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Critical Review 2014 Discussion:Public Health and Components of Particulate Matter: The Changing Assessment of Black CarbonJohn G. WatsonDesert Research Institute, Reno, NV, USA

Presented atAir & Waste Management AssociationAnnual Conference and ExhibitionLong Beach, CAJune 25, 20141ObjectivesNote strengths and deficiencies of review Clarify BC formation and measurement processesHighlight some other useful reviews of the topic

2Strengths of the ReviewIdentifies and summarizes a broad range of epidemiological and toxicological studies on the topicPoints to many useful resourcesHighlights exposure error of primary PM as a factor affecting epidemiological relationships

3Review LimitationsPreviously published reviews are not evaluated and used as a starting point. Much of the CR has already been publishedOveremphasizes BC in diesel engine exhaust. Solid fuel burning seems added as an afterthoughtInsufficient 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 becauseAlthough BC and associated pollutants is often said, a true multipollutant perspective is lackingEC and BC measurement method limitations and comparability, and their potential effects on health studies, are not addressedDidnt answer the so what? question4Pure elemental carbon probably isnt that harmful, and it isnt always black

DiamondGraphite5Pure 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.6Even 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)7BC 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 powerEngine operating conditions (e.g., idle, accelerate, and decelerate)Fuel formulations (e.g., sulfur or aromatic content)Dilution and agingMeteorology (e.g., sunlight, temperature, and relative humidity)Interactions with ground-level environment

Particle evolutionParticle size distribution8

Biomass burning

Dust

Acetylene soot

Diesel soot

PALAS arc generator sootNot all light absorbing carbon is black, nor are all light absorbers made of carbonInstrumentsOperating principleObservablesAvg timeDual wavelength Aethalometer (370, 880 nm)Filter-based light attenuationLight absorption (Mm-1) or BC (g/m3)5 minSeven color Aethalometer (370, 450, 571, 615, 660, 880, and 950 nm)Filter-based light attenuationLight absorption (Mm-1) or BC (g/m3)5 minParticle Soot Absorption Photometer (PSAP; 467, 530,and 660 nm)Filter-based light attenuationLight absorption (Mm-1) or BC (g/m3)5 minMulti Angle Absorption Photometer (MAAP; 670 nm)Filter-based light attenuation with compensating light scattering effectsLight absorption (Mm-1) or BC (g/m3)5 minDMT Photoacoustic (405, 532, and 781 nm)Light absorption of particles in air based on heating and cooling that creates a sound waveLight absorption (Mm-1) or BC (g/m3)5 minSunset carbon analyzer (660 nm)Thermal/optical transmittance (TOT; NISOH 5040 protocol)EC and OC (g/m3) and optical BC (g/m3)1-24 hourR&P 5400 carbon analyzerThermal OC/EC at 275 C and 750 CEC and OC (g/m3)1 hourPAS 2000 PAH monitorPhotoionizationParticle bound PAH (fA)5 minDRI carbon analyzer (633 nm)Thermal/optical reflectance (TOR; IMPROVE_A protocol)EC and OC (g/m3)1-24 hrBC 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)

107/24/2014 10:38 AMLight absorption to BC conversion factors are derived from comparisons with EC measurements

(EC absorption efficiency varies by source and wavelength)OC/EC split 11BC (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 DenverQuartz fiber filter samples from DenverChow et al., 2011, JAWMABC correlates with most other pollutants, and not only for nearby engine exhaustFresno winter 2002-2003

Fresno summer 2003-2004Watson et al, 2006, JAWMABCThe BC content of diesel exhaust is highly variable, and it is decreasing as newer technology penetrates the fleet

Chow et al., 2011, Atmos. Environ.14PM2.5 OC and EC abundances are even more variable for biomass burning

IWC: Industrial Wood Combustion; RWC: Residential Wood CombustionChow et al., 201115The 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 CGrabowsky 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 exhaustDiesel/biodiesel exhaustEC constitutes ~5% to 10% of PM2.5 and is correlated with PM2.5SiteEC/PM2.5 (%)PM2.5 (ug/m3)OC (ug/m3)EC (ug/m3)Atlanta9.814.33.21.3Baltimore7.212.72.00.8Birmingham9.114.33.21.3Detroit8.013.22.50.8Fresno6.513.43.00.9Houston5.710.61.80.6New York13.711.72.01.4Phoenix8.89.72.40.9Puget Sound11.37.12.20.8Rubidoux10.317.03.01.5Washington DC8.814.32.51.1reducing 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 effectsWintertime 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/m319Most 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.20General shortcomings of air quality and health studiesDominated 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 patternsLack 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 quotep. 638, par. 5. if an air pollution monitor is