Critical Review 2014 Discussion:

Public Health and Components of Particulate Matter: The Changing Assessment of Black

Carbon

John G. WatsonDesert Research Institute, Reno, NV, USA

Presented at

Air & Waste Management AssociationAnnual Conference and Exhibition

Long Beach, CA

June 25, 2014

Objectives

• Note strengths and deficiencies of review

• Clarify BC formation and measurement processes

• Highlight some other useful reviews of the topic

Strengths of the Review

• Identifies and summarizes a broad range of epidemiological and toxicological studies on the topic

• Points to many useful resources

• Highlights exposure error of primary PM as a factor affecting epidemiological relationships

Review Limitations• Previously published reviews are not evaluated and used as

a starting point. Much of the CR has already been published

• Overemphasizes BC in diesel engine exhaust. Solid fuel burning seems added as an afterthought

• Insufficient explanation and critical evaluation of uncertainties related to measurements, methodologies, and health end-points.

• Too much “so and so did this or that”, not enough “this study agrees or disagrees with that study because…”

• Although “BC and associated pollutants” is often said, a true multipollutant perspective is lacking

• EC and BC measurement method limitations and comparability, and their potential effects on health studies, are not addressed

• Didn’t answer the “so what?” question

Pure elemental carbon probably isn’t that harmful, and it isn’t always black

Diamond Graphite

Pure graphite is never found in the atmosphere. Soot derives from incomplete combustion with other pollutants. Soot is always a

combination of organic and elemental carbon, plus other contaminants.

Akhter et al., 1985, App. Spec.

Even some of the cleanest combustion processes have some soot emissions

(Courtesy of Doug Lawson, DOE National Renewable Energy Laboratory ww.cleanairinfo.com/slcf/agenda.htm)

BC is not the only pathway for PM formation from combustion sources

Kittelson (1998)Schneider et al. (2005)

Factors Affecting PM Carbon Emissions: • Engine types and power• Engine operating conditions (e.g., idle, accelerate, and decelerate)

• Fuel formulations (e.g., sulfur or aromatic content)

• Dilution and aging• Meteorology (e.g., sunlight, temperature, and relative humidity)

• Interactions with ground-level environment

0

0.05

0.1

0.15

0.2

0.25

1 10 100 1,000 10,000

Diameter (nm)

No

rmal

ized

Co

nce

ntr

atio

n (

1/C

tota

l)dC

/dlo

gD

p

Number Surface Mass

Fine ParticlesDp < 2.5 m

Ultrafine ParticlesDp < 100 nm

NanoparticlesDp < 50 nm

Nuclei Mode - Usually forms from volatile precursors as exhaust dilutes and cools

Accumulation Mode - Usually consists of carbonaceous agglomerates and adsorbed material

Coarse Mode - Usually consists of reentrained particles, crankcase fumes

PM10Dp < 10 m

In some cases this mode may consist of very small particles below the range of conventional instruments, Dp < 10 nm

Particle evolution Particle size distribution

Biomass burningDust

Acetylene soot

Diesel soot

PALAS arc generator soot

Not all light absorbing carbon is black, nor are all light absorbers made of carbon

Instruments Operating principle Observables Avg time

Dual wavelength Aethalometer (370, 880 nm)

Filter-based light attenuation Light absorption (Mm-1) or BC (μg/m3)

5 min

Seven color Aethalometer (370, 450, 571, 615, 660, 880, and 950 nm)

Filter-based light attenuation Light absorption (Mm-1) or BC (μg/m3)

5 min

Particle Soot Absorption Photometer (PSAP; 467, 530,and 660 nm)

Filter-based light attenuation Light absorption (Mm-1) or BC (μg/m3)

5 min

Multi Angle Absorption Photometer (MAAP; 670 nm)

Filter-based light attenuation with compensating light scattering effects

Light absorption (Mm-1) or BC (μg/m3)

5 min

DMT Photoacoustic (405, 532, and 781 nm)

Light absorption of particles in air based on heating and cooling that creates a sound wave

Light absorption (Mm-1) or BC (μg/m3)

5 min

Sunset carbon analyzer (660 nm)

Thermal/optical transmittance (TOT; NISOH 5040 protocol)

EC and OC (μg/m3) and optical BC (µg/m3)

1-24 hour

R&P 5400 carbon analyzer Thermal OC/EC at 275 C and 750 C

EC and OC (μg/m3) 1 hour

PAS 2000 PAH monitor Photoionization Particle bound PAH (fA) 5 min

DRI carbon analyzer (633 nm)

Thermal/optical reflectance (TOR; IMPROVE_A protocol)

EC and OC (μg/m3) 1-24 hr

BC is inferred from light absorption measurements, while EC is determined by thermal measurements with some optical corrections

(Light absorbing carbon is wavelength dependent)

Chow et al. (2009)

Light absorption to BC conversion factors are derived from comparisons with EC measurements

0

20

40

60

80

100

120

140

100 200 300 400 500 600 700 800 900 1000

Lig

ht

Ab

sorp

tio

n E

ffic

ien

cy

(m2

g-1

)

Wavelength (nm)

Smoldering Biomass

Diesel Exhaust

Flaming Biomass

(EC absorption efficiency varies by source and wavelength)

