With a functioning Nissan cabin air filter, the air quality in the passenger cabin will be improved as compared to the air outside of the vehicle. For most vehicles, including Nissan, this filter is a HEPA filter. To be considered a HEPA filter it must be able to remove 99.97% of all particulates that are 0.3 microns or larger. This standard is set by the USDOE. For comparison purposes the human hair has a diameter from 17 to 180 microns. The ability of the cabin air filter to trap and retain these very small particulates is why the air quality in the Nissan passenger cabin is better to breathe. This ability to trap small particulates is only hampered when the space between the fibers begins to fill up and the cabin air filter begins to become clogged. Unless the paper or charcoal element is replaced, stress will be applied to the duct fan and cause it to prematurely wear. The volume of air in that will be able to enter the passenger cabin will also be reduced. The location of the Nissan cabin air filter element is found next to the windshield just behind the firewall under the hood of your vehicle. It is easily accessed through the glove box. When this filter element is being replaced, the duct work should also be inspected for any large debris that might have become trapped there. If any is found in your Nissan's duct work, then it should be removed before the new filter element is put into place. The time period for the replacement of the cabin air filter will be dependent on the environment the Nissan is driven in. The dirtier or more polluted the air the vehicle is driven in, the more frequent the cabin air filter should be checked and replaced. As a general rule, annual replacement is a good benchmark.