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Chemical Characterisation Of Urban Particulate Matter In The UK

Chemical Characterisation Of Urban Particulate Matter In The UK. 1 st Year PhD Environmental Chemistry. Primary Particles Emitted directly into the atmosphere through man-made (anthropogenic) and natural processes. Sources of PM in the UK. Soot. Anthropogenic:. Traffic. Industry.

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Chemical Characterisation Of Urban Particulate Matter In The UK

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  1. Chemical Characterisation Of Urban Particulate Matter In The UK 1st Year PhD Environmental Chemistry

  2. Primary Particles Emitted directly into the atmosphere through man-made (anthropogenic) and natural processes Sources of PM in the UK Soot Anthropogenic: Traffic Industry Fe smelter

  3. Primary Particles cont. Natural: Pollen Sea spray Sources of PM in the UK cont.

  4. Secondary Particles Formed in the air, usually by chemical reactions of gaseous pollutants Anthropogenic: Nitrogen oxides - mainly emitted by traffic and some industrial processes Sulphur dioxide - resulting from the combustion of sulphur-containing fuels Biogenic Volatile organic compounds (VOC), e.g. terpenes Sources of PM in the UK cont.

  5. Broad chemical composition of UK urban PM PM10-2.5 • Determined by traditional filter-based chemical analyses PM10-2.5 • Main component: iron rich dust (32%) PM2.5 • Main component: organic compounds (27%) PM2.5 AQEG (2005)

  6. Why Are We Interested in PM? • health effects (contribute to respiratory and cardiopulmonary diseases and mortality) • climate change (scattering and absorbing sunlight) • local/regional visibility • contribute to atmospheric chemical processes (e.g. surface reactions, deposition of chemical components)

  7. How are PM size fractions discriminated? Dependence on aerodynamic or optical properties? What components are measured? Are some components lost? Are additional components measured? What is the averaging time? and data reporting time? What temporal resolution is desired: daily, hourly or less? Is there compliance with public reporting requirements? Cost? Mobility? Reliability? Reference Methods Inter-comparison and Equivalence Issues in PM measurement

  8. Intercomparison of particulate matter monitoring devices Location AURN site in Horley, ~1.5 km from Gatwick airport. OSIRIS Monitor Time Series Size and mass concentration derived from optical scattering intensity. • Could be used to provide preliminary wide-area assessment of airborne PM.

  9. Type-approved aerodynamic sampling inlet Filter-based gravimetric Instrumentation: Partisol 2025  - Equivalence status - Absolute mass measurement accurate - Sample available for subsequent analysis  • - Poor time resolution (24 h) • Data not available until days or weeks after sampling • - High operating costs; labour intensive • - Difficulties with precision (caused by handling, etc.) • - Immobile

  10. Sampling Sites in Edinburgh • St Leonards • - “Urban Background” • TEOM-FDMS • Haymarket • - “Roadside” • TEOM • OSIRIS

  11. Samples collected on high-purity quartz microfiber filters Pre-heated at 550 °C for 12 hours Extract each filter with ultra-pure water in an ultrasonic bath Remove suspended material centrifuge or filter Measure the DOC content of aqueous extract e.g. Shimadzu TOC-V Analyser Remove inorganic species Sampling and Extraction

  12. Solid Phase Extraction Aqueous Aerosol Extract pH = 2 • Reversed Phase SPE Columns • Silica-based • Polymeric SPE Column Methanol (activation) 0.01 M HCl (equilibration) Eluate WSOC (Hydrophobic) Methanol Ultrapure Water • Capable of isolating ~60% of the water-soluble organic compounds Effluent Inorganics Hydrophilic Carbonaceous Varga, B., Kiss, G., Ganszky, I., Gelencser, A. and Krivacsy, Z.: Isolation of water-soluble organic matter from atmospheric aerosol, Talanta, 55, 561-572, 2001.

  13. Isolation & Fractionation of WSOC: XAD Resins Duarte RMBO & Duarte AC (2005) Application of non-ionic solid sorbents (XAD resins) for the isolation and fractionation of water-soluble organic compounds from atmospheric aerosols, J Atmos Chem, 51, 79-93

  14. XAD-8 eluate (~58% of WSOC) highly conjugated compounds partially acidic hydrophobic functional groups XAD-4 eluate (~9% of WSOC) few conjugated systems higher content of hydrophilic structures low molecular size XAD-8 and XAD-4 Fractions

  15. % of C, H, N & O in sample Use molar ratios to help determine chemical characteristics O/C & H/C WSOC consist of polyfunctional compounds polyconjugated structural elements lower aromatic content as compared with fulvic and humic acids saturated systems in excess of that for aquatic fulvic acids polar groups: carboxyl, hydroxyl and carbonyl Elemental Analysis Kiss, G., B. Varga, I. Galambos, and I. Ganszky, Characterization of water-soluble organic matter isolated from atmospheric fine aerosol, J. Geophys. Res., 107(D21), 8339, 2002

