Relative Influence of Trans-Pacific and Regional Atmospheric Transport of PAHs in the Pacific Northwest, U.S

Abstract

The relative influences of trans-Pacific and regional atmospheric transport on measured concentrations of polycyclic aromatic hydrocarbons (PAHs), PAH derivatives (nitro- (NPAH) and oxy-(OPAH)), organic carbon (OC), and particulate matter (PM) less than 2.5 μm in diameter (PM2.5) were investigated in the Pacific Northwest, U.S. in 2010-2011. Ambient high volume PM2.5 air samples were collected at two sites in the Pacific Northwest: (1.) Mount Bachelor Observatory (MBO) in the Oregon Cascade Range (2763 m above sea level (asl)) and 2.) Confederated Tribes of the Umatilla Indian Reservation (CTUIR) in the Columbia River Gorge (CRG) (954 m asl). At MBO, the 1,8-dinitropyrene concentration was significantly positively correlated with the time a sampled air mass spent over Asia, suggesting that this NPAH may be a good marker for trans-Pacific atmospheric transport. At CTUIR, NOx, CO2, and SO2 emissions from a 585 MW coal fired power plant, in Boardman OR, were found to be significantly positively correlated with PAH, OPAH, NPAH, OC, and PM2.5 concentrations. By comparing the Boardman Plant operational time frames when the plant was operating to when it was shut down, the plant was found to contribute a large percentage of the measured PAH (67%), NPAH (91%), OPAH (54%), PM2.5 (39%), and OC (38%) concentrations at CTUIR and the CRG prior to Spring 2011 and likely masked trans-Pacific atmospheric transport events to the CRG. Upgrades installed to the Boardman Plant in the spring of 2011 dramatically reduced the plant's contribution to PAH and OPAH concentrations (by ∼72% and ∼40%, respectively) at CTUIR and the CRG, but not NPAH, PM2.5 or OC concentrations.

Figure 1

(A) Representative 10 day air mass backtrajectories from MBO for April 23, 2010 and the source region boxes used for both CTUIR and MBO (Oregon, OR; Washington, WA; Alaska; California, CA; British Columbia, BC, Siberia and Asia). (B) Location of air sampling sites in the Pacfic Northwest at MBO and CTUIR, as well as the locations of regional air quality sites near Pendleton, OR: ODEQ and CTUIR Mission Site. The location of the coal fired power plant in Boardman, OR is also indicated.

Figure 2

Temporal variation of mean ∑PAH₃₂, ∑OPAH₁₀, and ∑NPAH₂₇ concentrations at MBO during the sampling periods.

Figure 3

Three operational timeframes of the Boardman Plant (plant on (before upgrade), plant on (after upgrade) and plant off) and ∑PAH₃₂, ∑OPAH₁₀, and ∑NPAH₂₇ concentrations at CTUIR (Cabbage Hill) during the sampling periods.

Figure 4

A) PAH diagnostic ratio cross plot BaA/(BaA+CHR) vs IcdP/(IcdP+BghiP) using thresholds from Yunker et al. at CTUIR in 2010 and 2011 and B) the three operational timeframes of Boardman Plant (plant on (before upgrade), plant off and plant on (after upgrades).