2008 Progress Report: Sources of Organic Aerosol: Semivolatile Emissions and Photochemical Aging

EPA Grant Number: R833748
Title: Sources of Organic Aerosol: Semivolatile Emissions and Photochemical Aging
Investigators: Robinson, Allen , Adams, Peter
Institution: Carnegie Mellon University
EPA Project Officer: Chung, Serena
Project Period: September 1, 2007 through August 31, 2010 (Extended to October 31, 2011)
Project Period Covered by this Report: November 1, 2007 through October 31,2008
Project Amount: $600,000
RFA: Sources and Atmospheric Formation of Organic Particulate Matter (2007) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air

Objective:

1. To determine emission factors for and volatility distributions of low volatility organics emitted by three key sources: a diesel engine, gasoline engine (with and without a catalytic converter), and a wood stove.
2. To measure production of SOA and changes in the volatility distribution by photochemical aging of diluted primary emissions from the three target sources in a smog chamber across a range of atmospheric conditions.
3. To develop a photochemical aging operator, suitable for a regional air quality model, that describes transformations of higher volatility products into lower volatility products for primary emissions from each source class.
4. To develop a module for chemical transport models (CTM) based on the volatility basis-set framework that represents gas-particle partitioning and photochemical aging of primary emissions.
5. To conduct simulations using the CTM PMCAMx to investigate the effects of both gas-particle partitioning and photochemical aging of primary emissions on OA levels in the Eastern US.

Progress Summary:

Organic aerosol (OA) is directly emitted to the atmosphere (primary OA or POA); it is also generated in the atmosphere from gas-phase reactions that form low-volatility products (secondary OA or SOA). Current state-of-the-art models treat POA as nonvolatile and non-reactive. SOA in these models is dominated by the first generation products of very volatile species such as monoterpenes and light aromatics that have low yields (1-4). However, these models often substantially underpredict measured OA (3, 5-7), underscoring the substantial uncertainty regarding the sources of OA. This research investigates two major amendments to our current conceptual model for OA described in a recent paper from our group (8). The first amendment is that we must explicitly account for gas-particle partitioning of primary emissions. The second amendment is to account for SOA formation from lower volatility precursors than those in traditional SOA models.
 
Task 1. Emissions and gas-particle partitioning of low-volatility organics
 
A major goal of this research is to characterize the gas-particle partitioning of POA emissions from important source classes. During this project period the partitioning of POA from a diesel engine and a wood stove was investigated by isothermally diluting the emissions in a smog chamber and by passing them through a thermodenuder. The results illustrate how these two complimentary techniques can be used to constrain the gasparticle partitioning over a wide range of atmospheric conditions. The measurements focused included the most atmospherically relevant conditions, low concentrations and small temperature perturbations. The partitioning of the POA emissions from both sources varied continuously with changing concentration and temperature. In fact, the data indicate that wood smoke and diesel POA are quite “volatile;” for example, almost all of the POA emitted by both sources evaporated at temperatures less than 100 °C. The overall partitioning characteristics of diesel and wood smoke POA are similar, with wood smoke being somewhat less volatile than the diesel exhaust. The gas-particle partitioning of aerosols formed by flash-vaporized engine lubricating oil was also studied. Its partitioning properties are similar to diesel POA.
 
The partitioning data were used to evaluate the sensitivity of the changes in POA mass to changes in temperature and OA concentrations. The sensitivity to changes in temperature ranged from -1% to -6% °C-1 at 25 °C, which are comparable to published data for SOA formed in smog chambers (9). This implies that diurnal and seasonal temperature changes may drive large changes in POA partitioning. At a OA aerosol concentrations of 1 µg m-3 the sensitivity in POA mass to changes in COA is about -3% (µg m-3)-1 versus - 0.9% (µg m-3)-1 at a COA of 10 µg m-3 for both the wood-smoke and the diesel exhaust. Therefore, isothermally diluting POA from very high concentration conditions that exist very near a source to typical ambient concentrations will also cause large changes in POA partitioning.
 
During this project period we also purchased a GERSTEL Thermal desorption system for our Agilent gas-chromatograph mass spectrometer. Funds from this project covered about one-third of the cost with the balance of the funds provided by the COLCOM foundation. This system is being used to thermally desorb TENAX and quartz-filters samples collected to character the emissions of low volatility organic emissions. Work in was initiated this project period to bring this system online and to develop the necessary sampling and analysis protocols for the TENAX sorbent tubes.
 
The practical implications of this work are that both POA in diesel exhaust and wood smoke is semivolatile not non-volatile as currently assumed by chemical transport models for SIP development.
 
Task 2. SOA production from photochemical aging of primary emissions
 
A major research task is to investigate the secondary organic aerosol (SOA) formation from photo-oxidation of emissions in order to better understand the persistent discrepancies between ambient observations and CTM predictions. Currently CTMs underpredict the amount of SOA in many parts of the atmosphere.
 