OC/EC split λ

BC (light absorption) and EC are highly correlated, but the relationship depends on sampling, analysis, and particle

properties (size, shape, and composition)

Teflon membrane filter samples from Denver

Quartz fiber filter samples from Denver

Chow et al., 2011, JAWMA

BC correlates with most other pollutants, and not only for nearby engine exhaust

Fresno winter 2002-2003

Fresno summer 2003-2004

Watson et al, 2006, JAWMA

BC

The BC content of diesel exhaust is highly variable, and it is decreasing as newer technology penetrates the fleet

23050 LVOnRDIE

23075 LVOnRDIEs

3518 PHDIES

322062.5

322072.5

3913 NWHDc

n/a HDD

n/a MDD

3912 NWLDCPC

321042.5

n/a PEN_C

23051 LVOffRDIE

100 80 60 40 20 0 20 40 60 80 100

On-Road - Diesel (Winter)

On-Road - Diesel (Summer)

On-Road - Heavy-Duty Diesel

On-Road - Heavy-Duty Diesel

On-Road - Heavy-Duty Diesel

On-Road - Heavy-Duty Diesel (Winter)

On-Road - Heavy-Duty Diesel

On-Road - Medium-Duty Diesel

On-Road - Light-Duty Diesel (Winter)

On-Road - Light-Duty Diesel

Off-Road - Diesel

Off-Road - Diesel

OC and EC Percentage (%)

OC EC

Chow et al., 2011, Atmos. Environ.

PM2.5 OC and EC abundances are even more variable for biomass burning

3766 MZFFIREC

423202.5

4366 BVBURN

22073 LTRWCC

3770 MZRWCC

423032.5

423302.5

22071 LTFIREPL

3235 WRWCBC3

3921 NWFGPDa

22072 LTWOODST

421022.5

3236 WSTOVEC2

22069 LTRWSC

22070 LTRWHC

422022.5

422012.5

221032.5

4704

100 80 60 40 20 0 20 40 60 80 100

Forest FireOpen BurnOpen Burn

RWC - AllRWC - AllRWC - AllRWC - All

RWC - FireplacesRWC - FireplacesRWC - Fireplaces

RWC - WoodstovesRWC - WoodstovesRWC - Woodstoves

RWC - SoftwoodsRWC- HardwoodsRWC- HardwoodsRWC - Softwoods

IWCIWC

OC and EC Percentage (%)

OC EC

IWC: Industrial Wood Combustion; RWC: Residential Wood CombustionChow et al., 2011

The OC fraction of combustion products is complex and is not completely removed at lower temperatures. There are still

many OC compounds at T>140 and 280 ºC

Grabowsky et al., 2011, Anal. Bioanal. Chem.,.

Two-dimensional time temperature REMPI/TOF-MS-spectra of PM loaded filter from engine emissions using gasoline (left) and diesel (10% biodiesel) (right). Can be extended to the study of aged emissions

Gasoline exhaust Diesel/biodiesel exhaust

EC constitutes ~5% to 10% of PM2.5 and is correlated with PM2.5

Site EC/PM2.5 (%)PM2.5

(ug/m3) OC (ug/m3) EC (ug/m3)Atlanta 9.8 14.3 3.2 1.3Baltimore 7.2 12.7 2.0 0.8Birmingham 9.1 14.3 3.2 1.3Detroit 8.0 13.2 2.5 0.8Fresno 6.5 13.4 3.0 0.9Houston 5.7 10.6 1.8 0.6New York 13.7 11.7 2.0 1.4Phoenix 8.8 9.7 2.4 0.9Puget Sound 11.3 7.1 2.2 0.8Rubidoux 10.3 17.0 3.0 1.5Washington DC 8.8 14.3 2.5 1.1

“…reducing a unit of BC might prolong life by more 4 to 9 times than reducing a unit of PM2.5”

So why go after the rest of PM2.5?

PM2.5, EC, and OC levels are decreasing at U.S. monitors. Is BC really such a big deal for health?

Annual average concen-

trations at Washington

DC IMPROVE

site

Residential solid fuel combustion exposure is not just an issue in other countries. Many intermountain western communities still experience high exposures. Fresh

(residential) and aged (wildfire) smoke may have different compositions and effects

Wintertime evening spatial distribution of brown carbon in Sparks, NV, shows a relatively small footprint of effects in a low-income neighborhood heating with solid fuels ng/m3

Most sources have multiple emissions of reactive substances, and co-benefits can be derived for non-health effects by emission reductions

Cao et al., 2013, AAQR.

General shortcomings of air quality and health studies

• Dominated by populations, pollutant mixtures, and sources in major cities (LA, Boston, New York, Atlanta)

• Need new methods to address synergistic effects of multiple pollutant mixtures (gas and particle) that are often correlated, but with varying temporal/spatial patterns

• Lack of information on intermittent and poorly inventoried sources (non-road engines, high emitters, fugitive dust, wildfires, solid fuel burning, trans-ocean transport)

• Slow evolution of air quality networks from compliance to multiple purposes (e.g. exposure, forecast, and health)

Additional (uncited) review articles

Memorable quote

• p. 638, par. 5. “…if an air pollution monitor is <1.5 km from the residence of the mother, associations are often found with traffic emissions such as CO, but if the monitor is further from the home, such associations are rare.”