Portable units are usually not effective. If you must engage in these activities, use a face mask. Try to avoid woods where mold growth on rotted logs is high. Or buy commercial products such as X-14 in a spray dispenser. Mold allergy is only one cause of allergic fatigue.
Allergies are actually shockingly widespread in today's society.
Over twenty million Americans suffer from hay fever. About ten million are victims of asthma, and another eleven million suffer from skin disorders like eczema, hives, and rashes. Many allergic individuals don't realize that their unusual fatigue, irritability, and mood swings may be due to allergic reactions. Dust allergy is one of the most common unrecognized allergies I see in my practice, and like other allergies, it inevitably causes fatigue. These particles are so fine that the slightest gust makes them airborne.