Since the early 1960s, the Ministry of Environment has implemented a range of policies and air pollutant standards to improve and manage air quality for its people. The "Special Act on the Improvement of Air Quality in the Seoul Metropolitan Area" was passed in December 2003. Its 1st Seoul Metropolitan Air Quality Improvement Plan (2005–2014) focused on improving the concentrations of PM10 and nitrogen dioxide by reducing emissions. As a result, the annual average PM10 concentrations decreased from 70.0 μg/m3 in 2001 to 44.4 μg/m3 in 2011 and 46 μg/m3 in 2014. As of 2014, the annual average PM10 concentration was still at least twice than that recommended by the WHO Air Quality Guidelines. The 2nd Seoul Metropolitan Air Quality Improvement Plan (2015–2024) added PM2.5 and ozone to its list of managed pollutants.