The big air quality story today is the Four Mile Canyon Fire, located 5 miles west of Boulder, Colorado, near Denver. As Kevin reported yesterday in his post, the fire began yesterday (Monday) at approximately 10 AM local time. According to the Incident Information System, the fire is currently over 6,000 acres with 0% contained. Many structures have already been lost, and more are currently threatened. 3,500 residents are under mandatory evacuation. The Incident Information System indicates that the fire was caused by lightening, but I'm watching the Weather Channel, and they are reporting that the fire may have been sparked by an overturned gas tanker truck. Although the cause of the fire is not clear, there's no question that current weather conditions are contributing to its growth: at the Denver International Airport, winds are from the south, sustained at 21 mph with gusts to 32 mph, and the dew point is 28 °F (18% humidity). The location and extent of the fire are evident in today's MODIS Terra true color image (below on upper left, overlaid with AQI values), and a local Boulder webcam image (below on upper right, courtesy of boulderflatironcam.com) shows the smoke in the distance, near the mountains. Air quality in the vicinity of the fire was in the Code Orange (Unhealthy for Sensitive Groups) range today (below on lower left, courtesy of AIRNow), and hourly PM2.5 concentrations in Boulder reached over 160 ug/m3 this afternoon (below on lower right, courtesy of AIRNow-Tech). Due to the wildfire, the Colorado Department of Health and Environment has issued an Action Day Alert through Wednesday at 4 PM for the Front Range Urban Corridor from El Paso County north to Larimer and Weld counties, which includes the Denver-Boulder area, Colorado Springs, Fort Collins, and Greeley. This afternoon, I heard from a colleague who lives in Boulder, and he said that the air quality and visibility were very poor from the fire. For more information, check out the CIMSS Satellite Blog, which has a great summary of the Four Mile Canyon fire using satellite information.
Elsewhere in the nation, air quality was in the Code Green (Good) to Code Yellow (Moderate) range. A band of smoke/haze across the Great Lakes and Mississippi Valley regions is visible in today's MODIS Terra true color imagery, ahead of an advancing cold front (below on left, overlaid with AQI values). AOD is elevated in the areas affected by the haze/smoke (below on right, overlaid with true color imagery). NOAA's Hazard Mapping System Fire and Smoke Product reports that this area of haze/smoke includes smoke from the Four Mile Canyon fire and numerous agricultural fires that were burning in the Mississippi Valley yesterday.