SOA Volatility Evolution: Formation and Oxidation over the Lifecycle of PM2.5EPA Grant Number: R833746
Title: SOA Volatility Evolution: Formation and Oxidation over the Lifecycle of PM2.5
Investigators: Donahue, Neil , Kroll, Jesse H. , Pandis, Spyros N. , Worsnop, Douglas R.
Institution: Carnegie Mellon University , Aerodyne Research Inc.
EPA Project Officer: Chung, Serena
Project Period: September 1, 2007 through August 31, 2011
Project Amount: $599,990
RFA: Sources and Atmospheric Formation of Organic Particulate Matter (2007) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air
Secondary Organic Aerosols are a major, possibly dominant, source of organic PM2.5 that remain enigmatic. Enormous progress has been made in the past 15 years regarding SOA formation, starting with recognition that most SOA products are semivolatile, continuing to a formal description of the thermodynamics of SOA mixtures from Pankow and Odum, and culminating in recent findings that condensed-phase chemistry can significantly alter SOA composition and possibly volatility. However, there remain very substantial gaps between model predictions and observations in almost all facets of organic aerosol behavior, including the primary-secondary and biogenic-anthropogenic ratios.
Our objective is to extend our recently-developed volatility basis set to maturity with a succession of experiments coupled to module development for air-quality models. An issue of great importance in the Eastern U.S. is regional transport of SOA and its attendant vapors, and a major hypothesis to be examined in this proposed research is how the aging of this combination of vapors and SOA influences SOA behavior through long-range transport.
The proposed experiments will quantify SOA formation and aging from terpenes and aromatic compounds in the CAPS temperature-controlled smog chamber. Advanced instrumentation, including high-resolution thermal desorption Aerosol Mass Spectrometry (HR- TD-AMS) and techniques including dilution sampling and thermal denuder volatility measurement, will permit near mass closure while separating products by volatility. Data will be obtained as functions of key variables, including NOx levels, humidity, UV illumination, and reaction temperature. First-generation product distributions will be fit with the volatility basis set; extended exposure to oxidants will constrain “volatility operators” that describe the aging of this volatility distribution due to both gas and condensed-phase chemistry. The results will be incorporated in a compact SOA Integrated Aging Module for use in air quality models. The module will be implemented in PMCAMx will be easy to implement in CMAQ. After model evaluation against supersite and network data, model runs will evaluate the role of multi-generation chemistry and NOx controls on SOA levels in areas strongly influenced by long-range transport, such as the Eastern U.S.
We shall provide significant new measurements of SOA formation and aging; we shall combine these results with literature data to build an accurate and efficient new module of these processes; and we shall implement those modules in air-quality models and test potential control strategies for PM2.5. The expected outcomes are both significantly advanced fundamental understanding of SOA chemistry, especially the derivatives significant to control policy, as well as direct assessment of the effects of likely emission controls of SOA formation in the U.S.