According to the EPA, ozone and nitrogen dioxide are considered "criteria pollutants", and as such, are used to help determine the current air quality level. An elevated presence of criteria pollutants in outdoor air can cause harm to both the environment and human health, so tracking where these levels are highest can give scientists and regulators a better chance of reducing them.
Ground-level ozone, unlike the ozone blanket surrounding the Earth, is created when volatile organic compounds (such as pollution from a petrochemical factory) interact with nitrogen oxide. It is typically measured by drawing in ambient air through a large intake and passing it through an analyzer which determines how much UV light is unable to pass through the sample.
Nitrogen dioxide, on the other hand, is an excellent indicator of pollution that is created by burning liquid fuels, such as gasoline. Its levels are quantified by passing a sample of nitrogen oxide-filled ambient air into a chamber that combines it with ozone to produce light that can be picked up by a sensor.The ZMOD4510
The methods outlined above are great for accurately determining levels of certain pollutants, but the equipment, power, and space required to perform measurements is quite high. The ZMOD4510 outdoor air quality sensor platform from Renesas, however, is a tiny 3mmx3mm module that can produce Outdoor Air Quality (OAQ) values using a small integrated heater and metal-oxide chemresistor which measures the current amount of ambient ozone and nitrogen dioxide. It also has an ultra-low power mode for taking selective ozone measurements.
To get started with the ZMOD4510's example software, you'll need to install Raspberry Pi OS onto either a Raspberry Pi 3 or 4, which can be accomplished by first downloading the Raspberry Pi Imager utility. From here, select the latest version of "Raspberry Pi OS (32-bit)" and a Micro SD card. Best of all, the Imager allows users to enter configuration options such as a hostname, SSH, WiFi credentials, and keyboard settings before the Pi is even powered on for the first time.
Additionally, insert the 40-pin header through the header on the board before placing it on the Raspberry Pi.
Make a directory in the home directory (I called mine ZMOD) and enter it with:
$ mkdir ZMOD && cd ZMOD
$ sudo apt update && sudo apt upgrade && sudo raspi-config
At which point, head to Interface Options > I2C > and select 'Yes' to enable.
After rebooting, run
$ sudo apt install pigpio && sudo systemctl enable pigpiod.service && sudo systemctl start pigpiod.service
and reboot one more time. Finally, extract the tar archive file using:
$ tar xzvf GasSensorEvaluation7.8.0a.tgz
and start the GUI:
To begin tracking the air quality, I selected my sensor, the ZMOD4510, and the desired method of operation, OAQ 1st Gen. This method is the normal one that takes periodic measurements of both ozone and nitrogen dioxide and then computes the air quality. The other mode only measures ozone in an ultra-low power configuration. I also kept the name of the target CSV readings file as the default
Data.csv. This file can be loaded back into the software for future analysis if desired.
After letting the software take about ten measurements at night, I was able to see that the outdoor air pollution around my house was very low with an OAQ of zero. The next morning, I set up a solar panel and battery to let the device take far more measurements throughout the day, which would let me observe if the increased traffic around my neighborhood led to any noticeable change in air quality.
As seen from the above chart, the results were a bit surprising. I was able to see how the cars nearby and the wind interacted to move more ozone over the sensor, as well as notice how more traffic in the afternoon versus the morning led to worse air quality.Real-world applications
The small size and low power consumption make the ZMOD4510 module a great choice for measuring air quality in a constrained setting. Imagine a city-wide grid of sensors that each report the air quality in real-time that can allow scientists to pinpoint where automobile transportation causes the worst pollution. Industrial parks that deal with chemical/building material manufacturing could also have several of these modules in order to quickly detect hazardous leaks.Going further
Avnet's Renesas ZMOD4510 Air Quality HAT can be found here, and it features the ZMOD4510 module, a temperature/humidity sensor, several LEDs for easier debugging, and jumpers for selecting the desired power option. The datasheet, sample application, firmware, and design files can all be downloaded from Renesas's website.