carbonaceous aerosol: properties, sources and...

ACAAR Symposium, 15 May 2014 1

Carbonaceous aerosol: properties, sources and analytical methods

Willy Maenhaut1,2

1 Ghent University (UGent), Department of Analytical Chemistry,

Krijgslaan 281, S12, 9000 Gent, Belgium

2 University of Antwerp (UA), Department of Pharmaceutical Sciences, Universiteitsplein 1, 2610 Antwerpen, Belgium


Carbonaceous aerosols consist of organic matter (OM) and black or elemental carbon (BC/EC) BC and EC refer to roughly the same component, but term BC is used when the component is measured with an optical

technique term EC used when the measurement is done with a thermal

technique There may also be inorganic carbon [mostly carbonate carbon (CC)] present in the carbonaceous aerosol (especially in PM10 or TSP), but this will not be discussed


Organic matter (OM) and EC Primary sources of OM incomplete combustion of fossil fuels and biomass biological particles (PBAP)

Secondary sources of OM (SOA) oxidation of volatile organic compounds (VOCs) of natural and

anthropogenic origin

EC / BC / soot primary aerosol component formed by incomplete combustion of fossil fuels (e.g., diesel) or of

biomass

Distinction between OM and EC not so straightforward more on this later there is also something like brown carbon (normally included with OM)

Distinction between primary and secondary OM also less clear in recent years oxidized (aged) primary OM counted as secondary OM


Primary biological aerosol particles (PBAP)

POLLEN

BACTERIA VIRUSES

FUNGI

ALGAE PLANT DEBRIS

PBAP have not traditionally been considered part of the OA budget, but this has been revised in recent years

Not much is known about emissions, processing, climate effects

Very large and likely short-lived


VOC oxidized to less-volatile OC

Partitioning to aerosol phase depends on vapor pressure high equilibrium vapor pressure high tendency to stay in

gas phase low equilibrium vapor pressure partitions to aerosol

phase – non-volatiles

Large organics (C> 6) tend to form aerosols while organics with C<6 do not

Oligomerization on/in acid aerosol

Secondary organic aerosol (SOA) formation


Anthropogenic SOA-precursors = aromatics (emissions are 10x smaller)

Isoprene (C5H8)

Monoterpenes (C10H16)

Sesquiterpenes (C15H24)

Biogenic hydrocarbons (BVOCs)


SOA production from BVOCs

Biogenic VOC

Emissions

Oxidation Reactions (OH, O3,

NO3)

Nucleation (oxidation products)

Growth

Condensation on pre-existing aerosol

Over 500 reactions to describe the formation of SOA precursors, ozone, and other photochemical pollutants [Griffin et al., 2002; Griffin et al., 2005; Chen and Griffin, 2005]


Formation of SOA from BVOCs

(C5H8)

Monoterpenes (C10H16)

OH, O3

Aldehydes RC(O)H Ketones RC(O)R Dicarbonyls RC(O)-C(O)R

absorption into aerosol

oxidation

Carboxylic acids RC(O)OH

polymerization


Properties and environmental importance of carbonaceous aerosols Carbonaceous aerosols

have effects on human health (e.g., respiration, cardiovascular problems) scatter (OM) or absorb (BC) solar and IR radiation decrease visibility have effects on climate direct (the particles themselves) indirect (particles can act as CCN)

water-soluble and/or hydrophilic OM can act as CCN and plays thus a role in cloud formation are involved in heterogeneous (and multi-phase) reactions …


Off-line chemical analysis of aerosol samples for

carbonaceous components

Aerosol samples collected with filter devices or cascade impactors

at ground level (or towers) on land on ship platforms with aircraft platforms


OC/EC differentiation

Pöschl, 2005


OC/EC analysis by thermal-optical methods

quartz fibre filter punch heated in quartz oven first phase (in pure He): OM compounds desorb -> CO2 -> CH4 second phase (in He/O2 mixture): EC and PC combusted -> CO2 -> CH4

transmission (TOT) or reflectance (TOR) of laser light through/by the filter punch continuously monitored


Thermogram for Gent PM10 sample of 13 July 2010 (transmission)

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EC OC1 PC

OC = OC1 + PC (with PC: pyrolytic carbon) : area below the blue line prior to the OC/EC split point (vertical brown line)

EC : area below the blue line after the OC/EC split point


Thermogram for Gent PM10 sample of 13 July 2010

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Full brown line : laser transmission (T) signal vertical full brown line : OC/EC split point for T

Dashed purple line : laser reflectance (R) signal vertical dashed purple line : OC/EC split point for R


Analysis for water-soluble OC (WSOC) normally done with a total organic carbon (TOC) analyzer (part of) sample extracted with high-purity water filtered extract injected in TOC instrument 2-step procedure (2 different injections) water-soluble total carbon (WSTC) analysis: OM combusted to CO2 ->

measured with NDIR detector water-soluble inorganic carbon (WSIC) analysis: filtered extract injected

in reaction vessel, where the sample is acidified with phosphoric acid to obtain a pH <3; evolved CO2 measured with NDIR detector

