The NASA Pacific Oxidants, Sulfur, Ice, Dehydration, and cONvection (POSIDON) Experiment was an airborne science mission that studied the OH and sulfur chemistry, cirrus clouds, and dehydration in the tropical upper troposphere and lower stratosphere over the western Pacific.

This mission:

1. Provided measurements from which we can better evaluate a hypothesis of an O3/OH minimum in the upper troposphere and its possible impact on VSLS (very short-lived species) and sulfur abundances,
2. Constructed a species-resolved sulfur inventory over a geographic region with active and strong convection that drives rapid transport from the lower and mid-troposphere to the tropopause region,
3. Investigated the transport and chemistry of sulfur species to assess the validity of global chemistry transport model projections of anthropogenic sulfur impacts, and
4. Obtained measurements of the microphysical properties and water vapor concentration in anvil cirrus detrained from deep convection as well as thin cirrus near the tropopause that regulate the abundance of water vapor entering the stratosphere.

Flights were conducted from Guam during October 2016 using the NASA WB-57F aircraft with state-of-the-art instrumentation.