By Chris Spears

DENVER (CBS4) – With all of the negative that surrounds most COVID-19 related headlines here’s something positive that came from China during their shutdown last month. Satellites that track air pollution detected significant decreases in nitrogen dioxide, a noxious gas emitted by human activities that burn fossil fuels, such as the operation of motor vehicles, power plants and factories.

Nitrogen dioxide can irritate people with respiratory problems and long-term exposure can lead to the development of asthma or increase susceptibility to respiratory infections. The gas can also turn into ground-level ozone which is the main ingredient in smog.

(credit: NASA)

The left map above shows nitrogen dioxide levels in China during the first part of January 2020, before the COVID-19 outbreak caused a massive quarantine. The right map shows levels during the quarantine in February. The data comes from the Tropospheric Monitoring Instrument on the Sentinel-5 satellite operated by the European Space Agency. A related Ozone Monitoring Instrument on NASA’s Aura satellite makes similar observations.

The Sentinel-5 satellite. (credit: European Space Agency)

Aura satellite. (credit: NASA)

A recent story from NASA pointed out the drop in nitrogen dioxide in China also coincided with the Lunar New Year celebrations, a time when businesses and factories usually close down to celebrate. Past observations have shown that air pollution usually decreases during this period, then increases again after the celebrations are over.

“This is the first time I have seen such a dramatic drop-off over such a wide area for a specific event,” said Fei Liu, an air quality researcher at NASA’s Goddard Space Flight Center.

Additionally, Liu and colleagues did not see a rebound in nitrogen dioxide after the holiday. “This year, the reduction rate is more significant than in past years and it has lasted longer,” she said. “I am not surprised because many cities nationwide have taken measures to minimize spread of the virus.”

Liu also recalled seeing a drop in nitrogen dioxide over several countries during the economic recession that began in 2008, but those decreases were gradual. Scientists also noticed a significant reduction in pollution around Beijing during the 2008 Olympics but levels rose again once the games ended.

Much like we saw in China last month, preliminary data is showing similar results across other places such as Italy and the United States, especially over major population centers like Los Angeles and New York City.

(credit: CBS)

It is important to note that while these studies show improvement over time, one specific area on a particular date could still experience poor air quality, such as in Denver on Thursday when a brown cloud was present. Localized weather, including wind patterns and the presence of a temperature inversion, combined with the terrain, all play a role in creating problems with air quality along Colorado’s Front Range, even during a time of reduced human activity.

Chris Spears


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