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Research on global surface ozone levels shows populations most affected by air pollution

February 05, 2018

  • Ozone found at the Earth's surface (the troposphere) is an air pollutant harmful to human health. The regulatory ozone limit values designed to protect human health vary by country. This study uses a variety of ways of measuring the occurrence of high ozone levels to assess the frequency of periods a given population is exposed to harmful ozone levels and how this has changed over time.

  • A large international team has produced the first surface ozone assessment report based on all available surface observations across the globe using data from over 4,800 monitoring stations.

  • Surface ozone levels potentially detrimental to human health are found in many regions around the globe, both in urban and non-urban areas.

  • Our different methods of determining high and peak ozone levels worldwide produce generally similar results.

  • While ozone has decreased in much of Europe and the North America over the past 15 years, the study shows it is increasing in parts of East Asia with increasing development and pollution emissions.

  • A large publicly available database has been compiled which includes a complete set of statistics and graphics available for viewing and download.

Maps of present-day ozone levels and changes between 2000 and 2014 throughout North America, Europe and East Asia are available here:

"Despite improvements in air pollution emissions in Europe and North America, ozone levels that are harmful to human health are still a cause for concern across the world and ozone is rising in East Asia" - Dr Zo? Fleming, National Centre for Atmospheric Science, University of Leicester

New research led by the Universities of Leicester and Edinburgh and twelve other institutions worldwide (listed below) has analysed ozone levels across the globe, with some regions of East Asia showing increasing levels of ozone air pollution.

The other institutions involved were the Institute for Advanced Sustainability Studies (IASS) and Forschungszentrum Jülich in Germany, the Universities of Colorado, North Carolina-Chapel Hill, and Maryland as well as A.S.L. and Associates in the U.S., the Stockholm Environment institute in the UK, INERIS in France, the Chinese Academy of Meteorological Sciences and Chinese Academy of Science in China, NILU (Norwegian Institute for Air Research) and the Norwegian Meteorological Institute in Norway, Chalmers University in Sweden and the University of Witwatersrand in South Africa.

The research is a component of the Tropospheric Ozone Assessment Report (TOAR), an international effort to improve scientific understanding of ozone's global distribution and trends. Published today in the scientific journal Elementa: Science of the Anthropocene, the results provide the most ambitious ever ground-level ozone assessment, using data from over 4,800 monitoring stations across the globe.

As part of the study, ozone levels potentially detrimental to human health have been assessed where data are available, both in urban and non-urban areas worldwide. There is considerable variation within regions and hot-spot locations with the highest ozone levels have been identified.

Changes in ozone levels from trend analysis shows that ozone has decreased in much of Europe and North America over the last 15 years. However, the research shows that ozone is rising in some parts of East Asia over the same period, reflecting increasing development and pollution emissions.

Previously, analyses of ozone trends at individual or smaller groups of sites often left researchers unable to draw robust conclusions about regional trends in areas such as Europe and North America. The large number of sites now included in this more comprehensive dataset have allowed for more robust conclusions that reveal that a decrease predominates in these regions.

Dr Zo? Fleming, from the National Centre for Atmospheric Science (NCAS) at the University of Leicester's Department of Chemistry, said: "TOAR is the most ambitious project to date to assess global ozone levels at the surface of the Earth, helping us to better understand potential human health impacts.

"Despite some improvements in air pollution emissions in Europe and North America, human health impacts from ozone are still a cause for concern across the world and are rising in East Asia, with the potential for serious health consequences on their populations.

"There is an increasing awareness of the issues of human health from poor air quality and making such a database freely available and disseminating the results from the study will inform the public on the health implications of ozone."

The data come from certified monitoring stations with rigorous calibration procedures. Statistical analysis was carried out on the data, in order to calculate peak and high ozone levels and to interpret trends and changes in the data. The study uses five different recognized methods for measuring the daily or seasonally highest ozone levels. These so-called metrics show similar patterns and highlight the different assessment methods. TOAR has created a large publicly available database which also includes a complete set of statistics and graphical downloads.

Air quality monitoring is a crucial element for quantifying current air pollution levels and evaluating the effectiveness of emissions controls and informing the evolution of air pollution policy. There are still large regions of the world where such monitoring is sparse or non-existent. To effectively understand and tackle air pollution, expanded monitoring is critical.

Professor Ruth Doherty, from the School of Geosciences, University of Edinburgh, said: "The ability to quantify for urban regions worldwide the changes in high and peak ozone levels over the last 15 years and longer is an exciting research development, that we hope will be useful to air quality managers to inform and evaluate strategies to protect human health from the adverse effects of ozone."

Dr Owen Cooper, from the Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, US, said: "TOAR was made possible by an international team of scientists who volunteered their time and expertise to build the world's largest database of ozone metrics and then made those data completely open access."
The research is funded by the International Global Atmospheric Chemistry project (IGAC), the World Meteorological Organization (WMO), the National Oceanic and Atmospheric Administration (NOAA) and Forschungszentrum Jülich with the support of a large international team of experts who recognized the need for an up-to-date tropospheric ozone assessment.
  • More information about the Tropospheric Ozone Assessment Report (TOAR) is available here:

  • A copy of the paper 'Tropospheric Ozone Assessment Report: Present-day ozone distribution and trends relevant to human health' published in Elementa: Science of the Anthropocene is available here (DOI: from Monday 5 February 2018.

    University of Leicester

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