Tiny particle matter called PM2.5 is measured in micrograms per cubic meter (ug/m3). EPA standards had called for a maximum measure of 15 ug/m3 over a three-year period that was lowered to 12 ug/m3 in 2012. Knox County had been judged "non-attainment" for going over that limit in the past and is hoping to get that designation lifted. The air quality had been measured at three sites before a fourth site was added in 2001. There is no information provided for 2010. Light blue represents the Knox County testing number and dark blue the EPA standard.