Fig. 3: Correlation of δ¹⁸O-NO₃⁻ values with ozone, BrO and day length in the Northern and Southern Hemispheres.

Panels a–f show the relationship between δ¹⁸O-NO₃⁻ and O₃ (a and b), BrO (c and d), and day length (e and f), respectively. The monthly average O₃ from 2006 to 2021 (the time range of all field observation cruises) for eight latitude bands (0–10°N, 10–30°N, 30–60°N, 60–90°N, 0–10°S, 10–30°S, 30–60°S, and 60–90°S) were obtained from National Aeronautics and Space Administration Ozone Watch (NASA Ozone Watch, https://ozonewatch.gsfc.nasa.gov/). The correlation between δ¹⁸O-NO₃⁻ and O₃ is the average O₃ value in a certain latitude range (one out of the eight bands) in a specific month corresponds to the average δ¹⁸O-NO₃⁻ value in that latitude range during that month. The monthly average BrO for eight latitude bands were obtained from the GOME-2 satellite instrument²⁸ and the data presented by Schmidt et al.²⁰. Each sample corresponds to a day length value according to the sampling date and latitude. Solid lines represent the linear regressions and the light shading represents the 95% confidence intervals.