Total Ozone Observation

Total ozone

Total ozone is defined as the amount of ozone contained in a vertical column with a base area of 1 cm2 at standard pressure and temperature. The units is m atm-cm or DU. For example, a total ozone value of 300 m atm-cm is equivalent to a thickness of 3 mm at standard pressure and temperature.

Observation types

Observation using direct sunlight

This is the most accurate method of observation, allowing theoretical calculation of total ozone. However, total ozone cannot be observed when direct sunlight is blocked by clouds.

Observation using solar light scattered from the zenith sky

This type of observation is implemented when there is no direct sunlight, such as in cloudy conditions. Total ozone determination is based on an empirical formula derived from comparison with direct light observation.

Observation using moonlight

This type of observation is implemented during the polar night in high-latitude areas such as Antarctica. Since moonlight is weak, there are limitations on the moon phase and the atmospheric path length of moonlight.

Observation results

Total ozone observation is performed dozens of times a day except in rainy and snowy conditions. Daily average data are submitted to the World Meteorological Organization (WMO) as representative values. The WMO Ozone Mapping Centre creates and publishes total ozone maps based on such data. See the Ozone Mapping Centre website for further information.

Total ozone data are also quality-controlled and submitted to the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) for publication on its website.

Annual variations in total ozone
(Red line: daily total ozone in 2013; grey area: mean ± standard deviation)