Air Pollution and Air Pollution Control. Air. Air

Transcription

1 Air Pollution and Air Pollution Control Air Troposphere ambient air nearest to Earth's surface weather occurs here Properties: approximately 80% of the atmosphere's mass 99% of its water vapor and aerosols average depth of approximately 17 km (11 mi) in the middle latitudes deeper in the tropics, up to 20 km (12 mi) Air Troposphere Ozone here is considered a pollutant Stratosphere situated between about 10 km (6 mi) and 50 km (30 mi) altitude location of protective ozone layer: absorbs high energy UV B and UV C energy waves from the Sun Three more layers above 1

2 The Earth s Atmosphere Earth's Atmosphere Has Changed Dramatically since the Time it was Formed some changes the result of chemical and physical characteristics of the earth and the gases The Earth s Atmosphere Early Earth no oxygen at that time Instead high in CO 2, H 2 O vapor, and probably NH 3, H 2 and CH 4 Now considerable reduction in CO 2 ; significant increase in O 2 If true, Where did the C of CO 2 go? Current Composition of Atmosphere 78.08% N % O 2 0.9% Ar 0.036% CO 2 trace amounts of gases, vapors, particulates naturally occurring: Ne, He, Kr, Xe, H 2, CH 4, O 3, N 2 O these have remained relatively constant for at least several hundred million years 2

3 Current Composition of Atmosphere whatever humans emit considered trace amounts example CFC = % But still can have a significant impact Atmosphere Bombarded by Solar Radiation Some is reflected back to space by stratospheric ozone or clouds while others penetrate Air Pollutants 3

4 Air Pollution Accumulation of substances in the atmosphere that can cause harmful health effects to living things or can negatively affect the public welfare Matter cannot be created or destroyed, it only changes form: Pollutants just don t disappear but they may change form Fate of Air Pollutants in the Environment Dispersion Deposition Degradation Transfer to other compartments Effects of Air Pollutants Wildlife health including forests Impact on agriculture Buildings and other property Visibility and navigation Human health effects: Irritation of the respiratory passages including nose, throat, trachea and bronchii Eye irritation Increased susceptibility to the common cold Neural disorders (from toxics like lead) Other toxic effects 4

5 Air Pollution Sources Anthropogenic Geogenic Biogenic Anthropogenic Sources Stationary Sources Stack emissions Fugitive emissions Major stationary sources Small sources Mobile Sources Accidental spills Air Pollutant Types and Sources Energyrelated? 5

6 (ozone related) Geogenic volcanoes dust storms Other Sources Other Sources Biogenic decomposition gases organic molecules released from plants and animals cow gas? 6

7 Progress Being Made? Other Pollutants Hazardous Air Pollutants (HAPS) asbestos, benzene, mercury, vinyl chloride, radionuclides, numerous others Each has its own sources and effects Toxicity/carcinogenicity, persistence, and bioaccumulation the key issues General Air Pollution Control Strategies Source Shutdown Source Location Fuel Substitution and Process Changes Very successful with autos Correct Operation and Maintenance, Efficiency Emissions Trading End of Pipe Pollution Control Technologies 7

8 End of Pipe controls Consider only after other options are exhausted? Selection heavily regulated by environmental statutes Pollution Control Technologies Form of substance dictates control technology used Gases Particulates Physical and chemical properties of the pollutant also dictate which particular methods will be effective Control Technologies Various levels of control technologies exist Best Available Control Technology (BACT) Maximum Achievable Control Technology (MACT) Ultimately, choice depends on: Form of contaminant Regulatory requirements for a particular industry Quantity generated Installation costs Maintenance and operational costs 8

9 Characteristics of Pollutants Physical state Size (µm) Size distribution Density Reactivity Characteristics of Carrier Gases Flow rate (cfm) Moisture content Temperature Flammability Particulate Emissions Control Common control devices include Settling chambers Cyclones Wet scrubbers Electrostatic precipitators Fabric filters (baghouse filters) 9

10 Settling Chambers Cyclones Wet Scrubbers 10

11 Electrostatic Precipitator Baghouse Filters Gaseous Emissions Control Four Major Techniques Adsorption Absorption Condensation Combustion 11

12 Attachment of gas/vapor to a solid Adsorption Dissolving gaseous pollutants in a liquid Absorption Condensation Removal of gas or vapor by condensing it into liquid form Uses changes in temperature and/or pressure The pollutant(s) must be condensable at achievable temperature 12

13 Combustion 13