Every September and October, a "hole" of varying size emerges in Earth's ozone layer over Antarctica, an effect of a buildup of ozone-depleting human-made chemicals high in the atmosphere. During 2013, the ozone hole reached a maximum size of 20.8 million square kilometers (about 8 million square miles) on September 22. Now that levels of ozone-depleting chemicals are declining as a result of international agreements put in place decades ago, scientists predict that the annual ozone hole is poised to begin a shrinking trend.
The maps in this visualization are satellite measures of total ozone values across the globe: Each pixel represents all the ozone measured in a vertical column of atmosphere at that point. Ozone levels are shown in measurements of Dobson units. The area defined as the ozone "hole" is not actually free of ozone - instead, it represents ozone levels lower than 220 Dobson units.
DAILY SERIES: The visualization begins with a daily sequence of false-color ozone measurements from May 2012 through September 2013 as measured by the SBUV/2 and TOVS instruments aboard the NOAA Polar Operational Environmental Satellite system, a dataset by the name of TOAST. Since ozone acts as a "color filter" for distinct wavelengths in the electromagnetic spectrum, these instruments measure the amount of ozone across the atmosphere by detecting how much of a given wavelength of light passes through it at any point. The SBUV/2 instrument detects ultraviolet wavelengths, while TOVS senses infrared radiation. Infrared detection is a benefit in polar areas because it works even in the absence of light, permitting ozone to be continuously measured even during the darkness of the polar night period.
MONTHLY AVERAGES: After the daily images, a series of three images show the average level of ozone across the globe from September 15 through October 15 for the years 1982, 1987, and 2013. The 1982 and 1987 images use data from NASA's Total Ozone Mapping Spectrometer sensor aboard NASA's Nimbus-7 satellite, the first to map global ozone at high resolution. The 2013 image is NOAA's from TOAST dataset.
FUTURE PROJECTIONS: The projections of the size of future ozone holes are based on the work of NASA's Paul A. Newman and colleagues.