Publications grouped by topic. Links lead to journal sites if open-access; if not (boo!) then links lead to abstracts & you can get the paper from us.(-) submitted; (*) in press. There are other publications in which my group had lower fractional involvement.

State of the science reviews
2013 Bounding-BC Black carbon, all its effects, and all its sources. 180 pages, so here's the 2-page summary

Emission inventories (past-present-future)
2014 Uncertainty in on-road emissions Fleet model uncertainties; retirement rate matters. (Yan et al.)
2014 End of the age of aerosols SO2+BC importance dwindle in comparison to CO2. (Smith and Bond)
2011 Future on-road emissions Global technology fleet model for projections; retirement differs by income; superemitters important. (Yan et al.)
2007 Historical biofuel consumption Biofuel since 1850, considering drivers beyond population. (Fernandes, Trautmann, Streets, Roden, Bond)
2007 Historical BC/OC inventory Black & organic carbon since 1850, considering technology change. (Bond & lots of group members)
2004 Future BC/OC emissions Technology considerations. BC/OC plateau in the near future. (Streets, Bond, Lee and Jang)
2004 Global emission inventory of black & organic carbon Emissions of BC/OC from everywhere. Really long paper. Sorry. (Bond, Streets et al.)
2003 Asian emission inventories for TRACE-P Emissions of everything from Asia. (Streets, Bond et al.)
2001 Black carbon emissions in China. Technology-based emission inventory. (Streets, Gupta et al.)

Aerosol optical properties, especially absorption
2011 Absorption change with RH Measured growth of absorption with RH. Biomass aerosol increases abs x2. (Brem, Mena et al.)
2010 Absorption by wood OC Measured spectra of wood-combustion aerosol. Much OC is not water-soluble. (Chen and Bond)
2007 Brown carbon color Spectra of yellow and brown carbon (Sun, Biedermann, Bond)
2006 Coating limitations Probable range of absorption amplification by coated particles. (Bond, Habib & Bergstrom)
2006 Optics review Review of why light is absorbed by soot particles, and how much. Another long one. (Bond & Bergstrom) ** Inquire about Annotated Version
2001 Spectral dependence of light absorption by carbon particles Yellow and brown carbon, and hypotheses about causes. (Bond)

Policy discussions
2011 Metric for short-lived pollutants Use energy added per emission. Shows atmosphere & snow contributions to warming/cooling. (Bond, Zarzycki, Flanner, Koch)
2007 Why not black carbon? Reasons why aerosols don't end up in climate policy; reasons why those reasons aren't supportable (Bond)
2005 Can BC save us from global warming? Policy comment on black carbon/climate, including estimate of direct GWP. (Bond & Sun)
2004 Residential fuels and atmospheric chemistry Impact of solid fuels, including daring attempts at combined GWP. (Bond, Venkataraman & Masera)

Source characterization
2014 Brick kilns Emission factors from a few kinds of kilns. First BC measurements. (Weyant et al)
2012 Kerosene lamps Simple kerosene lamps have very high BC emission rates (Lam et al)
2012 PaRTED Crunch real-time combustion emissions into patterns (Chen, Roden, Bond)
2009 Diesel particulate emissions Climate-relevant properties-- EC content, absorption, and water uptake (Subramanian, Bond et al.)
2009 Lab & field cookstoves In-use cookstoves don't behave like lab stoves. Some improved stoves are better. 3 years of doing this stuff. (Roden, Bond & lots of others)
2006 ARACHNE in Honduras Emission factors and optical properties from real cooking fires. (Roden, Bond, Conway & Osorto)
2006 Oil & gas boiler Optical properties, size distributions, etc. Net effect of technology switch.(Bond, Wehner et al.)
2002 Primary particle emissions from residential coal burning Optics & size distribution of chunk coal burning. (Bond, Covert et al.)
1999 Light absorption by particles from a lignite plant. Lignite stoker boiler. Very little absorption. (Bond, Wehner et al.)
1999 Climate-relevant emissions from a lignite plant. Size distributions from stoker boiler. (Wehner, Bond et al.)
1998 Quantifying emissions of light absorption: Measure light absorption at the source. (Bond, Charlson and Heintzenberg)

Analytical techniques (again, mostly absorption, optics & "elemental" carbon)
2014 Carbon in rainwater Comparison of methods for carbon in precip. Be careful when using filters. (Torres et al.)
2009 Nephelometer truncation corrections Need to use size distributions to calculate error when measuring brown carbon.
2008 Physical basis of thermal-optical analysis Express the whole mess as a matrix reactor equation. How to live with an underdetermined system. (Boparai, Lee & Bond)
2007 Beads on fiber filters Absorbing liquid particles on filter samples alter absorption. (Subramanian, Roden, Boparai, Bond)
1999 Calibration of light absorption measurements: The infamous PSAP calibration paper. (Bond, Anderson and Campbell)

Process modeling
2014 CCN sensitivity No clouds from diesel engines until high supersat. Then depends on secondary condensation. (Fierce, Riemer & Bond)

Models of radiative impacts and climate forcing
2010 Vertical distribution BC altitude: 25% uncertainty in forcing. (Zarzycki and Bond)
2007 Future forcing Future climate forcing by individual source sectors. (Koch, Bond, Streets, Unger)
2007 Forcing by individual sectors Present-day climate forcing by individual source sectors. (Koch, Bond et al.)

