Typical air vs. spike days
- Annual average PM2.5 (8.89 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (28.87 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 Franklin without contradicting EPA-aligned thresholds.
Seasonal Pollen and Mold Factors
Pollen and mold are the primary drivers of filter loading in Warren County. The Great Miami River corridor contributes to higher humidity levels, which can sustain mold growth during the damp spring and fall months. Tree pollen in the spring and ragweed in the late summer create a heavy biological load. These particles are much larger than PM2.5, but they clog filter media quickly, reducing airflow and forcing your blower motor to work harder. If you notice a gray or yellow tint on your filter pleats, it is usually a sign that seasonal allergens are bypassing your primary defenses.
Technician's Filter Recommendations
Because PM2.5 spikes exceed 25 µg/m³ and ozone peaks are relatively high, a MERV 13 filter is the professional choice for Franklin homes. MERV 13 is dense enough to capture the fine particulates seen during those worst-day spikes without severely restricting airflow in modern HVAC units. However, because ozone levels hit 0.0814 ppm, I also recommend a filter with an activated carbon layer or a standalone carbon canister if you are sensitive to smells or chemical irritants. Change these filters every 60 to 90 days. In this part of Ohio, the combination of high humidity and seasonal pollen can cause filters to cake over, which leads to pressure drops and potential equipment failure.