John G. Watson Desert Research Institute, Reno, NV, USA Presented at

1. Critical Review 2014 Discussion:Public Health and Components of Particulate Matter: The Changing Assessment of Black Carbon John G. Watson Desert Research Institute, Reno, NV, USA Presented at Air & Waste Management Association Annual Conference and Exhibition Long Beach, CA June 25, 2014

2. Objectives • Note strengths and deficiencies of review • Clarify BC formation and measurement processes • Highlight some other useful reviews of the topic

3. 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

4. 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

5. Pure elemental carbon probably isn’t that harmful, and it isn’t always black Diamond Graphite

6. 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.

7. 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)

8. BC is not the only pathway for PM formation from combustion sources Particle evolution Particle size distribution 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 Kittelson (1998) Schneider et al. (2005)

9. Not all light absorbing carbon is black, nor are all light absorbers made of carbon Biomass burning Acetylene soot PALAS arc generator soot Diesel soot Dust

10. 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)

11. Light absorption to BC conversion factors are derived from comparisons with EC measurements (EC absorption efficiency varies by source and wavelength) OC/EC split λ

12. 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

13. BC correlates with most other pollutants, and not only for nearby engine exhaust Fresno winter 2002-2003 BC Fresno summer 2003-2004 Watson et al, 2006, JAWMA

14. The BC content of diesel exhaust is highly variable, and it is decreasing as newer technology penetrates the fleet Chow et al., 2011, Atmos. Environ.

15. PM2.5 OC and EC abundances are even more variable for biomass burning IWC: Industrial Wood Combustion; RWC: Residential Wood Combustion Chow et al., 2011

16. 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 Gasoline exhaust Diesel/biodiesel exhaust 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 Grabowsky et al., 2011, Anal. Bioanal. Chem.,.

17. EC constitutes ~5% to 10% of PM2.5 and is correlated with PM2.5 “…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?

18. 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

19. 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

20. 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.

21. 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)

22. Additional (uncited) review articles

23. 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.”