SGP30 Air Quality Sensor Breakout 5A which we've found is the

which we've found is the best all-around gauge

768 KHz crystal for clock generation & RTC

You can use all of the connectors on the edges of the Pi: HDMI

is fixed at 5 V

DAC+ connects to the 40-pin GPIO header of Raspberry Pi 1 Model B+

SGP30 Air Quality Sensor Breakout 5A which we've found is theMeasure indoor air qualitytotal volatile organic compounds (TVOC) and equivalent CO2 (eCO2)with this digital sensor for Raspberry Pi and Arduino. The SGP30 sensor measures two different types of gases: volatile organic compounds (like hydrocarbons) and equivalent carbon dioxide (H2 level is used as a proxy for this). The sensor does some nifty real time baseline compensation to give you the most accurate readings, with just a 10 15% margin of error