Emissions from South Asian brick production
C. Weyant, V. Athalye, S. Ragavan, U. Rajarathnam, D. Lalchandani, S. Maithel, E. Baum, and T. C. Bond
Environmental Science and Technology, 87, 189-199, 2014

Thirteen South Asian brick kilns were tested to quantify aerosol and gaseous pollutant emissions. Particulate matter (PM2.5), carbon monoxide (CO), and optical scattering and absorption measurements in the exhaust of six kiln technologies demonstrate differences in overall emission profiles and relative climate warming resulting from kiln design and fuel choice. Emission factors differed between kiln types, in some cases by an order of magnitude. The kilns currently dominating the sector had the highest emission factors of PM2.5 and light absorbing carbon, while improved Vertical Shaft and Tunnel kilns were lower emitters. An improved version of the most common technology in the region, the zig-zag kiln, was among the lowest emitting kilns in PM2.5, CO, and light absorbing carbon. Emission factors measured here are lower than those currently used in emission inventories as inputs to global climate models; 85% lower (PM2.5) and 35% lower for elemental carbon (EC) for the most common kiln in the region, yet the ratio of EC to total carbon was higher than previously estimated (0.96 compared to 0.47). Total annual estimated emissions from the brick industry are 120 Tg CO2, 2.5 Tg CO, 0.19 Tg PM2.5, and 0.12 Tg EC.

Global emission projections of particulate matter (PM): II. Uncertainty analyses of on-road vehicle exhaust emissions, Atmospheric Environment
F. Yan, E. Winijkul, T. C. Bond and D.G. Streets
Atmospheric Environment, 87, 189-199, 2014

Estimates of future emissions are necessary for understanding the future health of the atmosphere, designing national and international strategies for air quality control, and evaluating mitigation policies. Emission inventories are uncertain and future projections even more so, thus it is important to quantify the uncertainty inherent in emission projections. This paper is the second in a series that seeks to establish a more mechanistic understanding of future air pollutant emissions based on changes in technology. The first paper in this series (Yan et al., 2011) described a model that projects emissions based on dynamic changes of vehicle fleet, Speciated Pollutant Emission Wizard-Trend, or SPEW-Trend. In this paper, we explore the underlying uncertainties of global and regional exhaust PM emission projections from on-road vehicles in the coming decades using sensitivity analysis and Monte Carlo simulation. This work examines the emission sensitivities due to uncertainties in retirement rate, timing of emission standards, transition rate of high-emitting vehicles called “superemitters”, and emission factor degradation rate. It is concluded that global emissions are most sensitive to parameters in the retirement rate function. Monte Carlo simulations show that emission uncertainty caused by lack of knowledge about technology composition is comparable to the uncertainty demonstrated by alternative economic scenarios, especially during the period 2010-2030.

Measuring organic carbon and black carbon in rainwater: Evaluation of methods
A. Torres, T. C. Bond, C. Lehmann, R. Subramanian, and O. L. Hadley
Aerosol Science and Technology, 48, 239-250, 2014

Measuring wet deposition of organic carbon (OC) and black carbon (BC) is crucial for the complete understanding of the global circulation, lifetime, and radiative forcing of these aerosols. There is currently no accepted standard analytical method for measuring OC and BC concentration in precipitation. Different analytical methods have been employed for this purpose, but their feasibility has yet to be assessed. This manuscript evaluates the use of thermal-optical analysis (TOA), single-particle soot photometry (SP2), and ultraviolet-visible (UV/VIS) spectrophotometry for measuring BC in precipitation. In addition, total organic carbon (TOC) analysis was evaluated for the measurement of dissolved organic carbon (DOC) in precipitation. Potential interferences and sources of bias were assessed for each method. Precipitation samples and reference materials containing carbon particles generated from wood combustion and a natural gas diffusion flame were used in this study. The UV/VIS spectrophotometer, despite showing linearity with BC concentration, had inadequate sensitivity (18g/L) to measure the low concentrations expected in precipitation. The SP2 analysis was adequate to measure refractory BC in precipitation in terms of precision and detection limit; however, systematic loss was estimated to be 34% (+/- 3%). Sample filtration followed by TOA was inefficient for measuring particulate carbon in rainwater, as the quartz fiber filter captured less than 38% of the BC mass. Filtration was improved by adding salts and acids into the water samples, and ammonium dihydrogen phosphate, (NH4)H2PO4, was determined to be the best additive by increasing the collection efficiency of quartz fiber filters up to 95% (+/- 5%). The TOC analyzer proved to be precise in the expected concentration range (200-5000g-C/L) for measuring DOC and total carbon (TC), including particulate OC and 94% (+/- 2%) of the refractory BC in solution.

When is cloud condensation nuclei activity sensitive to particle characteristics at emission?
Laura Fierce, Nicole Riemer and Tami C. Bond
Journal of Geophysical Research, 118(24), 13476-13488, 2013

The cloud condensation nuclei (CCN) activity of an aerosol population depends on individual particles' size and composition. However, these properties are modified shortly after emission by condensation of semivolatile substances and coagulation with other particles. It is, therefore, unclear to what extent particle characteristics at emission affect CCN activity after aging by condensation and coagulation. We present a process-level analysis of particles emitted from a particular source, diesel engines, in which we isolate the separate effects of condensation and coagulation on the CCN activation of primary aerosol. We simulated aerosol dynamics in a polluted area with the Particle Monte Carlo model coupled to the Model for Simulating Aerosol Interactions and Chemistry and evaluated three factors influencing particle CCN activity shortly after emission: (1) particle characteristics at the time of emission, (2) aging conditions near the emission source, and (3) the water vapor supersaturation at which CCN activity is evaluated. CCN concentrations were sensitive to particle properties at emission only under specific environmental conditions. Diesel emissions did not strongly influence local CCN concentrations at low cloud supersaturation thresholds (s<0.2%), regardless of particle characteristics at emission or aging conditions. At higher supersaturation thresholds (s>0.2%) and under conditions of rapid secondary aerosol formation, changes in CCN concentrations showed a greater sensitivity to particles' emission size than composition.

