We remain mired in the inversion, but there are some curious oddities with the PM2.5 concentrations that warrant analysis by people who know more about emissions and air chemistry than me.
From a stability perspective, there's been little change over the past couple of days. The inversion remains very strong, with a temperature increase of about 13ºC sitting on top of the valley cold pool.
During this period, the 24-h average PM2.5 concentrations at the DAQ sites in Logan and North Provo climbed fairly steadily. Utah County is now approaching a putrid 100 ug/m3.
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| Source: Utah DAQ |
In contrast, the 24-h average PM2.5 concentrations in Ogden and Salt Lake have declined somewhat.
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| Source: Utah DAQ |
Perhaps someone can chime in and explain these declines. Yes, there are differences in the magnitude and timing of weekday and weekend emissions, but why would Logan and North Provo keep climbing steadily while Salt Lake and Ogden decline? Chew on that while I get back to football.
I made a trip to a friend's house today, at about 6300 feet elevation up at Suncrest in hopes of escaping the inversion. Armed with a car thermometer, GPS and some geeky inclinations to measure stuff, I looked at the structure of the inversion early in the afternoon. The temperature initially dropped from about 20F at the valley floor, to a minimum of 13F between about 5700 and 6000' MSL. I took some interesting photos showing a very distinct top to the smoggy mixed layer right at 6100'. The temperature then rose something like 10 degrees between there and the 6300' level, getting into the stongly inverted layer.
ReplyDeleteAs far as the pm levels, I noticed a lot of nucleation and small ice crystal precipitation last night around midnight, when pm 2.5 spiked down. Given that winds were nearly calm at the site, I suspect that perhaps a lot of it precipitated out. Maybe higher dew points in SLC and Ogden areas contributed to this activity?
To me the odd one out here is the Salt Lake Hawthorne monitor. As I have suggested before there have been issues related to monitor icing before. I do not know if that is the case now or not, but I'm uncomfortable using the hourly data without that caveat. As I recall, the monitor being used at Hawthorne is a state of the art machine, its just that we have very unusual conditions here that may not get figured into the design or tested under these conditions. I dont know, but it does make me uncomfortable.
ReplyDeleteOne thing about today's data that you can see if O3 ran higher today than in previous days. Solar radiation at the site was about the same as yesterday so the likely culprit is a reduction NO emissions on a Sunday. NO eats O3. On weekdays we generally have tons of NO around and O3 formation is limited by VOCs. Sunday looks to be different.
The other notable thing here is that we had 6 to 12 hours of W and NW winds today which can push pollution out from the Valley and over the Lake. Even when the winds are light you can still move a lot of volume over time.
I think that in general, the small ice crystal precip has been occurring each night this week (at least here in Sugarhouse) so I dont see that as different today.
The Cache Valley is a completely locked in Valley and Utah Valley (with a frozen Utah Lake) is much more locked in compared to the SLV with its large open north end. This is the reason that we see less variation in their PM2.5 (and because they both use the same kind of monitor that is different than the one at Hawthorne).
Up in Ogden, PM began decreasing slightly on Saturday. This may be due to 2 things: First, emissions look to be lower on the weekend and 2) persistent NNW winds bring cleaner air down from the north. Brigham City even further north is cleaner yet. You can imagine the gradient of PM2.5 as it relates to population and emissions concentration.
Finally, this kind of intermittent fog can create complexity. You do have precipitation of the particulate, you might get gases diffusing into droplets, you can have particulate moving into aqueous phase depending on the RH, etc etc and then add to that instrument issues.
teruicks, on your comment of NO emissions destroying ozone. I believe we have different chemistry for ground level ozone around here (see UBAQS and current Uintah Basin Study).
DeleteHO2• + NO → •OH + NO2
NO2 + hν → NO + O(3P)
O(3P) + O2 → O3
I am not a professional air quality chemist but this can lead to a potential conversation later on maybe. As we see high level of ozone in the Uintah Basin, which does have many VOC's as well to be taken into account, and ozone issues for Houston.
Interesting stuff Jim, David and Tyler. Amazingly enough NW Oregon has been outdoing n. Utah for inversion strength. The 12Z Saturday (1/19) KSLE sounding peaked at a 22C difference between 1000 ft and 2350 ft. When the subsidence inversion started lowering, Mt Hood Meadows' base warmed 27F in an hour during the middle of the night. Eugene has stayed in a 1/2 mile or less fog for 36+ hours. It's quite the episode around the western US. -Colby
ReplyDeleteThis morning KUER (I think) reported it was snowing out of the fog in NSL, apparently enough to be a drive time warning. Could the steam of the refineries & Gadsby be creating nucleation and lowering 2.5 levels by causing more pollution to fall out? Cache & Utah Counties lack industrial sources.
ReplyDeleteRe the Hawthorne monitor: Bryce Bird discussed monitor values briefly at the WFRC AQC meeting on 1/17. He said they just weighed a bunch of midnight to midnight filters at various locations, thru the state, and the data on the real time monitors [displayed on the trends pages] is tracking the filter weights pretty well. He didn't discuss individual monitors, but I guess he would have called out Hawthorne if it didn't fit the pattern, because of this controversy.
There's enough pollution distributed around the valley at this point that the snowfall in that area is probably due more to the local meteorological conditions there than a local pollution source. That is, however, an educated guess and I am prepared to stand corrected.
Delete