The Ozone Instrument

The Harvard ozone instrument is an in situ ultraviolet photometer that measures ozone via the absorption of 254 nm radiation emitted by a feedback-stabilized mercury Pen-Ray lamp through a 60 cm long folded path. A top view of the instrument schematically illustrates the airflow through the 3-way valve, absorption cell, and scrubber, as well as optical components. Ambient air is ram-fed into the instrument through a forward facing Teflon-coated 0.75" id inlet tube plumbed through the skin of the aircraft. The air is pre-warmed as it passes through a Teflon-coated heat exchanger serving as a heat sink for the mercury lamp power supply, which dissipates up to 20 watts. The air then proceeds through a 3-way Teflon solenoid valve that controls the air flow alternately through a MnO₂ scrubber assembly and into the absorption cell to measure Ι₀, or directly into the cell to measure Ι.