Household Light Makes Global Heat: High Black Carbon Emissions From Kerosene Wick Lamps
Nicholas L. Lam,Yanju Chen, Cheryl Weyant, Chandra Venkataraman, Pankaj Sadavarte, Michael A. Johnson, Kirk R. Smith, Benjamin T. Brem, Joseph Arineitwe, Justin E. Ellis, Tami C. Bond
Environmental Science and Technology, 46: 13531-13528, 2012

Kerosene-fueled wick lamps used in millions of developing-country households are a significant but overlooked source of black carbon (BC) emissions. We present new laboratory and field measurements showing that 7-9% of kerosene consumed by widely used simple wick lamps is converted to carbonaceous particulate matter that is nearly pure BC. These high emission factors increase previous BC emission estimates from kerosene by 20-fold, to 270 Gg/year (90% uncertainty bounds: 110, 590 Gg/year). Aerosol climate forcing on atmosphere and snow from this source is estimated at as 22 mW/m2 (8, 48 mW/m2 ), or 7% of BC forcing by all other energy-related sources. Kerosene lamps have affordable alternatives that pose few clear adoption barriers and would provide immediate benefit to user welfare. The net effect on climate is definitively positive forcing as co-emitted organic carbon is low. No other major BC source has such readily available alternatives, definitive climate forcing effects, and co-benefits. Replacement of kerosene-fueled wick lamps deserves strong consideration for programs that target short-lived climate forcers.

Characterizing Biofuel Combustion with Patterns of Real-Time Emission Data (PaRTED)
Yanju Chen, Christoph A. Roden, Tami C. Bond
Environmental Science and Technology, 46: 6110-6177, 2012

Emission properties and quantities from combustion sources can vary significantly during operation, and this characteristic variability is hidden in the traditional presentation of emission test averages. As a complement to the emission test averages, we introduce the notion of statistical pattern analysis to characterize temporal fluctuations in emissions, using cluster analysis and frequency plots. We demonstrate this approach by comparing emissions from traditional and improved wood-burning cookstoves under in-field conditions, and also to contrast laboratory and in-field cookstove performance. Compared with traditional cookstoves, improved cookstoves eliminate emissions that occur at low combustion efficiency. For cookstoves where the only improvement is an insulated combustion chamber, this change results in emission of more light-absorbing (black) particles. When a chimney is added, the stoves produce more black particles but also have reduced emission factors. Laboratory tests give different results than in-field tests, because they fail to reproduce a significant fraction of low-efficiency events, spikes in particulate matter (PM) emissions, and less-absorbing particles. These conditions should be isolated and replicated in future laboratory testing protocols to ensure that stove designs are relevant to in-use operation.

Global emission projections of particulate matter (PM): I. Exhaust emissions from on-road vehicles
Fang Yan, Ekbordin Winijkul, Soonkyu Jung, Tami C. Bond and David G. Streets
Atmospheric Environment 45, 4830-4844, 2011

We present global emission projections of primary particulate matter (PM) from exhaust of on-road vehicles under four commonly-used global fuel use scenarios from 2010 to 2050. The projections are based on a dynamic model of vehicle population linked to emission characteristics, SPEW-Trend. Unlike previous models of global emissions, this model incorporates more details on the technology stock, including the vehicle type and age, and the number of emitters with very high emissions (“superemitters”). However, our estimates of vehicle growth are driven by changes in predicted fuel consumption from macroeconomic scenarios, ensuring that PM projections are consistent with these scenarios. Total emissions are then obtained by integrating emissions of heterogeneous vehicle groups of all ages and types. Changes in types of vehicles in use are governed by retirement rates, timing of emission standards and the rate at which superemitters develop from normal vehicles. Retirement rates are modeled as a function of vehicle age and income level with a relationship based on empirical data, capturing the fact that people with lower income tend to keep vehicles longer. Adoption dates of emission standards are either estimated from planned implementation or from income levels.

We project that global PM emissions range from 1100 Gg to 1360 Gg in 2030, depending on the scenario. An emission decrease is estimated until 2035 because emission standards are implemented and older engines built to lower standards are phased out. From 2010 to 2050, fuel consumption increases in all regions except North America, Europe and Pacific, according to all scenarios. Global emission intensities decrease continuously under all scenarios for the first 30 years due to the introduction of more advanced and cleaner emission standards. This leads to decreasing emissions from most regions. Emissions are expected to increase significantly in only Africa (1.2-3.1% per year). Because we have tied emission standards to income levels, Africa introduces those standards 30-40 years later than other regions and thus makes a remarkable contribution to the global emissions in 2050 (almost half). All Asian regions (South Asia, East Asia, and Southeast Asia) have a decreasing fractional contribution to global totals, from 32% in 2030 to around 22% in 2050. Total emissions from normal vehicles can decrease 1.3-2% per year. However, superemitters have a large effect on emission totals. They can potentially contribute more than 50% of global emissions around 2020, which suggests that they should be specifically addressed in modeling and mitigation policies. As new vehicles become cleaner, the majority of on-road emissions will come from the legacy fleet. This work establishes a modeling framework to explore policies targeted at that fleet.

How much can the vertical distribution of black carbon affect its global direct radiative forcing?
Colin M. Zarzycki and Tami C. Bond
Geophysical Research Letters, 37, L20807, doi:10.1029/2010GL044555, 2010

Black carbon (BC) has an increased forcing per unit mass when it is located above reflective clouds. To explore sensitivity of forcing to aerosol vertical location, we used a column radiative transfer model to produce globally-averaged values of normalized direct radiative forcing (NDRF) for BC over and under different types of clouds. We developed a simple column-weighting scheme based on the mass fractions of BC that are over and under clouds in measured vertical profiles. The resulting NDRF is in good agreement with global 3-D model estimates, supporting the column-weighted model as a tool for exploring uncertainties due to diversity in vertical distribution. BC above low clouds accounts for about 20% of the global burden but 50% of the forcing. We estimate maximum-minimum spread in NDRF due to modeled profiles as about 40% and uncertainty as about 25%. Because models overestimate BC in the upper troposphere compared with measurements, modeled NDRF might need to be reduced by about 15%. Redistributing BC within the lowest 4 km of the atmosphere affects modeled NDRF by only about 5% and cannot account for very high forcing estimates.

