The Impact of Monthly Variation of the Pacific-North America (PNA) Teleconnection Pattern on Wintertime Surface-layer Aerosol Concentrations in the United States

Abstract:

The Pacific-North America teleconnection (PNA) is the leading general circulation pattern in the troposphere over the region of North Pacific to North America during wintertime. The PNA exhibits positive (negative) phases with positive (negative) anomalies in geopotential height in the vicinity of Hawaii and over the intermountain region of North America, and negative (positive) anomalies in geopotential height over south of the Aleutian Islands and the Gulf Coast region of the United States. This study examined the impacts of monthly variation of the PNA phase on wintertime surface-layer aerosol concentrations in the United States by analyzing observations during 1999-2013 from the Air Quality System of Environmental Protection Agency (EPA-AQS) and the model results for 1986-2006 from the global three-dimensional Goddard Earth Observing System (GEOS) chemical transport model (GEOS-Chem). The composite analyses on the EPA-AQS observations over 1999-2003 showed that the average PM_2.5 concentrations were higher in the PNA positive phases than in the PNA negative phases by 1.0 µg m^-3 (8.6%), 2.1µg m^-3 (24.1%), and 1.1 µg m^-3 (10.6%) in the eastern, western, and whole of United States, respectively. Relative to the PNA negative phases, the number of exceedance days (days with the PM_2.5 concentrations exceeding 35 µg m^-3) in the PNA positive phases increased by 5-8 days month^-1 in California and the contiguous Great Salt Lake and by 2-3 days month^-1 in Iowa. The simulated geographical patterns of the differences in concentrations of PM_2.5, nitrate, sulfate, ammonium, OC, and BC between the PNA positive and negative phases were similar to observations. The PNA influences surface-layer aerosol concentrations in the United States by changing meteorological variables such as temperature, precipitation, planetary boundary layer height, relative humidity, and wind speed. We found that that the PNA-induced variation in planetary boundary layer height was the most dominant meteorological factor that influenced the concentrations of PM_2.5, sulfate, ammonium, OC, and BC, and the PNA-induced variation in temperature was the most important parameter that influenced nitrate aerosol. Our study has important implication for understanding and prediction of air quality in the United States.