My understanding (which may be wrong, so I am open to being corrected) is that the greatest power consumption you'll see from ESP32 is connecting to a network and uploading data, the idea being less connections mean less power consumption. The ePaper display should be nice and low power consumption, too. I'd expect a common pocket battery bank to power it for a few weeks if one were using it to gather data for later use.

Again, happy to be corrected. It's really fortunate that this post showed up on HN since just last month, I ordered a few components to start making my own air quality sensors, the goal being to create some units that I can strap on my car and gather data while I travel for work (personal curiosity, mostly). There's tons of great projects and info being referenced in this thread.