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The widespread and rapid social and economic changes from Covid-19 response might be expected to dramatically improve air quality. However, national monitoring data from the US Environmental Protection Agency for criteria pollutants (PM 2.5 , ozone, NO 2 , CO, PM 10) provide inconsistent support for that expectation. Specifically, during stay-at-home orders, average PM 2.5 levels were slightly higher (~10% of its multi-year interquartile range [IQR]) than expected; average ozone, NO 2 , CO, and PM 10 levels were slightly lower (~30%, ~20%, ~27%, and ~1% of their IQR, respectively) than expected. The timing of peak anomaly, relative to the stay-at-home orders, varied by pollutant (ozone: 2 weeks before; NO 2 , CO: 3 weeks after; PM 10 : 2 weeks after); but, by 5–6 weeks after stay-at-home orders, the concentration anomalies appear to have ended. For PM 2.5 , ozone, CO, and PM 10 , no US state had lower-than-expected pollution levels for all weeks during stay-at-home-orders; for NO 2 , only Arizona had lower-than-expected levels for all weeks during stay-at-home orders. Our findings show that the enormous changes from the Covid-19 response have not lowered PM 2.5 levels across the US beyond their normal range of variability; for ozone, NO 2 , CO, and PM 10 concentrations were lowered but the reduction was modest and transient. Unlabelled Image • Impacts of stay-at-home orders on air pollution were evaluated using EPA monitoring data from 100s of stations across the US. • During stay-at-home orders, ozone, NO 2 , CO and PM 10 were lower and PM2.5 were higher than expected levels by 1%-30% of their IQR. • Concentration anomalies ended only 5-6 weeks after stay-at-home orders were issued. • Ozone, NO 2 , and CO concentrations returned to expected levels and PM 2.5 and PM 10 levels were higher than expected. • Reductions in ozone, NO 2 , and CO levels were modest and short-lived. PM 10 levels did not change and PM 2.5 levels increased. [ABSTRACT FROM AUTHOR]