Typical air vs. spike days
- Annual average PM2.5 (10.10 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (26.31 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 O Fallon without contradicting EPA-aligned thresholds.
Pollen and Mold Loads in Saint Clair County
The local environment in Saint Clair County contributes a significant amount of organic material to your home's air. Seasonal pollen from local grasses and trees, combined with mold spores common in the Illinois climate, creates a steady stream of debris for your HVAC filter to manage. These allergens often peak during the spring and fall, coinciding with when many residents are switching between heating and cooling. This transition is often when filters become most clogged, reducing system efficiency and allowing allergens to bypass the filter if it is not seated correctly in the housing.
HVAC Filter Advice for O Fallon Residents
Because the peak PM2.5 levels hit 26.31 µg/m³, I recommend a MERV 11 or MERV 13 pleated filter for most homes. A MERV 11 is a solid baseline for general dust and pollen, but a MERV 13 is better if anyone in the home has respiratory sensitivities or if you want to capture the finer particulates seen during local spikes.
- Filter Type: Avoid the cheap, see-through fiberglass filters. They are designed to protect the equipment from large debris, not to clean the air for people.
- Carbon Layers: With ozone peaks at 0.0681 ppm, a filter with an activated carbon layer can help reduce outdoor odors and gaseous pollutants.
- Maintenance: Change your filter every 90 days. If you live near construction or have multiple pets, check it every 30 days and replace it as soon as the media looks grey or loaded with dust.