Sunday, January 13, 2013

The Approaching Mother of All Inversions

I'm either a pessimist or a realistic optimist about the forecast for this coming week depending on your perspective.  It looks like a very strong inversion will set in and that it could persist for some time.  From a meteorological perspective, it has the potential to be even stronger than the last.  From an air quality perspective, much will depend on emissions, chemistry, and other factors.

This is a long post, but it is important because inversions have such a huge impact on the lives and health of northern Utahn's.  It has two parts.  The first discusses inversion nomenclature.  The second the forecast for the approaching event.

a. Inversion nomenclature

As discussed recently in a Salt Lake Trib article by Judy Fays, there is quite a bit confusion about the terms used to describe inversions.

A cold pool is a topographically confined layer of air that is colder than the air above it.  An inversion is a layer of air in which the temperature decreases increases with height.  As depicted below, it is possible for the inversion to sit on top of a cold pool and not extend all the way to the valley floor.  The red line shows the profile of temperature with height.  Note how it increases in the inversion layer.


In Utah, the term inversion is commonly used to describe any situation in which one can see pollution in the valley.  This is meteorologically incorrect as some so-called inversions do not feature a layer in which the temperature increases with height.  In the atmosphere, the density of air depends on both temperature and pressure and, as a result, situations in which the temperature decreases only a little with height are still quite stable.  These situations can feature elevated pollution levels and are commonly called inversions even if an inversion is not present.

When an inversion is present, it's height relative to the valley floor can be important because there can sometimes be mixing within the airmass below the inversion.  When the inversion is at or near the valley floor, all our urban emissions are trapped in a very shallow layer.  When it is higher, there is mixing through a deeper layer.  All else being equal, the pollution on the valley floor will be worse when the inversion is near the valley floor than when it is elevated.  The benches, however, can sometimes be above the inversion and in the clean (or cleaner) air if the inversion is located at or near the valley floor.

Haze is a visibility obstruction caused by dry or wet particles suspended in the sky.  Haze can be natural or have a strong human-caused component.    

Smog was originally used to describe smoky (i.e., polluted) fogs, but is now used to describe a wide variety of pollution related visibility obstructions related to particulate matter and photochemical smogs.

I've never much liked the term haze to describe the poor visibility during our so-called inversion events.  There are some inversion events in which natural haze would form, but most of the crappy air is due to pollution.  Therefore, I believe the term smog should be used.  Smog also has the advantage that it is inclusive of fog, which also forms during some inversion events.  There are some disadvantages as well, but this is my blog and I do what I want.

b. The Forecast

I'm quite concerned about the long-range forecast and the potential for unhealthy particulate matter levels in the Salt Lake Valley for several reasons.  First, we have an incredibly cold airmass and deep layer of snow over the valley.  As the forecast stands now, there's no hope that the snow will melt and very little hope that we'll erode out the cold airmass over the next couple of days.

Second, we are transitioning from a deep large-scale upper-level trough to a persistent, high-amplitude upper-level ridge over the next several days.


Forecast temperatures on the top of Mt. Baldy (11,000 ft) climb from below -10ºF today (the actual temperature on Mt. Baldy is currently -17ºF) to near freezing by Tuesday night.


That is more than a 40ºF increase, while the cold air is likely to remain entrenched in the valley.  Further, this could be a long-lived event based on the long range forecasts.  The forecast above covers 7-days, but many ensemble members keep us stagnant for longer.

The bottom line is that meteorologically this has the potential to be the Mother of All Inversions.  OK, that's hyperbole, but it will be a strong and persistent event.  What happens with pollution will depend on emissions and chemistry.  As Vince Lombardi said, the best defense is a good offense.  Today is the day to get the word out and run errands.  Tomorrow is the day to implement red burn conditions, encourage people to cut down on travel, etc.  Our air quality defense system for this event needs to be proactive.

32 comments:

  1. It does look bad. How effective are the indoor HEPA filters against the particulates, by the way? The advisories telling people who are sensitive to the smog to simply stay indoors imply that the air inside is much cleaner inside, but I really doubt that is the case. It would be interesting to know if these filters are worth running during our smog episodes. Has anyone done tests on this?

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    1. This is an important issue and I suspect you are correct that being indoors is not a true "escape" from the pollution. Perhaps someone can dig into the literature and fill us in.

