Combustion Aerosol
Emission Measurements
Lisa Graham
Senior Chemist
Emissions Research and Measurement Division
Environment Canada
Environment Canada
Emissions Research and Measurement Division1

OverviewWith the objective of highlighting sources ofdiscrepancies and uncertainties…
Combustion sources of aerosols
 Characteristics of combustion aerosols
 Measured properties – Inventory vs. Climate Modeling Form of Carbon?
 Measurement Issues
 Sampling Issues
 Illustrative Examples of Results
Environment Canada
Emissions Research and Measurement Division

2

Combustion Sources of PMMobile Sources

On-road and off-road vehicles


Non-roadMarine, rail, aviation

Stationary SourcesCars, trucks, equipment (construction, lawn and garden,agriculture)

Residential and commercial heating and cooking (fossilfuel, biomass, food)Open or Area Sources


Forest fires, open biomass burning (grass, agriculturewaste)
Environment Canada
Emissions Research and Measurement Division3

Non-Combustion Sources
Resuspended and windblown dust
 Biogenic sources (detritus, mould, spores) Sea salt
 Tire and brake wear
 Secondary formation
Environment Canada
Emissions Research and Measurement Division4Characteristics of Combustion PMMobile Sources

Gasoline fueled vehicles (MPFI engines)

Mostly OC (>70%)

Diesel fueled vehicles
2-stroke engines 40-60% OC
 4-stroke engines 5-20% OCIn both cases, with low sulphur fuel, PM is >95%
carbonEnvironment CanadaEmissions Research and Measurement Division

5

Characteristics of Combustion PM

Changes due to advanced combustion and aftertreatment
systems

PM controls:
Oxidation catalysts
 Reduce organic carbon content of PM
 Diesel particulate filters Virtually eliminate carbonaceous particle emissions Nucleation particles (hydrocarbon or sulphate) form

NOX Controls:

Selective Catalytic Reduction (urea or ammonia)
 Lean NOX catalysts ?
 NOX absorbers ?


Direct injection spark ignited engines:

Higher PM emissions compared to MPFI engines
 Similar to diesel PMEnvironment CanadaEmissions Research and Measurement Division

6

Characteristics of Combustion PM

Stationary Combustion Sources

Natural gas
Very low PM emissions1
 62% OC, 6% EC


Oil (light and heavy fuel oil) 2
PM mostly sulphate (>40% by mass, depending on fuel sulphur) Heavy metal content higher in HFO emissions
 TC content low (long residence time in combustion zone) OC and EC approximately equal, <15% total carbon
Coal 3

Varies greatly by source, fuel type1

NYSERDA Report 04-05.

Environment Canada
Emissions Research and Measurement Division2

Lee et al. 2002

3

Bond, 1999, 2002

7

Characteristics of Combustion PM
Open Sources


Forest firesFlaming and smoldering: Lower BC/OC ratio

Grassesmostly flaming: Higher BC/OC ratio

Environment Canada
Emissions Research and Measurement Division

8Primary and Secondary PM

Combustion sources emit both primary PMand precursors to atmospheric formation of
secondary PMAmmonia, SOX, NOX
 VOCs, semivolatile organics

In many cases, emissions of precursors aregreater than primary PM emissions

Environment CanadaEmissions Research and Measurement Division9

Measured Properties
Emission Inventory Measurements
PM mass by gravimetry with or without particle
size cut (TPM, PM10, PM2.5, PM1)
 Chemical characterization

Organic and elemental carbon (TOR or TOT, variations) Ions (sulphate, nitrate, inorganic and organic ions,ammonium) by ion chromatography or capillaryelectrophoresis
 Detailed organic composition
 MetalsEnvironment Canada
Emissions Research and Measurement Division10

Measured PropertiesClimate Relevant Measurements
Light Absorption at various wavelengths
Light Scattering at various wavelengths


Aethalometer, PSAP, Photoacoustic, Optical Extinction
Cell, Integrating Plate, Soot Photometers, …
Nephelometer, …

Measured optical properties depend on particle
chemistry, particle size, relative humidity,
matrix gases
Environment Canada
Emissions Research and Measurement Division11Particle Size and NumberParticle Size Distributions
Aerodynamic or mobility diameter depending oninstrument
 SMPS, PCASP, FSSP, ELPI, cascade impactors


Number Concentrations
Condensation Particle Counter (CPC)

Chemistry of particles changes with size
 Measured size distributions depend on sampling
conditions
Temperature, relative humidity, residence time
Environment CanadaEmissions Research and Measurement Division

12

What Form is the Carbon?
BC, Soot and EC are used interchangeably and loosely BUT
they are not the same thing!
 Black carbon (BC)Light absorbing carbon, microcrystalline graphitic form of carbon

Elemental Carbon (EC)Operationally defined by instrument
 Some forms of EC are “blacker” than others




Soot



Carbonaceous PM formed by combustion processes

Organic Carbon (OC)Operationally defined by instrument
 Not the same as organic matter (OM)
 Evidence suggests it can either scatter or absorb light, depending onchemistry

Environment CanadaEmissions Research and Measurement Division13

Measurement MethodsBC measured by light absorption methods
Results are to some extent instrument dependent.
 A number of studies have been published comparing
methods, identifying issues and proposing approaches toaddress issues.


