When inhaled, nitrogen dioxide can penetrate relatively deep into the airways, where it can cause irritation and damage to tissue. It can also aggravate both asthma and allergic reactions. It also impairs the defense mechanisms of the lungs against bacteria, viruses, and other air pollutants such as ozone and particulate carcinogens. Repeated exposure to nitrogen dioxide, either alone or in combination with other factors, is suspected of triggering asthma in children. The main contributor to the concentrations of nitrogen oxides in urban surroundings is usually road traffic.
Sulphur dioxide also causes irritation of the airways. Long-term exposure in combination with airborne particles increases the likelihood of respiratory infections in children. The main sources of emissions are the burning of coal and oil. The contribution from road traffic is small.
When the concentration of small particles in air rises, even from low levels, there is a rise in mortalities from respiratory, cardiac and circulatory diseases, and more people seek hospital care for bronchitis and asthma. Even exposure to low levels for long periods is considered harmful. The long-term effects have not yet been very well researched, but living in regions where there are high concentrations of particles is believed to reduce life expectancy. It is the very smallest particles that are believed to be the most harmful, because when they are inhaled they can penetrate deep into the lungs.
Particles are classed as either primary or secondary. Primary particles are those that are formed during combustion, but may also consist of dust, small soot flakes, pollen, etc. Major sources are combustion processes and internal combustion engines. Secondary particles consist mainly of sulphate and nitrate salts that are formed in the air from sulphur dioxide and nitrogen oxides. They are small and can remain suspended in the air for long periods. There is extensive transboundary migration of these particles.
These comprise a very large group of pollutants, including known carcinogens such as benzo-(a)pyrene, ethene and benzene, as well as various aromatic hydrocarbons. They can occur either as gases or bound to particles, and several of the substances in this group contribute to the formation ofground-level ozone — which probably is the most significant health effect of this group as a whole. Petrol-driven cars that have ineffective catalytic converters, or none at all, are a major source of emissions of volatile organic compounds in urban air. Small-scale combustion, such as the household burning of wood or coal, can also make a significant contribution.
Source: Air and the environment by P.Elvingson and C.Ågren
Guidance on GAINS application (pdf, 2.4 MB) model in the state environmental management system of the Russian Federation (Russian; English version is under development)
Guidance document on Critical Load assessments (in Russian) (pdf, 790.3 kB)