Sources of Organic Aerosol: Semivolatile Emissions and Photochemical AgingEPA 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 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
The proposed research integrates emissions testing, smog chamber experiments, and regional chemical transport models (CTMs) to investigate the sources of organic aerosol in urban and regional environments.
The objective of this project is to investigate two major revisions to our current conceptual model for organic aerosols: (i) gas-particle partitioning of primary organic aerosol (POA) emissions and significant evaporation of POA at ambient conditions; (ii) photochemical aging of low-volatility organic vapors as an important source of secondary organic aerosols (SOA).
Our approach relies heavily on the “basis set” framework developed at Carnegie Mellon University. The basis set lumps low-volatility organics into a set of “volatility bins” according to their vapor pressures, thereby representing the volatility distribution of the mixture. The volatility basis set, in conjunction with absorptive partitioning theory, is an efficient means for tracking gas-particle partitioning of all organics in CTMs. It also allows for multiple generations of SOA chemistry. Using dilution samplers and a smog chamber, we propose experiments to measure the effects of dilution and temperature on the gas-particle partitioning of organic aerosol from three key source classes: diesel exhaust, gasoline exhaust (with and without a catalytic converter), and wood smoke. These data will be fit using partitioning theory to determine the volatility distribution of the emissions from each source. Smog chamber experiments will be conducted to measure the SOA produced from photo-oxidation of diluted exhaust from each source across a range of atmospheric conditions. In the basis-set framework, the effects of photochemical aging are represented using a transformation matrix that maps more volatile reactant species into lower volatility bins as they undergo oxidation. This matrix will be derived from the chamber data, providing an empirical description of how the initial volatility distribution of the emissions evolves in order to match the SOA produced in the experiments. Finally, results from the experiments will be use to develop a module for CTMs such as PMCAMx and CMAQ to represent gas-particle partitioning and photochemical aging of primary emissions. This module will be implemented in PMCAMx and simulations will be performed to investigate the effects of our proposed revisions on urban and regional air quality and to evaluate model performance.
Expected results from this research include detailed characterization of emissions and gas-particle partitioning of low-volatility organics emitted by the target sources; smog chamber quantification of SOA production from photochemical oxidation of diluted exhaust across a range of atmospheric conditions for each source; development of a CTM module for gas-particle partitioning and photochemical aging of primary emissions; CTM simulations assessing the impacts of these processes on urban and regional OA levels in different seasons; and a detailed evaluation of model predictions using ambient data.