In this project period, experiments were conducted to investigate the effects of photooxidation on organic aerosol (OA) emissions from flaming and smoldering hard- and soft-wood fires under plume-like conditions. This was done by exposing the dilute emissions from a small wood stove to UV light in a smog chamber and measuring the gas- and particle-phase pollutant concentrations with a suite of instruments including a Proton Transfer Reaction Mass Spectrometer (PTR-MS), an Aerosol Mass Spectrometer (AMS) and a thermodenuder. The experiments highlight how atmospheric processing can lead to considerable evolution of the mass and volatility of biomass burning OA. Photochemical oxidation produced substantial new OA, increasing concentrations by a factor of 1.5 to 2.8 after several hours of exposure to typical summertime hydroxyl radical (OH) concentrations. Less than 20% of this new OA could be explained using a state-of-the-art SOA model and the measured decay of traditional SOA precursors. The thermodenuder data indicate that the primary OA is semivolatile; at 50°C between 50 and 80% of the fresh primary OA evaporated. Aging reduced the volatility of the OA; at 50 °C only 20 to 40% of aged OA evaporated. The predictions of a volatility basis-set model that explicitly tracks the partitioning and aging of low-volatile organics was compared to the chamber data. The OA production can be explained by the oxidation of low-volatility organic vapors; the model can also reproduce observed changes in OA volatility and composition. The model was used to investigate the competition between photochemical processing and dilution on OA concentrations in plumes.
 
During the wood smoke aging experiments, the changes in OA composition were characterized using a unit mass resolution AMS. The results highlight how photochemical processing can lead to considerable evolution of the organic mass composition. With explicit knowledge of the condensed-phase mass spectrum (MS) of the POA emissions from each fire, each MS can be decomposed into primary and residual spectra throughout the experiment. The residual spectra provide an estimate of the composition of the photochemically produced OA. These residual spectra are also very similar to those of the oxygenated OA that dominates ambient AMS datasets. In addition, aged wood smoke spectra are shown to be similar to those from OA created by photo-oxidized dilute diesel exhaust and aged biomass-burning OA measured in urban and remote locations. This demonstrates that the oxygenated OA observed in the atmosphere can be produced by photochemical aging of dilute emissions from different sources operating on fuels containing both modern and fossil carbon.
 
In addition investigating the photo-oxidation of wood smoke, chamber experiments were also performed to measure SOA formation from individual and simple mixtures of intermediate volatility and semivolatile organic compounds (IVOCs and SVOCs). These experiments demonstrate that photo-oxidation of n-heptadecane, a proxy for IVOC emissions, can produce highly oxygenated SOA. The SOA has a calculated O/C ratio of 0.59, which is higher than typical for chamber-generated SOA. The level of oxidation is consistent with multiple generations of oxidation chemistry resulting from OH radical exposure equivalent to ~0.5 days of atmospheric processing under high-NOx and low-OA-concentration conditions. The mass spectrum of the SOA, as measured with a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), is similar to the OOA-2 factor determined for Mexico City. SOA formed from the low-NOx, low-OA-concentration conditions is less oxidized because of differences in the chemical mechanism and less integrated OH exposure. SOA formed from both the oxidation of n-heptadecane under high-NOx, high-OA-concentrations conditions and the oxidation of n-pentacosane, a proxy for semivolatile organic emissions, does not produce highly oxygenated SOA, largely because of the condensation of early-generation oxidation products.
 
There are two practical consequences of this work. First, photo-oxidation of wood smoke produces substantial amounts of SOA that cannot be explained using current atmospheric chemistry models, highlighting the problems with these models. Second, photo-oxidation of low volatility organic vapors can produce SOA with a mass spectrum that is similar to ambient data. Therefore, low-volatility organic vapors appear to be an important class of precursors that is largely unaccounted for in current chemical transport models used for SIP development.
 
Task 3. CTM module development
 
A major objective of this research is to develop a new organic aerosol module for chemical transport models. The module under development accounts for both the gasparticle partitioning and aging of primary emissions using the volatility basis set (VBS) approach. The VBS lumps organics into a set of “volatility bins” that span a basis set of effective saturation concentrations. If this volatility distribution is known, one can calculate the organic aerosol mass from partitioning theory. A volatility operator is used to treat SOA production; this operator represents how the volatility distribution evolves with photochemical aging. The VBS framework has been implement in the chemical transport model (CTM) PMCAMx and is being implement into CMAQ as part of an EPRI supported project.
 
In this project period the experimental data from Task 1 for diesel and wood smoke POA were fit using absorptive partitioning theory to derive a volatility distribution. By combining data from three complimentary techniques -- dilution sampler measurements, in-chamber dilution experiments, and thermodenuder measurements -- we have been able to derive a volatility distribution that describes the gas-particle partitioning of the POA emissions over a wide range of atmospheric conditions. The thermodenuder data were especially useful at constraining the fits in the lowest volatility bins.
 
