N2O temporal variability from the middle troposphere to the middle stratosphere based on airborne and balloon-borne observations during the period 1987-2018
Résumé
Nitrous oxide (N2O) is the third most important greenhouse gas in the atmosphere and is now considered as the most important depleting source gas of stratospheric ozone (O3). Its sources are both natural and anthropogenic, mainly as an unintended by-product of human food production activities. Scientifically, a major issue is the identification and quantification of trends in the N2O concentration from the middle troposphere to the middle stratosphere (MTMS) by in-situ and remote sensing observations due to the paucity of measurements. To address the temporal variability of N2O, we assembled the first comprehensive dataset for in-situ and remote sensing N2O concentrations from 1987 to 2018, based on aircraft and balloon measurements in the MTMS. Using statistical methods, we quality-controlled all the measurements to exclude outliers and particular dynamic cases (tropospheric intrusion, stratospheric descent). This allowed us to determine N2O trends in the MTMS, based on selected observations during the period 1987-2018. This consistent dataset was also used to study the N2O seasonal cycle in order to investigate the relationship with its emission sources through zonal means and atmospheric dynamic. The results show a long-term (30 years) increase in global N2O concentration in the MTMS with an average of 0.89 ± 0.09 ppb/yr in the troposphere and 0.95 ± 0.13 ppb/yr in the stratosphere, consistent with 0.80 ppb/yr derived from ground measurements and ACE-FTS satellite measurements.