Global emissions impact springtime ozone increase above western North America
Western North America is recording higher springtime ozone levels, triggered mostly by the air that flows eastward from the Pacific Ocean, new research shows. Published in the journal Nature, the study's findings are part of the EU-funded MOZAIC ('Measurements of ozone and water vapour by Airbus in-service aircraft') project, which was initially supported under the Third Framework Programme (FP3), and continued under the Fourth, Fifth and Sixth Programmes (FP4, FP5 and FP6 respectively). In a statement, the National Oceanic and Atmospheric Administration (NOAA) of the US Department of Commerce said the rise in springtime ozone levels is especially strong when the air originates in Asia. This rise could potentially hinder US efforts to comply with the standards outlined in the 'Clean Air Act' - the law that defines the Environmental Protection Agency's (EPA) responsibilities for safeguarding and enhancing the country's air quality and stratospheric ozone layer. This latest international study evaluated large sets of ozone data compiled over the last 25 years. The scientists focused on springtime ozone measurements because researchers found in the past that air transport from Asia to North America is strongest in spring, effectively helping them determine how distant pollution impacts the North American ozone trends. 'In springtime, pollution from across the hemisphere, not nearby sources, contributes to the ozone increases above western North America,' explained lead author Dr Owen R. Cooper of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado in the US. 'When air is transported from a broad region of south and east Asia, the trend is largest.' Central to this study was the scientists' assessment of springtime ozone that is found in the atmosphere from two to five miles (around three to eight kilometres) above the surface of western North America. The scientists say the ozone in this intermediate region is much lower than the protective ozone layer but above ozone-related, ground-level smog that is detrimental to both human health and cultivated produce. The team analysed almost 100,000 ozone observations that were collected in exclusive studies by instruments on aircraft, balloons and other platforms. According to the scientists, pollutants such as volatile organic compounds (VOCs) or nitrogen oxides are released when fossil fuels combust. On a positive note, the team found no evidence that North American emissions are fuelling the trend in increased ozone above western North America. They do, however, contribute to ozone levels worldwide. In order to determine the origin of ozone-producing emissions, the team from Canada, France, Norway and the US used historical data of global atmospheric wind records and advanced computer modelling to match each ozone measurement with air-flow patterns for a number of days before they recorded the information. The scientists discovered the biggest hikes in ozone measurements when the dominant airflow originated from south and east Asia. Ozone increased albeit at lower rates when airflow patterns originated elsewhere. So the team speculates that emissions from other places could possibly be fuelling ozone increases above North America. On the whole, the team found that springtime ozone jumped 14% from 1995 to 2008. 'This study did not quantify how much of the ozone increase is solely due to Asia,' Dr Cooper said. 'But we can say that the background ozone entering North America increased over the past 14 years and probably over the past 25 years.' Despite the results obtained in this study, further exploration is needed, according to Dr Cooper. More work will help researchers determine whether similar trends are affecting ground-level air quality. Launched in 1993, MOZAIC has evolved into the European Research Infrastructure IAGOS ('In-service aircraft for a global observing system'), a design study that is part of FP6 and that pursues the preparation of a resilient distributed infrastructure for routine observations of atmospheric composition, aerosols, clouds and contrails (visible 'condensation trails') from commercial in-service aircraft. The MOZAIC project completed three phases between 1993 and 2004. The project partners used ozone and water vapour sensors aboard five European commercial aircraft (one each from Air France, Austrian Airlines and Sabena, and two from Lufthansa).
Countries
Canada, France, Norway, United States