by Robin Kemp

UPDATED 10:34 a.m. 8/12: EXPLAINS color coding/AQI number on map, reason for placing data on its own page

Clayton County has very few local air or water quality monitoring stations. Now, residents will benefit from the first “citizen science” air quality sensor south of I-20 in metro Atlanta.

Clayton County’s first crowdsourced air quality station measures particles in the air that flows through holes in the two blue sensors. (Photo: Robin Kemp/The Clayton Crescent)

The Clayton Crescent’s executive editor and CEO, Robin Kemp, paid for the monitor herself but is sharing the data with anyone who wants it, by way of a free crowdsourced map. The sensor is built by a company called Purple Air, which collects the data from air quality sensors that people buy and install at their own locations. Purple makes three different air sensors: an outdoor monitor that sends data by wi-fi, another outdoor monitor that sends data by wi-fi but has a micro SD card backup in case the wireless signal goes down, and an indoor air quality monitor.

How it works

The sensor collects data and performs calculations to simulate the results of Environmental Protection Agency sensors. (Purple offers a more detailed explanation here.) Air flows through holes in two sensors. A laser particle counter measures contamination floating in that air. From that measurement, the sensor uses the average particle size to calculate a “mass concentration.” The sensor then converts the mass concentration into the Air Quality Index (AQI) number in the dot on the map.

On the Forest Park sensor, the data is sent via wi-fi to the map at It also is recorded to a micro SD card inside the sensor in case the wi-fi goes out, allowing any “missing” data to be uploaded to the map later.

The sensors are suitable for mounting on the sides of buildings, on poles, or on fences–anywhere the sensor can get electricity to run and a wi-fi signal to send the data.

This outdoor air quality monitoring sensor is named “Forest Park, GA – Clayton Crescent” (Photo: Robin Kemp/The Clayton Crescent)

You can see air quality readings in real time on our Air Quality page at while we work out some bugs in the code that prevented it from working well in the sidebar.

As of press time, stormy conditions prevented installation of the monitor outside, so its first readings reflected indoor air quality. Over time, as the sensor gathers more outdoor data, the average will likely show a higher AQI number (meaning lower air quality). If you ever see a gray dot on the map, that means the monitor is offline. When it’s online, you’ll see a colored dot (ranging from green to dark red) with a number in it that represents the air quality at the sensor’s Forest Park location.

The big picture

Ideally, at least one monitor will go up in each city in Clayton County, giving residents a better idea of how clean (or dirty) their air really is. More monitors mean more data, and more data means a clearer picture overall.

Each sensor costs about $250, which is about the cost of a Little Free Library. (See our map of Clayton County’s Little Free Libraries–with several new locations coming soon!).

If other people and organizations in Clayton County and the Southern Crescent install air quality monitors, we will add them to a similar map here on the website.

Funding citizen science

One way to make things like air quality sensors and water quality testing kits more affordable is through a fundraiser or similar group effort. Schools or nonprofits might be able to apply for grants (The Captain Planet Foundation makes grants in Clayton County) as part of a STEM education project.

“Citizen science” offers a hands-on, real-world way for students to learn about their immediate environment and to make larger connections about the world around them. From monitoring air and water quality to building devices and coding data into interactive maps and apps, plenty of opportunities abound.


Here are some resources to get you started with your own citizen science projects:

The Clayton Crescent encourages local Girl Scouts and Boy Scouts, 4-H, schools, community centers, parks, and interested citizens to consider locating similar sensors across the county and adding their data to crowdshared maps.

If you or your group install a similar sensor, please let us know and we will add your sensor’s widget to our website. If you do your own citizen science monitoring project, please be sure to let us know in advance so we can cover you in action!

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