"Modelling future air quality is very complex, because so many factors need to be taken into account at both a global and local scale," says Dr Val Martin. "The picture isn't uniform across the USA, with some areas seeing much higher surface ozone levels than others. However, our findings show that the emissions reductions we're expecting to achieve won't guarantee air quality on their own, as they will be offset by changes in climate and land use and by an increase in wildfires. This is an issue that will affect all parts of the world, not just the USA."
...The model showed that, if greenhouse gas emissions peak in 2040, then by 2050 surface ozone will remain below levels set to safeguard human health, despite increases in ozone caused by higher temperatures and changes in agriculture and forestation. If emissions continue to rise until 2100, then some areas of the USA will see surface ozone above the safe levels set for human health.
However, when the researchers looked at the cumulative impact of ozone over three months in the summer - a standard growing season - they found that under both scenarios, the surface ozone levels would be high enough to cause damage to plants. This was particularly because during the summer, there were higher emissions from transport and industry of nitrogen oxides, which react with sunlight to create ozone.
...Co-researcher Professor Colette Heald, from Massachusetts Institute of Technology, adds: "Poor air quality is not just an issue in cities. Air pollution in pristine regions such as National Parks degrades visibility and can damage ecosystem health. Protecting natural ecosystems - and our enjoyment of them - will require us to consider and manage the impacts of emissions and climate change on future air quality."