Need to monitor Pm. NOx, HC and CO from a diesel locomotive.
Can you replace CO2 detector and install a CO detector board. there is a recommendation of MiCS-4514 on ESPHome. Also need to detect Hydrocarbons. Is there a extra urart connection or I2C connection. If so any recommendations for a HC module?
There’s an open JST connector on the board that has pins to I2C bus. Any sensor you can connect over I2C can be connected, and there is quite enough space inside the case to put an sensor in (though possibly not enough free airflow to make measurements accurate.)
The kicad files for PCB design are available on the website so you can look at that.
I took a look at the datasheet for the MiCS-4514. It appears to tick your boxes since it is a sensor designed to detect CO and a range of HCs including nitrogen dioxide, ethanol, hydrogen, ammonia, and methane.
This describes it as a sensor designed for detection of automobile pollutants. With that in mind since there is an open connector that may be the easiest option for you, adding it to the package while leaving other sensors in place.
I am considering an O3 detector for mine since that is the main airborne pollutant in my region along with particulates and I will likely add one to the board using the open slot once I find one.