What does each node consist of?


Each node consists of several parts:





A 3D Visualization of the Node

Our sensors include CO, NO, NO2 and O3 sensors along with a RH Temperature sensor. This 3D visualization let's you see what is inside each node's casing. It represents the Dylos particle sensor, the alphasense sensors, the Raspberry Pi, and the electronic boards. Feel free to rotate and zoom to get a better look!

What are we measuring?


We are measuring five pollutants: nitric oxide, nitrogen dioxide, carbon monoxide, ozone, and particulate matter. The NOx group (nitric oxide and nitrogen dioxide) is emitted from automobiles, power plants, and turbines. Carbon monoxide comes from automobile exhaust and burning fuel. Particulate matter is the result of a wide range of manmade and natural sources, while ozone is the result of reactions between chemicals already in our air. Together, these pollutants paint a comprehensive picture of air quality impacts from the interaction of human activity with natural processes.




Carbon Monoxide

CO is an odorless, colorless gas that is highly toxic in when encountered in high concentrations! The main contribution of CO is vehicle exhaust but other sources include fuel combustion, fires, and volcanoes. Harmful health effects of CO occur when it enters the bloodstream through the lungs and binds to hemoglobin, reducing the amount of oxygen that reaches the bodys' tissues and organs.

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Nitric Oxide

Nitric Oxide is colorless and odorless, and of the nitrogen oxides (NOx) emitted, NO is the primary pollutant. While NO is non-toxic by itself, it quickly converts to NO2 in the air.

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Nitrogen Dioxide

Nitrogen Dioxide (NO2) is strongly tied to the presence of O3 and particulate matter. The largest sources of NO2 are combustion processes, such as heating and power generation. Long-term exposure to NO2 has been linked to adverse respiratory effects.

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Ozone

Ozone (O3), when found in the upper atmosphere, protects earth from the sun's harmful rays. However, ground level ozone is the main component of smog and can harm our health. This ground level ozone is formed from reactions between nitrogen oxides and volatile organic compounds.

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Fine Particles

Particulate matter (PM) consists of a mixture of solid and liquid droplets. Particles less than 10 micrometers are so small that they can enter the lungs, posing a serious threat. These small particles are typically divided into two categories: fine particles (<2.5µm) and coarse particles (>2.5µm and <10µm).

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Coarse Particles

Particulate matter (PM) consists of a mixture of solid and liquid droplets. Particles less than 10 micrometers are so small that they can enter the lungs, posing a serious threat. These small particles are typically divided into two categories: fine particles (<2.5µm) and coarse particles (>2.5µm and <10µm).

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How have we calibrated our sensors?


Every node is outfitted with 4 electrochemical sensors, which output millivolt readings. Using research grade instrumentation in the Parsons laboratory, we calibrated every sensor individually. The goal of the calibration process was to provide a precise conversion of the electrochemical sensor millivolt readings to a parts per billion unit of measurement for the individual gas species. Using an airtight metal chamber which fit two nodes at a time, we created a system where air was pumped in through tubing to the nodes and out through tubing to the equipment, so that both the nodes and the equipment could measure the same gas pulses. Using a linear regression, the relationship between the millivolt readings from the sensors and the ppb concentrations from the instruments created.

How are we measuring air quality?


Air quality is monitored in the United States by the Environmental Protection Agency (EPA), which determines air quality using a composite Air Quality Index (AQI). We devised our own AQI by adjusting for the unique measurement schemes calibrated on our sensor nodes. The index determines overall quality based on concentrations of fine particulate matter, carbon monoxide, and ozone. Concentrations are used to produce an index value, ranging from good to unhealthy.

Contact Us


Please contact us at clairity@mit.edu with any questions.