Lab 3

• Acid rain: is a rain or any other form of precipitation that is unusually acidic (~pH <5 or 6), i.e. elevated levels of hydrogen ions (low pH)
• Acid rain is caused by emissions of sulfur dioxide and nitrogen oxides which react with the water molecules in the atmosphere to produce acids. Main factors causing increase of acidity of atmospheric falls are: oxides of Sulphur (Sulphur dioxide)

  nitric oxides (dinitirc oxide)

  converted into the sulphuric acid and nitric acid.
• Wet deposition: this occurs when any form of precipitation (rain, snow, etc.) removes acids from the atmosphere and delivers it to the Earth's surface. This can result from the deposition of acids produced in the raindrops or by the precipitation removing the acids either in clouds or below clouds. Wet removal of both gases and aerosols are both of importance for wet deposition.
• Dry deposition: Acid deposition also occurs via dry deposition in the absence of precipitation. This can be responsible for as much as 20 to 60% of total acid deposition. This occurs when particles and gases stick to the ground, plants or other surfaces.
• The principal natural phenomena that contribute acid-producing gases to the atmosphere are emissions from volcanoes.
• Counteracting acid rains prevention:

  • higher chimneys • applying of lime

  • desulphurization of smokes to remove sulphuric gas

  • finishing off the motor exhaust fumes •

  • energy conservation through thermal insulations

  • utilization of the energy of the sun, wind, water and applying alternative energy sources (biogas)
• Photochemical smog composition: carbon monoxides, nitric oxides, hydrocarbons. These compounds undergo photochemical reactions and produce: peroxyacyl nitrates (PAN) aldehydes, ozone
• Classical smog composition: oxide of sulphur (IV), nitric oxide, carbon monoxide, soot, dusts with difficulty falling.
• An air quality index (AQI): Is a number used by government agencies to communicate to the public how polluted the air is currently or how polluted it is forecast to become. As the AQI increases, an increasingly large percentage of the population is likely to experience increasingly severe adverse health effects.
• The conditions needed for the coming into existence of the photochemical smog:

  • Source of forerunners

  • Motionless atmosphere

  • High temperature

  • Intense solar radiation