Senin, 20 April 2020

What Is the Air Quality Like Near You?

Stay at home orders due to the novel coronavirus pandemic mean there are far fewer cars on the road. Traffic is down so far that the state of California has seen a 50 percent decrease in car accidents, down to about 500 per day, which has saved the state an estimated $40 million per day.

In a previous episode, we discussed how all of this inactivity has led to drastic reductions in ozone-destroying greenhouse gases like nitrous oxide as mapped by NASA and ESA satellites. But what about other forms of pollution—in particular, the ones we can see with our own eyes?

Photos show empty streets and clear skies in Bangkok, Sao Paulo, and Bogota.

Anecdotal evidence is popping up all over the world where people are highlighting lower levels of smog—or visible air pollution—including nitrous oxide but also sulfur oxide, ozone, smoke, and other particles. Photos of the India Gate war memorial and the Gopaldas Ardee commercial building in New Delhi, India, show huge differences in visibility from just six months ago. Other photos show empty streets and clear skies in Bangkok, Sao Paulo, and Bogota. From my home in Los Angeles, I’ve never witnessed so many clear days in a row. 

How can you assess the air quality where you live?

How do we measure air quality?

One major source of smog is particulate matter—or organic and inorganic matter suspended in the air—including sulfates, nitrates, ammonia, sodium chloride, black carbon, mineral dust, and water. Particulates are usually classified as those with sizes of 2.5 microns or less in diameter (PM2.5) and those with sizes of 10 microns or less (PM10). For comparison, a typical air molecule has a size of around 0.33 nanometers—around 10,000 times smaller than particulate matter. A human hair is about 60 microns in diameter and a grain of sand is 90 microns. PM10 are dangerous because they can get in...

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