Changes in criteria air pollution levels in the US before, during, and after Covid-19 stay-at-home orders: Evidence from regulatory monitors

The widespread and rapid social economic changes from Covid-19 response might be expected to dramatically improve air quality. However, national monitoring data the US Environmental Protection Agency for criteria pollutants (PM2.5, ozone, NO2, CO, PM10) provide inconsistent support that expectation. Specifically, during stay-at-home orders, average PM2.5 levels were slightly higher (~10% of its multi-year interquartile range [IQR]) than expected; PM10 lower (~30%, ~20%, ~27%, ~1% their IQR, respectively) expected. timing peak anomaly, relative varied by pollutant (ozone: 2 weeks before; CO: 3 after; PM10: after); but, 5–6 after concentration anomalies appear have ended. For PM2.5, PM10, no state had lower-than-expected pollution all stay-at-home-orders; only Arizona orders. Our findings show enormous not lowered across beyond normal variability; concentrations but reduction was modest transient.