These air quality monitors were deployed around the community for 2-3 years. They were typically mounted onto a tripod on a flat roof tops, weighed down with sand bags and there was an AC power outlet available. 

The electronics were housed in a plastic enclosure with 2 holes drilled out on the bottom side. 

1. The AC power is stepped down to 12v DC by an LED lighting power supply that connects to the main board.

2. The brains of the monitor is the Arduino Mega 2560 connected to main board. It provides enough inputs for all the add on board and 9 sensors.

3. Pololu D24V22F5 step down voltage regulator to bring the 12v DC down to 5v DC

4. Adafruit FONA gsm quad band radio (2G) with SimCom SIM800H 

5. There is 12v DC fan acting as an intake, with the second hole allowing air out. The large main board acts as an air break, keeping the air flowing over the sensors. The fan runs continuously, so it also helps keep the electronics dry. Fiberglass window screen is used to keep large debris and critters from coming into the case.

The large main board was developed by a grad student named Graeme at UW in 2019. It allows all the add on components to communicate and get power. It also has an on board RTC (DS3234), bi-directional logic level converters to the arduino, a 16 bit ADC (MAX1302) for the gas sensors and another level shifter (74HC4050D) for the micro SD card slot.

The bottom side of the main board shows the Alphasense individual sensor board for B4 series of sensors. There are two Carbon Monoxide (CO-B4) and two Nictric Oxide (NO-B4) sensors attached. These were selected to measure the difference in levels of exhaust from semi trucks. There are also two Shinyei Dust Sensor (PPD42NJ).

Removing the gas sensor boards reveals another set of sensors flush mounted to the main board. These are particulate matter sensors from Plantower (PMSA003) that give PM2.5 and PM10 readings. They are connected via a small header and attached with screws. There is also an Adafruit temperature and humidity sensor board (Sensirion SHT31-D) on the left. You can also see the connectors for the dust sensors and brackets that attach the main board to the case.