Many types of air fresheners are designed specifically for cars. Regardless of the type you get, be sure to place it in an area that receives enough airflow to circulate the scent throughout the car. Dash air vent clips and air fresheners clip into or over air vents. On the other hand, tree-style air fresheners and other air fresheners can be placed in the rearview mirror or hung under the dashboard. Where the passenger's feet go to get the most circulation.