Trans-Pacific and regional atmospheric transport of polycyclic aromatic hydrocarbons and pesticides in biomass burning emissions to western North America

Abstract

The trans-Pacific and regional North American atmospheric transport of polycyclic aromatic hydrocarbons (PAHs) and pesticides in biomass burning emissions was measured in air masses from April to September 2003 at two remote sites in western North America. Mary's Peak Observatory (MPO) is located in Oregon's Coast Range and Cheeka Peak Observatory (CPO) is located on the tip of the Olympic Peninsula in Washington State. During this time period, both remote sites were influenced by PAH and pesticide emissions from forest fires in Siberia and regional fires in Oregon and Washington State. Concurrent samples were taken at both sites on June 2 and August 4, 2003. On these dates, CPO had elevated gas phase PAH, alpha-hexachlorocyclohexane, and retene concentrations (p < 0.05) and MPO had elevated retene, particulate phase PAH, and levoglucosan concentrations due to trans-Pacific transport of emissions from fires in Siberia. In addition, during the April to September 2003 sampling period, CPO and MPO were influenced by emissions from regional fires that resulted in elevated levoglucosan, dacthal, endosulfan, and gas phase PAH concentrations. Burned and unburned forest soil samples collected from the regional forest fire area showed that 34-100% of the pesticide mass was lost from soil due to burning. These data suggest that the trans-Pacific and regional atmospheric transport of biomass burning emissions results in elevated PAH and pesticide concentrations in western North America. The elevated pesticide concentrations are likely due to re-emission of historically deposited pesticides from the soil and vegetation during the fire event.

Figure 1

MODIS 10-day fire detects overlaid with 10-day air mass back trajectories and corresponding PAH and pesticide concentrations measured at MPO (purple) and CPO (orange) for the concurrent sampling on A) June 2, 2003 and B) August 4, 2003. Smoke plumes extended across the Pacific Ocean to Western North America. (Figure SI.2 A and B).

Figure 2

Concentrations of pesticides and polychlorinated biphenyls (PCBs) (pg/g dry weight) in burned and un-burned forest soil collected from the B&B complex forest fire in the Deschutes National Forest, Oregon.