Influence of Asian and Western United states agricultural areas and fires on the atmospheric transport of pesticides in the Western United States

Abstract

Historic and current use pesticides (HUPs and CUPs), with respect to use in the United States and Canada, were identified in trans-Pacific and regional air masses at Mt. Bachelor Observatory (MBO), a remote high elevation mountain in Oregon's Cascade Range located in the United States, during the sampling period of April 2004 to May 2006 (n = 69), including NASA's INTEX-B campaign (spring 2006). Elevated hexachlorobenzene (HCB) and alpha-hexachlorocyclohexane (alpha-HCH) concentrations were measured during trans-Pacific atmospheric transport events at MBO, suggesting that Asia is an important source region for these HUPs. Regional atmospheric transport events at MBO resulted in elevated dacthal, endosulfan, metribuzin, triallate, trifluralin, and chlorpyrifos concentrations, with episodic increases in concentration during some spring application periods, suggesting that the Western U.S. is a significant source region for these CUPs. Endosulfan I, gamma-HCH, and dacthal concentrations were significantly positively correlated (p-value < 0.05) with increased air mass time in Western U.S. agricultural areas. Elevated gamma-HCH concentrations were measured at MBO during both trans-Pacific and regional atmospheric transport events, including regional fire events. In addition to gamma-HCH, elevated sigmachlordane, alpha-HCH, HCB, and trifluralin concentrations were associated with fires in Western North America due to revolatilization of these pesticides from soils and vegetation. Trans-chlordane/cis-chlordane and alpha-HCH/gamma-HCH ratios were calculated and may be used to distinguish between free tropospheric and regional and/or Asian air masses.

Figure 1

MBO, black triangle, (43.98° N 121.69° W, 2.7 km a.s.l.) is located in Oregon’s Cascade Range. A Asia and Siberia source regions (boxes) with respect to MBO. Example trajectories 25–26 April 2004 (red, Asia) and 12–13 May 2006 (blue, Siberia). B Western Oregon (W. OR), Eastern Oregon/Washington (E. OR/WA), and Central California (CA) agriculture source regions (boxes). Example trajectories 4–5 April 2006 (yellow, Central California), 13–14 March 2005 (green, Eastern Oregon/Washington), and 28–29 April 2006 (black, Western Oregon). Also shown is the percent cropland on the county level (17) and national parks/forests in Western North America.

Figure 2

Pesticide concentrations 2004–2006. A α-HCH (black, circle) and γ-HCH (red, triangle). B HCB (black, circle) and Σchlordanes (red, triangle). C chlorpyrifos (black, circle) and trifluralin (red, triangle). D Σendosulfans (black, circle) and metribuzin (blue, triangle). E dacthal (black, circle) and triallate (blue, triangle). Metribuzin and triallate (blue) were only detected in the spring 2006 samples. Winter (W) (Dec. Jan., Feb.), Spring (Sp) (Mar., Apr., May), Summer (Su) (June, July, Aug.), Fall (F) (Sept., Oct., Nov.) are separated by dashed lines. Background colors designate different years.