Wednesday, August 19, 2015

There's No Escape from the Worsening Pollution

Smoky sunrise over the Salt Lake Valley this morning.  Note the faint outline of the Wasatch Mountains on the left side.
Over the past three days, air quality over the Salt Lake Valley has deteriorated as smoke from fires to our west and northwest is transported into the area.

This morning, hourly averaged PM2.5 concentrations sit at 32 ug/m3 and are approaching the transition from moderate to unhealthy for sensitive groups.  
Source: DAQ
There was a spike to even higher values the day before yesterday, but I'm not sure if I believe it.  We didn't see it in our data from the University of Utah, which shows we're currently sitting at the highest PM2.5 concentrations of the entire event.  

Source: MesoWest
Making the situation even more miserable is the ozone.  Ozone is photochemically produced (i.e., produced by sunlight) and thus tends to reach a peak in the afternoon.  We've been topping out each afternoon at about 70 parts per billion, which is also in the moderate category.

So basically, we have a noxious mix of both PM2.5 and ozone in the afternoon and evening and I suspect we'll see the highest levels of the former this afternoon.  I may elect to skip my bike ride later today.  

Unlike wintertime inversion events, you can't climb above this stuff.  Mixing in the summer extends through a deeper layer.  The photo below was taken yesterday by the KSL Helicopter and you can see the top of the gunk sitting above the crest of the Wasatch.  

This summer, a major field program is taking place to examine the aerial extent and underlying processes of high surface ozone concentrations in the Great Salt Lake Basin called the Great Salt Lake Summer 2015 Ozone Study.  It involves collaborations between the University of Utah, Utah State University, Weber State University, and the Utah Division of Air Quality (more info here).

As part of the project KSL has graciously allowed sensors to be placed on their news chopper and the data is extremely illuminating.  The data below was collected yesterday.  The blue line is the chopper altitude (above mean sea level) and the green line is the ozone concentration.  Ozone concentrations were between 60 and 65 ppb when the chopper was below about 3000 m, but as the chopper ascended above 3000 m, they climbed to nearly 70 ppb right at the top of the gunk layer (about 17:05 local time).  Then, the chopper briefly penetrated into cleaner air aloft and the concentrations dropped to less than 50 ppb.  The chopper then descended back into the gunk layer, finding the 60 ppb air once again below about 3000 m.

So, you have no hope of climbing above this in Utah unless you have a plane or helicopter.  Further, and this has been found in other areas, ozone concentrations may actually be somewhat higher at higher elevations near the top of the gunk layer.  We're stuck in it and there's no escape.  Our best hope is a shift in the flow direction.  Next week looks cleaner with southwesterly or southerly flow, but it's hard to say if the weak systems coming through later this week and this weekend will crack the smoke or just give us temporary or partial relief.  


  1. We can't climb above it and I wonder if the indoor air quality is any better right now?
    Through a past post comment* I've learned that winter PM2.5 particles are largely ammonium nitrate (NH4NO3) that volatilizes at room temps. Therefore, winter indoor air quality is a whole lot better than outdoors. But obviously that is not the summer smoke scenario.


    1. Good question. I have no idea. Perhaps others can comment.

  2. What time of day is our best bet for breathable air in this scenario? Does this stuff settle overnight?

    1. Ozone is easier. It's lower at night and in the morning. Afternoon and evening are worse.

      PM2.5 in this event is not so easily generalized and you can't count on a time of day when the air quality might be better or worse. In part, that might reflect small changes in transport direction, which can dominate over the effects of local emissions and photochemistry.

  3. I'm curious - the NWS shows the smoke clearing a bit tonight into tomorrow. But I just read an article in the Tribune in which they said our first glimmer of a hope is Tuesday. Any chance the NWS is right and we might get a little relief tomorrow?

    1. Actually, the NWS says there's a slight chance visibility improves Saturday, but that the improvement will be short lived:

      Challenge with this forecast is that the smoke isn't from local areas, but is transported in. Fire intensity, coverage, and long-term transport all make for a tricky forecast and there's the chance we get into a clearer pocket as the winds shift with the passage of weather systems the next couple of days. However, that's tough to forecast with precision with existing capability. In the long run, we need to get into a different large-scale airstream. That will probably happen next week.