Influence of Free Tropospheric Ozone and Particulate Matter on Surface Air Quality in the Western U.S.

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Measurements of the atmospheric concentrations of many important air pollutants have been ongoing for over 10 years at the Mt. Bachelor Observatory (MBO) located at the summit of Mt. Bachelor in the Deschutes National Forest in central Oregon. MBO is the only high elevation (2.8 km) atmospheric research station on the west coast of the U.S. To date, measurements taken at this site have been able to identify a significant trend in baseline ozone entering the U.S. due to long-distant transport from Asia during spring, explain some of the causes for variability in ozone production in wildfire plumes, and demonstrate the first evidence for a significant pool of oxidized mercury in the free troposphere. This project continues to support the collection of these data at MBO and also supports the collection of several new types of data. The new data will provide information on aerosol optical properties and on the concentration of a chemical that is predominantly produced by wildfires. The new measurements are designed to help distinguish between the sources of ozone and particulate matter related to biomass burning from those associated with urban and industrial activity and from those transported from Asia.The primary goals for the project are: (1) Examine the concentrations, interannual variability and controlling factors for ozone (O3), particulate matter (PM) and other key pollutants in the spring at MBO and throughout the Western US. The purpose is to better understand the cause for the recent positive trends in ozone at MBO and the contribution from long-range transport and from upper troposphere/lower stratosphere (UTLS) events; and (2) Examine the concentrations, interannual variability and controlling factors for O3, PM and other key pollutants in summer at MBO and throughout the Western US. Emphasis will be placed on understanding the relationship between carbon monoxide (CO), O3, PM, peroxyacetyl nitrate (PAN), and acetonitrile (CH3CN) to improve the understanding of the processes that control O3 and PM in wildfire plumes. Several specific hypotheses about the sources and transformation of various atmospheric compounds measured at MBO will be evaluated in this study. New measurements at the site will facilitate this investigation. The new measurements include: aerosol absorption using a Tricolor Absorption Photometer; particle sizing using a scanning mobility particle size spectrometer; and measurements of the concentrations of acetonitrile.