Enviro Ib Chem Guide - Air Pollution

IB Chemistry III: Air Pollution The book: pp. 131, 133, 134, 139-141

Guide outline: 1. Definitions and lists 2. Causes and effects 3. Methods of removal

I. Definitions and lists Primary Pollutants: Damaging substances directly released into air, that are not normally present or are present in unnatural proportions 1. CO 2. NOx 3. SO2 and SO3 4. Particulates: eg. Soot, ash, burned fossil fuels 5. VOC’s: Volatile organic compounds Secondary Pollutants: Damaging substances formed by reaction of primary pollutants with catalysts or other present substances. 1. Hydroxyl radicals (OH∙) 2. Nitric acid (HNO3) 3. Radicals in general 4. PAN (peroxyacylnitrate…) Greenhouse Effect: The warming of the earth due to radiation-retentive atmospheric gases (radiation is either trapped and accumulated in the air or reflected by earth’s surface and absorbed upon return to the stratosphere). Gases allow short-wave radiation through, later to absorb it. Greenhouse Gases: 1. O3 2. CO2 3. CH4 4. H2O 5. NOx

Radioactive Waste: Radioactive material of varying intensity. High-level: Directly radioactive material, eg. spent fuel rods Low-level: Material exposed to radiation, eg. experimental packaging Smog: Poisonous mixture of smoke, fog, air, and other chemicals. Reducing smog = Result of combustion of coal and oil, producing sulfur dioxide and soot/ash. Pea soup color. Photochemical smog = Consists of primary pollutants (NOx and VOCs) then converted into secondary pollutants by sunlight. Yellow-brown color. (* see equations section for formation) Other definitions may be found in the following sections.

II. Causes and Effects Primary Pollutants: Sources and effects Pollutant Man-made Natural CO Incomplete Incomplete combustion of oxidation of fossil fuels methane NOx

Internal combustion engines

SO2 and SO3

Combustion of coal and smelting of ores

Particulates

Burning of fossil fuels,

Effect Prevents hemoglobin from carrying oxygen Electrical Respiratory storms; irritant; can biological cause acid processes rain Oxidation of Respiratory H2S from irritant; can volcanoes; also cause decay of org’c acid rain matter Soot, ash, Respiratory dust, irritant; can

VOCs

esp. coal and diesel

asbestos, sand, smoke, pollen, bacterial/fung al spores

Unburned/par tly burned gasoline; solvents

Plants (like rice—so real plants); terpenes

Ozone and CFCs Type Ozone (O3 gas) CFCs (chlorofluorocarbons)

cause lung disease (emphysema, cancer) *They can also reverse global warming by scattering short-waved light Carcinogenic (esp. benzene); can form PANs

Effect Greenhouse gas; retains radiation to warm earth and reflects it to cool it Destroys ozone; reverses greenhouse effect

III. Methods of Removal Primary Pollutants: Methods of Removal/Reduction Method

Description

Electrostatic Precipitation

Particulates are charged and attracted to electrodes, then removed Coal burned on bed of limestone, which removes

Fluidized Bed Combustion

Pollutant(s) it reduces Particulates

Sulfur dioxide

sulfur Coal cleaning Coal crushed and sulfur removed Coal scrubbing Alkaline slurry: coal gas exposed to limestone, which removes sulfur into sludge Thermal exhaust CO reacted with Reactor excess oxygen to produce CO2 Lean-burn engines Ratio of NOx to CO altered; one reduced but other increased Catalytic converter NOx catalyzed (using palladium, platinum, or rhodium) with CO to produce CO2 and nitrogen

Sulfur dioxide Sulfur dioxide

CO NOx or CO

NOx and CO

Nuclear Waste: Removal Processes Type Process High-Level Vitrification (waste is dried and then melted, solidified in steel, cooled, and buried in geologically stable conditions) Low-Level Discharge into sea; cooled in ‘ponds’ and passed through ion exchange to remove strontium and cesium; kept in concrete vaults

When in doubt The universal answer for reduction of pollutants: CUT BACK!!! IV. Formulas Creation of primary pollutants Pollutant Man-Made CO C8H18 + 17/2 O2  8CO + 9H2O NOx N2 + O2  2NO SO2 H2S + O2  H2 + SO2

Natural CH4 + 3/2 O2  CO + 2H2O Etc. S + O2  SO2

Alkaline Scrubbing: CaCO3 + SO2  Ca SO3 + CO2 CaO + SO2  Ca SO3 2CaSO3 + O2 + 4H2O  2CaSO4.2H2O Catalytic Conversion: 2CO + 2NO –platinum/rhodium/palladium –> 2CO2 + N2 Creation of Ozone w/UV catalyst O2  2O∙ O∙ + O2  O3 Depletion of Ozone Cause Natural (UV) CFCs

Nitrogen oxides

Formula(s) O3  O2 + O∙ O3 + O∙  2O2 CCl2F2  CClF2 + Cl∙ Cl∙ + O3  ClO∙ + O2 ClO∙ + O∙  Cl∙ + O2 2O3 –NO2—> 3O2

Formation of Secondary Pollutants (pay especial attention to top and bottom rxns) Nitrogen oxide radicalization NO2  NO + O∙ Hydroxyl radicalization O∙ + H2O  2OH∙ Nitric Acid formation OH∙ + NO2 HNO3 Radical Propagation OH∙ + RH  R∙ + H2O Peroxide Radical formation R∙ + O2  ROO∙ PAN formation Peroxide radical + nitrogen dioxide

Waste disposal is left to you, because it is relatively straightforward and well-organized in the book. Thank you and good luck!