The cleanest air in the world is at the South Pole. As the “emptiest” continent, there are few manmade sources of pollution in Antarctica. Air samples collected here are considered to be indicative of uncontaminated background air, which is why the atmosphere has been studied at the South Pole since establishment of the first permanent station in 1956. Indeed, Charles Keeling…of Keeling (Carbon Dioxide) Curve fame…took biweekly air samples here beginning in 1957.
The National Oceanographic and Atmospheric Administration (NOAA) currently runs the Atmospheric Research Observatory (ARO) in a state-of-the-art building situated about 500 meters upwind of the main Elevated Station in what is known as the Clean Air Sector (CAS). The CAS was established to reduce any influences from the nearby Amundsen-Scott South Pole Station and is off-limits to pedestrian, as well as vehicular traffic. ARO is part of NOAA’s global monitoring division that monitors certain aerosols and gases in the atmosphere. The prevailing winds at the South Pole are typically from the CAS, meaning they have travelled thousands of kilometers over pristine terrain and arrive here unpolluted.
Since carbon dioxide levels were first measured at the South Pole in 1957, they have been steadily rising. Air samples are collected via “snorkels” atop ARO and analyzed on site in real-time, as well as collected in flasks and sent to the Scripps Institute of Oceanography in California for analysis, as they have been for many decades. During the winter the air flask samples are stored, as there are no flights into or out of the South Pole for about 8 months.
Another gas measured at the South Pole is ozone. Ozone is important to us since it acts as the Earth’s sunscreen, blocking or reducing certain wavelengths of ultraviolet radiation. Ozone does not absorb the longer wavelength UVA (320 – 400 nanometers) radiation, but does reduce the more energetic and harmful UVB (280 – 320 nanometers) radiation, and prevents the UVC (less than 280 nanometers) radiation from reaching the Earth’s surface. The medical effects of too much ultraviolet radiation include premature skin aging, skin cancer, cataracts, and suppression of the body’s immune system. So having a “healthy” ozone layer is important to human health, as well as any influence it might have upon the global climate.
Ozone is formed high in the atmosphere in a region called the stratosphere by the interaction of short-wavelength, energetic UV light with oxygen molecules. The UV light splits the oxygen molecule (O2) into two oxygen atoms, which can then interact other oxygen molecules to form ozone, a molecule made up of three oxygen atoms (O3). UV light also interacts with the ozone, breaking it apart into a molecule of oxygen and one oxygen atom. This constant interaction between UV light, oxygen, and ozone is called the ozone-oxygen cycle. It basically converts the UV light into heat and absorbs about 98 percent of the harmful UV radiation.
Ozone is measured at the South Pole both directly via instruments carried aloft by high-altitude balloons and indirectly by measuring UV light absorption from using the Sun in summer and the Moon in winter.
The balloons carry an instrument package containing an electrochemical concentration cell that uses the reaction between potassium iodide and ozone to produce an electric current. The amount of current produced is proportional to the amount of ozone in the atmosphere. These measurements are then transmitted to a ground station at the South Pole so that we can generate a profile of ozone concentrations in the air as the balloon ascends to altitudes reaching 21 miles or 34 kilometers above the ice.
Ozone is also measured from the ground using a Dobson spectrophotometer. Gordon Dobson at Oxford University not only developed the instrument in 1924, but used it to study total ozone in the atmosphere. By comparing the relative intensity of UVA light (which is not absorbed by ozone) to that of UVB light (which is absorbed by ozone), the Dobson instrument can determine the total amount of ozone, measured in Dobson units, along the light path. It was with this instrument that a scientist from the British Antarctic Survey first discovered the Antarctic Ozone “Hole” in the 1980s, which led to the subsequent banning of ozone layer destroying CFCs or chlorofluorocarbons. Unfortunately, long-lived CFCs remain in the stratosphere and it will be take another 30 – 40 years before the ozone layer is fully healed.
So even today, an early 20th Century instrument in the hands of a master science technician at the South Pole is still making important contributions to 21st Century science and adding to our knowledge of the atmosphere.