Tropospheric ozone pollution declining in Europe and U.S. but rising in East Asia

Desdemona Despair

5 February 2018 (University of Edinburgh) – Potentially harmful levels of the air pollutant ozone are present in many regions around the world, a widespread study has shown.

Levels of ozone in the troposphere – the lower region of the atmosphere – have decreased in much of Europe and the US over the past 15 years. However, they are increasing in parts of East Asia in line with economic development.

Relatively high levels are found in both in urban and rural areas of the globe, with identifiable hot-spots in regions with major emissions, according to the results.

The study uses data from more than 4,800 monitoring stations across the globe, and is the biggest assessment to date on ground-level ozone, which can be harmful to breathe.

The highest daily ozone levels were measured in five different ways, and statistical analysis was used to calculate peak levels and to interpret trends and changes in the data at urban and rural locations.

The study is a component of the Tropospheric Ozone Assessment Report (TOAR), an international effort to improve scientific understanding of ozone’s global distribution and trends.

The international team of researchers behind the study, who volunteered their time and expertise to take part, have released their data, including statistics and graphics available, for wider use.

The research, led by the Universities of Leicester and Edinburgh in collaboration with 12 other institutions worldwide, was published in the journal Elementa: Science of the Anthropocene.

The TOAR project 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.

Global air pollution highlighted in ozone study

ABSTRACT: This study quantifies the present-day global and regional distributions (2010–2014) and trends (2000–2014) for five ozone metrics relevant for short-term and long-term human exposure. These metrics, calculated by the Tropospheric Ozone Assessment Report, are: 4^th highest daily maximum 8-hour ozone (4MDA8); number of days with MDA8 > 70 ppb (NDGT70), SOMO35 (annual Sum of Ozone Means Over 35 ppb) and two seasonally averaged metrics (3MMDA1; AVGMDA8). These metrics were explored at ozone monitoring sites worldwide, which were classified as urban or non-urban based on population and nighttime lights data.

Present-day distributions of 4MDA8 and NDGT70, determined predominantly by peak values, are similar with highest levels in western North America, southern Europe and East Asia. For the other three metrics, distributions are similar with North–South gradients more prominent across Europe and Japan. Between 2000 and 2014, significant negative trends in 4MDA8 and NDGT70 occur at most US and some European sites. In contrast, significant positive trends are found at many sites in South Korea and Hong Kong, with mixed trends across Japan. The other three metrics have similar, negative trends for many non-urban North American and some European and Japanese sites, and positive trends across much of East Asia. Globally, metrics at many sites exhibit non-significant trends. At 59% of all sites there is a common direction and significance in the trend across all five metrics, whilst 4MDA8 and NDGT70 have a common trend at ~80% of all sites. Sensitivity analysis shows AVGMDA8 trends differ with averaging period (warm season or annual). Trends are unchanged at many sites when a 1995–2014 period is used; although fewer sites exhibit non-significant trends. Over the longer period 1970–2014, most Japanese sites exhibit positive 4MDA8/SOMO35 trends. Insufficient data exist to characterize ozone trends for the rest of Asia and other world regions.

Tropospheric Ozone Assessment Report: Present-day ozone distribution and trends relevant to human health