Despite significant steps to cut air pollutants, one of the most dangerous products of these gases remains stubbornly prevalent in our atmosphere.
Overall, between 2000 and 2018 North America and Europe has brought ‘ozone precursor emissions’ down by around 50%. This covers nitrogen oxides (NOx) and volatile organic compounds, among others, which contribute to the development of ozone gas, a proven cause of long term lung damage and respiratory infection.
However, despite this success scientists have been left to speculate on why levels of ozone itself have not been falling. Until now, at least. A new study published in Atmospheric Chemistry & Physics has concluded that the sustained presence of this stubborn gas is due to transport from overseas – and, specifically, regions of the world where the presence of precursors has remained largely unaddressed during the last two decades.
‘The observed seasonal and annual changes have been discussed in studies since the early 2000s. These refer to a variety of possible causes, for example increased intrusion of ozone from the stratosphere due to climate change and higher ozone imports from regions with rapidly rising emissions, particularly in East Asia,’ said Tabish Ansari of the Research Institute For Sustainability (RIFS), lead author of the research.
‘In addition, there is a reduced removal of ozone in winter due to decreases in local NOx emissions. It is important to understand that the same NOx which produces ozone in the presence of sunlight also removes it in the absence of sunlight,’ Ansari continued. ‘However, these explanations have largely remained within the realm of statistical conjecture.’
The investigation. is based on modelling of atmospheric transport, and a novel tagging system which allows observers to accurately follow emissions across regions without losing track of their point of origin. From this, it was possible to conclude that progress at a local level was offset by a lack thereof in other regions. While this had always been a hunch, it has never been proven before.
‘The increase in NOx emissions from regions such as East Asia, especially China, and the increasing contribution of international shipping contribute significantly to the hemispheric and intercontinental transport of ozone,’ Ansari added.
It is also worth pointing out that another phenomena has been identified specific to NOx. simply put, in areas where nitrogen oxides have from human activity have fallen – including industry and transport – naturally occurring NOx as is produced by forest fires, lighting and vegetation, is becoming more active. This is due to reduce competition between the ‘artificial’ and ‘inherent’ forms of the gas.
Image: Patrick Hendry / Unsplash
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