What does a disposable dust/surgical mask filter out?

A disposable dust or surgical mask is designed primarily to filter out larger particulate matter from the air. These types of masks are effective at blocking larger particles, including dust, pollen, and droplets that may contain biological contaminants. The filter mechanism is geared toward preventing these larger particles from being inhaled, thus providing a basic level of respiratory protection.

While they may provide some level of protection against biological contaminants, such as bacteria and viruses in certain situations, they are not specifically designed to filter out smaller particles or chemical vapors. Filters in these masks are not capable of effectively blocking smaller particulate matter, which requires more advanced filtration technology, such as that found in N95 respirators or similar filters. Therefore, they serve their primary purpose well by addressing the larger particulate matter aspect.