We also evaluated and updated the aging mechanism proposed by Robinson et al. (8) using the SOA data measured in the wood smoke aging experiments performed in Task 2. The SOA yield, composition, and volatility data were used to assess model performance. The original mechanism predicted the SOA production, but underestimated its oxygen content and overestimated its volatility. The parameters of the volatility operator proposed by Robinson et al. (8) were modified to improve model performance. However, much research remains to define a robust aging operator.
 
The practical results from this task are updated parameters for use in chemical transport models to simulate regional fine particle concentrations.
 
Task 4. Chemical Transport Modeling
  
The chemical transport model PMCAMx was extended to investigate the effects of partitioning and photochemical aging of primary emissions on OA concentrations in the Eastern United States during July 2001 and January 2002. One goal was to help reconcile ambient observations, which show that OA tends to be highly oxidized, and models, which predict that OA concentrations in urban areas are dominated by POA (10, 11). A second goal was to assess whether the revisions help close the persistent gap between predicted and observed OA concentrations (3, 5, 7, 12). A final goal was to investigate the sensitivity of the revised framework to uncertainty in emissions, aging and partitioning.
 
In both the summer and the winter, much of the traditionally defined POA emissions evaporate, creating a large pool of low-volatility organic vapors. During the summertime, photochemical aging of these vapors creates substantial oxygenated OA that is regionally distributed. Little production of oxygenated OA is predicted in the winter because oxidant levels are low. OA formed from the oxidation of low-volatility vapors is most important in and around urban areas located in the northeast and midwest. In rural locations and throughout the southeast, traditional SOA formed from biogenic precursors is predicted to be the dominant class of oxidized OA. The model can not reproduce the large fractional contributions of oxidized OA observed in the atmosphere unless some of the POA in the model evaporates. Sensitivity analysis illustrates that the volatility distribution of emissions and the amount of intermediate volatility compounds not accounted for in current inventories are key uncertainties. At an upper bound, better accounting for emissions of low-volatility organics has the potential to increase summertime OA concentrations in Northeastern and Midwestern cities by as much as 50%.
 
The practical implication of this work is that explicit accounting for partitioning and aging of primary emissions improves predictions of chemical transport models used for SIP development.

Future Activities:

During the upcoming 12 months we shall focus on the following objectives:

  • Measure the SOA production from gasoline vehicle exhaust and compare measurements to predictions of a state-of-the-art SOA model.
  • Quantify the total emissions of low volatility organics using the combination of TENAX sorbent and quartz filters from diesel exhaust.
  • Investigate the gas-particle partitioning of diesel and gasoline vehicle exhaust using a thermodenuder system.
  • References:

    1. Koo, B. Y.; Ansari, A. S.; Pandis, S. N., Integrated approaches to modeling the organic and inorganic atmospheric aerosol components. Atmospheric Environment 2003, 37(34), 4757-4768.
    2. Pun, B. K.; Wu, S. Y.; Seigneur, C.; Seinfeld, J. H.; Griffin, R. J.; Pandis, S. N., Uncertainties in modeling secondary organic aerosols: Three-dimensional modeling studies in Nashville/Western Tennessee. Environmental Science & Technology 2003, 37(16), 3647-3661.
    3. Vutukuru, S.; Griffin, R. J.; Dabdub, D., Simulation and analysis of secondary organic aerosol dynamics in the South Coast Air Basin of California. Journal of Geophysical Research-Atmospheres 2006, 111(D10S12), doi:10.1029/2005JD006139.
    4. Kanakidou, M.; Seinfeld, J. H.; Pandis, S. N.; Barnes, I.; Dentener, F. J.; Facchini, M. C.; Van Dingenen, R.; Ervens, B.; Nenes, A.; Nielsen, C. J., et al., Organic aerosol and global climate modelling: a review. Atmospheric Chemistry and Physics 2005, 5, 1053-1123.
    5. Morris, R. E.; Koo, B.; Guenther, A.; Yarwood, G.; McNally, D.; Tesche, T. W.; Tonnesen, G.; Boylan, J.; Brewer, P., Model sensitivity evaluation for organic carbon using two multi-pollutant air quality models that simulate regional haze in the southeastern United States. Atmospheric Environment 2006, 40(26), 4960-4972.
    6. Held, T.; Ying, Q.; Kleeman, M. J.; Schauer, J. J.; Fraser, M. P., A comparison of the UCD/CIT air quality model and the CMB source-receptor model for primary airborne particulate matter. Atmospheric Environment 2005, 39(12), 2281-2297.
    7. Heald, C. L.; Jacob, D. J.; Park, R. J.; Russell, L. M.; Huebert, B. J.; Seinfeld, J. H.; Liao, H.; Weber, R. J., A large organic aerosol source in the free troposphere missing from current models. Geophysical Research Letters 2005, 32(L18809), doi:10.1029/2005GL023831.
    8. Robinson, A. L.; Donahue, N. M.; Shrivastava, M.; Weitkamp, E. A.; Sage, A. M.; Grieshop, A. P.; Lane, T. E.; Pierce, J. R.; Pandis, S. N., Rethinking organic aerosol: Semivolatile emissions and photochemical aging. Science 2007, 315, 1259-1262.
    9. Stanier, C. O.; Pathak, R. K.; Pandis, S., Measurements of the Volatility of Aerosols from alpha-Pinene Ozonolysis. Environmental Science & Technology 2007, 41(8), 2756-2763.
    10. Karydis, V. A.; Tsimpidi, A. P.; Pandis, S. N., Evaluation of a three-dimensional chemical transport model (PMCAMx) in the eastern United States for all four seasons. Journal of Geophysical Research 2007, 112(D14211), doi:10.1029/2006JD007890.
    11. Gaydos, T. M.; Pinder, R.; Koo, B.; Fahey, K. M.; Yarwood, G.; Pandis, S. N., Development and application of a three-dimensional aerosol chemical transport model, PMCAMx. Atmospheric Environment 2007, 41(12), 2594-2611.
    12. Johnson, D.; Utembe, S. R.; Jenkin, M. E.; Derwent, R. G.; Hayman, G. D.; Alfarra, M. R.; Coe, H.; McFiggans, G., Simulating regional scale secondary organic aerosol formation during the TORCH 2003 campaign in the southern UK. Atmospheric Chemistry and Physics 2006, 6, 403-418.


