Typical air vs. spike days
- Annual average PM2.5 (8.07 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (38.80 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 Alameda without contradicting EPA-aligned thresholds.
Seasonal Allergen Load
Pollen and mold spores act as a constant tax on your filtration system. In this coastal environment, proximity to the bay and local green spaces like Washington Park ensures that biological allergens are present year-round. Mold thrives in the humid air, while various trees and grasses release pollen in distinct seasonal waves. These particles are much larger than PM2.5 but are equally effective at clogging filters and reducing HVAC airflow. If you notice a musty smell or increased sneezing indoors, your filter is likely saturated with these organic materials, regardless of the current PM2.5 readings.
Technician's Filter Recommendation
Because the max PM2.5 exceeds 25 µg/m³, I recommend a MERV 13 filter for your central system. A standard MERV 8 or 11 will not catch the fine combustion particles that characterize those 38.8 µg/m³ peak days. MERV 13 is dense enough to trap sub-micron particles without putting excessive strain on most modern blowers. Given the coastal humidity and seasonal pollen load, change these filters every 60 to 90 days. If the filter looks gray or fuzzy, it is already past its prime. For the ozone peaks of 0.0616 ppm, consider a filter with an activated carbon layer to help neutralize odors and gaseous pollutants that standard pleated filters cannot stop.