Arctic ozone depletion has been increasing due to colder temperatures, with 2011 showing similar losses to Antarctica. Scientists used a data assimilation technique to analyze ozone depletion in Arctic winters. They found that different chemical processes, like PSC formation and NOx chemistry, contribute to ozone loss at different altitudes. The study categorized Arctic winters into cold (PSC-related), warm (NOx-induced), and intermediate based on stratospheric stability.