2012 Progress Report: Development of a Quantitative Accounting Framework for Black Carbon and Brown Carbon from Emissions Inventory to ImpactsEPA Grant Number: R835039
Title: Development of a Quantitative Accounting Framework for Black Carbon and Brown Carbon from Emissions Inventory to Impacts
Investigators: Schauer, James J. , Bergin, Michael
Institution: University of Wisconsin - Madison , Georgia Institute of Technology
EPA Project Officer: Chung, Serena
Project Period: October 1, 2011 through September 30, 2014 (Extended to September 30, 2016)
Project Period Covered by this Report: October 1, 2011 through September 30,2012
Project Amount: $899,600
RFA: Black Carbon's Role In Global To Local Scale Climate And Air Quality (2010) RFA Text | Recipients Lists
Research Category: Global Climate Change , Climate Change , Air
The overall goal of this project is to develop a framework, and the necessary supporting data, to quantitatively account for the contributions of source emissions and atmospheric processing to the radiative absorption by carbonaceous aerosols in the atmosphere. This goal will be achieved through two integrated approaches: (1) quantification of the relationships of the optical and chemical properties of the major components of light absorbing carbon in the emissions from key air pollution sources, and (2) elucidating how these relationships evolve during atmospheric processing and transport. The project team will integrate expertise in molecular marker source apportionment tools as well as in the measurement of aerosol optical properties that will provide a mechanism to quantitatively determine the source contributions to light absorbing carbon. The work will combine direct measurements of the emissions of dominant light absorbing carbon sources with field measurements in both urban and background locations to understand the influence of sources and atmospheric aging on aerosol light absorption.
In year 1 of the project, methods for source testing, atmospheric sampling, and the measurement of laboratory and fractionated aerosols were refined and optimized for the project activities. These efforts included the evaluation of thermal denuder techniques to strip brown carbon from aerosols emitted from combustion sources and the generation of organic aerosols extracted from source samples. The activities conducted in Year 1 of the project can be summarized into five major thrusts, which all focus on the development, evaluation, and application of techniques to determine the relative contributions of black carbon (BC) and brown carbon to wavelength dependent particulate absorption. Specifically the following items have been investigated: (1) source testing from a diesel engine under various operating and after treatment configurations to assess impact of mixing state and particle composition of black and brown carbon quantification; (2) suspension of pure absorbing and non-absorbing aerosols to assess measurement techniques, including filter based artifact of the Aethalometer, particularly in the absence of elemental carbon; (3) biomass emissions have been investigated to assess the optical properties of direct emission from the source and compared to resuspened water soluble extracts of biomass particulate matter (PM) to investigate the non-elemental carbon component of biomass emission on scattering and absorption at multiple wavelengths; (4) application of a MIE theory, single spherical particle model of scattering and absorption to compare results to observed optical properties of source and ambient PM; and (5) preliminary field measurements in an urban location (Atlanta) to determine the influence of semi-volatile organic compounds to light absorption.
Source testing optical properties of Diesel Engine Emissions: Over 90 emission tests were conducted at multiple engine operational parameters and with various PM control conditions. Through this manipulation of engine operation and controls, multiple diesel soot mixing states and compositions were investigated. In addition to altering the engine and control operation, emissions were manipulated by both varying dilution ratios, leading to a change in emission aging and through the application of a Thermodenuder to assess the impact of semi-volatile organic compounds on the light absorption and scattering characteristics of diesel emissions.
Suspension of pure absorbing and non-absorbing aerosols: To assess the impacts of non-refractory carbon on black carbon measurements, and to elucidate light absorption measurement artifacts, absorbing and non-absorbing aerosol optical properties were measured under a controlled environment. A variety of both highly absorbing and purely light scattering aerosols were generated using an atomizer/desiccant dryer system, and then selectively sized using a Electrostatic Classifier/Differential Mobility Analyzer (DMA) to create a mono-disperse aerosol at aerodynamic diameters ranging from 50 to 300 nm. The mono disperse aerosol’s optical properties were measured using an AE31 filter based Aethalometer and Radiance Research Nephelometer. In general, the non-absorbing aerosol artifact of the Aethalometer behaves in a predictable manner, i.e an increase of measured scattering by non-absorbing aerosols results in a linear increase of absorption as measured by the Aethalometer. This predictability allows for correction of Aethalometer results, but more importantly the artifact is small compared to measurement of light absorbing aerosol by the Aethalometer.
Optical properties of biomass burning emissions based on resuspended water soluble extracts: In a controlled combustion chamber, biomass emissions (commercially available incense) optical properties were measured at multiple mono-disperse aerodynamic diameters (100 to 300 nm). Emissions were investigated using the TD method to determine the impact semi-volatile organics have on the optical properties at multiple wavelengths. As expected, the biomass shows a strong absorption signal at the lower wavelengths of the AE31, this result continues when looking at resuspended WS fraction of biomass emissions. These tests are an important step towards ongoing efforts in which both the WS and organic solvent soluble fraction of source and ambient materials will be measured using similar techniques. This will allow the measurement of the optical properties of various fractions of PM composition with and without elemental carbon present.
Field measurements in urban Atlanta: The influence black carbon and brown carbon on wavelength dependent light absorption: As a means of characterizing the relative contributions of organic and elemental black carbon (BC) to wavelength dependent light absorption a volatility-based approach was developed for field measurements somewhat similar to that used in the laboratory experiments mentioned above. Two Magee Scientific Multi-wavelength Aethalometers and one Thermo-Scientific Multiangle Aerosol Absorption Photometer (MAAP) were first inter-compared for absorption coefficient measurements in ambient air in urban Atlanta. The purpose of the intercomparision was to ensure that the instruments that would be used in the field volatility studies were in agreement prior to field measurements.
To determine losses through the Dekati Inc. thermal denuder being used in the volatility experiments at room temperature, ambient air was sampled in parallel by two Aethalometer and a MAAP. The comparison of the BC mass concentrations measured from both the Aethalometer show slope and intercept values of 1.01 and 0.91 indicating fairly good agreement. Similarly, MAAP and Aethalometer compared fairly with a slope and intercept of 0.91 and 0.95, respectively at 660 nm.
A set of ambient aerosol measurement in urban Atlanta during the summer from June 25-30 was carried out to study the relative amount of absorption by light absorbing organic carbon aerosols. A 20 percent loss in absorption in the lower wavelength (370 nm) is evident when the aerosols are heated to 100°C. On the contrary, higher wavelength (880 nm) showed only 10 percent loss in absorption due to heating. This loss in absorption could be due to the volatilization of light absorbing organic carbon aerosols.
The focus of Year 2 will be the optical characterization of the organic matter emitted from combustion sources using the methods developed in Year 1 of the projects, through source testing and atmospheric testing. Efforts will be directed at biomass burning and mobile source emissions. Towards the end of Year 2, we expect to start addressing coal combustion aerosol. We plan to further advance our mathematical model calculation in Year 2 to help better explain our atmospheric, source testing, and laboratory observations.