Climate-relevant properties of diesel particulate emissions: Results from a piggyback study in Bangkok, Thailand
R. Subramanian, Ekbordin Winijkul, Tami C. Bond, Worrarat Thiansathit, Nguyen Thi Kim Oanh, Ittipol Paw-armart, and K. G. Duleep
Environmental Science and Technology, 43, 4213-4218, 2009

This paper describes results from a “piggyback” approach to characterizing aerosol emissions to obtain input for large-scale models of atmospheric transport. Particulate and gaseous emissions from diesel trucks, light-duty vehicles and buses were measured by the Bangkok Pollution Control Department as part of the Developing Integrated Emissions Strategies for Existing Land Transport (DIESEL) project. To this effort, we added filter-based measurements of carbonaceous composition, particulate light absorption, and water uptake. We interpret the emission rates in terms of fuel mass. For 88 “normal” diesel vehicles (PM emission rate < 4.7 g/kg), our best estimate of the average PM2.5 emission rate is 2.2±0.5 g/kg, while for 15 high emitters, it is 8.4±1.9 g/kg. The effect of Euro standards on PM emission rates was apparent for heavy-duty vehicles, but not for light-duty vehicles. Emission composition appears relatively consistent, with particulate (artifact-corrected) OC at 17±1% and EC at 40±2% of PM (average and standard error) for 103 pickups, vans, heavy-duty trucks and buses. The median absorption cross-section for EC is 10.5 m2/g at 532 nm. The history of average emission rate and chemical composition during the project suggests that about 25 vehicles can provide a regional PM emission rate, with superemitters considered separately.

Laboratory and field investigations of particulate and carbon monoxide emissions from traditional and improved cookstoves
Christoph A. Roden, Tami C. Bond, Stuart Conway, Anibal Benjamin Osorto Pinel, Nordica MacCarty, and Dean Still
Atmospheric Environment, 43, 1170-1181, 2009

We implemented a program in which emission characterization is enabled through collaborations between academic, US and international non-governmental entities that focus on evaluation, dissemination, and in-use testing, of improved cookstoves. This effort resulted in a study of field and laboratory emissions from traditional and improved biofuel cookstoves. We found that field measured particulate emissions of actual cooking average three times those measured during simulated cooking in the laboratory. Emission factors are highly dependent on the care and skill of the operator and the resulting combustion; these do not appear to be accurately reproduced in laboratory settings. The single scattering albedo (SSA) of the emissions was very low in both lab and field measurements, averaging about 0.3 for lab tests and around 0.5 for field tests, indicating that the primary particles are climate warming. Over the course of three summers in Honduras, we measured field emissions from traditional cookstoves, relatively new improved cookstoves, and ‘‘broken-in’’ improved cookstoves. We found that well-designed improved cookstoves can significantly reduce PM and CO emission factors below traditional cookstoves.
For improved stoves, the presence of a chimney generally resulted in lower emission factors but left the SSA unaffected. Traditional cookstoves had an average PM
emission factor of 8.2 g/kg – significantly larger than previous studies. Particulate emission factors for improved cookstoves without and with chimneys averaged about
6.6 g/kg1 and 4.5 g/kg, respectively. The elemental carbon (EC) fraction of PM varied significantly between individual tests, but averaged about 25% for each of the categories.

Color of brown carbon: A model for ultraviolet and visible light absorption by organic carbon aerosol
Haolin Sun, Laura Biedermann, and Tami C. Bond
Geophysical Research Letters 34, L17813, doi: 10.1029/2007GL029797, 2007

We recommend ultraviolet and visible absorption spectra to represent particular types of atmospheric organic particles. Spectra of liquids and particles can be compared using the absorption coefficient of bulk material divided by material density. Reported absorption by combustion-derived aerosol is greater than that of organic material isolated by humic acid extraction. We analyze ultraviolet and visible spectra of over 200 organic compounds, concluding that visible absorption may be attributable to n->pi* electronic transitions in a small fraction of oxygenated compounds. Absorption spectra can be communicated using the band-gap and Urbach relationships instead of the absorption Angstrom exponent. Water-soluble atmospheric aerosol has a band-gap of about 2.5 eV; insoluble combustion aerosol may have a lower band-gap and higher absorption. Although different types of organic carbon may exhibit a continuum in absorption, there is a sharp distinction between the most-absorbing organic carbon and black carbon.

Historical Emissions of Black and Organic Carbon Aerosol from Energy-Related Combustion, 1850-2000
Tami C. Bond, Ekta Bhardwaj, Rong Dong, Rahil Jogani, Soonkyu Jung, Christoph Roden, David G. Streets, Nina M. Trautmann
Global Biogeochemical Cycles 21, GB2018, doi:10.1029/2006GB002840, 2007

We present an emission inventory of primary black carbon (BC) and primary organic carbon (OC) aerosols from fossil fuel and biofuel combustion between 1850 and 2000. We reconstruct fossil fuel consumption and represent changes in technology on a national and sectoral basis. Our estimates rely on new estimates of biofuel consumption, and updated emission factors for old technologies. Emissions of black carbon increase almost linearly, totaling about 1000 Gg in 1850, 2200 Gg in 1900, 3000 Gg in 1950, and 4400 Gg in 2000. Primary organic carbon shows a similar pattern, with emissions of 4100 Gg, 5800 Gg, 6700 Gg, and 8700 Gg in 1850, 1900, 1950, and 2000 respectively. Biofuel is responsible for over half of BC emission until about 1890, and dominates energy-related primary OC emission throughout the entire period. Coal contributes the greatest fraction of BC emission between 1880 and 1975, and is overtaken by emissions from biofuel around 1975, and by diesel engines around 1990. Previous work suggests a rapid rise in BC emissions between 1950 and 2000. This work supports a more gradual increase between 1950 and 2000, similar to the increase between 1850 and 1925; implementation of clean technology is a primary reason.

