustion of fossil fuels. Chemical factories cause the allergic diseases.

Meanwhile, urban air pollution has worsened in most large cities in the developing world, a situation driven by population growth, industrialisation, and increased vehicle use. Despite pollution control effects, air quality has approached the dangerous levels.

As dangerous as polluted outdoor air can be to health, indoor air pollution actually poses a greater health risk on a global level. Indoor air pollution is a concern in developed countries, where, for example, energy efficiency improvements sometimes make houses relatively airtight, reducing ventilation and raising indoor pollutant levels. In such circumstances, even small pollution sources - emanating from a furnace, a new carpet, or from naturally occurring radon gas - can lead to significant human exposures.

Air pollution can irritate the eyes, throat and lungs. Burning eyes, cough and chest tightness are common with exposure to high levels of air pollution. However, different people can react very differently to air pollution. Some people may notice chest tightness or cough, while others may not notice any effects. Because exercise requires faster, deeper breathing, it may increase the symptoms. People with heart disease, such as angina, or with lung disease, such as asthma or emphysema, may be very sensitive to exposure to air pollution and may notice symptoms when others do not.

Fortunately for most healthy people, the symptoms of air pollution exposure usually go away as soon as the air quality improves. However, certain groups of people are more sensitive to the effects of air pollution than others. Children probably feel the effects of pollution at lower levels than adults. They also experience more illness, such as bronchitis and earaches, in areas of high pollution than in areas with cleaner air.

People with heart or lung disease also react more severely to polluted air. During times of heavy pollution, their condition may worsen to the point that they must limit their activities or even seek additional medical care. In the past, a number of deaths have been associated with severely polluted conditions. Pollution this bad is rare today in the United States. The health effects of long-term exposure to low levels of air pollution are being studied.