Grantee Research Project Results
2011 Progress Report: Improving chemical transport model predictions of organic aerosol: Measurement and simulation of semivolatile organic emissions from mobile and non-mobile sources
EPA Grant Number: R834554Title: Improving chemical transport model predictions of organic aerosol: Measurement and simulation of semivolatile organic emissions from mobile and non-mobile sources
Investigators: Robinson, Allen , Donahue, Neil
Institution: Carnegie Mellon University
EPA Project Officer: Chung, Serena
Project Period: April 1, 2010 through March 31, 2013
Project Period Covered by this Report: April 1, 2011 through March 31,2012
Project Amount: $500,000
RFA: Novel Approaches to Improving Air Pollution Emissions Information (2009) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Objective:
Organic material contributes a significant fraction of PM2.5 mass across all regions of the United States. However, the sources of ambient organic aerosols are not well understood; for example, state-of-the-art chemical transport models often substantially underpredict measured organic aerosols concentrations. To improve model performance, emissions inventories must explicitly account for the emissions of all low-volatility organic species. This project is characterizing these emissions for important classes of mobile sources. The new emissions data, inventories and other products developed by this project will allow the next generation of chemical transport models to directly simulate gas-particle partitioning of primary organic aerosol and to account for secondary organic aerosol production from emissions of low-volatility organic vapors.
Specific technical objectives are to:
- Investigate methodologies for routine measurement of the volatility distribution of emissions of low volatility organics from combustion systems.
- Measure emission factors for and volatility distributions of low-volatility organics emitted by on-road and non-road mobile sources, including high and low emitting gasoline powered vehicles and diesel vehicles.
- Quantify the effects of emission control technologies such as diesel particulate filters on emissions of low-volatility organics.
- Develop techniques to efficiently update existing emission inventories for use with the volatility basis set approach and the next generation of chemical transport models.
- Conduct PMCAMx simulations to evaluate updated inventories in the Eastern United States and California.
Progress Summary:
Task 1. Characterization of mobile source emissions
Two vehicle test campaigns were conducted this project period: one in June/July 2011 at the California Air Resources Board (CARB) Heavy Duty Vehicle Laboratory in Los Angeles, California, and a second in January/February 2012 at the Haagen-Smit Laboratory in El Monte, California. During each campaign, emissions from a fleet of in-use vehicles were measured while they were operated on a chassis dynamometer. This testing was done in collaboration with the CARB.
At the CARB Heavy Duty Vehicle Laboratory, comprehensive emission measurements were made on three heavy duty diesel tractors selected to span a range of control technologies: a 2006 tractor with no exhaust aftertreatment, a 2007 tractor equipped with a diesel particulate filter (DPF), and a 2010 tractor equipped with a DPF and selective catalytic reduction system. Each tractor was tested on multiple drive cycles, including the Urban Dynamometer Driving Schedule (UDDS), the high-speed cruise mode of the heavy heavy duty diesel truck (HHDDT) schedule, the creep mode of the HHDDT, and idle. The DPF equipped tractors also were tested during a forced DPF regeneration. In addition, the tractors were tested on three different types of fuel: a commercial California ultra-low sulfur diesel (ULSD), a federal high aromatic ULSD, and an ultra-low aromatic ULSD.
The final campaign tested 21 light duty gasoline vehicles and 7 small off road engines (SORE). The light duty gasoline vehicles were recruited from the in-use California fleet and spanned model years from 1987 to 2012. The base test cycle for the light duty gasoline vehicle experiments was the cold-start unified cycle (UC). Selected vehicles also were tested on a hotstart UC, arterial, and freeway cycles. A total of seven SORE were tested: six gasoline from a variety of applications (backpack leaf blower, soil tiller, string lawn trimmer and lawnmower) and a larger diesel engine for a transportation refrigeration unit (TRU). The SORE were taken from the inventory at the CARB Haagen-Smit Laboratory.
A comprehensive set of samples was collected from the constant-volume sampler to characterize the gas- and particulate-phase emissions from every vehicle/source. Measured gaseous emissions included carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), nitric oxide (NO), nitrogen oxides (NOx), and non-methane organic gases (NMOG). Filter samples were collected to determine emissions of gravimetric particulate matter (PM) mass, organic and elemental carbon, and major ions. Finally, quartz filter and Tenax™ TA sorbent samples were collected to characterize low-volatility organic emissions. Comprehensive speciation was performed on the organic emissions, including quantification of carbonyls, C2 to C30 hydrocarbons, and many commonly used molecular markers (e.g., hopanes, steranes, and polycyclic aromatic hydrocarbons).
