No more pandemic blue skies

After months of cleaner air because of lockdowns, air pollution in many major cities has nearly returned to pre-pandemic levels — and in a few cases, exceeded it.

Why it matters: Smoggy skies are a major, if under-recognized, danger to human health and a substantial drag on the economy. If the lockdowns demonstrated what city life could be like with cleaner air, the fact that pollution has rebounded before the global economy has, underscores how difficult it is to stop.

By the numbers: Levels of nitrogen dioxide (NO2) — a key ingredient in smog — declined by an average of 27% in 12 major global cities 10 days after lockdowns were initiated, compared to the same period during 2017–2019, according to the Centre for Research on Energy and Clean Air (CREA), an environmental think tank.

• Levels of particulate matter less than 2.5 micrometers wide (PM2.5) — which is directly harmful to health — fell by an average of about 5%.
• In often heavily polluted cities like Beijing or Los Angeles, the difference in the cleaner air was visible.

Air pollution isn't just about what we see. Its real impact is felt in human health, from cardiovascular disease to neurological development to more severe cases of COVID-19.

• Air pollution is estimated to contribute to at least 5 million premature deaths around the world each year.
• CREA estimates that the temporarily improved air quality during lockdowns in 12 major cities saved about 15,000 lives.

But, but, but: Even during the tightest periods of the lockdown, when city streets were essentially emptied of passenger cars, air pollution didn't fall as much as scientists expected — a sign of just how difficult it is to keep the skies clear.

• In some U.S. cities, levels of ozone — another key ingredient in smog — barely decreased compared to a five-year average, despite traffic reductions of more than 40%, according to an NPR analysis from May.
• One likely reason is that even with far fewer cars on the road, heavily polluting trucks kept running, as did coal-burning power plants.

The big picture: Environmentalists are increasingly arguing that climate action would more than pay for itself through the additional health and economic benefits of reduced air pollution, as David Roberts wrote last month for Vox.

• The global economic burden caused by outdoor and indoor air pollution was estimated to be $2.9 trillion in 2018, or 3.3% of global GDP.
• Drew Shindell, an earth scientist at Duke University, testified before Congress last month that reducing U.S. greenhouse gas emissions enough to keep global temperatures from rising above 2°C would prevent 4.5 million premature deaths over the next 50 years.
• Greenhouse gas emissions from burning fossil fuels, which fell by 17% compared to the previous year during peak lockdowns in April, are now almost back to 2019 levels, according to a new report by the World Meteorological Organization.

My thought bubble: Given the economic sacrifices we've made — more or less willingly — to reduce COVID-19 deaths, it would seem to make even more sense to act aggressively to reduce air pollution.

• But while we can track how the novel coronavirus spreads and directly kills, deaths connected to air pollution are far more diffuse, spread out over both space and time.
• And as the name indicates, the novel coronavirus is new, so its effects show up clearly. Air pollution has been an urban threat for more than a century, so we've learned to live with it — even as millions of people die from it.

What to watch: Whether stimulus spending in response to the pandemic favors cleaner energy sources.

• Early data from China shows that air pollution in many areas is overshooting pre-pandemic levels, indicating what experts call a "dirty recovery."
• As my Axios colleague Amy Harder reported, the U.S. has allocated just 1.1% of its pandemic stimulus money to clean energy — even less than China — while the EU is allocating more than 20%.

The bottom line: The average person takes at least 17,280 breaths per day, providing plenty of opportunities for air pollution to do its damage — and the pandemic air holiday is just about over.