Typical air vs. spike days
- Annual average PM2.5 (8.10 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (35.27 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 Pacifica without contradicting EPA-aligned thresholds.
Coastal Humidity and Allergen Load
The primary challenge for filters in the city is the combination of coastal humidity and biological matter. Pollen from coastal scrub and grasses, along with mold spores common in damp environments, creates a sticky load on HVAC filters. High humidity can cause these organic materials to bind to the filter media more aggressively, which restricts airflow faster than dry dust would. This makes regular filter maintenance essential to prevent the HVAC system from straining and to stop mold from developing within the ductwork.
Technician Filter Recommendations
Given the PM2.5 spikes exceeding 35 µg/m³, I recommend a MERV 13 filter for all local homes. This rating is necessary to trap the fine particulates that characterize the area's worst-day events. Due to the coastal humidity, filters can become saturated with moisture and organic debris more quickly than in drier climates.
- Filter Grade: MERV 13 is the standard for peak protection.
- Replacement Cycle: Inspect every 60 days; replace immediately if damp or dark.
- System Care: Ensure the condensate drain is clear to manage indoor humidity.
A MERV 11 is the absolute minimum for coastal homes, but it will not capture the same level of fine particulates as a MERV 13 during a spike. For the best results, supplement your central system with a portable HEPA unit in the rooms where you spend the most time.