Abstract
The stratospheric ozone layer protects life on Earth by absorbing harmful ultraviolet (UV) radiation from the sun. The spatial and temporal distribution of stratospheric ozone is determined by chemical and dynamical processes. Maximum ozone mixing ratios are found in the tropical middle stratosphere as the result of photochemical processes involving oxygen. From its tropical production region ozone is then transported to higher latitudes by the meridional circulation. In addition, ozone is destroyed in catalytic chemical cycles involving reactive, so-called ozone depleting substances (ODSs). These ODSs include chlorine, bromine, hydrogen and nitrogen compounds from source gases emitted at Earth’s surface by industry and transported into the stratosphere. With increasing production and consumption of ODSs since the 1970s stratospheric ozone began to decline globally. Due to a combination of cold meteorological conditions and specific chemical reactions, the ozone hole developed over Antarctica each springtime since the early 1980s. In a tremendous effort, scientists, politicians and industry managers responded to this threat to the ozone layer. In 1987, the Montreal Protocol was accepted by the member states of the United Nations. The regulations of ODSs defined by the Montreal Protocol and its Amendments and adjustments ultimately led to a turning point of ozone depletion and a slow recovery of stratospheric ozone since the 2000s. This article provides the background of ozone chemistry and dynamics and reviews anthropogenic ozone depletion in the past as well as recent model projections of future ozone recovery and its interaction with climate change.
Highlights
Ozone, the three-atomic form of oxygen, is a minor gas naturally present in Earth’s atmosphere
The source gases of these halogen radicals are emitted at Earth’s surface by human activities or natural processes. They accumulate and are globally distributed in the troposphere before they are transported into the stratosphere, where they are converted to reactive halogen gases. While these reside in the form of inactive reservoir gases (ClONO2, BrONO2, and hydrogen chloride HCl) in the lower stratosphere, they are converted to chlorine (Cl) and chlorine monoxide (ClO) radicals higher up, where they catalytically destroy ozone
Given the larger ozone abundance in the lower stratosphere, the net effect will be a future decline of stratospheric tropical ozone column which is strongest for the extreme Representative Concentration Pathways (RCPs) 8.5 greenhouse gas (GHG) scenario
Summary
The three-atomic form of oxygen (chemical formula: O3), is a minor gas naturally present in Earth’s atmosphere. About 90% of the atmospheric ozone resides in the lower to middle stratosphere between about 15 and 35 km altitude (often referred to as the “ozone layer”), while only ~ 10% are found in the troposphere (Fig. 1). It is assumed that the evolution of life on the continents was only possible after the atmospheric ozone layer had developed. Ozone was discovered in 1839 by the German chemist and professor at the University of Basel, Christian Friedrich Schönbein (Fig. 2). He had noticed an intense odour during experiments with the electrolysis of water and named the unknown smelling substance “ozone” after the Ancient Greek word οζειν (ozein: to smell).
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