Atmospheric Chemistry Measurements – Organics in Air

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Atmospheric Chemistry Measurements Organics in
Air

• ATMS 360

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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)

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Compounds

• Alkanes CnH2n2 (CH4, C2H6, etc)
• Alkenes CnH2n (C2H4, etc)
• Alkynes - CnH2n-2 (C2H2)
• Aromatic compounds (C6H6, benzene)
• Polycyclic aromatic hydrocarbons - PAH
  (naphthalene, C10H8)

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Models
CH3 CH3
Ethane
Methane
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Ethylene (Etene)
Pentane
CH3-CH2-CH2-CH2-CH3
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CH3CH2OH
Ethanol
Benzene
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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)

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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
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Biomass Burning
Biomass cellulose, hemi-cellulose, lignin,
resins
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Other sources - testing
Residential wood Combustion
Meat cooking
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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

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Volatile, Semi-Volatile and Particulate Matter
Organic Compounds (VOC, SVOC, PM)

• Vapor pressure ranges
• VOC gt 102 Pa (10-1 Torr)
• SVOC 102 and 10-6 Pa (10-1 and 10-8 Torr)
• PM lt 10-6 Pa (10-8 Torr)

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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

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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

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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)

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

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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

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Operational Definitions of SVOC and PM -
Associated OC
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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.

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Gas Chromatography (GC)

• Columns
• Packed columns, 1-10 m long, 2-4 mm ID (filled
  with solid support material coated with liquid or
  solid stationary phase)
• Capillary columns, 10 60 m long, lt1 mm ID (the
  inner column walls are coated with stationary
  phase)

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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)

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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
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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 MH B (proton transfer)
• M X MX (electrophilic addition)
• M X M? X (charge exchange)
• M X ? M-A AX (anion
  abstraction)

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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

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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 ).

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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.htmlInfo_Ae
  rosolMS).

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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 331-2(49-70),
2000. Jimenez et al., Journal of Geophysical
Research, 108(D7), 8425, doi10.1029 /
2001JD001213, 2003.
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Aerodyne Aerosol Mass Spectrometer (AMS)
100 transmission (60-600 nm), aerodynamic
sizing, linear mass signal. Jayne et al., Aerosol
Science and Technology 331-2(49-70),
2000. Jimenez et al., Journal of Geophysical
Research, 108(D7), 8425, doi10.1029 /
2001JD001213, 2003.