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    2. The Utah DEQ has a PowerPoint where they compare indoor and outdoor PM2.5 levels during cold pool events: (http://health.utah.gov/ search "Effects of Inversions", it should be the first link, sorry, I can't find a hard link for it)
      Slides 9-10 have some interesting plots suggesting that indoor air quality is significantly better than the outdoor air. I ran a GRIMM particle spectrometer in my office on campus during this last inversion, and I was pleasantly surprised by the relatively low PM2.5 levels indoors.

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    3. Yes, those numbers are good to see and better than I expected. Any thoughts on how things would look in older homes?

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    4. I would guess that an older home would be worse, but Hawthorne Elementary (1700S, 700E in SLC) is not a new building and it looks like it fares pretty well. My office is upstairs CME and I think it represents old construction pretty well, it has original single-pane glass that should be pretty leaky. I'm planning on running the GRIMM throughout this next event to compare with clean air samples. I guess we'll find out!

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    5. Looking forward to seeing the results. BTW, my office when I first got to Utah was on the 4th floor of the CME, so there's good Karma there.

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    6. Do the high priced black carbon furnace filters offer any additional advantage during an inversion? I have read that they help a lot with the summer ozone, but I haven't heard anything about their effect on the winter inversion air.

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  2. Typo paragraph 2:

    "An inversion is a layer of air in which the temperature decreases with height." Sentence should read "increases" with height.

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    1. Egad! I just fixed it. Thanks for the heads up.

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  3. Several years ago I bought a HEPA filter in the $100 range, and I try to run it when the smog gets real heavy. I really have no idea how much it is filtering out, though. I wonder if anyone has compared inflow/outflow PM levels for these types of filters during one of our local smog episodes.

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  4. A couple of thoughts:

    HEPAs

    HEPA filters are P100s I believe. At the P100 level particles with a diameter of >30 ug are trapped by the fabric. DAQ's monitors measure PM2.5 which includes all particles with a diameter of <= 2.5 ug. The diameter of particles that form via chemical reaction in the atmosphere (secondary particulates) will be in the range of 0 to 1 ug within the nucleation and accumulation mode particle categories. Ammonium nitrate and ammonium sulfate as well has organic particulates make up between 50% and 75% of our total PM2.5. DAQ does not run instruments that look at the diameter profile of the particles, but it is pretty safe to say that a solid chunk of our particulate would be filtered by a HEPA.

    Inside vs. Outside

    The deal with our particulate is that so much of it is ammonium nitrate (NH4NO3). Ammonium nitrate happens to be volatile at warmer temperatures and stable at cold temperatures. In our case, the cold temperatures help to keep NH4NO3 as a particle, but once you go indoors the particulate tends to volatilize into it gas phase components. Therefore, indoor air quality is a whole lot better than outdoors. DAQ has done a fair bit of work on this very issue. They conducted numerous studies inside/outside schools. I think they may have worked at Hawthorne among others. Dr. Steve Packham at DAQ would be the contact on that.

    This week:

    As you say Jim, the key this week will be how close the inversion is to the Valley floor and whether or not we even get a mixed layer at all. With this snow pack it is possible that we get very little near-surface mixing. Emissions are basically the same day to day so that wont be much of a question mark. In terms of chemistry we can watch for sky cover because photochemistry (sunshine) can drive particulate formation. We have already begin to build PM2.5 concentrations today. It will be interesting to watch (breathe) and see how long this episode lasts.

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    1. A "solid chunk" ??? Care to put a number on that? Are we talking 50%? More? Less?

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    2. A "solid chunk" ??? Care to put a number on that? Are we talking 50%? More? Less?

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  5. One other thought ...

    2004 was the most recent "mother" episode especially in Logan. 24 hr concentrations made it into the 100s if I remember correctly. There was a deep snow cover that season ....

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  6. +1 for getting some real information on improving indoor air quality. Very useful discussion. Thanks all for your insights.

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  7. It's posts like this, and its associated commentary, that have made this site one of my daily and favorite readings. Thank you for all the work you put into these posts!

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  8. What about face masks? How effective are those?

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  9. Inversion may be the cause, but the effect is SMOG!!!! Why not just call it Smog or polution, maybe Utah will take air quality a lot more serious. Inversion just doesn't sound that bad for you.

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  10. There are some really good face masks to use if you have to be outdoors in this toxic soup. I found a carbon NIOSH mask online and I notice a huge difference.

