Typical air vs. spike days
- Annual average PM2.5 (8.36 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (38.49 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 Los Altos without contradicting EPA-aligned thresholds.
Regional Pollen and Mold Loads
Pollen and mold spores are the primary hidden loads on your filtration system in this part of Santa Clara County. The proximity to the Santa Cruz Mountains contributes to a steady flow of oak and grass pollens during the spring and summer months. These biological particles are much larger than PM2.5 but they clog filter media quickly, reducing airflow and straining your blower motor. In the wetter months, mold spores become the dominant concern. If you notice your filter looks grey or heavy after only two months, it is likely due to this local biological load rather than industrial soot. Keeping a fresh filter prevents these allergens from recirculating through the house.
Technician Filter Recommendations
Based on the peak PM2.5 levels exceeding 25 µg/m³, I recommend a MERV 13 pleated filter for your central air system. This rating is high enough to capture the fine particulates that spike during bad air days without being so restrictive that it kills your airflow. Because ozone peaks also reach 0.0749 ppm, a filter with an activated carbon layer is a smart upgrade. Carbon is the only effective way to strip ozone and odors out of the air as it passes through the return. Change these filters every 60 to 90 days. If you wait six months, the accumulated dust and pollen will create a pressure drop that makes your system run longer and hotter, eventually leading to a cracked heat exchanger or a frozen evaporator coil. If you have pets or high foot traffic in your home, stick to the 60-day mark to ensure the blower motor isn't overworking.