Typical air vs. spike days
- Annual average PM2.5 (8.73 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (21.66 µg/m³) is what filtration must handle during bad-air events.
Sections below reference one or both metrics on purpose — that is how HVAC vs. portable guidance differs for San Diego without contradicting EPA-aligned thresholds.
Coastal and Inland Allergens
Seasonal pollen and mold spores from the marine layer create a heavy, often invisible particulate load for local homes. Proximity to the coast and various canyons introduces a mix of salt air and native plant allergens that can saturate a standard filter quickly. These particles accumulate on the filter media and can eventually bypass low-quality fiberglass filters, entering your ductwork and living spaces. Regular replacement is the only way to ensure these biological loads don't degrade your indoor air quality.
HVAC Technician's Advice
For the typical home in the city, a MERV 11 filter provides the best balance between air cleaning and system performance. Since ozone peaks reach 0.0788 ppm, I highly recommend using a filter with activated carbon to help remove gaseous pollutants and odors that standard pleated filters miss. If you live near high-traffic areas or have respiratory issues, upgrade to a MERV 13. You must replace these filters every 60 to 90 days. Neglecting this schedule leads to dust buildup on the evaporator coils, which reduces cooling efficiency and significantly increases your monthly energy costs.