ultrafine smoke particles, these things are tight. if you basically look at air quality, the issue is it is harmful but invisible. if i put a dirty glass of water in front of you you would not drink that. you have that choice you can see that. you do not have that choice with air quality thus important of concert filtration. eric: you umc cannot see the sw tiny is it? what does that mean? and can you always smell it? you know, you cannot always smell in the size is not visible to the eye. you are talk about micron sizes of .1 for instance. you can see dust sometimes and things floating in the air. if you put it light audit these are tiny particles are quite harmful. eric: look and it difficult air pollutants there s a lot of controversy over gas stoves the science of showing it is there. you ve got radon and mold and