Purple line is typical summertime conditions in Boulder.
Green line is conditions measured during Four Mile Canyon fire event.

The Four Mile Canyon fire started in Emerson Gulch about 5 miles west of Boulder on September 6, 2010. The fire was contained eleven days later, on September 16, 2010 after it grew to 6,181 acres and burned 169 houses. The total cost of the fire was nearly $217M in damages. Before the 2012 Waldo Canyon, it was Colorado’s most costly fire.

Smoke plume from Four Mile Canyon fire
Burn scar from Four Mile Canyon fire

The proximity of the fire to Boulder resulted in the effects of the fire on atmospheric properties being studied and published by scientists at NOAA and University of Colorado, for example:
Stone, R. S., Augustine, J. A., Dutton, E. G., Neill, N. T., Saha, A., "Empirical determinations of the longwave and shortwave radiative forcing efficiencies of wildfire smoke," J. Geophys. Res., 116, DOI: 10.1029/2010JD015471, 2011.
Boulder's daily newspaper also did a story on local scientists investigating effects of the fire.