Dust and Mold
Sorry it has taken so long to answer your question. the expert that was assigned this one took other employment and did not tell the expert system.
I suspect most of your problems are due to mold spores. Spores are the "seeds" that spread mold with the wind. Humid/wet environments have a cocktail of mold varieties that contain almost every type that we know. Most of us that are allergic to molds are allergic to nearly all of them. The environment has all of the elements to grow mold and produce mold spores. Cold or dry weather are the only environmental conditions that slow the production of mold spores. There in east Tennessee, you have all the moisture and food needed to grow mold. Organic dust is one of the favorite foods of mold. Your best bet is to maintain an indoor humidity near 50%, which will give you an island of relief from the spore laden outdoors. That means venting cooking and bathing areas to get most of the moisture those activities produce out of the home. Using air conditioning to further reduce the humidity. If necessary, use a dehumidifier to finish the job. But, 50 to 55% indoor relative humidity is needed to minimize the mold growth in your home.
As far a the dust goes, I think they report those numbers to show the organic dust that can grow mold. Some folks are allergic to organic dusts of some plants. Sources of organic dusts are food processing industries, lawn mowing, hay and grain harvests and others that may be in your community of which I am not aware. In your home you have pet dander, human skin dander, dust mites, lint and mold spores, among others.
In short the list of possibilities in nearly endless. And our environment contains a mixture of nearly all of the possibilities.