3 HK 1-hour Air Quality Objectives for various air pollutants AQ Objectives (mg/m3)AQ Objectives (ppm)US AQ Standards (ppm)Carbon monoxide3000026.235Sulfur dioxide0.3060.50aNitrogen dioxide0.1590.05 bOzone8000.1220.12a: 3-hr standard, b: annual arithmetic mean
4 Carbon monoxide: Health effect CO enters the blood stream and binds preferentially to hemoglobin, thereby replacing oxygen.FeO2COC-OO-OHemoglobin is the substance that carries oxygen to the cells320 times stronger than hemoglobin-O2 binding
5 Carbon monoxide: sources and sinks Such as automobilesSourcesIncomplete combustion (internal engine)Biomass burningMethane oxidationOxidation of non-methane hydrocarbonDecay of plant matterSinkReaction with OH radical.OH + CO CO2 + H.H. + O2 + M HO2. + MRemoval by soil microorganism
8 Carbon monoxide: Atmospheric chemistry CO + OH + O2 CO2 + HO2.HO2. + NO NO2 + OHNO2 + hv NO + OO + O2 + M O3 + MNet: CO + 2 O2 + hv CO2 + O3The net reaction can be viewed as a catalytic oxidation of CO to CO2. Net formation of O3 occurs.
9 Carbon monoxide: control strategies on the automobile source Employ a leaner air/fuel mixture (higher air/fuel ratio)Employ catalytic exhaust reactorsExcess air is pumped into the exhaust pipe.Air-exhaust mixture pass through a catalytic converter to oxidize CO to CO2.Addition of oxygenates to gasolineExamples of oxygenates: methanol, ethanol, MTBE
10 Sulfur dioxide: Health effect Produce irritation and increasing resistance in the respiratory tract.Mucus secretionIn sensitive individuals, the lung function changes may be accompanied by perceptible symptoms such as wheezing, shortness of breath, and coughing.may also lead to increased mortality, especially if elevated levels of suspended particles are also present.
11 Sulfur dioxide: Sources and sinks Combustion of S-containing fuel in electric power plants, vehicles.S (organic S + FeS2 pyrite) + O2 --> SO2Oxidation of H2S: 2H2S + 3 O2 --> 2 SO2 + 2 H2OH2S is produced as an end product of the anaerobic decomposition of S-containing compounds by micro organisms.Oxidation of DMSSinkConverted into sulphuric acid in either gas or liquid phase
13 Formation of sulfuric acid and sulfate from SO2 In gas-phaseSO2 + .OH + M HOSO2. + MHOSO2. + O2 HO2. + SO3SO3 + H2O + M H2SO4 + MIn aqueous phase, dissolved SO2 is oxidized to sulfate byO3 (dominant pathway when pH>5)H2O2 (dominant pathway when pH<5)organic peroxidesO2 catalyzed by iron and manganeseSulfate formation:2 NH3 + H2SO4 (NH4)2SO4
14 Sulfur dioxide: Control strategies Removal of S before DURING burning.Fludized bed combustion: Coal is burned with limestone (CaCO3) (finely pulverized) or dolomite (Ca-Mg carbonate) or both.CaCO3 --> CaO + CO2,CaO + SO2 --> CaSO3.CaSO3 is removed from the stack by an electrostatic precipitator.removal of S from smokestacks before entering the atmosphere.Flue-gas desulfurization: SO2 is washed from the chimney (flue) gases by absorption in an alkaline solution.
15 Sulfur dioxide: Control strategies (Continued) 3. DilutionInstallation of tall stacks reduces SO2 levels in the immediate neighborhood by dispersing them more widely
16 Nitrogen oxides: Health Effects Cellular inflammation at very high concentrations.May be incorporated into hemoglobin in the blood to interfere with the transport of oxygen around the body.NO2irritate the lungslower resistance to respiratory infection such as influenza.
17 Nitrogen oxides: Sources and sinks Fuel combustion in power plants and automobiles.N2 + O2 --> NO2 NO + O2 --> 2 NO2Natural sources: electrical storms; bacterial decomposition of nitrogen-containing organic matter
19 Nitrogen oxides: Atmospheric chemistry Interconversion of NO and NO2NO2 + hv NO + O (1)O + O2 + M O3 + M (2)NO + O3 NO2 + O2 (3)No net O3 formationNO2 + hv NO + O (1)O + O2 + M O3 + M (2)HO2. + NO NO2 + OH (4)RO2. + NO NO2 + RO. (5)O3 is formed
22 Nitrogen oxides: Control strategies 1. Lower the combustion temperature of the furnace in electric power plants2. Install catalytic converters: catalytic converters in automobiles can remove 76% of NOx from tailpipes.
23 Two-stage combustion to reduce both NOx and VOCs First stage: combustion condition—rich in fuelSecond stage: combustion condition—rich in airThis approach is being incorporated into new power plants; It has been tried in cars via the “stratified-charge” engine, but with less success.
24 Three-way catalytic converter for automobile exhaust (Remove CO, NO and HC) HC + H2O = H2 + CO2NO + 2H2 = N2 + 2 H2O2CO + O2 = 2CO2HC + 2O2 = CO2 + 2H2OCatalyst: RhodiumCatalyst: RhodiumCatalyst: Platium/palladium
25 NOx control in power plants Ammonium reduction of NO4NH3 + 6NO = 5 N2 + 6 H2OUrea reduction of NO2CO(NH2)2 + 6NO = 5 N2 + 2 CO2 + 4 H2O