Mostly pollen filter is depending on the service time of the pollen filter. It should not be reused and should be replaced as soon as smoke or odor begins to penetrate. You can clean about 3000 miles at first. It can clean for about 3-4 times. Usually we replace every 10000-15000 miles or approximately one year. If you buy common short fiber media, you can change in 8000-10000 miles. If you use synthetic fiber media, you can change in 12000-15000 miles. You also can change each year, for example each February is the best month.