Executive Summary
The Air Quality Monitor senior design project designed and manufactured a low-cost, low-power, portable, autonomous device to accurately monitor ambient concentrations of several harmful gases. The intent of the project was to determine if low cost, commercially available gas sensors could be effectively used in ambient air pollution measurement. Further, the project demonstrated live visualization of collected data via wireless upload, which will open up many options for using the data. In accordance with project objectives, a fully functional device was displayed at E-Days.
The project was motivated by concerns about health risks associated with air pollution, estimated by the World Health Organization to be responsible for 7 million deaths annually worldwide. The beneficiaries of this project include researchers, industry, and concerned private citizens. The device must therefore fill an underserved need for sensor systems that are not prohibitively expensive, but are accurate enough to provide meaningful data.
Twelve inexpensive, commercially available sensors were tested, three for each of the gases investigated. Tests made use of laboratory reference instruments and controlled gas concentrations to simulate a full range of air conditions. Each sensor’s raw voltage data was fit to reference data to generate a calibration equation using linear regression. Final sensor selections were determined through statistical analysis, to ensure the device is as accurate as possible.
The finished device contains sensors for four different gases: carbon dioxide, carbon monoxide, nitrogen dioxide, and ozone. It also contains the accompanying Arduino controller, display, Bluetooth link, high capacity battery, fans, and temperature and humidity sensors. These interior components are protected by 3D printed enclosures, a sealed acrylic outer housing, and a built-in desiccant system to remove airborne moisture before it reaches the sensors. During design, Pugh matrices were used to determine configurations and components. The final product carries a total component cost of $785. This falls in a range that bridges current cheap but ineffective systems and expensive but highly accurate systems, and represents the best of both worlds.
A web interface was also constructed. Data is sent via Bluetooth to a local server, and a demonstration website contains scripts that pull from this server to generate graphs of concentration fluctuations, which update in real time. This display allows for both live measurements and analysis of long term trends.
The project as a whole cost $3,600, only 72% of the allotted $5,000 budget. The intent of the project was accomplished, and the majority of design objectives were met. Should the project be continued, some suggested areas for further development include investigation of sensor drift, incorporation of particulate matter sensors, and upgrades to the web interface.