Note: this software is aimed to only the AirGradient Pro 3.7 with TVOC. You can certainly adapt this script if you don't have the TVOC module in your Air Gradient.
This modification adds a http /metrics (for prometheus), and a /metricsjson endpoint on port 8080.
This script is not written from the ground up by any means. The base of this script was taken from https://github.com/airgradienthq/arduino. To make it easy to tell what was modified, all bits of code added by me have a comment denoting that.
Clone this repo and open air_gradient/air_gradient.ino. Install all libraries at the correct version listed in the comment. After installing those libraries, additionally install AirGradient Air Quality Sensor.
Then, downgrade EspSoftwareSerial to version 6.17.1. As of right now, version 7.0.0 causes frequent crashes. (Thank you to ken830 on the Air Gradient fourms for putting in a lot of work to figure this out!)