Regional dynamics and trends of N2O and O3 in the lower stratosphere

In the troposphere, N₂O is among the most important anthropogenic greenhouse gases, with its long lifetime and a global warming potential in the order of 300 times higher than the same mass of CO₂. Furthermore, in the stratosphere, it is the primary ozone(O₃)-depleting gas not regulated by the Montréal protocol. As N₂O’s anthropogenic emissions grow, its impact on the Earth’s climate also increases. This paper investigates the dynamics of both N₂O and O₃ in the lower stratosphere using data from the Aura satellite’s MLS (Microwave Limb Sounder) instrument which has been gathering data for both gases since 2004. The study focuses on the lower stratosphere (pressures between 68-22 hPa, corresponding to ~18-26 km at the equator), at 30 selected locations above equatorial and temperate land regions. Both long-term increase and positive correlations between simultaneous N₂O and O₃ concentrations were examined. The results showed weak increase for O₃ and more noticeable ones for N₂O, with the latter also including some negative trends, though that is likely related to the MLS instrument’s age. Regarding the relationship between N₂O and O₃, it was found that the correlation between the gases changes with altitude differently depending on the latitude of the study region. Near the equator, almost no correlation between the gases at 68 hPa level was found but as altitude increases, a negative correlation was observed; it increased up to at least 22 hPa level. At higher latitudes, an inverted version of this phenomenon was observed – negative correlations at lower altitudes first weakened and were afterwards replaced by positive correlations as altitudes increased.