Middle East conflict drastically 'improves air quality'
Political disturbance and armed conflict in the Middle East since 2010 have had the unintended consequence of making the air cleaner.
Researchers say that in countries like Syria and Iraq, levels of air pollutants have fallen dramatically.
The amount of nitrogen dioxide in the air over Damascus has fallen by up to 50% since start of the civil war.
The authors believe their work has important lessons for projections of global emissions.
Since 2004, scientists have been able to monitor atmospheric pollutants with high levels of precision thanks to the deployment of the Ozone Monitoring Instrument onboard the Nasa Aura satellite.
This new study used data from the spacecraft to see how economic, political and military activity has impacted levels of pollutants in and around the Middle East over the past decade.
Looking at levels of nitrogen oxides (NOx) that are generated from the burning of fossil fuels especially in transport, the team found a complex and unpredictable picture.
In countries like Syria, where millions of people have attempted to flee the fighting since 2011, levels of nitrogen dioxide plummeted over Damascus and Aleppo.
But in nearby Lebanon, there was a "drastic" rise of up to 30% of the same pollutant, thanks to the influx of refugees. The scientists say that this was very unusual as economic growth in Lebanon declined significantly at the same time.
"It's quite remarkable," lead author Dr Jos Lelieveld from the Max Planck Institute for Chemistry told BBC News.
"You can see where the people from Syria are going; you can identify the camps in northern Jordan but they are also moving to cities like Tripoli and Beirut.
"The energy consumption has increased; the traffic, more cars, make up a large proportion of the increase," he said.
In countries like Greece, global recession and new environmental laws have had a significant role. Similarly in Saudi Arabia and Israel.
But in Iraq, the rise of so-called Islamic State can also be clearly seen in the air quality data.
"In Karbala, to the south of Baghdad, a mostly Shiite area, the increase in pollutants continues," said Dr Lelieveld.
"But if you look to the area northwest of Baghdad, where Islamic State is in charge, there you see that things are going in another direction - there are very specific stories in each country."
The researchers say that the varying impacts on air pollutants seen across the Middle East have lessons for global projections of emissions.
The authors point to one climate change scenario that includes increases of NOx in the region every year between 2005 and 2030, which they say "deviates from the reality".
"For many countries for which we have little information, the emissions scenarios make very simple assumptions - these definitely do not work in the Middle East as they go in all directions," said Dr Lelieveld.
"For example, in Iran the energy consumption and CO2 have continued to grow but NOx and sulphur dioxide have declined. There isn't a general rule that you can apply in emissions scenarios."
The researchers say that it is difficult to use the technology to get a definitive picture. There may be less NOx in the air but people may have resorted to dirtier and cheaper fuels for heating.
Other scientists welcomed the study, saying that it followed on from previous research carried out during the Iraq war. They say that it highlights the critical role of accurate satellite information. It also highlights the scale of destruction across the Middle East and the huge impact on people.
"It is very sad that we have on the borders of Europe this huge conflict," said Prof John Burrows from the University of Bremen, Germany.
"But perhaps scientific information like this helps our understanding. It's proportional to people, so if emissions have gone down in Syria by 50%, I'd expect that 50% of the people might have been displaced, as indeed they have."
The research has been published in the journal, Science Advances.
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