Measurement of Hydroxyl Concentrations in Air Using a Tunable uv Laser Beam

Abstract

We report the first measurement of hydroxyl (OH) concentrations in air by detecting the resonance fluorescence excited by tunable radiation near 2825.8 \AA{}. On a particular day, the OH concentrations deduced from these measurements ranged from a high of 1.5 \ifmmode\times\else\texttimes\fi{} ${10}^{8}$ OH/${\mathrm{cm}}^{3}$ in the early afternoon to a level below 5 \ifmmode\times\else\texttimes\fi{} ${10}^{6}$ OH/${\mathrm{cm}}^{3}$ at night.