Run-down public schools made air quality a problem before COVID.
California has regulations, but it's been hard to get PPE to workers in the fields. There's no federal standard.
China says it has succeeded in cutting the city's pollution over 5 years.
A new report ranks air pollution as the greatest threat to human life, above war and disease.
Air pollution in Beijing over the weekend was 40 times worse than limits set by the World Health Organization and it has economic implications for China