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Atmospheric Chemistry Measurements – Organics in Air

Atmospheric Chemistry Measurements – Organics in Air. ATMS 360. Organic Chemistry - Carbon Compounds. Carbon - C, atomic number 6, molecular weight 12 Electron configuration: 1s 2 2s 2 2p 2

george-thornton
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Atmospheric Chemistry Measurements – Organics in Air

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  1. Atmospheric Chemistry Measurements – Organics in Air ATMS 360

  2. Organic Chemistry - Carbon Compounds • Carbon - C, atomic number 6, molecular weight 12 • Electron configuration: 1s22s22p2 • Tetravalent, covalent bonds – 4 single bonds (sp3); 2 double bonds (sp2) one triple (sp) plus one single bond • Other atoms: hydrogen, oxygen, nitrogen, sulfur, halogens (Cl, F, Br)

  3. Compounds • Alkanes – CnH2n+2 (CH4, C2H6, etc) • Alkenes – CnH2n (C2H4, etc) • Alkynes - CnH2n-2 (C2H2) • Aromatic compounds (C6H6, benzene) • Polycyclic aromatic hydrocarbons - PAH (naphthalene, C10H8)

  4. Models CH3 – CH3 Ethane Methane

  5. Ethylene (Etene) Pentane CH3-CH2-CH2-CH2-CH3

  6. CH3CH2OH Ethanol Benzene

  7. Sources of Organics in Air • Anthropogenic: • Incomplete combustion of fossil fuels • Biomass burning • Industrial processes • Cooking • Natural sources • Biogenic emissions (from vegetation) • Volcanic • Evaporation of sea spray • Atmospheric reaction products (from VOC, SVOC), secondary organic aerosol (SOA)

  8. Fossil fuels Complete combustion: CxHy + (x + y/4)O2 xCO2 + y/2H2O e.g. C5H12 + 8O2 5CO2 + 6H2O Incomplete: CO, soot, organics and (in air) NOx

  9. Biomass Burning Biomass: cellulose, hemi-cellulose, lignin, resins

  10. Other sources - testing Residential wood Combustion Meat cooking

  11. Secondary Organic Aerosol (SOA) • SOA processes are studied in photoreactors • European photoreactor (EUPHORE) in Valencia, Spain, is one of the largest (200 m3) and the best-equipped outdoor simulation chamber in the world • We are studying atmospheric transformation of diesel emissions under the influence of sunlight, ozone, hydroxyl radicals that occur during transport in ambient air

  12. Volatile, Semi-Volatile and Particulate Matter Organic Compounds (VOC, SVOC, PM) Vapor pressure ranges: VOC: > 102 Pa (10-1 Torr) SVOC: 102 and 10-6 Pa; (10-1 and 10-8 Torr) PM: < 10-6 Pa (10-8 Torr)

  13. Organic Aerosol • Organic aerosols are solid or liquid particles suspended in the atmosphere containing organic carbon • Semi-volatile organic compounds (SVOC) - distributed between gas and particle phases –reversibly condensable • Particle associated organics – complex mixture, incorporated into/onto particles; includes condensed SVOC and non-volatile organic compounds

  14. Criteria Pollutants – National Ambient Air Quality Standards (NAAQS) • Particulate Matter (PM) • Ozone • NOx • SO2 • CO • Lead (Pb) • Ambient standards established by the US EPA and reviewed every 5 years

  15. Why Particulate Matter? • Health effects: particulate matter (fine, PM2.5 and to lesser degree, coarse PM10-2.5) has been associated with adverse health effects at low-to-moderate concentrations • NAAQS exist for PM (since 1971): • current (since 1997): PM2.5 annual 15 µg/m3 and 24-hr 65 µg/m3; PM10 annual 50 µg/m3 and 24-hr 150 µg/m3 _ announced in September 2006: PM2.5 annual 15 µg/m3 and 24-hr 35 µg/m3; PM10 annual only • Climate change • Visibility problem (Haze Rule)

  16. Average Ambient PM2.5 Composition in Urban Areas EPA STN network

  17. Average PM10-2.5, PM2.5, and PM0.1 composition at EPA “supersite” in Los Angeles, CA, 10/2001 to 9/2002 US EPA OAQPS PM Staff Paper, June 2005

  18. Hazardous Air Pollutants (HAPs) • Full list – 188 compounds, most of them organics • The short list – 33 air toxics, most prevalent in urban area • No ambient standards – regulation of emissions from sources

  19. Measurement Methods • Collection of VOC and aerosol samples followed by off-site laboratory analyses • VOC collection: stainless steel SUMMA canisters, Tedlar bags • PM and SVOC: Filters followed by solid adsorbents. Extraction with organic solvents in the laboratory

  20. Filter-Adsorbent (FA) F A Filter-Filter-Adsorbent (FFA) F1 F A D E Denuder-Filter-Adsorbent (DFA) F A A Electrostatic precipitator (EA) Operational Definitions of SVOC and PM - Associated OC

  21. Analysis - Chromatography • Chromatography is a separation method that relies on differences in partitioning behavior between a flowing mobile phase and a stationary phase to separate the components in a mixture • Gas-liquid chromatography (GC) –mobile phase is gas (He, N2, H2) • Liquid chromatography (LC) – mobile phase is liquid. High performance liquid chromatography (HPLC) utilizes high-pressure pumps to increase the efficiency of the separation.