    I also purchased an IQAir HealthPro Plus Air Purifier as I was having some serious issues with breathing and it has helped. It's not cheap but well worth it.
    http://www.iqair.com/home-air-purifiers/healthproseries/features.php#hyper

    There are carbon air filters on the market as well which I have also with a merv rating of 14 which can't be used in an older furnace.

    I am very sensitive to the inversion so I had to research and find alternatives to oxygen!! :)

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  11. The technical definition of an inversion is a less than standard lapse rate (atmospheric cooling with increase in altitude) Standard lapse rate is ~ 2 degrees C or ~ 3 degrees F per 1000'. It doesn't really have to warm up at altitude, just not cool down as much as normal.

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    1. Jim -

      I've not seen that definition previously, but perhaps some have used it. If you can send along the source, please do.

      The Glossary of Meteorology definition is, "a departure from the usual decrease or increase with altitude of the value of an atmospheric property". One could interpret "usual" to be the standard lapse rate, although the National Weather Service glossary goes a step further and adds "it almost always refers to a temperature inversion, i.e., an increase in temperature with height, or to the layer within which such an increase occurs.". This definition, where an increase in temperature with height is needed, is the one that I've always used. It would not be surprising, however, if others have differing definitions.

      Jim

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  12. Hi Jim,
    I just found out about your blog through a friend. Recently, I had Roger Peng from Johns Hopkins give a talk on an air pollution intervention study at the UU. HEPA air filters were installed in the common area and bedroom of houses with asthmatic children in Baltimore, MD, and outcome measures studied included asthmatic episodes and PM 2.5 levels. They found both a significant reduction in PM 2.5 and fewer asthmatic episodes among children who received the intervention. We hope to have Roger back again in 1-2 years -- will keep you posted!
    Angela

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  13. How high up in elevation to be out of the pollution 100%? I have seen smog up on Suncrest where folks think it's out of the range of the inversion.

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    1. I was told that Suncrest is above the pollution, and have seen photos and videos taken from there looking down on the toxic soup..

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  14. I'd like to move to the Wasatch Front, but I need to have a way to overcome the effects from the Inversion. Do you think that a high quality air filtration system such as the IQAir Perfect 16 which installs into the HVAC system would be a good solution? I work at home, so I could stay home when the inversions occur without a lot of hassle.

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    1. I have been told that indoor PM levels are typically much lower than inside and have seen some data to support this view, but I'd like to see more comprehensive monitoring. Upper Suncrest is often (but not always) above the worst of the air pollution.

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    2. Suncrest is definitely nice, but there are things I've read about ongoing litigation, and the $200+ HOA fees to live up there aren't too attractive. I came across your blog while doing my research on these inversions. Maybe you can clarify something for me. Is the temperature inversion itself a permanent fixture in the winter months that is only broken up by a storm, only to form again? I don't think that is correct because I've read that, on average, inversion days average about 30 per year, and 30 days is obviously much less than the entire winter. What actually causes the inversion to happen? Also, when there is no inversion happening, I assume that the air quality in Utah County is pretty good? the DAQ right now says PM2.5 is 0.

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    3. High PM episodes occur primarily from Nov-Feb and then potentially during the fire season. Events are episodic and their intensity and frequency varies depending on the meteorology in any given season. Last year was a terrible year - a perfect storm if you will of meteorology. Other years are not as bad. Utah County has PM problems too - last year they had higher concentrations at times than Salt Lake. Look for posts on Air Quality and Cold Pools in the subject cloud in the right column of this blog for more info.

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    4. Yes, it seems that no place on the wasatch front is safe. Last question - From memory, what was the longest period of time that you recall an inversion lasting, e.g. 2 days, a week, etc? I will continue reading your informative blog...

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  15. I'm looking for an answer to my question and if the author of this blog can't answer it, I give up. :) I'm looking at a lot in Salt Lake City that is at 5200 feet in elevation (above the capitol). Will I be above the inversion (like it was mentioned Suncrest in Draper is) or am I still breathing that soupy mess?

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  16. I'm no longer looking to relocate to the area because of the air issue, it's just not a good move if avoidable. There are other nice places with great outdoors besides SLC area.

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  17. I just want to let you know that I just check out your site and I find it very interesting and informative..
    air purifiers for the home

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