Mark HammondsSchool of Chemistry, University of Edinburgh

Chemical Characterisation Of Urban Particulate Matter

In The UK

1st Year PhDEnvironmental Chemistry

Sources of PM in the UK

Primary Particles• Emitted directly into the atmosphere through man-made

(anthropogenic) and natural processes

Soot

Fe smelter

TrafficIndustry

Anthropogenic:

Sources of PM in the UK cont.

Primary Particles cont.

Natural:

• Pollen

• Sea spray

Sources of PM in the UK cont.

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

9%2%

2%

15%

21%27%

14%

10%

Iron rich dust

Calcium sulphate

Sodium chloride

Sodium nitrate

Ammonium sulphate

Organic compounds

Elemental carbon

Bound w ater

32%

12%

18%

13%

3%

13%

4% 5%

Iron rich dust

Calcium sulphate

Sodium chloride

Sodium nitrate

Ammonium sulphate

Organic compounds

Elemental carbon

Bound w ater

PM2.5

PM10-2.5

Broad chemical composition of UK urban PM

PM10-2.5

• Main component: iron rich dust (32%)

PM2.5

• Main component: organic compounds (27%)

AQEG (2005)

• Determined by traditional filter-based chemical analyses

–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)

Why Are We Interested in PM?

Issues in PM measurement

• 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?

Inter-comparison and Equivalence

Reference Methods

Intercomparison of particulate matter monitoring devices

OSIRIS Monitor

Size and mass concentration derived from optical scattering intensity.

• Could be used to provide preliminary wide-area assessment of airborne PM.

Location

Time Series

0

10

20

30

40

50

60

14

/07

/20

05

21

/07

/20

05

28

/07

/20

05

04

/08

/20

05

11

/08

/20

05

18

/08

/20

05

25

/08

/20

05

01

/09

/20

05

08

/09

/20

05

15

/09

/20

05

22

/09

/20

05

29

/09

/20

05

06

/10

/20

05

13

/10

/20

05

20

/10

/20

05

27

/10

/20

05

03

/11

/20

05

10

/11

/20

05

Date

[PM

10]

/ µg

m-3

TEOM (uncorr.) Edinburgh OSIRIS Brighton OSIRIS

TEOM (uncorr.) average = 17.5 µg m -3

Edinburgh OSIRIS average = 15.2 µg m -3

Brighton OSIRIS average = 19.5 µg m -3

AURN site in Horley, ~1.5 km from Gatwick airport.

Instrumentation: Partisol 2025

- Equivalence status

- Absolute mass measurement accurate

- Sample available for subsequent analysis

• Type-approved aerodynamic sampling inlet

• Filter-based gravimetric

- 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

Sampling Sites in Edinburgh

Haymarket

- “Roadside”

- TEOM

- OSIRIS

St Leonards

- “Urban Background”

- TEOM-FDMS

Sampling and Extraction

• 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

Solid Phase ExtractionAqueous Aerosol Extract

pH = 2

SPE Column

Methanol (activation)

0.01 M HCl (equilibration)

Effluent

Inorganics

Hydrophilic Carbonaceous

Eluate

WSOC (Hydrophobic)

Methanol

Ultrapure Water

Reversed Phase SPE Columns

• Silica-based

• Polymeric

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.

• Capable of isolating ~60% of the water-soluble organic compounds

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

XAD-8 and XAD-4 Fractions

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

Elemental Analysis

• % 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

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

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

UV-VIS Spectroscopy

• 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

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

IR 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

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)

1600–1660 cm−1 (C=C of aromatic rings; C=O of conjugated carbonyl groups)

1061 cm−1 (C-O of polysaccharides)

1220 cm−1 (C-O and OH of COOH groups)

1384 cm−1 (C-H of aliphatic CH3)

• WSOC

b) Autumn

a) Summer

NMR Spectroscopy

13C-NMR

• WSOC

b) Autumn

a) Summer

Un-substituted saturated aliphatic components

(10 to 50 ppm)

Aliphatic carbons singly bound to one oxygen or nitrogen atom (60–95 ppm)

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

Aliphatic carbons singly bound to two oxygen atoms (95-110 ppm)

Ester and carboxyl carbons (160–190

ppm)

Aromatic carbons (110–160 ppm)

• Autumn sample richer in aromatic carbons than summer- lignin breakdown component due to wood burning

14C Analysis of Urban PM

• 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.

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

Accelerator Mass Spectrometer

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 650C in stream of O2.

OC: combust for 10 min at 340C 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 650C 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.

aerosol carbon (TC)

elemental carbon (EC) organic carbon (OC)

contemporary OC

fossil EC

Anthropogenic:

fossil fuel combustion

Anthropogenic:

biomass burning

Anthropogenic:

fossil fuel combustion

contemporary EC

fossil OC

“Top down” Source Attribution of Carbonaceous Aerosol

AMS data

Biogenic:

SOA, e.g. terpenes

According to the method of Szidat et al

Further Work and Benefits

• 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:

1. Which part of the organic compound mass can be controlled through abatement of anthropogenic sources.

2. Which part arises from natural compounds released from vegetation, which is less readily amenable to control.

Acknowledgements

Supervisor

Dr Mat Heal

Friends

Colleagues

Catherine HardacreEmanuel BleiRyan Clark