WSOC = WSTC – WSIC WSOC is a proxy for secondary OC; WIOC for primary OC

Percentage of PM2.5 OC, which is WSOC urban sites: ~30-40%

rural & forested sites: ~60% biomass burning OC: ~70% marine sites: ~30%


(part of) sample extracted with high-purity water; filtered extract injected separation with ion exchange column eluent for anions: hydroxide (OH-) gradient

suppression of conductivity of the eluent conductivity of analyte ionic species measured

Analysis for water-soluble inorganic (and LMW organic) species by ion chromatography (IC)


Isotopic analysis of carbonaceous aerosols

e.g., 14C analysis with accelerator mass spectrometry (AMS) to differentiate between old (fossil fuel) and new (biogenic or

biomass burning) carbon


Analysis of atmospheric aerosols for individual organic compounds

ion chromatography (for C1 – C5 ionic species): aqueous extracts capillary electrophoresis

Organic mass spectrometry Sample preparation

sample extracted with organic solvent (e.g., methanol; CH2Cl2) extract pre-concentrated (evaporation) + re-dissolved derivatisation (methylation, trimethylsilylation) for gas chromatography (GC)

Techniques gas chromatography / mass spectrometry (GC/MS) liquid chromatography / mass spectrometry (LC/MS)

chromatographic separation with suitable column


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22.4 17.6 15.1

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LC/MS analysis of PM2.5 sample from Brasschaat TIC chromatogram [Gómez González, ACP, 2010]


Extent of OC explained by detailed organic analysis

PM2.5 samples from 2007 summer campaign in Brasschaat

Mean ± std.dev. WSOC % of OC 51 ± 9

MSA- C % of WSOC 1.43 ± 1.19 Oxalate C % of WSOC 2.9 ± 1.4 Malonate C % of WSOC 2.3 ± 1.1 Succinate C % of WSOC 1.09 ± 1.06 Glutarate C % of WSOC 0.33 ± 0.23 19 LC/MS species C % of WSOC 2.3 ± 0.9

∑(24 compounds) C % of OC 5.3 ± 2.1 ∑(24 compounds) C % of WSOC 10.3 ± 3.1

} measured by IC


Extent of OC explained by detailed organic analysis PM10 samples from 1998 W & S campaigns in Ghent [Kubátová et al., JGR, 2002]

samples analysed by GC/MS ~100 compounds identified and quantified identified compounds accounted for ~3.1% of the organic matter (OM)


On-line (in-situ) chemical analysis of atmospheric aerosols

for carbonaceous components


Measurement of OC/EC (thermal) & BC (optical, PASS) OC/EC measurement

semi-continuous OC-EC field analyzer (Sunset Lab) 45 min filtration followed by 15 min analysis analysis based on TOT (cfr. lab OC-EC analyzer)

BC (LAC) measurement aethalometer (7-wavelength) aerosol collected on filter tape light absorption by the aerosol measured at 7 wavelengths

multi-angle absorption photometer (MAAP) aerosol collected on filter tape

photo acoustic soot spectrometer (PASS) measures aerosol absorption at three wavelengths without first

collecting particles on a filter


Measurement of BC with 7-wavelength aethalometer

Åabs = 1

For traffic BC (diesel soot) Abs. coeff ~ λ-1

Åabs = 1

For BC from wood burning: brown carbon Åabs : 2 – 10


Timonen et al., AMT, 2010

Measurement of WSOC and water-soluble ionic species by particle-into-liquid sampler PILS-TOC-IC


Saarnio et al., AMT, 2013

Measurement of levoglucosan with Particle-into-Liquid Sampler – High-Performance Anion Exchange Chromatography – Mass Spectrometry (PILS-HPAEC-MS)


Several AMS instruments available from Aerodyne, including Aerosol Chemical Speciation Monitor (ACSM) High-resolution (HR) Time-of-Flight (TOF) AMS

The instruments collect the PM1 aerosol

In most instrument types only the non-refractory (NR) components of the aerosol are analysed NH4

+, NO3-, SO4

2-, Cl- organic matter (OM)

The contribution from the various aerosol types (and for the organic matter from HOA, OOA, BBOA, …) is obtained by PMF of the data set (time series of intensities of m/z ions)

m/z marker ions for levoglucosan 60 (and 73)

− there are contributions from several other species

Aerosol Mass Spectrometry (AMS)


Measurement of non-refractory aerosol components with Aerodyne aerosol mass spectrometer (AMS)

Canagaratna et al., 2007


Organic aerosol components worldwide (PM1)

Jimenez et al., Science, 2009


Ng et al., ACP, 2010

CO2+

mostly C2H3O+


Off-line: sample collection in the field followed by chemical analysis in the lab collection with filters or cascade impactors analysis for inorganic and/or organic constituents

On-line: in situ sampling and analysis (in real time) Aerosol Mass Spectrometry (AMS) Aethalometer Model (AeM) Particle-into-Liquid Sampler (PILS) and analysis for levoglucosan

Off-line techniques vs On-line (real-time) techniques for assessing the contribution from biomass burning


Chemical mass balance (CMB) method

Multivariate methods, such as Positive Matrix Factorization (PMF)

