Abstract: A filter medium of an air purifying respirator captures one or more substances from the air in a worker's environment as the worked breathes. Air contaminants captured by the respirator filter media can be subsequently analyzed and measured. An air flow meter placed at an air channel of the respirator measures air flow and/or total air volume inspired by the worker wearing the respirator. Personal chemical exposure of the worker can be assessed from the filter media measurements and air flow data.