What Is the Air Quality Like Near You?

Is the air noticeably clearer where you live right now? For Earth Day, you can become a citizen scientist by using an app to track air pollution in your neighborhood.

Sabrina Stierwalt, PhD
4-minute read
Episode #371

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 our lungs when we inhale them, but PM2.5 are small enough to enter our bloodstream. 

Particulate matter concentrations are typically given in measures of micrograms per cubic meter. The World Health Organization provides guidelines as to what levels are acceptable for annual and daily averages. Delhi, which has repeatedly ranked as the world’s most polluted city, has an average measure of 98.6 micrograms of PM2.5 per cubic meter, almost ten times the level recommended by the World Health Organization (WHO).

But if micrograms per cubic meter don’t really speak to you, in the US, the Environmental Protection Agency uses the Air Quality Index (AQI) to assess the levels of particulate matter. (They also measure AQI for four additional pollutants: ground-level ozone, carbon monoxide, sulfur dioxide, and nitrogen dioxide.) Higher values mean higher levels of pollution in the air and thus greater risks to your health. An AQI of 100 generally marks the boundary between healthy and unhealthy air. Above 300 signals emergency conditions where actions need to be taken to mitigate the pollution levels and to keep people indoors.

Air pollution poses a serious threat to human health. Prolonged exposure to particulate matter leads to cardiovascular and respiratory issues. According to the WHO, 4.2 million premature deaths worldwide, especially in South East Asia and the Western Pacific, were attributed to ambient pollution in 2016. One study out of Harvard University found that an increase of only 1 ug/m3 in PM2.5 was associated with a 15 percent increase in the death rate from COVID-19

How can you help track air pollution and find out air quality near you? 

One way to check air pollution levels where you live is to use a new app developed by the international Earth Day Network to help mark the 50th anniversary of Earth Day. The app is part of a large citizen science effort to track levels of air pollution globally. There is evidence that these particulates can travel a long way, thanks to wind and the local topography, so even if your town or city is not the one doing the polluting, you can still experience the negative effects.

There is evidence that these particulates can travel a long way, thanks to wind and the local topography.

To contribute to the global project, you upload a photo of the air/smog conditions in your area. Scientists will then match the photos from volunteers like you with their associated professional measurements of PM2.5.  By comparing tens to hundreds of thousands of images with their measured PM2.5 values, researchers will train computer programs, via machine learning, to be able to take visual clues like the ones seen in your photos and translate them into a PM2.5 measurement using just the image.

So you can get an assessment of the current air quality conditions in your area before you head out for a walk (while wearing a mask and properly social distancing, of course). Or if you’re staying inside, you can contribute to a global effort to measure how air pollution varies from place to place. 

How else can I participate in Earth Day 2020?

If you are looking for other ways to celebrate Earth Day 2020 (#EarthDayAtHome) while staying at home, the Earth Day Network is here for you. The Great Global Cleanup, which hoped to get something like 400,000 people cleaning up beaches and parks, obviously can't happen. But you can still participate in a virtual clean up by picking up plastic litter in your neighborhood and logging your efforts in an app that hopes to track what kind of plastic makes it into litter most often and how far discarded plastics can spread.

We know that we dump more than 28 billion pounds of plastic into the ocean, so if you need a few reminders of why the oceans are worth protecting, I highly recommend the series of live cams offered by the Monterey Bay Aquarium.

Please note that archive episodes of this podcast may include references to Ask Science. Rights of Albert Einstein are used with permission of The Hebrew University of Jerusalem. Represented exclusively by Greenlight.

About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.