Using a single marker compound, typically levoglucosan

Quantification of contribution from biomass burning with Off-line methods


Source profiles are needed

Can be done on a single ambient aerosol sample

Classical example: Schauer et al. [AE, 1996] measured: EC, Al, Si, and 101 organic species, of which

there were 8 wood smoke markers source profiles for fireplace combustion of hardwood and

softwood were combined to form an emissions-weighted average wood smoke source profile

Average contribution (%) to the measured fine PM for 1982 Pasadena 9.6 Downtown LA 5.7 West LA 10.8 Rubidoux 1.3 Uncertainty of the method: about 20% (relative)

Quantification of contribution from biomass burning with Off-line methods - CMB


NO source profiles needed

Several species are needed

A series of samples is needed (> 30)

Recent example Gianini et al. [STE, 2013]

Quantification of contribution from biomass burning with Off-line methods - PMF


Study at 4 Swiss sites

Uncertainty: “the overall uncertainty of the applied source apportionment methods is unknown and their results should whenever possible be verified by comparison of different methods”

Gianini et al. [STE, 2013] – PMF and CMB


Concentration ratio of the PM mass to a marker compound in biomass smoke needs to be known

Concentration of marker compound in each ambient sample then multiplied by that ratio implies that the marker compound in the ambient sample originates

exclusively from biomass burning

The concentration ratio of the PM mass to a marker compound in wood smoke depends on many parameters type of fuel burnt (hard wood / soft wood) type of wood stove or fireplace operating / burning conditions (flaming / smoldering) the PM size fraction

Ratios used in studies for the VMM [Maenhaut et al., STE, 2012] PM10 mass / levoglucosan: 10.7 PM10 OC / levoglucosan: 5.6

− estimated that the uncertainty that is associated with the wood smoke OC and PM mass contributions is around 30%

Quantification of contribution from biomass burning with Off-line methods, using a single marker compound, typically levoglucosan


Using mass spectrometry (MS) for detection Gas Chromatography (GC)/MS Thermal Desorption (TD)-GC/MS High-Performance Liquid Chromatography (HPLC)-MS High-Performance Anion Exchange Chromatography

(HPAEC)-MS

Using pulsed amperometric detection (PAD) Ion Chromatography (IC)-PAD HPLC-PAD HPAEC-PAD

Methods for the determination of levoglucosan (in ACTRIS 2013 intercomparison)


%PM10 from wood burning as a function of season

5 5 6 13 6 6 52.8 2.7 3.8 7.3 3.5 3.4 1.90.7 0.7 0.9 5.0 1.0 1.1 0.57 8 9 19 10 9 79 9 11 22 11 10 90

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Borgerhout Gent Mechelen Hamme Lier Retie Houtem

mea

n ±

s.d.

ALL Spring Summer Fall Winter

In winter (blue) for 6 of the 7 sites: around 10% of PM10 mass, on average, from wood burning At Hamme in winter: 22% of PM10 mass, on average, from wood burning

7-site study in Flanders in 2010-2011 (Chemkar-3) [Maenhaut et al., STE, 2012]


Techniques Aerosol Mass Spectrometry (AMS) Aethalometer Model (AeM) Particle-into-Liquid Sampler (PILS) and analysis for levoglucosan,

e.g., Saarnio et al. [AMT, 2013] − is less sensitive than Off-line methods

Common features provide much better time resolution than Off-line methods assessing the contribution from biomass burning with AMS and

AeM is more involved (and has thus a larger uncertainty) than in the case of Off-line methods

On-line (real-time) techniques for assessing the contribution from biomass burning


Example of AMS study: Elsasser et al. [ACP, 2012]

Other sources than levoglucosan contribute to the intensity of the m/z = 60 ion


Uses a 7-wavelength Aethalometer

Introduced by Sandradewi et al. [EST, 2008]

PMWB = c babs(490 nm)WB

with absorption coefficient babs(490 nm)WB derived from the Aethalometer data

for estimating c independent data are needed (e.g., 14C, AMS, HiVol filter data) − c can be considered a site-specific constant

Aethalometer Model (AeM)


Wintertime study in Grenoble; deployed HiVol filter, data analysed by CMB c-TOF AMS, data analysed by PMF 7-wavelength Aethalometer, data analysed by AeM

Example of AeM study: Favez et al. [ACP, 2010]


It is increasingly realized in recent years that biomass burning gives also rise to SOA, e.g., Yee et al. [ACP, 2013] chamber study on SOA formation from biomass burning

intermediates: phenol and methoxyphenols

SOA compounds from wood or biomass burning in field samples methyl-nitrocatechols [Iinuma et al., EST, 2010] several nitro-aromatic compounds [Kitanovski et al.,

JChrA, 2012] several nitro-organic compounds [Kahnt et al., AE, 2013]

− their summed concentration at Hamme in winter was only 7% of the concentration of levoglucosan

It is unclear how much SOA from biomass burning is included (if any) in the several apportionment or contribution calculations discussed in this presentation

Some words on SOA from biomass burning


Thank you

carbonaceous aerosol: properties, sources and...

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