Airborne measurement of OH reactivity during INTEX-B

A new airborne OH reactivity instrument was designed and deployed for the first time on the NASA DC-8 aircraft during the second phase of Intercontinental Chemical Transport Experiment-B (INTEX-B) campaign, which was focused on the Asian pollution outflow over Pacific Ocean and was based in Hawaii and Alaska.

The OH reactivity was measured by adding OH, generated by photolyzing water vapor with 185 nm UV light in a moveable wand, to the flow of ambient air in a flow tube and measuring the OH signal with laser induced fluorescence. As the wand was pulled back away from the OH detector, the OH signal decay was recorded; the slope of −Δln(signal)/Δ time was the OH reactivity. The overall absolute uncertainty at the 2σ confidence levels is about 1 s⁻¹ at low altitudes (for decay about 6 s⁻¹), and 0.7 s⁻¹ at high altitudes (for decay about 2 s⁻¹).