You may have read about the greatly improved air quality in some places, including India and some South American Countries.
It is supposedly caused by the huge drop in vehicle traffic caused by Stay-at-Home anti-Coronavirus initiatives.
Officials with the Alabama Department of Environmental Management say the state's air is already so much cleaner than those other countries, well below even stricter U.S. EPA limits, that the reduction in ozone and other pollutants in Alabama will be measurable, but not a big improvement in the already cleaner air.
The counties with the highest pollution readings are Jefferson and next door Shelby. But with the exception of some readings on some Summer days, ADEM says even their readings are within EPA guidelines.
But an article on the nature.com website questions whether there really has been a reduction caused by less traffic:
"Unclear causes
The situation is fuzzier in the United States.
Reports that air pollution has dropped in New York and other large
cities because of COVID-19 precautions imposed in March are premature,
says Dan Goldberg, an atmosphere researcher at Argonne National
Laboratory in Lemont, Illinois.
Source: European Space Agency TROPOMI instrument (data); Dan Goldberg, Argonne National Laboratory (analysis)
“I haven’t seen any statistically significant changes in air
pollution in most US cities, which is contrary to the claims in some
media articles,” he says. According to the TROPOMI data, the only US
city that is seeing a statistically significant improvement in air
quality is Los Angeles, California (see ‘Weather factor’). The caveat,
he says, is that it has been unusually rainy there in the last few
weeks. So it is still unclear what fraction of the observed improvement
in pollution is due to favourable weather and what fraction is due to
COVID-19 precautions. “Probably both are simultaneously helping,” he
says."
While Alabama's air is now cleaner, there was a time when Birmingham was smog central.
I took the photo on the left from a helicopter in 1976. It shows the air above the U.S. Steel Plant in Ensley.
Officials with the Alabama Department of Environmental Management say the state's air is already so much cleaner than those other countries, well below even stricter U.S. EPA limits, that the reduction in ozone and other pollutants in Alabama will be measurable, but not a big improvement in the already cleaner air. 
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