Abstract: Discussed herein are methods and apparatuses for dispensing precise quantities of reagents, wherein air pressure is controlled to pilot a liquid syringe or diaphragm that provides an air to liquid interface. The resultant pressurized liquid is then in series with dispensing element, such as an aerosol dispenser, solenoid valve or piezo dispenser. The pump may be controlled by air pressure to provide an incremental quantity or continuous flow of reagent to the dispenser. The pump and dispenser may be operated in cooperation with one another such that the quantity or flow rate of liquid dispensed by the dispenser can be precisely metered substantially independently of the particular operating parameters of said dispenser to attain a desired flow rate, droplet size or mist quality, droplet frequency or droplet velocity.