Sunday, August 23, 2020

Improving Air Quality and Some Mountain Showers

After two days of cowering inside due to high PM2.5 and afternoon ozone, I was glad to get out for a hike this morning.  In the Salt Lake Valley, PM2.5 has slowsly been declining since it's peak very early Friday morning and is now sitting near the transition from low to moderate (top graph below, with green indicating low values and yellow moderate).  

Additionally, although ozone peaked at unhealthy levels the last two afternoons, it appears to be leveling out at moderate levels this afternoon, although I can't rule out a spike to higher levels later.  

There are two big differences between summer smoke and winter particular matter events.  The first is that, as evident in the graphs above, summer smoke can be accompanied by unhealthy ozone concentrations during the day.  Basically, it's a double whammy for bad air quality.  The second is that mixing during the summer occurs through a deep layer, so when the smoke is thick, it's usually thick everywhere including in the mountains.  I'll add that the mountains are not necessarily an escape from the ozone and I suspect that in the Wasatch, the ozone concentrations in the afternoon might be higher than found in the city.  This has been observed in mountains adjacent to other urban areas (e.g., Vancouver, Seattle).  

One special treat was a band of showers that moved through the central Wasatch at just before 11 AM.  They produced just enough to dampen the ground and encourage my son to throw on his hard shell.  

They lasted about 10 minutes, but the cloud cover prevailed for most of our hike, which was wonderful.  It was only in the mid 50s while we lounged on Mt. Baldy, and that was damn comfortable.  

Forecasts right now suggest the worst of the smoke will remain to our north through tomorrow.  Below is the near-surface smoke forecast from the HRRR smoke for 1800 UTC tomorrow (noon).  We're not clear, but hopefully concentrations will remain below "nasty" levels.  

There's enough emissions sources and mixing of smoke throughout the west that the only region of the western contiguous US forecast to be pretty much smoke free is the far northwest.  These experimental smoke forecasts are at if you want to monitor for yourself.  They aren't perfect and emissions from new starts aren't always included right away.  However, I find them helpful for planning. 

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