Typical air vs. spike days
- Annual average PM2.5 (9.29 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (31.23 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 Evanston without contradicting EPA-aligned thresholds.
Seasonal Load and Lake Effects
Pollen and mold represent the primary hidden load on local air filters. Proximity to Lake Michigan can increase local humidity, which often leads to higher mold spore counts during the spring and fall. Tree pollen from oak and maple in the spring, followed by ragweed in the late summer, creates a steady stream of large particulates that settle in ductwork. These biological loads require a filter that can capture fine particles without restricting the airflow of your furnace or air conditioner.
Technician Filter Recommendations
Because the max PM2.5 exceeds 25 µg/m³, I recommend a MERV 13 filter for most Evanston homes. A MERV 13 is dense enough to capture the fine particulates found during peak pollution days without putting excessive strain on modern blower motors. Given the ozone peaks of 0.0822 ppm, residents should also consider filters with an activated carbon layer to help neutralize gaseous pollutants. Standard maintenance should include:
- Change MERV 13 filters every 60 to 90 days.
- Inspect filters monthly during peak summer and winter usage.
- Supplement with a standalone HEPA purifier in primary living areas for additional protection during peak ozone days.