Typical air vs. spike days
- Annual average PM2.5 (8.76 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (100.68 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 Puyallup without contradicting EPA-aligned thresholds.
Pollen and Mold Loads
Pollen and mold are the primary drivers of filter loading in the Puyallup River valley. Douglas fir, alder, and various grasses create a heavy seasonal dust load that coats HVAC coils and clogs filter pleats. The damp climate also contributes to mold spore activity, which hitches a ride on larger dust particles. This biological material becomes a food source for bacteria if left sitting in a dirty filter for too long. Residents often notice a significant increase in indoor dust during the spring and fall transitions, which is a direct indicator that the HVAC filter has reached its capacity.
Technician's Filter Advice
Because the peak PM2.5 exceeds 100 µg/m³, a MERV 13 filter is the minimum requirement for local HVAC systems. A MERV 11 might handle the 8.76 µg/m³ average, but it will fail to stop the fine particulates during a 100.68 µg/m³ event. I recommend changing these filters every 60 days, especially during the transition from spring to summer when pollen is heaviest. If your system is older and cannot handle the static pressure of a MERV 13, stick with a MERV 11 and supplement with a standalone HEPA unit in the main living area. Always check the seal around the filter rack; a high-quality filter is useless if air leaks around the edges.