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...