Typical air vs. spike days
- Annual average PM2.5 (11.95 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (36.21 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 Los Angeles without contradicting EPA-aligned thresholds.
Seasonal Pollen and Mold Loads
Seasonal allergens in the Los Angeles basin create a heavy physical load for HVAC filters. Pollen from oaks, sycamores, and various grasses travels easily across the basin, often settling in areas near Griffith Park or the foothills. Beyond pollen, mold spores can fluctuate with the marine layer's moisture. These biological particles are larger than PM2.5 but are produced in massive quantities. When they enter the HVAC system, they don't just affect air quality; they coat the evaporator coils, which can lead to reduced cooling efficiency and biological growth inside the air handler. Regular filter replacement is the primary defense against this seasonal buildup.
Technician's Filter Recommendations
For the city homes, I recommend a MERV 13 filter as the standard. With PM2.5 peaks hitting 36.21 µg/m³, lower-rated filters like MERV 8 simply won't catch the fine particles that do the most damage. Furthermore, because the ozone max is high at 0.0939 ppm, a filter with an activated carbon or charcoal layer is highly beneficial. Carbon is specifically designed to adsorb gaseous pollutants like ozone that standard pleated media cannot stop. Change your filter every 60 days during peak summer and winter months. If you notice the filter looks dark or fuzzy after only 30 days, it is doing its job—don't wait until the 90-day mark to swap it, or you will risk burning out your blower motor due to restricted airflow.