What do the dots on the “current” tab indicate?

The dots on the current map show PM2.5 measurements from four different types of sensors:

1. University of Utah’s AirU sensors;
2. Tellus AirUPro sensors, which are the commercial update to the University of Utah’s sensor (sensors located on high school athletic fields are denoted with a square);
3. Purple Air sensors;
4. The Utah Division of Air Quality (denoted with a triangle) regulatory monitors.

The lower part of the legend on the right tells you which dot (sensor) is provided by which organization. Clicking an element in that legend makes the sensors belonging to that group more visible by outlining them. Moving the mouse cursor over a dot opens a popup with the sensor's name or ID.

If you click on the eyeball (upper left area of your screen), you can turn the dots off and on.

What does the heatmap on the “current” tab show?

If you click on the stack of papers (upper left area of your screen), you will see a heatmap of PM2.5 concentrations. To produce this heatmap, we exclude outliers and integrate the corrected sensor measurements using a Gaussian Process model that has optimized covariates for time, distance, and elevation. More information about our model can be found here.

What do the colors indicate?

The colors on the heatmap, the dots, and the forecast indicate the PM2.5 concentration, the corresponding air quality index, and the health implications of this concentration. See the scale on the right side of the map to link PM2.5 concentrations and the health implications. More information about EPA’s air quality index and health implications of various pollution levels can be found here.

Where do the forecasts come from?

University of Utah researchers developed automated air quality forecasts that are optimized for the intermountain west, and these forecasts are intended to complement the Utah Division of Air Quality’s (UDAQ) forecasts. These forecasts are particularly important for individuals who reside in counties that do not receive air quality forecasts (because these counties lack reference monitoring stations). If you click on the outline icon on the forecast page, you can scroll through the 3-day forecast for your area.

How accurate are the measurements on the “current” tab?

The University of Utah AirU, the Tellus AirUPro, and Purple Air sensors all measure light scattering, and we convert scattering measurements to our best estimates of PM2.5 concentrations using a correction factor. We co-locate all three types of sensors with regulatory monitors to develop appropriate correction factors. Some information about our correction factors can be found here. It is also worth noting that these three sensors are low cost, and they are less accurate than regulatory monitors.

What does the timeline at the bottom of the page show?

For the “current” tab, clicking on a dot (sensor) will add a black border around the sensor and a timeline for that sensor will pop up at the bottom of the screen. You can click on multiple sensors to add them to the timeline. To know which line in the timeline belongs to which sensor, move the mouse cursor over the line and a text box with the sensor ID will appear over the sensor in the map visualization. The default time range in the timeline is the past 24 hours, but you can change this to the past 3 days or the past week.

For the “forecast” tab, clicking on the timeline will allow you to see the forecast for the next three days for your location.

Do you measure anything besides PM2.5?

Not yet, but we are working on adding additional measurements.

What is PM2.5?

PM2.5 is the mass of particulate matter that is smaller than 2.5 µm in diameter, and it is about 1/10th the size of a human hair. This is one of the key pollutants that the US EPA measures because of its potential for adverse health effects. The Wasatch Front experiences elevated levels of PM2.5 during our wintertime inversions as well as periodically because of dust storms, wildfires, and fireworks. To understand the potential health impacts of PM2.5 concentrations, you can use the following EPA guidance. 24-hour average PM2.5 concentrations greater than:

• 35 µg/m³ are considered unhealthy for sensitive groups
• 55 µg/m³ are considered unhealthy
• 150 µg/m³ are considered very unhealthy

You can get more information on the health effects of PM2.5 on EPA’s AirNow site.