  22. Gas Chromatography (GC) • Columns: • Packed columns, 1-10 m long, 2-4 mm ID (filled with solid support materialcoated with liquid or solid stationary phase) • Capillary columns, 10 – 60 m long, <1 mm ID (the inner column walls are coated with stationary phase)

  23. Detectors for GC and HPLC • Gas Chromatography detectors: • Flame Ionization (FID)- hydrocarbons • Thermal Conductivity (TCD) - universal • Electron Capture (ECD) – halogenated organics • Photoionization (PID) - aromatics, olefins • Fourier Transform Infrared (GC-FTIR) – all organics • Mass Spectrometer (GC-MS) – any species • HPLC Detectors: • UV-VIS absorption spectroscopy • Photo diode-array UV-VIS • Fluorescence • MS (LC-MS)

  24. Mass Spectrometry measures the mass-to-charge ratio (m/z) of charged particles to find the composition of a sample by generating a mass spectrum representing the masses of sample components. Mass Spectrometer: Sample Inlet High vacuum Mass Analyzer Detector Ion Source Data Analysis

  25. Ion Source • Ionization methods: Electron Impact (EI), Chemical Ionization (CI), Field Ionization (FI), Field Desorption (FD), Fast Atom Bombardment (FAB), Matrix-Assisted Laser Desorption/ Ionization (MALDI), Electrospray Ionization (ESI), and others.. • EI (unimolecular): bombarding neutral analyte M with high energy (70 eV) electron beam M + e- M+· + 2e- • CI (bimolecular): M interacts with ions from reagent gas M + [BH]+ [M+H]+ + B (proton transfer) M + X+ [M+X]+(electrophilic addition) M + X+ M+· + X (charge exchange) M + X +· [M-A]+ + AX (anion abstraction)

  26. Principle of mass analysis When the ion beam experiences a strong magnetic field perpendicular to its direction of motion, the ions are deflected in an arc whose radius is inversely proportional to the mass of the ion (mass-to-charge ratios m/z). Lighter ions are deflected more than heavier ions. By varying the strength of the magnetic field, ions of different mass (m/z) can be focused progressively on a detector fixed at the end of a curved tube

  27. Mass Analyzers • Types of mass analyzers: • magnetic sector (deflection of ion beam, separation by momentum); • linear quadrupole (4 rod electrodes, the pair of opposite rods are each held at the same potential composed of DC and AC component; a mass spectrum is obtained by monitoring the ions passing through the quadrupole filter as the voltages on the rods are varied); • quadrupole ion trap (three-dimensional RF quadrupole field to store ions within defined boundaries); • time-of-flight (TOF, uses the differences in transit time through a drift region to separate ions of different masses ).

  28. Advances in Mass Spectrometry • "Aerosol -MS" is the measurement in real-time of the aerosol composition using a mass spectrometer. Almost always the particle size is measured simultaneously with the composition. Two approaches: • Single particle MS –Laser desorption-ionization MS. Example: Aerosol Time of Flight MS (ATOFMS, available commercially from TSI, Inc.) • Thermal desorption aerosol MS. Example Aerodyne Aerosol MS, available commercially (http://cires.colorado.edu/~jjose/ams.html#Info_AerosolMS).

  29. Aerodyne Aerosol Mass Spectrometer (AMS) Particle Aerodynamic Sizing Particle Beam Composition Generation Quadrupole Mass Spectrometer Chopper Thermal Vaporization & Electron Impact Ionization TOF Region Aerodynamic Lens (2 Torr) Turbo Pump Turbo Pump Turbo Pump Particle Inlet (1 atm) 100% transmission (60-600 nm), aerodynamic sizing, linear mass signal. Jayne et al., Aerosol Science and Technology 33:1-2(49-70), 2000. Jimenez et al., Journal of Geophysical Research, 108(D7), 8425, doi:10.1029 / 2001JD001213, 2003.

  30. Aerodyne Aerosol Mass Spectrometer (AMS) 100% transmission (60-600 nm), aerodynamic sizing, linear mass signal. Jayne et al., Aerosol Science and Technology 33:1-2(49-70), 2000. Jimenez et al., Journal of Geophysical Research, 108(D7), 8425, doi:10.1029 / 2001JD001213, 2003.

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