The SparkFun gator:environment micro:bit Accessory Board utilizes the popular CCS811 and BME280 ICs to take care of all of your environmental readings of atmospheric quality. This sensor board can provide a variety of environmental data, including barometric pressure, humidity, temperature, equivalent TVOCs and equivalent CO2 (or eCO2) levels. The gator:environment connects to the SparkFun gator:bit via alligator-clip cables, allowing for easy access to the micro:bit's I2C pins.
The CCS811 is a digital metal oxide (MOX) gas sensor that detects wide range of Volatile Organic Compounds (VOCs). With an integrated microcontroller that implements special algorithms to process the raw measurements, the CCS811 outputs the equivalent total VOC (eTVOC) and equivalent CO2 (eCO2) values over an I2C connection. It provides readings for the total volatile organic compounds in the parts per billion (PPB) and equivalent CO2 (or eCO2) in the parts per million (PPM). It also has a feature that allows it to fine tune its readings if it has access to the current humidity and temperature. Luckily for us, the BME280 provides humidity, temperature, and barometric pressure! This allows the sensors to work together to give us more accurate readings than they'd be able to provide on their own.
Note: Unfortunately, CO2 isn't a VOC and MOX type of sensors can't directly measure CO2, despite being great at VOC detection. However, in an indoor setting, humans are a primary source of VOCs through the process of breathing. The equivalent CO2 (eCO2) values are then estimated based on algorithms that are used to analyse the sensor data to determine the TVOC attributed by the presence of humans. This type of sensor should not be used in applications that directly require the measurement of CO2; it is an inferred value.