A massive wildfire smoke episode impacted the western US and Canada in summer 2017. We measured CO, other trace gases, PM, BC, and aerosol optical properties at a heavily impacted, ground-based site affected by this event. Brown carbon diminished as smoke aged but was a persistent component of the regional smoke, accounting for about half of aerosol absorption at 401 nm on average. The PM / CO ratios suggested aerosol evaporation was dominant at the surface at smoke ages of up to ~ 1–2 days.