Ozone levels across Northern Hemisphere increased 

#GS3 #Environment 

The levels of ozone have increased across the Northern Hemisphere in the last 20 years, a new study has showed.

  • The study, conducted by the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder in the United States, was done using data from international flights. 
  • The researchers used aircraft data from Europe’s In-Service Aircraft for the Global Observing System (IAGOS) programme, a statement from CIRES, said. 
  • Commercial aircraft captured 34,600 ozone profiles between 1994 and 2016. 
  • The researchers found that increase anthropogenic emissions in the tropics were likely driving the increase in ozone levels in the Northern Hemisphere. 

What is ozone? 

  • Ozone (O3) is a gas which is present naturally within Earth’s atmosphere. It is formed of three oxygen atoms (giving it the chemical formula, O3).  
  • Its structure means that it’s much less stable than oxygen (O2), and is therefore much more reactive; this means it can be more easily formed and broken down through interaction with other compounds. 

Ozone and its impact through the atmosphere 

  • To understand the importance of the ozone layer, it’s crucial to first establish the difference in concentrations of ozone throughout the Earth’s atmosphere. 
  • Ozone plays a different role in atmospheric chemistry at different heights in the Earth’s atmosphere. We can differentiate this profile into two key zones: 
  • Tropospheric ozone is that which is present in the lower atmosphere (the troposphere; with a height of 5km to 15km depending on your latitude). Throughout most of the troposphere, ozone concentrations are relatively low (as shown in the diagram). However, concentrations of ozone can be higher very close to the surface at local levels; there it forms as an air pollutant and can negatively impact on human health. Ground-level ozone can form through chemical reactions between local air pollutants such as nitrous oxides (NOx), volatile organic compounds (VOCs) and sunlight. These air pollutants are emitted from motor vehicle exhausts, industrial processes, electric utilities, and chemical solvents. Ground-level ozone can have negative impacts on human health; breathing ozone is particularly harmful for the young, elderly and people with underlying respiratory problems. It is therefore commonly referred to as ‘bad’ ozone. 
  • Stratospheric ozone is that which is present in the upper atmosphere (the stratosphere; typically extending from around 10 to 15km up to 50km depending on latitude). As shown in the diagram, concentrations of ozone are higher in the stratosphere than in the troposphere. The stratosphere includes the zone termed the ‘ozone layer’.Ozone in the stratosphere plays a very different role to that in the layer below. In the ozone layer, it is often referred to as ‘good’ ozone since it plays a crucial role in absorbing potentially dangerous ultraviolet (UV-B) radiation from the sun. The ozone layer typically absorbs 97-99 percent of incoming UV-B radiation. Higher concentrations of ozone in the stratosphere is therefore crucial to ensure life (including humans) at Earth’s surface are not exposed to harmful concentrations of UV-B radiation. 
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