    Journal Articles on this Report : 6 Displayed | Download in RIS Format

    Other project views: All 83 publications 21 publications in selected types All 21 journal articles
    Type Citation Project Document Sources
    Journal Article Donahue NM, Robinson AL, Pandis SN. Atmospheric organic particulate matter: from smoke to secondary organic aerosol. Atmospheric Environment 2009;43(1):94-106. R833748 (2008)
    R833748 (2010)
    R833748 (Final)
    R833746 (2008)
    R833746 (2009)
    R833746 (2010)
    R833746 (Final)
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  • Journal Article Grieshop AP, Logue JM, Donahue NM, Robinson AL. Laboratory investigation of photochemical oxidation of organic aerosol from wood fires 1: measurement and simulation of organic aerosol evolution. Atmospheric Chemistry and Physics 2009;9(4):1263-1277. R833748 (2008)
    R833748 (2009)
    R833748 (2010)
    R833748 (Final)
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  • Journal Article Grieshop AP, Miracolo MA, Donahue NM, Robinson AL. Constraining the volatility distribution and gas-particle partitioning of combustion aerosols using isothermal dilution and thermodenuder measurements. Environmental Science & Technology 2009;43(13):4750-4756. R833748 (2008)
    R833748 (2009)
    R833748 (2010)
    R833748 (Final)
  • Abstract from PubMed
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  • Journal Article Grieshop AP, Donahue NM, Robinson AL. Laboratory investigation of photochemical oxidation of organic aerosol from wood fires 2: analysis of aerosol mass spectrometer data. Atmospheric Chemistry and Physics 2009;9(6):2227-2240. R833748 (2008)
    R833748 (2009)
    R833748 (2010)
    R833748 (Final)
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  • Journal Article Presto AA, Miracolo MA, Kroll JH, Worsnop DR, Robinson AL, Donahue NM. Intermediate-volatility organic compounds: a potential source of ambient oxidized organic aerosol. Environmental Science & Technology 2009;43(13):4744-4749. R833748 (2008)
    R833748 (2009)
    R833748 (2010)
    R833748 (Final)
    RD834554 (Final)
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  • Journal Article Shrivastava MK, Lane TE, Donahue NM, Pandis SN, Robinson AL. Effects of gas particle partitioning and aging of primary emissions on urban and regional organic aerosol concentrations. Journal of Geophysical Research-Atmospheres 2008;113(D18):D18301 (16 pp.). R833748 (2008)
    R833748 (2009)
    R833748 (2010)
    R833748 (Final)
    R832162 (Final)
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  • Abstract: Wiley-Abstract & Full Text HTML
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  • Supplemental Keywords:

    Airborne particulate matter, aerosol, emission characterization, atmospheric chemistry, regional modeling, source/receptor analysis, photochemistry.

    Relevant Websites:

    http://airquality.web.cmu.eduexit EPA

     

    Progress and Final Reports:

    Original Abstract
  • 2009 Progress Report
  • 2010 Progress Report
  • 2011
  • Final Report