Gravitational separation of major atmospheric components of nitrogen and oxygen in the stratosphere

Abstract

To investigate the gravitational separation of atmospheric components in the stratosphere, air samples collected over Japan, the Arctic and the Antarctic were analyzed for δ15N of N2 and δ18O of O2. The gravitational separation is a function of latitude, showing the largest effect inside the polar vortex over the Arctic. The relationship between the gravitational separation (calculated using a steady‐state 1‐dimensional eddy‐diffusion/molecular‐diffusion model) and the CO2 age (calculated using a 1‐dimensional time dependent eddy‐diffusion model) suggests that the observed gravitational separation is fundamentally a result of diffusive separation but modified by meridional circulation of air in the stratosphere. We also obtain a compact relationship between the gravitational separation and the N2O concentration. By comparing the gravitational separations at two height intervals with the N2O concentrations >125 ppb and <45 ppb, the effect of descending air is found to be more significant over the Arctic than over Japan. The variation in the gravitational separation with height is found to be weaker in region with the N2O concentrations between 45 and 125 ppb than in other regions.