Typical air vs. spike days
- Annual average PM2.5 (9.66 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (96.52 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 Marshall without contradicting EPA-aligned thresholds.
Local Allergen Load
Marshall residents deal with a heavy biological load on their filters. The surrounding pine forests and local vegetation contribute significant amounts of pollen throughout the spring and fall. Humidity levels in East Texas also encourage mold growth, particularly in shaded areas or near Caddo Lake. This organic matter accumulates quickly on HVAC coils and filters. If you notice a musty smell when the A/C kicks on, it is often a sign that the filter is overloaded with damp biological debris. This reduces airflow and can lead to microbial growth within the ductwork, making seasonal filter changes a technical necessity rather than a suggestion.
Technician Filter Recommendations
Given the extreme PM2.5 spikes of 96.52 µg/m³, I recommend a MERV 13 filter for Marshall homes. A standard MERV 8 or 11 filter simply will not catch the fine particulate matter present during peak pollution days. Because ozone levels also spike near 0.080 ppm, look for filters that include an activated carbon layer to help neutralize odors and gases. In this climate, you should check your filter every 30 days and replace it at least every 60 to 90 days. The combination of high pollen counts and humidity can lead to filter blinding, where the material becomes clogged and forces your blower motor to work harder, increasing your utility bill and risking a frozen evaporator coil. A secondary HEPA purifier in the bedroom is recommended for those with respiratory sensitivities.