2 / Pack. Air purifier pre-filter features an advanced design to help capture harmful and potentially dangerous gasses and VOCs such as ammonia from the air that pass through the filter. Potassium permanganate calcite helps reduce common household odors to keep rooms smelling fresh. Larger particles such as dust, lint, fibers and pet fur are also captured from the air that passes through the filter. Easy-to-install design allows quick, simple replacement to ensure optimal performance. For the best performance, this air purifier filter should be replaced every three months.