Just over a month ago we released the new APIS 2020-2022 data. Recently, some users have pointed us out to us that the NH3 concentrations were abnormally high compared to the N depositions. We, together with the CBED team, investigated this further. We just discovered that there was a bug that caused the CBED NH3 concentrations to be calculated in ppm instead of ug/m3. This is only affecting NH3 concentrations for midyear 2021. This means that the ammonia concentrations were higher than they should have been. The new CBED and APIS data has been re-calculated and now the concentration estimates are more consistent with the deposition estimates. The fix is now live in the APIS app as well as a notification and news item.
We are sorry this happened, in the APIS team we thought this increase in NH3 concentration was due to the observations used in the calibration step, where an increased amount of observations stations were added in Northern Ireland (28 sites now vs 3 sites in previous years), where the ammonia concentration is higher than average, skewing the average conversion factors. They indeed still skew the UK average conversion factors but to a lesser extent.
If you have any questions and if we can help you further contact us via the APIS contact form.
APIS team