Both outside and recirculated air are routed through a passenger compartment air filter. Pollen, dust particles and other contaminants are removed by the filter. Airflow reductions indicate that the filter needs to be replaced. For a replacement filter see your dealer/retailer. See Scheduled Maintenance for replacement intervals.
The access panel for the air filter is behind the glove box. To replace the filter:
Replacing the air filter is recommended, but will not damage the vehicle if it is not.