The 2009-2010 academic year marked the achievement of ...

U.S. EPA 2018 Air Trends Report Methodologies. ... Take a closer look at how the number of days with unhealthy air has dropped since 2000 in 35 major U.S. cities. ... The table also shows the number of sites used for computing the national statistics (10th 50th and 90th percentiles) shown on the charts. ... ................
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