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 Stratosphere Three more layers above 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

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: Current Theory of Evolution of Atmosphere Early Earth no oxygen at that time Instead high in CO2, H2O vapor, and probably NH3, H2 and CH4 Now considerable reduction in CO2; significant increase in O2 If true, Where did the “C” of CO2 go?

Current Composition of Atmosphere 0.9% Ar 0.04% CO2 trace amounts of gases, vapors, particulates naturally occurring: Ne, He, Kr, Xe, H2, CH4, O3, N2O these have remained relatively constant for at least several hundred million years

Current Composition of Atmosphere whatever humans emit is considered ‘trace amounts’ – example CFC = 0.000000002% But still can have a significant impact

Atmosphere Bombarded by Solar Radiation: Greenhouse Effect Keeps Earth Warm Some is reflected back to space by stratospheric ozone or clouds while others penetrate

Air Pollutants

Air Pollution Accumulation of substances in the atmosphere that can cause harmful health effects to living things or can negatively affect the public welfare Fate - Matter cannot be created nor destroyed, it only changes form: Pollutants just don’t disappear, they may Dilute - Dispersion Change form - Degradation ‘Sink’ – Deposition, 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

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 Energy-related?

(ozone related)

Other Sources Geogenic volcanoes dust storms

Other Sources Biogenic decomposition gases organic molecules released from plants and animals Pollen Insect parts cow gas?

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

‘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/vapors Particulates Physical and chemical properties of the pollutant also dictate which particular methods will be effective

Control Technologies Various levels of control technologies exist Examples: Best Available Control Technology (BACT) Lowest Achievable Emissions Rate (LAER) Ultimately, choice depends on: Form of contaminant Regulatory requirements for a particular industry Quantity generated Installation costs Maintenance and operational costs

Characteristics of Pollutants Physical state Particulate Size (µm) Size distribution of particulates 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)

Settling Chambers

Cyclones

Wet Scrubbers

Electrostatic Precipitator

Baghouse Filters

Gaseous Emissions Control Four Major Techniques Adsorption Absorption Condensation Combustion

Adsorption Attachment of gas/vapor to a solid

Absorption Dissolving gaseous pollutants in a liquid

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

Combustion