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Challenges in Speciation of Organic Aerosols

This presentation outlines a workshop held in Las Vegas in 2004 focused on organic speciation in atmospheric aerosols. It covers sampling issues, analytical challenges, sources of semi-volatile organic compounds, partitioning between gas and particle phases, and more.

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Challenges in Speciation of Organic Aerosols

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  1. Challenges in Speciation of Organic Aerosols Barbara Zielinska Division of Atmospheric Sciences (Barbara.Zielinska@dri.edu)

  2. Outline of the Presentation • Brief summary of the Organic Speciation in Atmospheric Aerosol Workshop, hold in Las Vegas, NV, on April 5-7, 2004 • Focused on topics: • Sampling issues related to organic speciation of PM and SVOC (L.Gundel, D. Lane, J. Volckens) • Unexplained & unresolved mass (H. Puxbaum, A. Gelencser) • Advances in organic characterization (R. Niessner, M.Kalberer, P.Ziemann, K.Prather, T.Hoffman) • Other topics: Analytical Challenges; Source-Receptor Modeling; Health; Atmospheric Chemistry and Climate; Exposure Assessment and Indoor

  3. Sampling Issues Related to Organic Speciation • 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

  4. SVOC • Vapor pressure ranges (pick your units) • 10-4 and 10-11 atm, bar; • 101 and 10-6 Pa; • 10-1 and 10-8 Torr • Sources of SVOC: • Direct emissions (alkanes, PAHs, PCBs, PCDDs, nitro-aromatics, terpenes, acids, carbonyls, lipids, others) • Atmospheric reaction products (from VOC, SVOC), secondary organic aerosol (SOA)

  5. Relationship of SVOC to PM-OC • Partitioning between gas/particle phase: SVOC + PM  (SVOC * PM) is controlled by: Adsorption and desorption Absorption and evaporation Chemisorption • Partitioning coefficient, Kp(Yamasaki, Bidelman, Pankow) A: SVOC species, gas (measured from Adsorbent) TSP: particle concentrations (ug/m3) F: adsorbed/absorbed SVOC species (from Filter)

  6. Langmuir adsorption: Absorption into a liquid film: Partition Coefficient Kp: Adsorption & Absorption From Lara Gundel presentation, Organic Speciation Workshop

  7. mr = -1 log Kp log Po(L) log Kp = mrlog PoL + br • PAHs, • alkanes • chlorinated organics If br is constant….

  8. Challenges in SVOC - PM Measurements • Particulate POM and OC can include or exclude SVOC depending on • Sampling methods • Analytical techniques • Presently there are not any “truly perfect” methods to simultaneously measure gas and particle SVOC. Also, no method for total SVOC. • We need a new generation of analytical techniques…

  9. Filter-Adsorbent (FA) F A Filter-Filter-Adsorbent (FFA) A1 F A2 A E Denuder-Filter-Adsorbent (DFA) F1 F2 A Electrostatic precipitator (EA) Operational Definitions of SVOC and PM-Assoc OC From Lara Gundel presentation, Organic Speciation Workshop

  10. Side by side chamber tests - Filter-Adsorbent (FA) - Denuder-Filter-Adsorbent (DFA) - Electrostatic Sampler-Adsorbent (EA) - Filter-Filter-Adsorbent (FFA) - Kp varies by a factor of 2–100 depending on method used Denuder performed well during chamber tests with alkanes No gas breakthrough Minimal particle loss to denuder From John Volckens presentation, Organic Speciation Workshop Sampler Influence on Partition Coefficient Kp

  11. PAH Phase Distribution in Source Testing From Zielinska et al, ES&T, 2004

  12. Problems with Denuders • XAD-4 denuders are difficult to use and labor intensive • Denuders that adsorb gases can act as chromatographic columns • The diffusion coefficient of a compound increases with temperature - at higher temp. it will be more efficiently trapped by the denuder, but chromatographic effects will increase • Particles that are less than 50 nm behave more like gases than particles in a denuder • Longer denuders are more effective gas traps, but increase the transit time and result in much larger particle losses • Increased transit times - a greater chance for particle-associated molecules to leave the particle while it passes through the denuder • Learning to balance the trade-offs is a necessary skill for interpreting and successfully using denuder technology (From Doug Lane presentation, Organic Speciation Workshop)

  13. Unexplained & Unresolved Mass • A large and until recently unaccounted fraction of the continental organic aerosol consists of polymeric and/or oligomeric substances • These substances include cellulose, fungal spores, lignin, fragments of bacteria, polyols, etc. • The important constituents of the organic aerosol are the “Humic Like Substances” (HULIS), occurring as water soluble as well as water insoluble fractions • HULIS are present at concentrations (HULIS-carbon) from 7-24 % of the OC

  14. Properties of HULIS • Not amenable to organic speciation • Quantification is generally possible with respect to reference humic or fulvic acids • Composition: neutral/basic compounds (hydroxylated/alkoxylated aliphatic species), mono- and dicarboxylic acids, and polycarboxylic acids • Average molar ratio of C:H:N:O = 24:34:1:14 • Average MW in the 200-300 Da range

  15. Suggested Routes for HULIS Formation OH, H2O2 multiphase heterogeneous direct emission droplet HULIS Kalberer et al. 2004 H2SO4 Jang et al. 2002 TMB Limbeck et al. 2003 Iinuma et at., 2004 Zappoli et al., 1999, Mayol-Bracero et al., 2002 carbonyls condensation aerosol Gelencsér et al., 2003 Hoffer et al., 2004 Isoprene, terpenes Gelencsér et al., 2002 Lignin pyrolysis products Decomposition products From Andreas Gelencser presentation, Organic Speciation Workshop

  16. Advances in Organic Characterization • Polymeric substance (bioaerosol, HULIS, SOA) may constitute up to 50% of organic aerosol mass • These species require new analytical techniques • A variety of new in situ and on-line techniques is recently emerging, including various MS, immunoassays (pollen proteins, metal species analysis),chip technologies with multiple recognition targets in a high-parallel arrangement, and others

  17. New Mass Spectrometric Tools • Electrospray Ionization (ESI) MS, LC-ESI-MS • (Matrix/Graphite Assisted) Laser Desorption/Ionization MS (MALDI-MS, GALDI-MS, LDI-MS) • Photoionization Aerosol MS (PIAMS) • Two-step laser mass spectrometry (L2MS) • Laser Desorption –Atmospheric Pressure Chemical Ionization-MS (LD-APCI-MS) ESI-MS of (-Pinene + O3 + acid seed) Aerosol(Tolocka et al, Environ. Sci. Technol. (2004) 38, 1428-1434)

  18. Mass Spectrometric Tools, cont. • Thermal Desorption Aerosol Mass Spectrometry • Aerodyne Aerosol Mass Spectrometer (AMS) • Thermal Desorption Particle Beam Mass Spectrometer (TDPBMS) • On-Line, Aerosol GC-Mass Spectrometry • Real-Time Single Particle Mass Spectrometry (SPMS) • Aerosol time-of-flight MS (ATOFMS) and ultrafine (UF) ATOFMS • Photoelectron resonance capture ionization (PERCI) MS

  19. http://ocs.fortlewis.edu/aerosols/SPECIATION/default.htm

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