The thing with anything in the air.
Is directly related to the cf of space available and how fast that air is turned over. Air quality is generally measured in ppbv or parts per billion by volume, or parts per trillion (million million) by volume (pptv). Pollutant concentrations are also measured by the weight of pollutant within a standard volume of air, for example microgrammes per cubic metre (µgm-3) or milligrammes per cubic metre (mgm-3).
In considering the buildings use before you. How clean is the floor? Has the "spilled" hydrocarbons been cleaned out of it? Someone asked, "Do you "smell" anything when you first enter the space?"
Well, do you?
How much air is turned over and how fast?
3-4 ft of space between the canopy and the light is a bit much but, not the cause of your problem... I would go nearer 2.5 as you have plenty of space for the heat to rise. - Why I ask for canopy temps and bellow. I'm trying to get a handle on your total environment conditions. AND RH is a very important part of that picture......
Then the feeding questions round out the story, along with the media used, nutrients, amounts of and water source.
Answer these questions, and the earlier ones I asked and we may get somewhere faster!