country spiked, Italy imposed a lockdown of its northern Lombardy region. Two days later, the prime minister expanded the quarantine to include the entire country.

Concentrations of nitrogen dioxide in the atmosphere over Italy also fell precipitously, as it did in China. An analysis by The Washington Post found that the most dramatic dropoff was observed over northern Italy.

Nitrogen dioxide can irritate the lungs and inhaling the pollutant can increase the risk of asthma and inflammation of the lungs. Though the noxious gas is not thought to be a major contributor to climate change, studying its concentration in the atmosphere can help scientists understand other heat-trapping greenhouse gases that do drive global warming.

Jacqueline Klopp, co-director of the Center for Sustainable Urban Development at Columbia University in New York City,to get wall funding, that's why he threatened to close the border last week before backing off.

NEW ACTING DHS BOSS HAS LONG RECORD IN BORDER SECURITY

And that's why he forced Kirstjen Nielsen out of her job.

The Homeland Security secretary walked into a meeting with the president Sunday night expecting to stay on the job and walked out unable to get her resignation letter out before he tweeted the news. That's not a voluntary departure. (Yesterday's firing of Secret Service chief Randolph Alles adds fuel to what The New York Times is calling a "purge.")

In the end, she got the worst of both worlds. She will forever be defined as the Cabinet member who presided over the forced separation of migrant children from their families, leading to such devastating