Grantee Research Project Results
2010 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: March 1, 2010 through February 28,2011
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 aerosol concentrations. To improve model performance, emissions inventories must explicitly account for emissions of all low-volatility organic species. This project characterizes these emissions for important mobile source classes. 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 aerosols and to account for secondary organic aerosol production from all 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
A major activity this project period was conducting the first test campaign in May/June 2010 at the California Air Resources Board Haagen-Smit Laboratory in El Monte, CA. During this campaign, comprehensive emission measurements were made on 47 different light-duty vehicles recruited from the in-use California fleet (45 gasoline-powered vehicles and 2 diesel-powered vehicles). The vehicles were tested using the cold start Unified Cycle while operated on commercial fuels. The exhaust from each vehicle was characterized extensively by collecting samples off a constant volume sampler (CVS), including filter and sorbent samples to characterize the low-volatility organics emissions. A number of preliminary conclusions have been drawn from the data collected during this campaign. First, primary organic aerosol emissions form light-duty vehicles are semivolatile, with a significant fraction of the primary organic aerosols 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 aerosols.
These results provide a critical test of the new conceptual model for primary organic aerosol emissions and provide important data for emissions inventories for next-generation chemical transport models.
Task 2: Development and testing new methodologies for measuring gas-particle partitioning and volatility distributions of primary emissions
We continue to develop two new approaches for characterizing the gas-particle partitioning of primary organic aerosol emissions. First, we sampled emissions from a combustion system into a smog chamber. As emissions continually were added to the chamber, the organic aerosol concentration increased, and dynamic gas-particle conversion was observed at equilibrium. We are using these smog chamber data to constrain and test our estimates of the volatility distributions. Second, volatility distributions were determined by collecting emissions (both vapor and particle phase) onto filters and sorbents. The samples were analyzed by gas chromatography-mass spectrometry (GC-MS) using a boiling point column that allowed us to correlate retention time with effective saturation concentration. We combined the gas-particle partitioning inferred from the GC-MS data with the measured emissions data in the smog chamber. The observed and predicted emissions, which change with dilution, offer a significant improvement compared to the traditional assumption of a nonvolatile primary organic aerosol emission factor.
The practical implications of this work are that emerging techniques may be 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
Filter and sorbent samples were collected on the California Institute of Technology campus in Pasadena, CA, over a 4-week period during the CalNex air quality study (May/June 2010). Samples were collected every four hours to characterize the diurnal concentration pattern of low-volatility organics. The samples are being analyzed using gas chromatography-mass spectrometry to quantify concentrations of individual organic species and to characterize the unresolved complex mixture. The data will be 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 shall focus on the following objectives:
- Conduct the final two test campaigns with the California Air Resources Board (heavy-duty diesel vehicles in summer 2011 and light-duty and non-road sources in winter 2012).
- Finalize the analysis of data from the first test campaign and write papers.
- Develop a preliminary emission inventory for chemical transport modeling using data from the first test campaign and other studies.
Journal Articles:
No journal articles submitted with this report: View all 57 publications for this projectSupplemental Keywords:
Airborne particulate matter, aerosol, emission characterization, atmospheric chemistry, regional modeling, source/receptor analysis, photochemistry.Relevant Websites:
http://caps.web.cmu.edu/index.html
Progress 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.