16 yr girl has rhinorrhea appear when exposed to dusty or plants rich environment what could reduce this discharge?

Allergy treatment. The nose is first and foremost an air processing structure. It warms, filters and humidifies the air we breathe by making mucous. Mucous adds water to the air, warms the air and traps particles cleaning the air. Sometimes this system goes crazy and excessive mucous is secreted. Calming the nose with steroid sprays can help. If allergies are an issue antihistamines can help as well.
Avoidance - meds. First avoidance when at all possible, other times try an antihistamine, and always consider seeing an allergist for desensitization.