Global multi-year stratospheric composition campaign

The strength and variability of stratospheric circulation (the large-scale patterns of air movement that transport gases and aerosols through the stratosphere) remains one of the key uncertainties in understanding and predicting the behavior of aerosols in the stratosphere. Current observational networks are insufficient to constrain the circulation and how it changes over time, largely because existing and upcoming satellite instruments cannot fully characterize the circulation on their own — they need in situ data (measurements taken directly in the stratosphere, rather than sensed remotely from orbit) to validate and calibrate what they observe from space. 

Researchers can map how circulation behaves by tracking multiple long-lived tracers (gases whose movement can be followed to reveal how air travels) at the same time and location. For example, nitrous oxide (N₂O), which can be observed by both satellite and in situ instruments, can be compared against carbon dioxide (CO₂), a more direct indicator of circulation that can only be measured in situ. The relationship between the two acts as a kind of fingerprint, revealing where a given parcel of air came from and how quickly it moves. These relationships vary with latitude, season, and likely with the phase of the Quasi-Biennial Oscillation (QBO), an oscillation of prevailing wind directions that occurs over a period of about two years — meaning any measurement campaign needs to cover enough locations and enough time to capture all of this variability.

The campaign will conduct at least one balloon launch per season (December–February, March–May, and so on) over a minimum of three years across 3–5 sites spanning the tropics through high latitudes in both hemispheres. The baseline configuration includes two Northern Hemisphere sites (one high-latitude, one mid-latitude) and one Southern Hemisphere mid-latitude site. The expanded scope includes a Southern Hemisphere high-latitude site and a tropical site ideally between 5°N–5°S. This scope of work will only be possible if suitable sites are located where instrumentation can be reliably recovered.

Each flight will carry an AirCore sampler with a mass spectrometer for in situ trace gas profiling. This research activity can be structured in two ways:

1. Permanent monitoring capability — training on-site staff and donating key pieces of equipment to establish more permanent monitoring capabilities in remote and under-resourced areas of the globe, for continued use after the campaign.
2. Centralized traveling team — a centralized research team travels with all necessary equipment to each site four times per year.

There is significant overlap in the timing and requirements for this research activity and the Southern Hemisphere In-situ monitoring activity. A coordinated approach to both research activities could allow significant cost savings by adding Portable Optical Particle Spectrometer (POPs) instrumentation to the AirCore balloon flights.