Creation of a unified sulfur hexafluoride dataset to generate age from pollution during a global, two oceans, pole to pole, airborne study over 2016-18.

Atmospheric sulfur hexafluoride (SF₆) is a powerful tracer for age of the air mass used to determine atmospheric transport, because of its relatively linear growth rate (~0.32 ppt/yr., 3.2 %/yr.), long atmospheric lifetime (~850 yrs.), and domination by NH sources (~95% of the total). It's used primarily in the distribution of electricity, resulting from its useful dielectric and insulation properties.

The NASA Atmospheric Tomography Mission (ATom) on the NASA DC-8 aircraft provided a unique opportunity to study the global remote atmosphere during the four seasons over a two-yr. period. There were four separate circuits with 11-13 flights/circuit, 4-9 vertical profiles/flight. During the first circuit (ATom-1, NH summer) there were four separate measurements by NOAA and CIRES scientists, two from Programmable Flask Packages (PFPs, one from EC-GC and one from MS-GC), and two from in situ instruments (PANTHER and UCATS). We had to cut back to just 3 independent measurements for the last three circuits (ATom-2, -3, & -4), due to logistical issues. Typically, there are 1-2 PFPs/flight with 12 glass flasks/PFP for a total of ~220 observations/circuit. The in-situGCs measured SF₆once every 70 seconds and not in sync, for a total of ~7700 observations/circuit. Typical instrumental precisions for SF₆are +/- 0.05 ppt or 1.8 months in age.

There exist sometimes small differences between the various measurements of SF₆. We will examine those differences and come up with a unified dataset for SF₆that permits a reliable determination of age from NH pollution sources (30^oto 50^oN) using various methods. We will compare the age to those from CF₄ and CO₂. Once created, we will examine differences in transport using age during each season of ATom.

Figure 1 Comparison of in situ EC-GCs and PFP flask measurements (MAGIC & Perseus) from sampling times (as sequence number) of PFPs. Generally, around +/- 0.05 ppt average difference.