Science Sunday: Air Pollution!

Science Sunday: Air Pollution!

Today’s blog post is brought to you by Dr. Ben Greenfield.


Air pollution is an ongoing problem throughout the world. In addition to affecting the climate (e.g., global warming), air pollutants can lead to death and disease in people, and can also harm plants and wildlife. For some harmful air pollutants, laws and policies have been developed to reduce levels in the atmosphere. To see how these policies have affected pollution, scientists and engineers have developed methods to monitor air pollution levels. In the US, there is an extensive network of federal and state monitoring stations to track air pollutant levels, focusing on more populated areas. The image below indicates such stations, recorded by the US Environmental Protection Agency (EPA). As we can see, there are many stations in some places, and fewer in other places:


Fine particulate matter is one of the types of air pollution that has been a major concern for human health. Scientists sometimes refer to fine particulate matter as PM2.5. PM2.5 stands for “particulate matter 2.5 micrometers or less” in size. To get a sense of how small that is, we can look at the below image, again developed by the EPA. The below image is a magnified comparison of the size of a single human hair to PM2.5 and other things. What the image shows is that about 20 particles of PM2.5 lined across fit into a single human hair. These PM2.5 particles are so small! 

Because these particles are so small, they can penetrate deeply into our lungs when we breathe them in. Furthermore, these particles often contain harmful chemicals that can hurt our lungs and circulatory system. For these reasons, fine particulate matter is important to monitor throughout the world. 

These pollution particles have been monitored in the air for many decades. Historically, this monitoring was conducted by research scientists who had many years of specialized training using very expensive equipment. Interestingly, over the past 10 years or so, technology has developed allowing many more people to do this monitoring. In particular, there are now monitoring devices that are relatively inexpensive, and not too hard to set up. These are called low cost sensors and they collect the same kind of monitoring data as the more expensive instruments. Using low cost sensors, we can examine local patterns in fine particulate matter, including in our own communities and neighborhoods. For example, here is a picture of SIUE Masters Student Josh Gifford setting up one of the air monitors at the SIUE campus:

Image Credit: Howard Ash/SIUE Marketing and Communications

The sensor Josh is setting up is made by a company called PurpleAir, and can be purchased from their website: In addition to being relatively cheap, these kinds of sensors have also performed very well in different kinds of testing (for more information on this you could see: 

Scientists and people interested in science are now setting up these and other sensors throughout the world, including locally in the St. Louis region. The next image below is a map of the PurpleAir sensors in the St. Louis area. Each colored dot is a place where a sensor has been set up and is collecting air quality data. The colors and numbers indicate the levels of PM2.5 fine particulate matter pollution at the sampling location, averaged over a 1 day period, on May 21, 2021. 

Image Credit: PurpleAir. Web query from PurpleAir’s interactive map of air quality monitoring results on May 20, 2021. 

At the time this image was created, 11 of these stations were collecting data in the St. Louis area (you can see this by counting the colored dots – you will find 11 of them). We see that the stations are fairly spread out and that there are a lot of areas without stations. For example, there is no monitoring in Venice, Madison, Granite City, Washington Park, East St. Louis, Ferguson, and Glen Carbon at the time the photo was taken. It would be beneficial to have stations in all of the missing areas. By setting up more stations, we could get more local information on the air pollution levels in these areas. 

You may have noticed the single green station in the lower left hand part of the map. This is actually an indoor station, whereas all the other stations are set up outdoors. We can see that the number in the dot is 1, much lower than the other stations. This indicates lower levels of particulate matter pollution. Indoor levels can be very different from nearby outdoor levels, depending on factors like whether people are smoking inside, cooking with gas stoves, or lighting incense. It would be interesting to do side-by-side comparisons of an indoor and an outdoor sensor. It would also be interesting to compare different indoor areas; for example, levels could be different in different parts of a restaurant, a factory, or an auto repair shop. It’s just a matter of finding interesting places to monitor.

Sometimes levels between the different outdoor sensors vary a lot also. For example, the following image compares the station in Brooklyn, Illinois vs. the station in Edwardsville, Illinois:

Image Credit: PurpleAir. Web query from PurpleAir’s interactive map of air quality monitoring results on May 20, 2021. 

The squiggly lines indicate the average levels of particulate matter over time at these stations. Each station actually has two sensors running at the same time – thus there are four squiggly lines. When the lines are higher, the particulate matter levels are higher. Notice that the four lines mostly overlap most of the time. Although most of the results are similar among the lines, we see a big difference around May 14. Here we see that the particulate matter levels were many times higher in the Brooklyn station than the Edwardsville station. This might indicate a local pollution event. Further study and comparison between the stations could see if there are local pollution sources affecting local areas. This would also benefit from adding more stations. 

In short, there are many different things we could do to monitor and track air pollution in our local area. This blog post focused on the air pollution monitoring, including local activities in the St. Louis area. We can also monitor for other local issues, such as noise pollution, soil pollution, and heat levels (i.e., temperature). Keep posted for future posts about these topics. 

Photo Credits

Photo of PurpleAir air quality sensor captured on June 2, 2021 by Xander Kalna from PurpleAir’s website.

Photo of US EPA’s Interactive Map of Air Quality Monitors on May 20, 2021 captured by Ben Greenfield.  

Photo of particulate matter size comparisons provided by the US EPA.

Photo of Josh installing a PurpleAir monitor by Howard Ash, SIUE Marketing and Communications.

Photo of the PurpleAir interactive map on May 20, 2021 captured by Ben Greenfield.

Photo of PurpleAir air pollution levels captured by Ben Greenfield on May 20, 2021 from the PurpleAir interactive map.