2013 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, 2012 through September 30,2013
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.
The following sections describe the ongoing research activities that have been conducted by the UW-Madison and Georgia Tech. These activities are a continuation of previously reported work summarized in the 2013 “Black Carbon” EPA grant progress report. The current progress focuses on continued source sampling with a focus on quantification of organic carbons’ role in multi-wavelength visible light absorption. Source sampling measurement results are being applied to elucidate the observed optical properties of ambient aerosols collected at rural and urban locations in the southeastern United States. Specifically the following research tasks have been conducted: 1) Results from diesel engine testing have been summarized to assess the impact of engine condition and after-treatment on the quantification of black carbon emissions and to estimate the brown carbon contribution of diesel engine sources. 2) Utilizing previous non-absorbing aerosol measurements and a multiple-linear regression data analysis technique, a multi-wavelength source specific correction methodology has been developed to account for multiple scattering and filter loading artifacts associated with the Aethalometer 3) biomass and petroleum combustion emission have been investigated to quantify the light absorption characteristics of organic carbon from these sources and 4) both water soluble and organic solvent soluble fractions have been re-aerosolized to quantify the non-elemental carbon absorption independent of black carbon the black carbon contribution and to assess mixing state’s impact on brown carbon quantification.
Diesel Black Carbon Emissions
Ongoing analysis of diesel emission test results have been used to assess the applicability of an angstrom exponent to predict the multiple wavelength absorption and the sensitivity of light absorption due to OC content (a function of test condition i.e. engine load and emission control).
Test Specific Aethalometer Correction Methodology
In order to appropriately quantify the multi-wavelength absorption coefficient, a test specific correction methodology has been developed that addresses known filter loading and multiple scattering artifacts of the Aethalometer. This correction uses non-absorbing aerosol results discussed in the 2013 progress report and a multiple linear regression data analysis to determine an emission source specific linear slope loading correction as a function of the total attenuation measured from the time of filter advancement on the Aethalometer. It should be noted that the correction can have a substantial impact of over 35% for some wavelengths as compared to non-corrected values.
Source emission optical properties characterization
Multiple source emissions have been investigated to quantify the brown and black carbon optical properties. These results advance the understating of biomass and petroleum combustion emission non-black carbon absorption characteristics. These results show the brown carbon component varies with sources. While the brown carbon absorption shows measureable absorption it clearly is dwarfed by the EC mass absorption of the black carbon component of the aerosol.
Water and organic solvent soluble fraction of emission impact on absorption
Direct measurement of the organic carbon absorption at multiple wavelenghs is conducted through the atomization of both water soluble and organic solvent extractions. This allows a direct measurement of the brown carbon component of absorption from sources. Through the application of these methods we can quantify the organic aerosols absorption without interference from black carbon absorption and mixing state artifacts.
Measurement Strategies for Light Absorbing Aerosols from Modern Diesel Engines
In response to concerns of the human health impacts of particulate matter (PM), regulatory bodies around the world have significantly tightened PM emission limits for diesel engines. These requirements have resulted in considerable changes in engine technology requiring updated Black Carbon measurements from modern engines equipped with after treatment systems. In this study, a variety of common ambient monitoring techniques were used to characterize the light absorbing properties of diesel aerosol. Aerosol optical properties were directly measured with an Aethalometer and Photoacoustic Extinctionmeter and compared to filter based analysis. The results showed excellent correlation (R2 = 0.95) between aerosol light absorption at the short IR wavelength with elemental carbon (EC) concentration from a thermal optical reflectance, NIOSH 5040 method. Resulting EC mass absorption cross-section efficiencies differed by 25 to 30% from manufacturer published values indicating the optical properties used by the instrument may not be representative of modern diesel engine emissions.
Light Absorption measurements
To study the relative contributions of the dominant sources of wavelength dependent light absorption (mobile and stationary source fossil fuel combustion, biomass burning, and biogenic emissions), three sampling sites were selected for the study with varying source profiles. Real-time measurements of absorption coefficients from the UV (370 nm) to NIR (880 nm) wavelengths were carried out at these sites using an Aethalometer (Magee Scientific) at ambient temperature, and after heating the aerosols to 200 C using a thermo-denuder (TD) (Dekati Inc.) to study the effect of volatility of aerosols on absorption.
The values of the absorption coefficients in Atlanta are significantly higher and more variable than for Centreville due to mobile source emissions in the Atlanta region. A clear reduction in absorption coefficient values downstream of the TD at both wavelengths indicates a more volatile fraction of light absorbing aerosols in Atlanta as compared to Centerville throughout the measurement period.
The modal ratio of 0.7 in Atlanta against 0.8 in Centerville indicates that fresh emissions of light absorbing particulate matter including BrC, result in a more volatile light absorption fraction in Atlanta. Relatively low volatility light absorbing aerosols in Centerville suggest that in the Southeastern US biogenic sources are potentially not an important source of light absorption. This is also supported by Aerosol Mass Spectrometer (AMS) data that shows a fairly good correlation between low volatile oxygenated organic aerosol (LVOOA) and BC mass concentration in Centreville.
Time integrated filter and impactor sampling
Simultaneous size-resolved and time-integrated filter sampling was carried out using two MOUDI (Micro Orifice Uniform Deposit Impactor) samplers at all the sites. Aerosol samples were collected on both quartz and Teflon filters. The filters will be extracted and analyzed to determine the light absorption coefficient as a function of wavelength and particle size as well as the relative contributions of both BC and BrC to the light absorption budget. The estimated light absorption will be compared directly to aethalometer measurements over similar time periods.
PM2.5 samples were also collected using a High Volume (HiVol+, Tisch Environmental Inc.) sampler in Atlanta and in Centreville. The HiVol filters will be analyzed for a variety of trace organics that will be used in source apportionment estimates. Also, a fraction of the samples will be re-aerosolized to determine the optical properties of the light absorbing fraction.
Source testing and ambient measurements will continue, allowing further characterization of sources and an investigation of the degree to which brown carbon absorption changes from sources. In particular a focus on connecting source optical properties to ambient measurements will be investigated. A next step priority is to publish our existing results focusing on methodology and the quantification of brown and black carbon absorption from a variety of sources including biomass and petroleum combustion emissions. Finally, application of a Mie theory model will be applied to the solvent extracted atomized aerosol results to calculated wavelength specific refractive indices of different source materials.
The effect of modern diesel engine operation and aftertreatment on black carbon emissions is currently in progress. The methodology for attribution of “Brown Carbon” light absorption at various engine conditions is in development.
Future work will include analyses of near real-time light absorption data, including the influence of thermo-denuding on wavelength dependent light absorption. We will also compare these measurements with chemical composition measurements made with the AMS in both Atlanta and Centreville to determine the general sources of particulate wavelength dependent light absorption. We will also extract and analyze size-resolved BC and BrC from the MOUDI filter samples and estimate relative absorption of both components as a function of size. In addition, HiVol filters will be extracted and analyzed for source determination as well as aerosol light absorbing optical properties.
The focus of Year 3 will be the optical characterization of the organic matter associated with coal combustion and biomass combustion including field studies in India that leverage an NSF project and coal and biomass burning in China in collaboration with researchers in China.