We report observations of normalized enhancement ratios (NER) for 32 wildfires measured at Mount Bachelor Observatory in central Oregon during June-September 2004-2011. All 32 plumes resulted from wildfires originating in the western United States and Canada. The observed NER of PM1 (particulate matter < 1 micron) to carbon monoxide (DPM1/DCO) ranged from 0.06 to 0.42 µg m-3 ppbv-1. The NER of ozone to CO (DO3/DCO) ranged from 0.01 to 0.51 ppbv ppbv-1 for the 13 observed plumes with a significant DO3/DCO NER (p £ 0.01, R2 ³ 0.30). For wildfire plumes transported <540 km, or approximately <2 days, the DPM1/DCO NER is found to increase with increasing distance, suggesting that there is significant secondary organic aerosol (SOA) production in these plumes. However, two plumes transported over greater time periods have relatively low DPM1/DCO NER, indicating that PM1 loss is greater than SOA production in these plumes. Of the three plumes transported the longest distance to MBO, only two have significant O3 production. These two plumes were transported in boundary layer air masses, while the third was transported in a free tropospheric air mass, suggesting that conversion of nitrogen oxides (NOx) to peroxyacetyl nitrate (PAN) may be a factor affecting O3 production in these plumes. Two wildfire plumes are mixed with urban emissions from the Seattle/Tacoma metropolitan area, and have relatively higher DO3/DCO NER than other wildfire plumes transported over similar distances. © 2013 Elsevier Ltd. All rights reserved.