Global Biofuel Use, 1850-2000
Suneeta D. Fernandes, Nina M. Trautmann, David G. Streets, Christoph A. Roden and Tami C. Bond
Global Biogeochemical Cycles 21, GB2019, doi:10.1029/2006GB002836

This paper presents annual, country-level estimates of biofuel use for the period 1850-2000. We estimate that global biofuel consumption rose from about 1000 Tg in 1850 to 2460 Tg in 2000, an increase of 140%. In the late 19th century, biofuel consumption in North America was very high, ~220-250 Tg/yr, because widespread land clearing supplied plentiful fuelwood. At that time biofuel use in Western Europe was lower, ~180-200 Tg/yr. As fossil fuels became available, biofuel use in the developed world fell. Compensating changes in the regional patterns of biofuel use caused global consumption to remain remarkably stable between 1850 and 1950 at ~1200 ±200 Tg/yr. It was only after World War II that biofuel use began to increase more rapidly in response to population growth in the developing world. Between 1950 and 2000, biofuel use in Africa, South Asia, and Southeast Asia grew by 170%, 160%, and 130%, respectively.

Yellow Beads and Missing Particles: Trouble Ahead for Filter-Based Absorption Measurements
R. Subramanian, Christoph A. Roden, Poonam Boparai and Tami C. Bond
Aerosol Science and Technology 41, 630-637, 2007

Particulate emissions from low-temperature biomass burning are dominated by organic matter. Here, we show that such particles have a liquid, bead-like appearance when collected on fibrous filters, and their numbers are far less than expected for solid spherical particles. These shapes are in line with published drop-on-fiber theories for liquids entrained on filaments. A smoldering pine sample is yellowish and chars substantially in thermal-optical analysis (TOA), indicating that such liquid particles could affect both TOA and absorption measurements of such samples. Similar colored samples collected in the field from burning of rice-straw and cook stove emissions also show a similar liquid appearance.

Linking future aerosol radiative forcing to shifts in source activities
Dorothy Koch, Tami C. Bond, David Streets, and Nadine Unger
Geophysical Research Letters, 34, L05821, doi:10.1029/2006GL028360.

We model future direct radiative forcings of the major anthropogenic aerosol species, sulfate, black and organic carbon, within industrial, power, transport, and residential sectors and biomass burning. A sectoral perspective helps to inform mitigation directions. More accurate projections are facilitated by recent carbonaceous aerosol emission estimates that incorporate projected technology changes, now available for the Intergovernmental Panel on Climate Change scenarios A1B and B1, for 2030 and 2050. Net present-day model anthropogenic forcing is-0.11Wm2. By 2050 this doubles (A1B) or drops by 30% (B1), depending mostly on sulfate changes in the industry and power sectors. Present-day (nonbiomass burning) BC forcing comes mostly from residential sources (+0.09Wm2), however this is projected to decrease by more than a factor of 10 by 2050. Future BC forcing is projected to come mostly from transport, changing from +0.06 W m2 in 2000 to +0.04 (B1) or +0.07 W m2 (A1B) by 2050.

Global Impacts of Aerosols from Particular Source Sectors and Regions
Dorothy Koch, Tami C. Bond, David Streets, Nadine Unger, and Guido R. van der Werf
Journal of Geophysical Research, 112, D02205, doi:10.1029/2005JD007024.

We study the impacts of present-day aerosols emitted from particular regions and from particular sectors, as predicted by the Goddard Institute for Space Studies GCM. We track the distribution and direct radiative forcing of aerosols, including sulfate and black and organic carbon, emitted from major source regions (North America, Europe, south Asia, Southeast Asia, South America, and Africa). We also partition the emissions by sector, including industrial, power, residential, transport, biomass burning, and natural. Southeast Asia produces 15% and 10% of the world’s black carbon and sulfate and exports over 2/3 of this burden over the Northern Hemisphere. About 1/2 of the SO2 emitted by Southeast Asia and Europe is not converted to sulfate because of oxidant limitation. Although Africa has the largest biomass burning emissions, South America generates a larger (about 20% of the global carbonaceous) aerosol burden; about 1/2 of this burden is exported and dominates the carbonaceous aerosol load in the Southern Hemisphere. Calculated direct anthropogenic radiative forcings are -0.29, -0.06, and 0.24 Wm-2 for sulfate, organic, and black carbon, respectively. The largest BC radiative forcings are from residential (0.09 W m-2) and transport (0.06 Wm-2) sectors, making these potential targets to counter global warming. However, scattering components within these sectors reduce these to 0.04 and 0.03 Wm-2, respectively. Most anthropogenic sulfate comes from power and industry sectors, and these sectors are responsible for the large negative aerosol forcings over the central Northern Hemisphere.

Limitations in the Enhancement of Visible Light Absorption due to Mixing State
T. C. Bond, G. Habib, and R. W. Bergstrom
Journal of Geophysical Research 111, D20211, doi:10.1029/2006JD007315, 2006

Absorption by light absorbing carbon (LAC) particles increases when the carbon is mixed with other material, and this change affects climate forcing. We investigate this increase theoretically over a realistic range of particle sizes. Perfect mixing at the molecular level often overestimates absorption. Assuming that LAC is coated by a concentric shell of weakly-absorbing material, we calculate absorption by a range of realistic particle sizes and identify regimes in which absorption behaves similarly. We provide fits to amplification in five regions: (1) small cores and (2) intermediate cores, both with large shells; (3) small to intermediate cores with intermediate shells; (4) cores with growing shells; and (5) intermediate to large cores with large shells. Amplification in region 1 is highest but physically implausible. Amplification in region 5 is constant at about 1.9 and represents an asymptote for particles with broad size distributions. Because absorption by aggregates is amplified by about 1.3 above spherical particles, and that factor is lost when particles are coated, we suggest that absorption by aged aerosol is about 1.5 times greater than that of fresh aerosol. The rate at which particles acquire sufficient coating to increase their original diameter by 60% is important in determining total absorption during their atmospheric lifetimes. Fitted amplification factors are not very sensitive to assumed refractive index of LAC, and can be used even in simple models.

