Реферат: Untitled Essay Research Paper Gifted Chemistry IBAlternative
cloud which may contain numerous chemical compounds, the combination of which, we call
photochemical smog.Both types of smog can greatly reduce visibility. Even more importantly, they pose a
serious threat to our health. They form as a result of extremely high concentrations of
pollutants that are trapped near the surface by a temperature inversion. Many of the
components which make up these smogs are not only respiratory irritants, but are also
known carcinogens.There are many conditions for the development of photochemical smog:1. A source of nitrogen oxides and volatile organic compounds.2. The time of day is a very important factor in the amount of photochemical smog present.• Early morning traffic increases the emissions of both nitrogen oxides (NOx) and
Peroxyacetyl Nitrates (PAN) as people drive to work.
• Later in the morning, traffic dies down and the nitrogen oxides and volatile
organic compounds begin to react forming nitrogen dioxide, increasing its concentration.
• As the sunlight becomes more intense later in the day, nitrogen dioxide is broken
down and its by-products form increasing concentrations of ozone.
• At the same time, some of the nitrogen dioxide can react with the volatile organic
compounds (VOCs) to produce toxic chemicals.
• As the sun goes down, the production of ozone is halted. The ozone that remains in
the atmosphere is then consumed by several different reactions.3. Several meteorological factors can influence the information of photochemical smog.
These conditions include :• Precipitation can alleviate photochemical smog as the pollutants are washed out of
the atmosphere with the rainfall.
• Winds can blow photochemical smog away replacing it with fresh air. However,
problems may arise in distant areas that receive the pollution.
• Temperature inversions can enhance the severity of a photochemical smog episode.
Normally, during the day the air near the surface is heated and as it warms it rises,
carrying the pollutants with it to higher elevations. However, if a temperature inversion
develops pollutants can be trapped near the Earth’s surface. Temperature inversions cause
the reduction of atmospheric mixing and therefore reduce the vertical dispersion of
pollutants. Inversions can last from a few days to several weeks.4. Topography is another important factor influencing how severe a smog event can become.
Communities situated in valleys are more susceptible to photochemical smog because hills
and mountains surrounding them tend to reduce the air flow, allowing for pollutant
concentrations to rise. In addition, valleys are sensitive to photochemical smog because
relatively strong temperature inversions can frequently develop in these areas.