A number of preliminary conclusions have been drawn from the data collected during these campaigns. First, primary organic aerosol emissions form heavy duty diesel and gasoline powered vehicles are semivolatile, with a significant fraction of the primary organic aerosol evaporating with either gentle heating or isothermal dilution. Second, the gas-particle partitioning of these emissions can be predicted using volatility distributions derived from gas chromatography analysis of quartz filter samples. Third, the emissions of low-volatility organic vapors greatly exceed the emissions of primary organic aerosol.
These results provide a critical test of the new conceptual model for primary organic aerosol emissions and provide important data for emission inventories for next-generation chemical transport models.
Task 2. Develop and test new methodologies for measuring gas-particle partitioning and volatility distributions of primary emissions
We published a paper this project period that describes a new technique for measuring the primary organic aerosol emissions from internal combustion engines. The method combines thermal-optical organic carbon (OC)/elemental carbon (EC) analysis and thermal desorption gas chromatography mass spectrometry (TD-GC-MS) of quartz filter samples collected using a dilution sampler to quantify the total emissions of low-volatility organics and to distribute them across the volatility basis set. These data can be used in conjunction with partitioning theory to predict the gas-particle partitioning and thus the total amount of primary organic aerosol over the entire range of atmospheric conditions. The approach was evaluated using primary organic aerosol emissions data from two gas-turbine engines and one diesel generator. To evaluate the new method, we directly measured the effects of temperature and concentration on gas-particle partitioning of the primary organic aerosol emissions from each source. Predictions based on the volatility distributions derived from the filter analyses are consistent with the direct partitioning measurements. The new approach represents a major improvement over the traditional assumption of nonvolatile primary organic aerosol emissions, which overpredicts actual primary organic aerosol emissions from these sources by a factor of 2-4 at typical ambient concentration and temperature. By using quartz filter samples, this new technique is designed to be applied to routine source test data. Volatility distributions derived using this new approach also can be applied to the large catalog of quartz filter data used by existing emission inventories and models. The emissions data derived from this approach are designed for use in the next generation of chemical transport models and emissions inventories that employ the volatility basis set approach to explicitly track the gas-particle partitioning of primary organic aerosol emissions.
The practical implications of this work are that emerging techniques may provide a quick and relatively simple way to measure the volatility distribution of all low-volatility organics emitted by combustion systems.
Task 3. Field measurements of concentrations and gas-particle partitioning of low volatility organics for model evaluation
We analyzed the filter and sorbent samples collected at the California Institute of Technology campus in Pasadena, California, over a 4-week period during the CalNex Air Quality Study (May/Jun 2010). The samples were collected every 4 hours to characterize the diurnal concentration pattern of low-volatility organics. The samples were analyzed using gas chromatography-mass spectrometry to quantify concentration of individual organic species and to characterize the unresolved complex mixture. The data are being combined with other data from the CalNex campaign to test chemical transport model simulations using the emission data being collected by this project.
Future Activities:
During the upcoming project period, we will focus on the following objectives:
- Finalize analysis of emissions data from all test campaigns.
- Develop preliminary emissions inventory for chemical transport modeling.
- Perform chemical transport model simulations.
- Write papers for publication.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 57 publications | 24 publications in selected types | All 24 journal articles |
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May AA, Saleh R, Hennigan CJ, Donahue NM, Robinson AL. Volatility of organic molecular markers used for source apportionment analysis: measurements and implications for atmospheric lifetime. Environmental Science & Technology 2012;46(22):12435-12444. |
R834554 (2011) R834554 (Final) |
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Presto AA, Hennigan CJ, Nguyen NT, Robinson AL. Determination of volatility distributions of primary organic aerosol emissions from internal combustion engines using thermal desorption gas chromatography mass spectrometry. Aerosol Science and Technology 2012;46(10):1129-1139. |
R834554 (2011) R834554 (Final) |
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Supplemental Keywords:
Airborne particulate matter, aerosol, emission characterization, atmospheric chemistry, regional modeling, source/receptor analysis, photochemistryRelevant Websites:
http://caps.web.cmu.edu/index.html ExitProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.