Which type of respirator removes specific air contaminants by filtering ambient air?

An air-purifying respirator (APR) is designed to remove specific air contaminants from the ambient air by filtering it. This type of respirator uses various filtration mechanisms, such as particulate filters, gas filters, or chemical cartridges, to clean the air before it is inhaled by the user. The effectiveness of an APR depends on the filter type used and its compatibility with the specific contaminants present in the environment.

In contrast, a supplied-air respirator (SAR) delivers clean air from an external source to the user, thus not filtering ambient air but rather providing a safe supply of breathable air. Open-circuit breathing apparatus, commonly used in firefighting, exhausts exhaled air to the environment rather than filtering it. Closed-circuit breathing apparatus recycles exhaled air but does not provide filtration from ambient air. Consequently, the air-purifying respirator specifically focuses on the removal of contaminants from the air, making it the correct choice for the question.