Which factor does NOT determine the life of an air filter?

The lifespan of an air filter is influenced by various factors, and understanding these is crucial for maintaining optimal air quality. Among these, the type of media plays a significant role, as different materials can have varying efficiencies and lifespans. Additionally, filter size and surface area are important, because larger filters with more surface area typically have a longer lifespan, as they can capture more particulate matter before becoming saturated. The frequency of maintenance is also a critical factor; regular checks and timely replacements can greatly extend a filter's effective life.

In contrast, outdoor air quality does not directly determine the life of an air filter in a specific or predictable sense. While it can impact a filter's performance and accumulation of contaminants, the filter's life is primarily dependent on its construction and maintenance practices rather than the varying conditions of outdoor air. Therefore, while poor outdoor air quality may contribute to a filter becoming dirty more quickly, it is not a fundamental determinant of how long the filter can last overall.