Emission Factors and Real-time Optical Properties of Particles Emitted from Traditional Wood Burning Cookstoves
C. Roden, T. C. Bond, S. Conway, and A. B. Osorto Pinel
Environmental Science and Technology 40, 6750-6757, 2006

It is estimated that the combustion of biofuel generates 20% of all carbonaceous aerosols, yet little is known about the properties of these particles.  We designed and built a portable, battery-operated emission sampling cart to measure real-time optical properties and other emission characteristics of biofuel cookstoves in Honduras.  We found average particulate emission factors of 10g/kg, much higher than emission factors found in previous laboratory studies.  During strongly flaming events, we observed very dark particles with low instantaneous single scatter albedos. Elemental carbon to total carbon ratios ranged from 0.07 to 0.64, confirming that high elemental carbon fractions can be emitted from biofuel combustion.  Absorption Ångstrom exponents, representing the dependence of absorption on wavelength, ranged from 1 to 5. Strongly-absorbing particles with absorption inversely dependent on wavelength were emitted separately from weakly-absorbing particles with strong wavelength dependence of absorption.  These distinct phases exhibited during combustion suggest that carbonaceous aerosols from biofuel combustion are externally mixed at emission.

Climate-Relevant Properties of Primary Particulate Emissions from Oil and Natural Gas Combustion
T. C. Bond, B. Wehner, A. Plewka, A. Wiedensohler, J. Heintzenberg, and R. J. Charlson
Atmospheric Environment, 40, 3574-3587, 2006

We report emissions of mass, light absorption, particle number, chemical composition and size-resolved organic species from an industrial boiler that burned natural gas and residual oil. Organic compounds detected from oil combustion are mainly alkanes; it is not a major source of identifiable polyaromatic hydrocarbons. Elemental carbon and organic carbon make up approximately 38% and 15% of the particles from oil burning, respectively. Mass emissions from natural gas were below detection limits. A number peak of ultrafine aerosol (diameters lower than 10 nm) was always associated with oil burning. Burning at full power produced the greatest number of particles in the accumulation mode. Natural gas also produced fine particles, but at a much lower rate. The emission rate of light-absorbing particles from this relatively new boiler is lower than that in current emission inventories. However, real-time measurements show a large contribution to emitted light absorption from boiler warm-up and transients, even those with very short durations. The measured absorption is best explained with a constant absorption cross-section for EC, rather than predictions based on size distribution or mixed aerosol; this finding is consistent with EC in fractal-aggregate form. We compare the emissions with those of a lignite stoker, which this boiler replaced during environmental cleanup in the mid-1990s. Emissions of mass, light absorption and particles are lowest from natural gas, but the oil boiler is also a substantial improvement: emissions of particulate matter are 100 times lower, and emitted absorption is three times lower. However, the oil-burning emissions have a greater net warming effect per mass than those of the lignite plant.

Can Reducing Black Carbon Emissions Counteract Global Warming?
T. C. Bond and H. Sun
Environmental Science and Technology, 39, 5921-5926, 2005

Field measurements and model results have recently shown that aerosols may have important climatic impacts. One line of inquiry has investigated whether reducing climate-warming “soot” or “black carbon” aerosol emissions can form a viable component of mitigating global warming. We review and acknowledge scientific arguments against considering aerosols and greenhouse gases in a common framework, including the differences in the physical mechanisms of climate change and relevant time scales. We argue that such a joint consideration is consistent with the language of the United Nations Framework Convention on Climate Change. We synthesize results from published climate-modeling studies to obtain a global warming potential for black carbon relative to that of CO2 (680 on a 100-year basis). This calculation enables a discussion of cost-effectiveness for mitigating the largest sources of black carbon. We find that many emission reductions are either expensive or difficult to enact when compared with greenhouse gases, particularly in Annex I countries. Finally, we propose a role for black carbon in climate mitigation strategies that is consistent with the apparently conflicting arguments raised during our discussion. Addressing these emissions is a promising way to reduce climatic interference primarily for nations that have not yet agreed to address greenhouse gas emissions, and provides the potential for a parallel climate agreement.

On the Future of Carbonaceous Aerosol Emissions
D. G. Streets, T. C. Bond, T. Lee, and C. Jang
Journal of Geophysical Research, 109 (D24), doi:10.1029/2004JD004902, 2004

This paper presents the first model-based projections of future emissions of the primary carbonaceous aerosols, black carbon (BC) and organic carbon (OC). The projections build on a new 1996 inventory of present-day emissions that contains detailed fuel, technology, sector, and world-region specifications. The forecasts are driven by two IPCC scenarios, A1B and B1 out to 2030, incorporating not only changing patterns of fuel use but also technology development. Emissions from both energy generation and open biomass burning are included. We project that global BC emissions will decline by 5% under the IPCC A1B scenario by 2030 and by 30% under the B1 scenario. We project that OC emissions will decline by 16% under A1B and 29% under B1. The introduction of advanced technology with lower emission rates, as well as a shift away from the use of traditional solid fuels in the residential sector, more than offsets the increased combustion of fossil fuels worldwide. We estimate that there are additional reductions of 15-30% possible, if some other, more drastic measures could be implemented. Though emissions generally are expected to improve, in some parts of the world—particularly South America, Northern Africa, the Middle East, South Asia, Oceania, and Southeast Asia— we project increasing BC emissions under the A1B scenario. Particularly difficult to constrain are BC emissions from the transport sector, which are projected to increase under both scenarios. We expect that the global BC/OC emission ratio for energy sources will increase under both scenarios and for all sources under A1B; this signifies a net shift toward increased global warming.

Global Atmospheric Impacts of Residential Fuels
T. C. Bond, C. Venkataraman, and O. Masera
Energy for Sustainable Development VIII (3), 54-66, 2004

We discuss the contribution of residential fuels to atmospheric composition on very large scales. The impacts of increased pollutant concentration may affect the behavior of the Earth-atmosphere system. We discuss the various species that lead to these changes and examine emissions of air pollutants from residential fuels in relation to emissions from other sources. We also present modeled atmospheric concentrations and identify regions in which residential fuels contribute greatly to the atmospheric aerosol. Finally, we compare total emissions from a variety of residential end-use technologies, with the implication that improvements could lead to a cleaner atmosphere on scales that are much larger than typically considered.