OC and EC usually measured by thermal-opticalmethods
Reflectance (DRI, IMPROVE)
 Transmittance (Sunset Labs, NIOSH)
 Methods agree for TC, OC/EC split differs due to methodof correcting for pyrolysis
 Neither TOR or TOT work well with very dark filtersEnvironment Canada
Emissions Research and Measurement Division

14

Sample Collection
Dilution sampling is the preferred approach toacquiring PM samples from mobile andstationary combustion sources.
 Samples from open burning sources areusually collected in-situ, in the smoke plume ata distance from the source.
 Most stationary source emission measurements
are made “in-stack” not by dilution methods.
Environment CanadaEmissions Research and Measurement Division15

Dilution SamplingGoal is to obtain an aerosol sample from a hot, wet,corrosive exhaust gas
representative of the aerosol as it is emitted in the realworld
 on a filter or presented to an instrument
 measure the mass emission rate of the aerosol.
Extractive or total exhaust sampling Sampling conditions (residence time, relativehumidity, temperature) influence measurements ofmass, number concentration, size distributions
Environment CanadaEmissions Research and Measurement Division

16

Filter Sample CollectionArtifacts
Positive – adsorption of semivolatile material onto filter
media or collected PM Negative – loss of semivolatile material from filter media
or collected PM Depend on

type of filter media
 sampling conditions (face velocity, pressure drop, sampling time) Composition of sample streamFor mobile sources, many studies use regulatory prescribedsampling procedures
PM sample collection at 47 +/- 5 oC
 How useful is this for atmospheric chemistry or climate modeling?
Environment CanadaEmissions Research and Measurement Division17

OC-EC Measurements
TOR and TOT methods most common
 Sample collection on pre-fired quartz filters
 Primary filter collects PM, adsorbs semivolatile material fromgas phase Artifact correction strategies


Ignore it Assume a constant factor (based on what?) Secondary quartz filter behind primary quartz filter
 Secondary quartz filter behind a Teflon membrane filterSample collection time is an important factor

Loss of material due to long sampling times and high pressure drops

All these issues make integrating results from different studies
into inventories very challenging.
Environment CanadaEmissions Research and Measurement Division

18

Variability Within a Source
Not all diesel engine
combustion is the same
 HHDDTs operating indifferent driving conditions
have very different
emissions

1600



EC/OC ratio varies from 0.2
to 4.5

4-stroke diesel generator
EC/OC ratio relatively
constant around 2.5
 2-stroke diesel generator
EC/OC ratio relatively
constant at 0.75

Environment Canada
Emissions Research and Measurement Division

mg/min or mg/miOC1400EC1200

PM

1000
800
600
4002000idle

creeptransienthw
cruiseShah et al. ES&T 2004, 38, 2544-2550
19

Effect ofSamplingConditions
Residence time andrelative humidity affectmeasured size
distributions andnumber concentrations
 Diluted PM emissions
from small commercial
boiler on #2 LFO.
Environment Canada
Emissions Research and Measurement Division20

What’s Needed?
Simultaneous measurements at the source ofPM mass emission rate (PM2.5 or smaller) Size resolved chemistry Chemistry as complete as possibleEC, OC, ions, metals
 Detailed OC characterization helps with source identification andapportionment
Optical properties: absorption and scattering at multiple wavelengths
 Size distributions and number emissions
 Other physical properties such as hygroscopicity


Understanding of relative contribution of primary emissions
and secondary formation in different regions
 Use of atmospheric chemistry and other models to takeemissions from source to climate model grid input scale.
Environment CanadaEmissions Research and Measurement Division21

Recommendations
Adoption of standardized protocols for OC/EC sample
collection and analysis is critical to enabling integration of
results from different studies to understand climate forcing,regional haze and air quality issues.
 A fundamental understanding of the relationship between
optical and chemical properties of aerosols must be developed
to support modeling activities to understand the role ofaerosols in climate change.
 Support continued development of inventories that aretechnology-based to take advantage of information in air
quality inventories and models and to better represent thevariation of aerosol optical properties as a function source
technology, chemistry and physical characteristics of aerosols.
Environment Canada
Emissions Research and Measurement Division22