I'm quoting Laurie's post, but only to elaborate on it, not to pick on it.
Vacuum them outside or ensure you have a good quality vacuum cleaner if you must vacuum your filters indoors, or just get a good vacuum in general and don't add to your indoor air quality challenges when you clean.
I'm not saying Laurie's vacuum cleaner is crap, but vacuuming your air filters isn't a great indoor air quality strategy to adopt if
yours is crap (
you, the reader of this post).
Also, only vacuum the air filter media on the "outside" -- the side away from the unit's fan, otherwise you can pull particles deeper into the filter (reducing its efficiency) because your vacuum creates more focused suction than your air purifier's fan does.
Another note regarding our air conditioning filters (or HVAC filters in general) is that most are there to protect your equipment, not you. You need a MERV 11 or higher to to even begin filtering out 0.30 micron fine particles that are problematic for respiratory health (
here's a chart). It's also not a simple matter to swap your MERV 4 filter for a MERV 13 filter since the higher MERV ratings also restrict the air flow, increasing static pressure in the system, and can cause equipment to fail or be less efficient. The air handlers in HVAC systems need to be sized appropriately to support higher MERV filters.
I change my air purifier filters every 6 months, but this really depends your air purifier and more importantly your environment -- the occupants of your home, how often activities are done which negatively affect indoor air quality, how much ventilation you have (and whether it's used), and the current quality of the outdoor air in your area.
Once PM2.5 and VOC air quality monitors that track levels over time are more accurate and reliable (and have been tested by an independent lab), I would suggest obtaining one to ensure things are at healthy levels. This type of monitoring will show increases in problematic elements with your indoor air when cooking, cleaning with chemicals, vacuuming with a crap vacuum, etc, and will also help to determine if your air filters are sized appropriately and doing their job (what's the normal baseline level, and how long do they take to return elevated levels to that baseline, etc).