Typical air vs. spike days
- Annual average PM2.5 (8.40 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (41.05 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 Biloxi without contradicting EPA-aligned thresholds.
Humidity and Coastal Allergens
Humidity and coastal proximity define the local allergen profile. Mold spores are a constant presence in Harrison County, thriving in the damp air near the Gulf of Mexico. Seasonal pollen from oak, pine, and grasses adds a heavy physical load to HVAC filters. This biological debris doesn't just affect your breathing; it settles on the evaporator coils, reducing system efficiency and potentially leading to biological growth inside the air handler. Because the air is often humid, these particles can become sticky, clinging to ductwork and filter media more aggressively than in drier climates. This makes regular filter inspections a technical necessity rather than a suggestion.
Technician's Filter Recommendations
Given the peak PM2.5 levels exceeding 40 µg/m³, I recommend a MERV 13 pleated filter for most modern HVAC systems. This rating is high enough to capture the fine combustion particles and smoke that contribute to those worst-day spikes. If your system is older and a MERV 13 causes too much static pressure—which can burn out a blower motor—drop down to a MERV 11 but supplement it with a standalone HEPA unit. Because ozone peaks reach 0.0723 ppm, look for filters that include an activated carbon layer to help neutralize gaseous pollutants. In this humid environment, you should change your filters every 60 days. Waiting 90 days often allows enough moisture and organic dust to accumulate on the filter media to restrict airflow or even start smelling musty. Always check the seal around the filter rack; if air bypasses the filter, the MERV rating doesn't matter.