The first two links with information about the sensors at the gasboard at the bottom of the page below are dead.
https://docs.smartcitizen.me/Components/Gas%20Pro%20Sensor%20Board/
I found the following information on the side of alphasense:
http://www.alphasense.com/WEB1213/wp-content/uploads/2018/12/NO2B43F.pdf
http://www.alphasense.com/WEB1213/wp-content/uploads/2018/12/OXB431.pdf