The SWPA Environmental Health Project uses a unique analysis tool called the Impact App to map where fine particulate matter (PM2.5) exposure may be coming from in relation to a home. PM2.5 is a mix of solid and liquid particles found in the air like dust, soot, and smoke and forms at industrial sites and during combustion processes such as in diesel engines. Particulate matter is fine enough to travel deep into the lungs and enter the blood stream. By itself, it produces its own health hazards such as reduced lung function and cardiovascular disease, but it also can carry with it other hazardous air pollutants.

The app uses local weather data and collected PM2.5 concentration values. The images below display three important aspects of outdoor monitoring results: the direction which the highest levels of PM2.5 come from, the intensity of the PM2.5 measurements, and the wind conditions at the times of exposure. In the plots, the air monitor is located in the center where the lines cross. The endpoints of the lines represent the cardinal directions of north, south, east, and west with north at the top. The range of colors shows the intensity of the PM2.5 levels from white (low exposure) to red (high exposure). The concentric circles represent the wind speed, with low wind speeds near the center and higher wind speeds further out. Mean concentrations show the average or background air quality. Peaks or max concentrations represent higher exposure to PM2.5.

Mean PM2.5 Concentration

Max PM2.5 Concentration

The polar plot on the left shows relatively low background levels, with the highest levels (which are moderate for background) coming from the south. The corresponding maximum plot shows peak levels coming exclusively from the south, during wind speeds around 10-15 mph. The plot depicting mean concentrations has a scale that spans from 0 to 35 µg/m3. This is because the Environmental Protection Agency (EPA) has set a 24-hour exposure limit of PM2.5 to not to exceed 35 µg/m3 in a given day. Because higher exposure events are hidden by this average, EHP expands the scale for maximum concentrations, the peaks, to reach 80 µg/m3 to better hone in on what direction peak exposures may be originating from. Peak exposures may have the largest impact on overall air quality and health.

Polar Plot Library

The plots below were generated using data collected from EHP Purple Air PM2.5 air monitors from various locations in Southwestern PA and Ohio. For Southwestern PA, weather data was downloaded from the National Oceanic and Atmospheric Administration (NOAA) Local Climatological Database (LCD) for the Pittsburgh Allegheny County Airport. Ohio weather data was pulled from the same database for Akron International Airport. Each row shows the mean and maximum values found near a particular type of infrastructure. Note: There may be other sources near the home that are contributing to the results displayed on the polar plot.

Example 1:

Well Pad Being Drilled to Southeast (mean)

Well Pad Being Drilled to Southeast (max)

The polar plot showing mean, or background levels of PM2.5, shows that low levels of PM2.5 (yellow) reached the monitor from all directions and were not a health concern. The orange value in the center of the plot shows that moderately high values reached the monitor during times of low wind speed. This indicates that there were nearby sources of PM2.5 that accumulated when the air was calm or stagnant. In the southeast quadrant there is evidence of a source, likely a little further away, and PM2.5 from that source reached the monitor when winds were in the 15-20 mph range. The corresponding maximum, or peak level plot shows that times of low wind speed bring the highest exposure of PM2.5 to the monitor. Low wind speeds correspond with poor air dilution, and pollutants remain concentrated under these conditions.

Example 2:

Landfill Accepting Fracking Waste to Southwest (mean)

Landfill Accepting Fracking Waste to Southwest (max)

These two polar plots show that very similar low wind conditions brought the highest levels of both mean and maximum concentrations. These results indicate that a nearby source emits relatively high levels of PM2.5 that do not disperse when winds are calm or light, under 10 mph.

Example 3:

FracSound Terminal to South (mean)

FracSound Terminal to South (max)

The polar plot on the left shows that background levels of PM2.5 were generally very low during this monitoring period, with slight increases during times when the wind came from the south/southeast. The maximum plot shows that all peaks of PM2.5 came from the south/southwest during times with low, moderate, and moderately high wind speeds.

Example 4:

Compressor Station to Southwest (mean)

Compressor Station to Southwest (max)

The polar plot showing mean, or background levels of PM2.5 indicates that this pollutant reached the monitor from all directions at various wind speeds. The highest levels, approaching 35 µg/m3, came from the south during low wind speeds and also from the southwest during higher wind speeds. The round dot in the southwest quadrant likely represents a stream of PM2.5 that was unable to disperse due to the higher wind speed. The monitor recorded the occurrence of a high intensity peak as the plume of pollutants passed by.

Credits: Environmental Health Project: Hannah Blinn, David Brown, Celia Lewis, Sherry Van Lange December, 2019