Many folks in Puget Sound smelled and saw smoke from the Bear Gulch Fire Friday afternoon, Sunday night and even a little this Monday morning. While some areas experienced elevated smoke for a few hours Sunday night, the smoke didn't hang around long enough that AQI NOWcast exceeded moderate (yellow) conditions. Most air monitors and sensors around Puget Sound returned to an AQI reading good (green) this morning, but have since gone back to moderate. With the exception of those communities closest to the fire, we do not expect air quality around the Puget Sound to get worse than moderate over the next few days, and will likely continue to vary between good and moderate. Sensors in the Cascades also report moderate air quality from smoke lingering at upper elevations. The following plot shows smoke yesterday afternoon and evening between 1 and 3 km elevation over Tacoma.
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| Ceilometer data from the Tacoma South L-Street air monitoring station, courtesy of Puget Sound Clean Air Agency |
Cooler temperatures and high relative humidity over the next few days will hopefully keep fire activity to a minimum, but we're really all looking at Wednesday. Forecasts predict a front moving through early Wednesday morning bringing showers throughout the day across all Western Washington, with potential for 0.3 to 1" precipitation around Cushman. It will likely not be enough to put the fire out altogether, but will be a huge help to our fire fighters and in clearing smoke from the air. Forecasts for this weekend and next week will be addressed in a post later this week.
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Probability of total rainfall exceeding 0.5" for Wednesday, August 6th |
Hello, can you help me understand why the air monitoring site “Purple Air” is consistently showing air quality levels about twice as high as AirNow? Monday 1:40 PM, purple air is showing levels of 130 while AirNow shows 64. This is for north Tacoma. It’s not just a few sensors - it’s a difference of all orange/red levels (purple air) and all yellow/green levels (AirNow). Thank you!
ReplyDeleteThere are a few reasons for your observation: 1) The Purple Air sensors are known to over report PM2.5 concentrations. To account for this, you should apply a conversion located in the upper left drop down menu of the Purple Air map. We recommend using US EPA, LRAPA, or woodsmoke for our region. 2) In the same drop down menu there is an option for averaging period. If your map is in "real time" you are getting the instantaneous reading from the monitor. The WA Ecology air quality map and the AirNow map are displaying the NowCast AQI. This value is a weighted average of the last several hours, with the most recent hour carrying most weight. Please see our blog post from June 13th, Navigating the Smoke Blog and Understanding the NowCast AQI, for a full description of NowCast values. Clicking on the 1-hour averaging period, will likely bring the maps into better, although not exact agreement. NowCast is based both on concentration and length of exposure, since both are important when it comes to health impacts. Hope this helps.
DeleteThere seems to be a lot more visible and smell-able smoke over the last hour in Seattle! Is it coming from the Olympics?
DeleteYes--current smoke in the region is from the Bear Gulch Fire on the Olympic Peninsula.
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