Interpreting Your Readings

How to turn numbers on a screen into meaningful information.

Ultra Violet Radiation

UV damage to skin based on UV intensity

A voltage is produced in the metal in the UVI-01 sensor when it is exposed to ultra violet radiation, by the photoelectric effect. As shown in the graph below, the greater the intensity of the radiation, the higher the voltage (it also depends on the resistance of the resistor used in the sensor's application circuit, shown by the multicoloured lines).

Voltage proportional to UV intensity

Sensor Datasheet

Nitrogen Dioxide

Nitrogen dioxide concentrations are a good measure of urban air pollution; NO2 plays a major role in atmospheric reactions that produce ground-level ozone, a major component of smog.[Clean Air Partnership]

Pie-chart showing where nitrogen dioxide comes from

It can be harmful because it can transform in the air to form gaseous nitric acid and toxic organic nitrates[CAP]- concentrations above 20ppm are classified as immediately dangerous to life or health and it can damage the lungs, cardiovascular system, respiratory tract and eyes[Airgas].

We tested the MICS-2710 sensor's response to NO2 concentration ourselves:

Raw data from our measurements
Official datasheet

Carbon Monoxide

Pie-chart showing where carbon monoxide comes from

Carbon monoxide is another major urban air pollutant, and also part of a series of reactions producing petrochemical smog. It's mainly produced by incompletely combustion of fossil fuels, and concentrations can rise to lethal levels in closed environments. CO poisoning is the most common type of fatal air poisoning in many countries.

Concentration Symptoms
35 ppm Headache and dizziness within six to eight hours of constant exposure
100 ppm (0.01%) Slight headache in two to three hours. Starts becoming dangerous to human health.
200 ppm Slight headache within two to three hours; loss of judgment
400 ppm Frontal headache within one to two hours
800 ppm Dizziness, nausea, and convulsions within 45 min; insensible within 2 hours
1,600 ppm Headache, tachycardia, dizziness, and nausea within 20 min; death in less than 2 hours
3,200 ppm Headache, dizziness and nausea in five to ten minutes. Death within 30 minutes.
6,400 ppm Headache and dizziness in one to two minutes. Convulsions, respiratory arrest, and death in less than 20 minutes.
12,800 ppm Unconsciousness after 2-3 breaths. Death in less than three minutes.

Raw data from our measurements
Datasheet from Manufacturer

Interpreting Your Gas Sensors

Our code takes the resistances of your gas sensors and turns them into gas concentrations according to our measurements, but if you'd like to have a go calibrating your AirPi's sensors yourself, here are the ranges we worked out.