Sensor Type

Carbon Dioxide (CO2)
Parts per Million (PPM)

CO2 is a colorless and odorless greenhouse gas, occurring at an average concentration of about 400 parts per million. In urban areas, concentrations are generally higher. Indoors, they can reach 10 times background levels. CO2 is a good indicator of the ventilation rate in tightly enclosed spaces or where occupancy is high.

Particulate Matter (PM 2.5)
Counts per Liter (counts/L)

PM is a mixture of solid and liquid particles made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles. Fine particulate matter (< 2.5 µm) is small enough to pass the blood-air barrier in our lungs and enter into our pulmonary system, potentially triggering heart and lung diseases.

Carbon Monoxide (CO)
Parts per Million (PPM)

CO is a colorless, odorless gas that can cause harmful health effects by reducing the oxygen delivery to the body’s organs (like the heart and brain) and tissues. At extremely high levels, CO can cause death. Most of the CO in the atmosphere is produced through photochemical reactions in the troposphere. In urban areas, CO concentrates because it is a byproduct of internal combustion.

Volatile Organic Compounds (VOC)
Parts per Million (PPM)

VOCs include both human-made and naturally occurring chemical compounds. Most scents or odors are made up of VOCs. VOCs evaporate at room temperature and are emitted by a wide array of products used in homes. They cause eye, nose, and throat irritation, headaches, nausea, and can damage the liver, kidney, and central nervous system.


Hourly Averages

These graphs plot the hourly average across a week’s worth of data of each city (the green line) on top of the entire sensor network’s hourly minimum and maximum readings (the gray area graph). At a glance we can see which city is pushing the network’s maximum with elevated average concentrations. Hover over individual graphs to see the axes and scales.

London
New York
San Francisco
Tokyo

Exceedences by Location Type

This graph tallies the number of exceedence events for each type of location for the defined time period. By comparing across location types we can begin to learn whether certain types of spaces have a tendency towards higher concentrations of certain pollutants. Do libraries tend to have a stronger concentration of CO2? Does Tokyo tend towards higher VOCs regardless of space type? Hover over city names to see numerical data. (An “event” is defined as a period of time in which the sensor detected readings that exceed the accepted healthy range of pollutant exposure.)


Portion of the Day in Exceedence

For each day of the week, we compare the number of hours in that day where the sensor reported concentrations that exceed the accepted healthy range of pollutant exposure. Are there certain days of the week that tend towards higher concentrations? Hover over city names to see numerical data.