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Natural Cleaning Process of the Atmosphere

Natural Cleaning Process of the Atmosphere . Objectives. What are the methods involved in the cleansing of the atmosphere? Learn about deposition velocity and factors affecting it. What are the cleansing processes involved with various contaminants?

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Natural Cleaning Process of the Atmosphere

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  1. Natural Cleaning Process of the Atmosphere

  2. Objectives • What are the methods involved in the cleansing of the atmosphere? • Learn about deposition velocity and factors affecting it. • What are the cleansing processes involved with various contaminants? • What are the major sinks for common air contaminants?

  3. Natural Cleansing Process • Nature regularly transforms oxygen into ozone through forces such as lightning and ultra-violet light striking the earth. • Ozone breaks down the pollutants and reverts back to oxygen at ground level.

  4. Residence Time for Air Contaminants • The time for which an air contaminant stays in atmosphere is known as the residence time.

  5. Deposition of Toxic Air Pollutants

  6. Cleansing of the Atmosphere * Methods involved in the cleansing of the atmosphere: • Deposition of the pollutants, and • Conversion of pollutants to other forms (oxidation, absorption etc.) • Deposition of contaminants on the earth surface: • Dry deposition: Toxic air contaminants are deposited to the land and water bodies by settling directly out of the air. Dry deposition rate = Deposition velocity * Pollution concentration • Wet deposition: Toxic air contaminants are deposited to the land and water bodies through precipitation.

  7. Deposition Flux

  8. Deposition Velocity The deposition velocity generally increases with: (a)    solubility of pollutant (b)    particle diameter and density (c)    wetness and roughness of surface (d)    wind speed and turbulence Typical values of deposition velocity under experimental conditions

  9. Cleansing Processes of SO2 The total world emissions are about 100 million tons/year. SO2 is removed from the atmosphere in about 40 days. The two theories for removal are mentioned below: • 1.   SO2  +  O2  >  SO3     + H2O > H2 SO4   + NH3, Lime    > Ammonia Sulfate, Calcium Sulfate. • 2.   SO2  + NH3, directly calcite of lime  > Sulfites    oxidation >  Sulfate (Precipitate) Ammonia sulfate is a good fertilizer.

  10. Cleansing Processes of H2S and NH3 Cleansing of H2S The total world emissions is about 300 million tons/year. Major sources are volcanoes and biological decay. There is no evidence of accumulation. • H2S      Chemically React - PbO, FeO (metal oxides)   > Insoluble metal sulfides. • In the laboratory odor can be removed by the addition of a few tenths of nitrogen oxides, which act as a catalyst to form H2SO4. Cleansing of Ammonia Ammonia is removed from the atmosphere by reaction with acids or acid forming oxides.

  11. Cleansing Processes of Fluorides and Carbon Monoxide Cleansing of Fluorides Hydrogen fluoride and SiF4 (Silica Fluoride) readily attack a variety of materials (carbonates, silicates, and organic compounds), and are readily removed from the atmosphere. Cleansing of CO Reaction with the hydroxyl radical. Oxidized in the upper atmosphere by atomic oxygen to yield CO2. No evidence of accumulation.

  12. Cleansing Processes of CO2 and NOx Cleansing of CO2 Consumption in photosynthesis. Removed slowly >  silicate rocks  >  limestone and dolomite.    The concentration of CO2 began increasing in the 18th century. Data reported in literature indicate that the increase has accelerated. Cleansing of NOx Nitric Acid formed   reacts with ammonia or lime > Ammonia nitrate or Calcium nitrate.

  13. Cleansing Processes of Smoke and Hydrocarbons Cleansing of Smoke Can be removed at source Smoke particles slowly settle as a result of gravitational effects, agglomeration, or rain.   Cleansing of Hydrocarbons Reactive hydrocarbons are removed by a series of photochemical reactions.

  14. Sinks for Air Contaminants

  15. Plants • Research has shown that these plants are the most effective all-around in counteracting off-gassed chemicals and contributing to balanced internal humidity. • Areca Palm • Australian Sword Fern • Boston Fern • Dwarf Date Palm • English Ivy • Ficus Alii • Janet Craig Dracaena • Lady Palm (Rhapis excelsa) • Peace Lily (Spathiphyllum)* • Reed Palm • Rubber Plant (Ficus elastica) • Weeping Fig • Zamioculcas Zamifolia

  16. Polluted Soil • Phytoremediation • Using plants to clean up polluted soil • Fast growing, easy to maintain, and capable of transforming the pollutants into a non-toxic form.

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