Typical air vs. spike days
- Annual average PM2.5 (8.99 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (50.22 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 Shepherdsville without contradicting EPA-aligned thresholds.
Regional Pollen and Humidity
The geography of Bullitt County, including the Salt River basin, creates a trap for seasonal allergens and moisture. High humidity levels often lead to elevated mold spore counts, which add a biological load to your HVAC filters. During the spring and fall, local pollen from oak, maple, and ragweed can saturate a standard filter in weeks. This organic matter, when combined with the high particulate spikes noted in the air data, creates a thick mat on the filter surface that forces your HVAC system to work harder, increasing energy costs and wear on the components.
Technician's Filter Advice
Because the PM2.5 max exceeds 25 µg/m³ and the ozone peaks are high, I recommend a MERV 13 filter for all Shepherdsville homes. A MERV 13 is necessary to capture the fine particulates that characterize the city's worst-day spikes. Furthermore, given the ozone peak of 0.0777 ppm, you should look for a MERV 13 filter that includes an activated carbon or charcoal layer. This is the only way to chemically scrub ozone from the air. Standard fiberglass or low-MERV pleated filters will not stop these pollutants. Due to the high particulate load during spikes and the local humidity, change your filters every 60 days. Waiting 90 days in this environment often results in a clogged filter that restricts airflow and can damage your heat exchanger or evaporator coil. If you have a high-velocity system, ensure it can handle the static pressure of a MERV 13 before upgrading.