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This will improve the air quality traveling through the vent system of your car. You should always apply new air freshener lightly to prevent it from being overpowering. You can do this by applying a purifying spray made from water and  hydrogen peroxide to your car's air intake. You can identify the intake by checking your car manual. You should shake the solution gently but thoroughly to mix. Spray your water/peroxide solution into your car's fresh-air intake. This spray will kill germs and mold living in your car, but it is a gentler cleaning agent than most and will not irritate your lungs or eyes. Fill a small jar with a 1/4 cup of baking soda and punch a few holes into the lid or stretch some cheesecloth across the mouth of the jar. You can put this in a cup holder or out of sight in a pocket. Add a few drops of essential oils to create a pleasant fragrance to accompany the refreshing effects of your baking soda. These will help your car fight persistent odors. If you participate in sports or a physical activity, tuck a dryer sheet in your trunk or in an interior pocket to fight strong, sports related odors.
Make a mold and germ killing spray. Refresh your car's air intake. Mix one cup of water and one tablespoon of the hydrogen peroxide in a spray bottle. Open doors and windows while running your car fans at full blast. Make an air freshener for your car. Hide dryer sheets under seats, floor mats, and in pockets.