Challenges in Speciation of Organic Aerosols Barbara Zielinska Division of Atmospheric Sciences

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

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

SVOC Vapor pressure ranges (pick your units) – and atm, bar; – 10 1 and Pa; – and 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)

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)

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

log K p = m r log P o L + b r  PAHs,  alkanes  chlorinated organics m r m r = -1 log P o (L) log K p b r is constant…. If b r is constant….

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…

Operational Definitions of SVOC and PM-Assoc OC Filter-Adsorbent (FA) AFF2F2 F1F1 A Denuder-Filter- Adsorbent (DFA) A E Electrostatic precipitator (EA) Filter-Filter- Adsorbent (FFA) A1A1 FA2A2 From Lara Gundel presentation, Organic Speciation Workshop

Sampler Influence on Partition Coefficient K p Side by side chamber tests - Filter-Adsorbent (FA) - Denuder-Filter-Adsorbent (DFA) - Electrostatic Sampler-Adsorbent (EA) - Filter-Filter-Adsorbent (FFA) - K p 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

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

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)

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

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 Da range

HULIS H 2 SO 4 Isoprene, terpenes carbonyls OH, H 2 O 2 Lignin pyrolysis products condensation Decomposition products droplet aerosol Jang et al Limbeck et al Iinuma et at., 2004 Zappoli et al., 1999, Mayol-Bracero et al., 2002 Gelencsér et al., 2003 Hoffer et al., 2004 Gelencsér et al., 2002 heterogeneousdirect emission multiphase Suggested Routes for HULIS Formation TMB Kalberer et al From Andreas Gelencser presentation, Organic Speciation Workshop

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

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 + O 3 + acid seed) Aerosol et al, ESI-MS of (  -Pinene + O 3 + acid seed) Aerosol (Tolocka et al, Environ. Sci. Technol. (2004) 38, )

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

SPECIATION/default.htm