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CE 5326 AIR POLLUTION CONTROL Fall 2008

This article explores atmospheric pollutants, specifically focusing on particulate matter (PM) and its sources, chemical components, and size distribution. It also discusses air pollution control methods and the calculation of atmospheric residence time.

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CE 5326 AIR POLLUTION CONTROL Fall 2008

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  1. CE 5326 AIR POLLUTION CONTROLFall 2008 Session 2: Atmospheric Pollutants Atmospheric Pollutants

  2. H.W. #2: Due Sep. 8, 2008 • Arya, Chapter 1, Problems 12, 17 (Notice that there are only 6 cirteria pollutants now) • De Nevers, Chapter 2, Problems 2.2 (Note: NAAQS for PM10 is 50 μg/m3, not 25 μg/m3 as mentioned in the problem); 2.5; 2.8; 2.9 • Reading Assignment: • Arya: Chapter 1 • S &P: Chapters 1and 2 Atmospheric Pollutants

  3. Atmospheric Residence Time Rate of accumu. of the species in the control volume = Rate of the species flowing in Rate of the species flowing out - + Rate of emission of the species Rate of removal of the species - Q = Total mass of the substance in the control volume Fin = Rate of the species flowing in Fout = Rate of the species flowing out P = Rate of emission of the species R = Rate of removal of the species Atmospheric Pollutants

  4. Atmospheric Residence Time For steady-state condition, or The average residence time, , if Fin = Fout = 0, Atmospheric Pollutants

  5. Atmospheric Residence Time by assuming that removal follows the first-order decay, R=kQ, and Pin: Natural emissions Pia: Anthropogenic emissions Pic: Emissions due to chemical reaction Rid: Removal by dry deposition Riw: Removal by wet deposition (precipitation scavenging) Ric: Removal due to chemical reaction Rit: Transport to the stratosphere; and kix : respective decay rate Atmospheric Pollutants

  6. Atmospheric Residence Time Thus, the residence time of a species is the inverse of the decay constant. Atmospheric Pollutants

  7. Atmospheric Residence Time For a species with more than 1 removal mechanisms in the atmosphere, the overall residence time will be Atmospheric Pollutants

  8. Atmospheric Residence Time Steady-state residence time Atmospheric Pollutants

  9. Atmospheric Pollutants • Particulate Matter (PM) • Solid or liquid particles suspended in a gas. Particulate matter may be emitted directly as particles or formed in the atmosphere by gas-to-particle conversion processes • Equivalent diameter is the used to characterize the size of the particles. • Atmospheric particulate matter ranges in size from a few nanometers to tens of micrometers in diameter (up to 30 - 50 m) Atmospheric Pollutants

  10. Particulate Matter (PM) Aerodynamic diameter: two particles with the same Stoke stopping distance for any initial velocity in air with the same viscosity are called to have the same aerodynamic diameter. If one refers to an unit density (1 g/cm3) and the same terminal gravitational settling velocity in still air as the actual particle in question, then the aerodynamic diameter is defined as daerodynamic = dparticle x (particle)0.5 , where daerodynamic = equivalent aerodynamic diameter of a particle, micrometer; dparticle = actual diameter of a particle, micrometer; particle = actual density of a particle, g/cm3 Atmospheric Pollutants

  11. Particulate Matter (PM) • By size distribution • Nano particles: particles < 10 nm • Ultrafine particles: particles cover the range from large molecules to about 100 nm (0.001 to 0.1 m) • Fine particles: particles less than 2.5 m in diameter • Thoracic coarse particles: particles that can be inhaled and penetrate into the thoracic region of the lung (tracheobronchial and the gas-exchange regions) • Coarse particles: particles greater than 2.5 m in diameter • By sampling methods • PM2.5: particles less than 2.5 m in diameter • PM10: particles less than 10 m in diameter • PMcoarse : particles greater than 2.5 m but less than 10 m in diameter Atmospheric Pollutants

  12. Air Pollutants Overview • Particulate Matter (PM2.5) Atmospheric Pollutants

  13. Atmospheric Pollutants

  14. Particle Modes: The mass distribution of particle size. More particles are found in three (or four) modes: • Nucleation mode: varies from 0.005 to 0.1 m and peaks at ~ 0.08 m, accounting for the preponderance of particles by number. • Accumulation mode: extends from 0.1 to 2.5 m, which accounts for most of the aerosol (particle) surface areas. • Coarse mode (or sedimentation mode): It varies between 2.5 to 25 m and peaks at around 10 m. Atmospheric Pollutants

  15. Atmospheric Pollutants

  16. PM Size Cutoff Atmospheric Pollutants

  17. Particulate Matter (PM) • Sources • Mechanical disruption of large particles, including fugitive emissions of dust, vehicular movements on soil, evaporation of sprays, … etc • Combustion • Formation • Nucleation of gas molecules to form new particles • Condensation of gases onto existing particles • Coagulation of particles • Uptake of water by hygroscopic components • Gas phase reaction Atmospheric Pollutants

  18. Particulate Matter (PM) • Chemical Components of Particles: • Sulfate • Ammonium • Nitrate • Sodium • Chloride • Trace metals • Carbonaceous material (organic carbon and element carbon) • Crustal elements (oxides of aluminum, silicon, calcium, titanium, and iron) • Water Atmospheric Pollutants