A Technology-Based Global Inventory of Black and Organic Carbon Emissions from Combustion
T. C. Bond, D. G. Streets, K. F. Yarber, S. M. Nelson, J.-H. Woo, Z. Klimont
Journal of Geophysical Research, 109, D14203, doi:10.1029/2003JD003697, 2004.

We present a global tabulation of black carbon (BC) and primary organic carbon (OC) particles emitted from combustion. We include emissions from fossil fuels, biofuels, open biomass burning, and burning of urban waste. Previous “bottom-up” inventories of black and organic carbon have assigned emission factors based on fuel type and economic sector alone. Because emission rates are highly dependent on combustion practice, we consider combinations of fuel, combustion type, and emission controls, and their prevalence on a regional basis. Central estimates of global annual emissions are 8.0 Tg for black carbon and 33.9 Tg for organic carbon. These estimates are lower than previously-published estimates by 25 to 35%. The present inventory is based on 1996 fuel-use data, updating previous estimates that have relied on consumption data from 1984. An offset between decreased emission factors and increased energy use since the base year of the previous inventory prevents the difference between this work and previous inventories from being greater. The contributions of fossil fuel, biofuel, and open burning are estimated as 38%, 20%, and 42% respectively for BC, and 7%, 19%, and 74% respectively for OC. We present a bottom-up estimate of uncertainties in source strength by combining uncertainties in particulate matter emission factors, emission characterization, and fuel use. The total uncertainties are about a factor of two, with uncertainty ranges of 4.3 to 22 Tg/year for BC and 17 to 77 Tg/year for OC. Low-technology combustion contributes greatly to both the emissions and to the uncertainties. Advances in emission characterization for small residential, industrial, and mobile sources, and top-down analysis combining field measurements and transport modeling with iterative inventory development, will be required to reduce the uncertainties further.

An inventory of gaseous and primary aerosol emissions in Asia in the year 2000
D. G. Streets, T. C. Bond, G. R. Carmichael, S. D. Fernandes, Q. Fu, D. He, Z. Klimont, S. M. Nelson, N. Y. Tsai, M. Q. Wang, J.-H. Woo, and K. F. Yarber
 Journal of Geophysical Research, 108(D21), 8809, doi:10.1029/2002JD003093, 2003
An inventory of air pollutant emissions in Asia in the year 2000 is developed to support atmospheric modeling and analysis of observations taken during the TRACE-P experiment funded by the National Aeronautics and Space Administration (NASA) and the ACE-Asia experiment funded by the National Science Foundation (NSF) and the National Oceanic and Atmospheric Administration (NOAA). Emissions are estimated for all major contributing sources, including biomass burning, in 64 regions of Asia. We estimate total Asian emissions as follows: 34.3 Tg SO2, 26.8 Tg NOx, 9870 Tg CO2, 279 Tg CO, 107 Tg CH4, 52.2 Tg NMVOC, 2.54 Tg black carbon (BC), 10.4 Tg organic carbon (OC), and 27.5 Tg NH3. In addition, NMVOC are speciated into 19 sub-categories according to functional groups and reactivity. Thus, we are able to identify the major source regions and types for many of the significant gaseous and particle emissions that influence pollutant concentrations in the vicinity of the TRACE-P and ACE-Asia field measurements. Emissions in China dominate the signature of pollutant concentrations in this region, so special emphasis has been placed on the development of emission estimates for China. China’s emissions are determined to be as follows: 20.4 Tg SO2, 11.4 Tg NOx, 3820 Tg CO2, 116 Tg CO, 38.4 Tg CH4, 17.4 Tg NMVOC, 1.05 Tg BC, 3.4 Tg OC, and 13.6 Tg NH3. Emissions are gridded at a variety of spatial resolutions from 1º × 1º to 30 sec × 30 sec, using the exact locations of large point sources and surrogate GIS distributions of urban and rural population, road networks, land-cover, ship lanes, etc. The gridded emission estimates have been used as inputs to atmospheric simulation models and have proven to be generally robust in comparison with field observations, though there is reason to think that CO emissions may be under-estimated. Monthly emission estimates for China are developed for each species to aid TRACE-P and ACE-Asia data interpretation. During the observation period of March/April, emissions are roughly at their average values (one-twelfth of annual). Uncertainties in the emission estimates, measured as 95% confidence intervals, range from a low of ±16% for SO2 to a high of ±450% for OC.

Primary particle emissions from residential coal burning: optical properties and size distributions
Tami C. Bond, David S. Covert, John C. Kramlich, Timothy V. Larson, Robert J. Charlson
Journal of Geophysical Research, 107(D21), 8347, doi:10.1029/2001JD000571, 2002
Particles generated by combustion of fossil fuels contribute to climate forcing by absorbing and scattering visible light. Residential combustion takes place in homes for heating or cooking purposes and is thought to contribute a large fraction of the global burden of anthropogenic primary particles. We present optical properties and size distributions of particulate matter emitted from three types of coal burned in residential combustors: bituminous coal, hard coal briquettes and lignite. Emissions from these coals differ significantly and can be partially explained by differences in coal composition. For bituminous coal, particulate matter emission factors are somewhat greater than those used in current emission inventories. We observe particles for which the light absorption is weak and has a strong spectral dependence. For hard coal briquettes and lignite, emitted light absorption is low, and, based on our measurements, current inventories of light-absorbing aerosols significantly overestimate the contribution from these sources. Hard-coal briquettes produce very few particles in the optically-active size range. For all coals tested, the size distributions required to represent the average of the emitted particles are broader than atmospheric size distributions, with geometric standard deviations between 2.2 and 3.0.

Spectral dependence of visible light absorption by carbonaceous particles emitted from coal combustion
Tami C. Bond
Geophysical Research Letters 28 (21), 4075-4078, 2001.
Particles that absorb visible light affect the radiative balance of the Earth, and their optical characteristics are needed to model radiative effects. We explore the strong spectral dependence of light absorption at visible wavelengths observed in particles emitted from coal combustion. We find that a spectrally-dependent imaginary refractive index is the most plausible explanation. Following previous work on the structure of amorphous carbon, we propose that both absorption efficiency and spectral dependence are controlled by the extent of graphitic clusters within the material, and can be explained using the optical band-gap approximation. This hypothesis presents an alternative to the current dichotomy between light-absorbing “black carbon” and non-absorbing “organic carbon”.

