Typical air vs. spike days
- Annual average PM2.5 (13.73 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (68.80 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 Selma without contradicting EPA-aligned thresholds.
Local Allergen Load
In the Central Valley, the pollen season is a year-round reality for HVAC systems. Proximity to the Kings River and surrounding agricultural operations contributes to heavy loads of nut tree pollen, grasses, and fungal spores. These large biological particles often settle in ductwork during the off-season and are redistributed into the living space when the system activates. Humidity shifts also trigger mold spikes that can bypass low-grade filters. For residents, the HVAC filter acts as a constant scrub for these heavy outdoor irritants before they settle into carpets and upholstery, making high-efficiency media a requirement rather than an upgrade.
Technician's Filter Recommendation
Based on PM2.5 spikes exceeding 60 µg/m³, I recommend a MERV 13 pleated filter for Selma homes. A standard MERV 8 or 11 will not capture enough of the fine combustion particles present during peak pollution days. Since ozone levels also hit 0.0846 ppm, look for a filter that includes an activated carbon layer to help neutralize gaseous pollutants and odors. In this part of Fresno County, filters should be inspected every 30 days and replaced at least every 60 days. The dust and agricultural particulate load here is heavy enough to restrict airflow quickly, which can damage your blower motor if the filter becomes blinded by debris. If your system cannot handle the static pressure of a MERV 13, stick with a MERV 11 and run a dedicated HEPA air purifier in the main living area to compensate.