  19. Atmospheric Pollutants

  20. AIR POLLUTANTS • Categories of Air Pollutants • Nitrogen-containing Compounds • - Nitrogen gas (N2) • - Nitrous Oxide (N2O) • - Nitric Oxide (NO) • - Nitrogen Dioxide (NO2) • - Nitrate radical (NO3) - Dinitrogen Pentoxide (C2O5) • - Nitrous Acid (HNO2) • - Nitric Acid (HNO3) • - Ammonia (NH3) • - Hydrogen Cyanide (HCN) • - NOx (NO + NO2) Atmospheric Pollutants

  21. Atmospheric Pollutants

  22. AIR POLLUTANTS • Categories of Air Pollutants • Sulfur-containing Compounds • - Sox (SO2; S O3; H2SO4) • - Species of reduced sulfur • - Hydrogen sulfide (H2S) • - Carbonyl sulfide (COS) • - Carbon disulfide (CS2) • - Dimethyl sulfide (CH3) 2S • - Sulfur dioxide can dissolve in fog, cloud, and rain droplet to form a diluted solution of sulfurous acid. Atmospheric Pollutants

  23. AIR POLLUTANTS • Categories of Air Pollutants • Halogen-containing Compounds • - Chlorofluorocarbons (CFCs) • - Hydrochlorofluorocarbons (HCFCs) • - Hydrofluorocarbons (HFCs) • - Perhalocarbons • - Halons Atmospheric Pollutants

  24. AIR POLLUTANTS • Categories of Air Pollutants • Criteria Pollutants • - Ozone • - Particulate matter less than 10 (or 2.5) microns • - Sulfur dioxide • - Nitrogen dioxide • - Carbon monoxide • - Lead Atmospheric Pollutants

  25. AIR POLLUTANTS • Categories of Air Pollutants • Hazardous Air Pollutants (HAPs) • 188 chemicals (captrolactam was recently removed) • 39 % - Mobile sources • 30 % - Point sources • 31 % - Area sources Atmospheric Pollutants

  26. AIR POLLUTANTS • Categories of Air Pollutants • Carbon-Containing Compounds • (Review of General Chemistry) Atmospheric Pollutants

  27. Organic Chemistry • Carbon containing compounds (chemistry of carbon). Example, CH4 (methane or more commonly known as natural gas) • Lewis Structures: They help us visualize how atoms connect with each other by ether sharing electrons (covalent bond) or losing / gaining electrons (ionic bond) as to achieve an octet of electrons therefore resembling the noble gases. H • • H • • C • • H • • H Lewis Representation of methane Atmospheric Pollutants

  28. 2.27 Draw the Lewis structure and the more common structural formulas for the following: • Ethylene, C2H4 • 2-Chloropropane, CH3CHClCH3 • Methanol, CH3OH Atmospheric Pollutants

  29. Isomers: Compounds having the same molecular formula, but different structural formula (different connectivity between atoms). Example CH3-CH2-CH2-CH3 CH3 butane | CH3-CH-CH3 isobutane Both molecules have the molecular formula C4H10 Alkanes and Alkenes (open-chain) Hydrocarbons in which each carbon atom forms four single bonds to other atoms are called saturated hydrocarbons, paraffins, or alkanes. Hydrocarbons that have at least two carbon atoms joined by a double bond are called undersaturated or alkenes. • Aromatic hydrocarbons (close-chain) are benzene compounds and compounds that resemble benzene in chemical behavior. Atmospheric Pollutants

  30. Example of important alkanes and alkenes on the environment as well as aromatic hydrocarbons. CCl3-CH3 CH2Cl-CH2Cl 1,1,1-Trichloroethane (TCA) 1,2-Dichloroethane (1,2-DCA) CCl2F-CF2Cl 1,1,2-Trichloro-1,2,2-trifluroethane CH2=CH2 CCl2=CHCl Ethyne (ethylene) Trichloroethylene (TCE) Cyclic Hydrocarbons Benzene Atmospheric Pollutants

  31. Nomenclature of open-chain compounds: 1- Find the longest continuous chain of carbon atoms. Assign a parent name based on total number of carbons. 2- Find whatever groups are not part of the longest continuous chain. Name these are prefixes. 3- Assign numbers to groups by counting from one end of the chain. A chain has two ends, and the end we start from is the one that gives the lowest possible numbers to the groups. Atmospheric Pollutants

  32. 4- If there are two or more identical groups, we use these prefixes: Number of identical groups prefix 2 di 3 tri- 4 tetra- 5 penta- 6 hexa- 5- If there are two or more different groups, we put all of them into the prefix in alphabetical order. 6- The four halogens are named by prefixes: F fluoro- Br bromo- Cl chloro- I Iodo- Atmospheric Pollutants

  33. Nomeclature of benzene derivatives (aromatic): -prefix the name of the substituent group to the word –benzene Ex. a b c d e f a- Chlorobenzene b-Bromobenzene c- Nitrobenzene d- methylbenzene (Toluene) e- aminobenzene (Aniline) f- hydroxybenzene (Phenol) Atmospheric Pollutants

  34. Nomenclature if several are attached to the benzene ring • We must not only tell what they are, but also indicate their relative positions. Ex. o- ortho position m- meta position p- para position a b c Name • 2- Chloronitrobenzene or o-chloronitrobenzene • 4-Bromomethylbenzene or 4-Bromotoluene or p-Bromotoluene • 2,4,6-triiodohydroxybenzene or 2,4,6-triiodophenol Atmospheric Pollutants

  35. 2.30From the names alone, write the structures for the following organics: • Dichloromethane e) 1,1,2,2 Tetrachlorethane • Trichloromethane f) o-Dichlorobenzene • 1,1-Dichloroethene g) Tetrachloroethene (PCE) • Trichlorofluoromethane (CFC-11) h) Dichlorofluoromethane Atmospheric Pollutants

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