I recently had an F/A-18 jet fly over my house and was amazed at how loud it was. That set me to wondering how loud it actually was.
Do any outdoor sensors exist that can track decibel level?
Try pairing a microphone with your favorite IoT platform. The problem with this approach is that, initially, you would have to find a way to calibrate it.
Another option would be the Grove (Arduino).
As for the "outdoor-ness" of a sensor, just shield it from the weather and other disrupting elements.
There is a product called IoTSENS Sound and Noise Sensor. As the specification say, it has following features.
(Ethernet is the default option, you can select other options too).
They do already exist, though they're not easy to find. Here's a bluetooth one on ebay for instance. Obviously, however, in order to remotely use that one, you would have to have it constantly paired with a computer that is nearby and connected to the internet.
However, there are also wifi enabled digital sound meters, such as the Noise Sentry RT-W.
Another option is this USB dongle with you are supposed to be able to connect to some sound level meters.