The unprecedented social distancing measures put in place by many countries to slow the spread of coronavirus have already produced a measurable effect in one important area—emissions.

The slowdown of human activity in many of the world's most populous, most heavily industrialized countries has led to the best air quality in decades.

Satellite images show that levels of nitrogen dioxide (NO2) over cities and industrial areas of Europe and Asia are dramatically lower than they would be with normal levels of activity, according to The Guardian.

NASA data cited by the newspaper for eastern and central China showed NO2 levels 10% to 30% lower than normal. And NO2 levels over Milan and other parts of northern Italy currently under lockdown have fallen by 40%, according to The Guardian.

In the United States, coronavirus shutdowns have virtually eliminated traffic congestion, according to data analysis firm Inrix. "For the first time ever, there is no congestion nationally on America's roadways," it said.

New York City skyline

New York City skyline

Reducing traffic reduces air pollution. In the U.S., transportation is responsible for 55% of nitrogen oxide (NOx, a broader category that includes NO2) emissions, according to the Environmental Protection Agency.

Given the economic damage that will result from idling so many people and businesses, this is short of a silver lining. But this time period will likely serve as a control set for a number of future efforts to reduce traffic congestion and air pollution.

It may also unite those championing better health care and those wanting reduced vehicle emissions. While there has been a general disconnect between these groups in the U.S., transportation-related emissions are very much a health issue.

Multiple studies have tied particulate matter emissions to various health issues, while another found that traffic noise alone can reduce life expectancy and increase the risk of strokes.

The results of another especially thought-provoking study suggested that emissions may cause as many deaths as car crashes.