The air quality sensor contains a non-dispersive infrared (NDIR) sensor to detect carbon dioxide gas using infrared (IR) spectroscopy. A Bosch SensorTec BME 280 is used for measuring meteorological variables: humidity, pressure and temperature. An Alphasense OPC-N2 optical particle monitor is used to measure particle matter (PM). The OPC-NE sensor uses a laser beam to detect particles with diameters from 0.38 to 17 microns in 16 size bins and converts these size distributions to PM1.0, PM2.5, PM10.0. All sensors are wired to a Raspberry Pi 3 Model B microprocessor that is used to automate data collection. The Raspberry Pi transmits data via a direct on-site ethernet connection or Adafruit Fona Cellular Breakout. An Adafruit Ultimate GPS Breakout is also connected to the Raspberry Pi to ensure timestamp accuracy. Students operate the Raspberry Pi through its Linux operating system to run specific data acquisition programs that are written in Python.
During 21-23 July 2017, an experiment using the air quality sensor was performed in a home in Toppenish, WA. The sensor was placed 20ft from the kitchen stove and ran continuously throughout the three-day experiment. The highest concentration of carbon dioxide occurred on 7/23/17 ~800am when all stove top burners were being used on high heat. The highest particulate levels (PM1.0, PM2.5, PM10.0) occurred on 7/23/17 ~1:30pm when the stove top was being used to cook large volumes of foods. During this time period, 40-50 house guests were visiting which likely impacted the carbon dioxide concentrations. In addition, other nearby sources of pollutants included a neighboring livestock facility and nearby automotive mechanic shops.
In the future, air quality sensors of this type will be deployed outdoor on rooftops in Spokane, WA as part of the Urbanova project. Future sensors will use a gas plenum that will serve as a sample chamber for the additional sensors to measure ozone, sulfur dioxide and carbon monoxide.