Eye Opening Pollution Observations

For some time I've been complaining about the lack of real-time PM2.5 sensors in the Salt Lake Valley (see for example, Inversion Snippets).  The Salt Lake Valley is simply too complex of a place for us to rely on guidance from a single sampler along 700 East (Hawthorne Elementary).  With two additional real-time samplers now in place, plus observations being taken by Trax (thank you University of Utah colleagues!), our eyes are now being opened to some of the spatial and temporal variability in PM2.5 across the valley.  

Let's begin with data from the two new fixed sites.  The first is at the Neil Armstrong Academy in West Valley City (G thumbnail below) and the second is out our mountain meteorology lab near the mouth of Red Butte Canyon on the University of Utah campus (H thumbnail).  

Source: ACME Mapper

At both sites, PM2.5 over the past three days has increased during the day, reached a maximum in the afternoon, and then decayed to an overnight minimum (note the differing scale in the two plots).  In addition, the afternoon peak has gotten larger each day.  

At Neil Armstrong Academy, however, PM2.5 is consistently higher than at our mountain meteorology lab, and the overnight minimum is more elevated.  This illustrates the importance of location, location, location when it comes to air pollution exposure.  The Neil Armstrong Academy is at only 4260 feet and well removed from the canyons that issue from either the Oquirrh or Wasatch Mountains.  It is deep within the valley cold pool and well removed from any sources of cleaner air.  In contrast, our mountain meteorology lab is at 4996 feet, which for the current inversion is near the top of the pollution, and it sits at the mouth of a canyon from which clean air can sometimes flow overnight.  As a result, at least for this event, PM2.5 levels have been lower on the upper University of Utah campus than found along the valley floor, especially at night (NOTE: This is not necessarily the case for all inversion events as their depth and characteristics can vary).

Further insights can be obtained from observations collected by the Trax mounted sensor.  Data along the red line collected during the 2 hours ending 5 PM yesterday shows consistently high values (>55 ug/m3) from West Jordan to the University of Utah campus with a peak of 89 ug/m3.  Folks, this is some seriously crappy air, qualifying as "unhealthy."  In the southwest valley, some lower PM2.5 concentrations were found near the end of the line in the Daybreak area.

Source: http://meso1.chpc.utah.edu/mesotrax

Contrast that with the run this morning when PM2.5 values are lower everywhere, but there is also more spatial variability.  The highest values are found along the valley floor from West Jordan to roughly I-80 where they are generally > 35 ug/m3 with a peak of 53 ug/m3.  Lower values are found elsewhere, including some remarkably low values (< 12 ug/m3) near and just west of the University of Utah campus where I suspect there has been an incursion of cleaner air from one of the canyons.  

Source: http://meso1.chpc.utah.edu/mesotrax

One of my favorite sayings is "all generalizations are wrong" and so I caution against generalizing these observations as applying to all inversion periods.  Much depends on the characteristics of the inversion, it's strength, depth, the presence of upper level clouds or snow cover, and other effects. The characteristics of this event, for example, might change as fog becomes more widespread and prevalent or as there are other meteorological changes.  Nevertheless, it's great to see more comprehensive real-time PM2.5 observations rolling in, although I'd be even happier to see clean air.