A number of air quality sites measured values of small particulates at unhealthy levels, particularly for those vulnerable to their effects (asthmatics, those with heart or lung disease, etc.). I was standing along the shores of Lake Washington last night and a smoky, sulfurous miasma was evident, both from commercial fireworks and from the numerous individual displays. (And this is with fireworks being ILLEGAL in much of the area!!) I believe this was a particularly bad air quality year from fireworks, for reasons I will explain.
Picture by Mik on the Capital Hill Blog.
Let's check the numbers, provided the Puget Sound Clean Air Agency, a really excellent organization that works to keep our air breathable. I will be showing you concentrations of small particles (PM2.5, less than or equal to 2.5 microns in size, particles that can make their way deep into your lungs and cause all kinds of problems).
First, Seattle in the Duwamish Valley. Big spike from a background level of roughly 10 (micrograms per cubic meter) to 60, getting well into the range of being unhealthy for sensitive groups. (click on this or subsequent figures to enlarge).
Lynnwood was MUCH worse, spiking well into the UNHEALTHY levels for everyone (about 120). The red line shows preceding 24-h averages.
Even a relatively small town, like Aberdeen, WA seems to have lots of firework smoke, with levels getting well into the unhealthy range (about 90).
Similar values were noted in suburban North Seattle at Lake Forest Park.
I haven't done a study of the levels each year, but if my memory serves me correctly these levels were higher than most previous years....something confirmed by an air quality scientist at Puget Sound Clean Air Agency. Why?
First, the winds were relatively light last night...as suggested by the following wind plot for 10 PM July 4. Circles with no wind barb indicate calm winds. A bard with a single small line indicates only a few knots. Low winds mean less turbulence and vertical mixing. Thus, less clean air being mixed down and less dispersion of the smoke.
Second, the vertical structure of the atmosphere was relatively stable (little mixing), with a stable layer (in this case one with temperature staying the same with height) from from roughly 925 hPa (about 2500 ft) to 850 hPa (around 5000 ft). Below is a vertical sounding at Quillayute on the Washington coast, provide temperature (right line) and dew point (left line) with height. The stable layer would act as a cap to keep pollutants in.
Air quality should improve today, although I suspect there will be some more fireworks tonight, which will keep the levels above background.