Typical air vs. spike days
- Annual average PM2.5 (12.34 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (35.98 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 North Hills without contradicting EPA-aligned thresholds.
Seasonal Pollen and Mold Loads
Pollen and mold are the hidden loads on your HVAC system in the Valley. While the air might look clear, local flora and the proximity to the Sepulveda Basin contribute to high seasonal counts. Grass and tree pollens are common, and during the transition between dry and wet periods, mold spores become a factor. These biological contaminants are larger than PM2.5, but they clog filter media rapidly. If you notice your AC running longer or a musty smell when the fan kicks on, the filter is likely saturated with organic debris. Regular replacement is necessary to maintain airflow and prevent these allergens from recirculating through the house during peak seasons.
HVAC Filter Recommendations
Based on a peak PM2.5 of 35.98 µg/m³, I recommend a MERV 13 pleated filter for most homes. A MERV 13 is dense enough to capture the fine particles seen during those worst-day spikes without putting excessive strain on a modern blower motor. Because ozone peaks hit 0.0917 ppm, look for a filter that includes an activated carbon layer. Carbon is the only effective way to neutralize ozone gas as it passes through the return air. In this climate, filters should be swapped every 60 to 90 days. If you have pets or live near high-traffic corridors, check the filter at 45 days. A gray, heavy filter is a sign it is doing its job but also a sign that your system is working harder than it should to pull air through the blockage. Standard fiberglass filters are insufficient for these conditions.