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 + 8O CO2 + 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

20. 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

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

22. 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.

23. 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, <1 mm ID (the inner column walls are coated with stationary phase)

24. 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)

25. 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

26. 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)

27. 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

28. 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 ).

29. 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 (

30. Aerodyne Aerosol Mass Spectrometer (AMS)
Particle
Particle Beam
Aerodynamic Sizing
Composition
Generation
Quadrupole
Mass Spectrometer
Chopper
Thermal Vaporization &
Electron Impact Ionization
TOF Region
Aerodynamic Lens
(2 Torr)
The particles enter the AMS and are focused by an aerodynamic lens into a tight beam (<1 mm diameter). In the size range nm we get 100% of the particles transmitted from the inlet to the detector.
The chopper wheel defines the beginning of a time-of-flight period. Smaller particles move faster, so when a packet travels from chopper to detector, the smallest ones arrive first.
The detector consists of a 600 degree C oven that flash vaporizes the particles. The oven is located inside the ionizer region of a quadrupole mass spectrometer. Most of the gas phase molecules are lost in the first chamber of the AMS, so what reaches the ionizer is almost exclusively material that was in the particle phase.
Can use single ion monitoring mode to get quantitative information about single particles, or scan the quadrupole to get complete MS of average particles.
Particle Inlet (1 atm)
Turbo Pump
Turbo Pump
Turbo Pump
100% transmission ( 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: / 2001JD001213, 2003.

31. Aerodyne Aerosol Mass Spectrometer (AMS)
The particles enter the AMS and are focused by an aerodynamic lens into a tight beam (<1 mm diameter). In the size range nm we get 100% of the particles transmitted from the inlet to the detector.
The chopper wheel defines the beginning of a time-of-flight period. Smaller particles move faster, so when a packet travels from chopper to detector, the smallest ones arrive first.
The detector consists of a 600 degree C oven that flash vaporizes the particles. The oven is located inside the ionizer region of a quadrupole mass spectrometer. Most of the gas phase molecules are lost in the first chamber of the AMS, so what reaches the ionizer is almost exclusively material that was in the particle phase.
Can use single ion monitoring mode to get quantitative information about single particles, or scan the quadrupole to get complete MS of average particles.
100% transmission ( 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: / 2001JD001213, 2003.