PLEA Network

4 January 2018, Geophysical Research Letters, Decline in Antarctic Ozone Depletion and Lower Stratospheric Chlorine Determined From Aura Microwave Limb Sounder Observations. The Antarctic ozone hole is healing slowly because levels of the man-made chemicals causing the hole have long lifetimes. We use Microwave Limb Sounder (MLS) satellite data to measure O₃ over Antarctica at the beginning of winter and then compare it to O₃ near the end of winter to calculate depletion. During this period, nearly all O₃ change is due to depletion. MLS also measures HCl, and when ozone levels are very low, nearly all the reactive chlorine species (Cl_y) are converted to HCl. Cl_yvaries a lot from year to year from atmospheric motions. Fortunately, MLS measures nitrous oxide (N₂O), a long-lived gas that also varies with the motions. Using the ratio of Cl_y to N₂O, we find that there is less chlorine now than 9 years ago and that Cl_y has decreased on average about 25 parts per trillion/yr (0.8%/yr). The O₃ depletion we calculate from MLS data responds to changes in the Cl_ylevels, and the ratio of the change in ozone loss to the change in Cl_y matches model calculations. All of this is evidence that the Montreal Protocol is working—the Cl_y is decreasing in the Antarctic stratosphere and the ozone destruction is decreasing along with it. Read More here