Black Carbon Emissions in China
David G. Streets, Shalini Gupta, Stephanie T. Waldhoff, Michael Q. Wang, Tami C. Bond, and Bo Yiyun
Atmospheric Environment 35, 4281-4296, 2001.
Black carbon (BC) is an important aerosol species because of its global and regional influence on radiative forcing and its local effects on the environment and human health. We have estimated the emissions of black carbon in China, where roughly one-fourth of global anthropogenic emissions is believed to originate. China’s high rates of usage of coal and biofuels are primarily responsible for high BC emissions. This paper pays particular attention to the application of appropriate emission factors for China and the attenuation of these emissions where control devices are used. Nevertheless, because of the high degree of uncertainty associated with BC emission factors, we provide ranges of uncertainty for our emission estimates, which are approximately a factor of eight. In our central case, we calculate that BC emissions in China in 1995 were 1,342 Gg, about 83% being generated by the residential combustion of coal and biofuels. We estimate that BC emissions could fall to 1,224 Gg by 2020. This 9% decrease in BC emissions can be contrasted with the expected increase of 50% in energy use; the reduction will be obtained because of a transition to more advanced technology, including greater use of coal briquettes in place of raw coal in cities and towns. The increased use of diesel vehicles in the future will result in a greater share of the transport sector in total BC emissions. Spatially, BC emissions are predominantly distributed in an east-west swath across China’s heartland, where the rural use of coal and biofuels for cooking and heating is widespread. This is in contrast to the emissions of most other anthropogenically derived air pollutants, which are closely tied to population and industrial centers.

Climate-Relevant Particulate Emission Characteristics of a Coal-Fired Heating Plant
B.  Wehner, T. C. Bond, W. Birmili, J. Heintzenberg, A. Wiedensohler, and R.J. Charlson
Environmental Science and Technology, 33, 3881-3886, September 1999
Studies of climate forcing by anthropogenic aerosols require knowledge of the number and properties of the emitted primary aerosol particles. Previous measurements, often limited by instrumental techniques, did not extend far into the nanometer range and considered modern sources with air pollution controls. In the summer of 1996, aerosol size distributions were measured between 3 and 700 nm particle diameter in the exhaust of a low-technology coal-fired heating plant in Leipzig (Germany) using a Twin Differential Mobility Particle Sizer (TDMPS)-System. The total number concentration of particles in the exhaust was approximately 107 particles/ cm3, which is an order of magnitude lower than a previously published calculation based on a nucleation/condensation model. An estimate for the number concentration of primary combustion aerosol particles demonstrates the potential importance of such anthropogenic sources.

Light Absorption by Primary Particle Emissions from a Lignite Burning Plant
T.C. Bond, M. Bussemer, B. Wehner, S. Keller, R. J. Charlson, and J. Heintzenberg
Environmental Science and Technology, 33, 3887-3891, September 1999
Anthropogenic aerosols from the burning of fossil fuels contribute to climate forcing by both scattering and absorbing solar radiation, and estimates of climate forcing by light-absorbing primary particles have recently been published. While the mass and optical properties of emissions are needed for these studies, the available measurements do not characterize the low-technology burning that is thought to contribute a large fraction of light-absorbing material to the global budget. We have measured characteristics of particulate matter (PM) emitted from a small, low-technology lignite-burning plant. The PM emission factor is comparable to those used to calculate emission inventories of light-absorbing particles. However, the fine fraction, the absorbing fraction, and the absorption efficiency of the emissions are substantially below assumptions that have been made in inventories of black carbon emissions and calculations of climate forcing. The measurements suggest that non-black, light-absorbing particles are emitted from low-technology coal burning. As the burning rate increases, the emitted absorption cross-section decreases, and the wavelength dependence of absorption becomes closer to that of black particles.

Calibration and Intercomparison of Filter-Based Measurements of Visible Light Absorption by Aerosols 
Tami C. Bond, Theodore L. Anderson, and Dave Campbell
Aerosol Science and Technology, 30, 582-600, June 1999
Data on light absorption by atmospheric particles are scarce relative to the need for global characterization. Most of the existing data come from methods that measure the change in light transmission through a filter on which particles are collected. We present a calibration of a recently developed instrument for continuous measurement of light absorption (model PSAP, Radiance Research, Seattle, WA) that has been incorporated in several measurement programs. This calibration uses a reference absorption determined as the difference between light extinction and light scattering by unaltered (suspended) particles. In addition, we compare the calibrated PSAP measurement to absorption measurements by two other common filter-based methods: an Integrating Plate and a Laser Integrating Plate. For each method, we assess the responses to both particulate light scattering and particulate light absorption. We find that each of the instruments exhibits a significant response to non-absorbing aerosols and overestimates absorption at 550 nm by suspended particles by about 20%. We also present correction factors for the use of the PSAP.

Quantifying the emission of light-absorbing particles: Measurements tailored to climate studies
Tami C. Bond, Robert J. Charlson, and Jost Heintzenberg
Geophysical Research Letters, 25, 337-340, 1998
The emission rate of light-absorbing aerosols, which contribute to climate forcing, has previously been calculated using mass emission factors combined with fuel-use inventories. Several assumptions made in this calculation lead to overestimates that are significant, but as yet unevaluated. We propose a new measurement approach that augments, and may be preferable to, the mass-based method for modeling radiative forcing by aerosols: direct measurement of the source strength of absorption. This quantity, in units of absorption cross-section per unit time, may be used directly in models of atmospheric dispersion and transport to predict the three-dimensional, time-dependent distribution of the absorption of visible light by aerosols. In demonstration measurements made at a coal-burning plant, the emitted absorption is an order of magnitude lower than would be inferred from the previous method of calculation.

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