I live north of LA in Lancaster, CA on the desert. While we get wind and dust the layout is in my 20 x 20 video room and runs around the top of the room. I keep the windows closed year round and use a swamp cooler during the summer months and a small quartz heater in the winter. Doesn’t matter the time of year the tracks become black after about 2-4 hours or run time. I have been told to clean the loco and rolling stock wheels but have not seen nor had to remove any black on the wheels.
Check the humidity in the room, with the swamp cooler, you are probably well into the + 70% range. While I know a window Air Conditioner will cost more to operate, I’d bet a lunch at McDonalds getting your humidity under 50% will go a long way toward keeping the track clean and being more comfortable in the train room as well.