Farmers have a higher chance of COPD, because of the environment we work in. I had an allergy test done last Monday and they did a breathing and lung function test as well. Results were My lungs are working at 100% capacity, luckily I quit smoking 10 years ago. I have gotten into the habit of wearing a mask in recent years whenever I'm in dust or near mold. I use one in the combine. I noticed I'd still blow black crap out of my nose every evening, even though I was in the cab all day. Since using the dust mask, nothing. I also clean the cabin filter and it's compartment everyday. I also change the filter every 100 hours.