  16. Molecular weight determination by MS • Electrospray Ionization Mass Spectrometry • Weight average molecular weight (MWW) • assuming all ions are singly charged • WSOC: 200 to 300 Da • Possible sources of error: • fragmentation in the ESI source • formation of multiply-charged ions • - differing ionization and detection efficiencies of different components Laser Desorption/Ionization Mass Spectrometry? [V. Samburova et al.] Kiss, G., Tombacz, E., Varga, B., Alsberg, T., and Persson, L.: Estimation of the average molecular weight of humic-like substances isolated from fine atmospheric aerosol, Atmos. Environ., 37, 3783–3794, 2003

  17. Presence of conjugated double bond systems continuous absorption up to about 400 nm E250/E365 (E2/E3) ratio inversely correlated with molecular weight and aromaticity in aquatic humic substances WSOC: higher E2/E3 ratio in summer samples than in autumn samples lower aromaticity in summer compared with autumn Use to estimate molecular weight based on correlations in the literature UV-VIS Spectroscopy Duarte, R., Pio, C. A., and Duarte, A. C.: Spectroscopic study of the water-soluble organic matter isolated from atmospheric aerosols collected under different atmospheric conditions, Analy. Chim. Acta, 530, 7–14, 2005

  18. IR Spectroscopy 3400 cm−1 (OH of phenol, hydroxyl, and carboxyl groups) 3000–2850 cm−1 (C-H of methyl and methylene groups of aliphatic chains) 1720 cm−1 (C=O) • WSOC • b) Autumn • a) Summer 1220 cm−1 (C-O and OH of COOH groups) 1061 cm−1 (C-O of polysaccharides) 1600–1660 cm−1 (C=C of aromatic rings; C=O of conjugated carbonyl groups) 1384 cm−1 (C-H of aliphatic CH3) Duarte, R., Pio, C. A., and Duarte, A. C.: Spectroscopic study of the water-soluble organic matter isolated from atmospheric aerosols collected under different atmospheric conditions, Analy. Chim. Acta, 530, 7–14, 2005

  19. NMR Spectroscopy Aromatic carbons (110–160 ppm) Aliphatic carbons singly bound to two oxygen atoms (95-110 ppm) Ester and carboxyl carbons (160–190 ppm) Un-substituted saturated aliphatic components (10 to 50 ppm) • 13C-NMR • WSOC • b) Autumn • a) Summer Aliphatic carbons singly bound to one oxygen or nitrogen atom (60–95 ppm) • Autumn sample richer in aromatic carbons than summer • - lignin breakdown component due to wood burning Duarte, R., Pio, C. A., and Duarte, A. C.: Spectroscopic study of the water-soluble organic matter isolated from atmospheric aerosols collected under different atmospheric conditions, Analy. Chim. Acta, 530, 7–14, 2005

  20. Organic carbon (OC) and elemental carbon (EC) together constitute at least a third on average of urban PM in the UK. It used to be assumed this total carbon (TC = EC + OC) was largely anthropogenically derived. Recent evidence suggests that a substantial fraction may have biogenic sources. First UK application of 14C measurements on airborne PM to distinguish between OC and EC of fossil and contemporary carbon origin. 14C Analysis of Urban PM

  21. Accelerator Mass Spectrometer Fossil C contains zero 14C; Contemporary C contains ~1 in 1012 atoms of 14C  Require very high resolution mass discrimination and low noise detection • Combust C present in sample to CO2 (using O2 or CuO) • Trap liberated CO2 and reduce to C by combustion with Zn and Fe powders • Compress graphite/Fe into pellet for AMS target

  22. Methodological Separation of OC and EC for 14C determination …following the method of Szidat et al. (in the first instance) TC: combust whole sample for 10 min at 650C in stream of O2. OC: combust for 10 min at 340C in stream of O2. EC: heat replicate sample for 4 h at 375 C in a muffle furnace to eliminate OC and then combust for 10 min at 650C in stream of O2. N.B. fraction will also include “polymerizable WSOC” (HULIS, polyacids). (Assume carbonate C is negligible). Szidat, S., Jenk, T. M., Synal, H. A., Kalberer, M., Wacker, L., Hajdas, I., Kasper-Giebl, A. and Baltensperger, U. (2006) Contributions of fossil fuel, biomass-burning, and biogenic emissions to carbonaceous aerosols in Zurich as traced by 14C, J. Geophys. Res.111,D07206, doi:10.1029/2005JD006590.

  23. “Top down” Source Attribution of Carbonaceous Aerosol According to the method of Szidat et al aerosol carbon (TC) elemental carbon (EC) organic carbon (OC) fossil EC contemporary EC fossil OC contemporary OC AMS data Anthropogenic: fossil fuel combustion Biogenic: SOA, e.g. terpenes Anthropogenic: fossil fuel combustion Anthropogenic: biomass burning

  24. Undertake analyses of the carbon fraction in order to characterise, in a more detailed manner, the nature of this complex component of airborne PM. Contribute to air quality policy by helping to determine: Which part of the organic compound mass can be controlled through abatement of anthropogenic sources. Which part arises from natural compounds released from vegetation, which is less readily amenable to control. Further Work and Benefits

  25. Supervisor Dr Mat Heal Friends Colleagues Catherine Hardacre Emanuel Blei Ryan Clark Acknowledgements

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