Typical air vs. spike days
- Annual average PM2.5 (8.39 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (38.69 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 Fremont without contradicting EPA-aligned thresholds.
Local Pollen and Mold Load
Proximity to the bay and local trails means seasonal pollen and mold are the primary drivers of filter clogs in the area. Grass and weed pollens are heavy in the spring and fall, while coastal humidity can lead to higher mold spore counts. These allergens act as a pre-filter on your HVAC system, filling up the pleats before the fine dust even gets there. This makes regular maintenance critical to prevent system strain and ensure the air stays clear of biological irritants.
HVAC Filter Recommendations
Given the PM2.5 max of 38.69 µg/m³ and ozone peaks over 0.070 ppm, I recommend a MERV 13 filter paired with activated carbon. The MERV 13 rating is necessary to trap the fine particles that spike during the worst days, while the carbon layer specifically helps mitigate the higher ozone levels and associated odors. In Fremont, you should swap these filters every 90 days. If you have pets or high foot traffic, move that schedule up to 60 days to maintain proper airflow and keep your cooling coils clean from the local dust and pollen load.