The AOT60 sums the difference between the concentrations above 120 μg/m³ and 120μg/m³ of the daily maximum 8-hour mean concentrations. In contrast to the NET60 indicator, the AOT60 considers the size and duration of the exceedance. In the draft version of the first ozone directive (2002/3/EC) and the National Emissions Ceilings Directive, 5800 (μg/m³).hours was proposed as the medium-term objective (MTO) for 2010, which corresponds to a NET60 equal to 25 days. The long-term objective is 0 (μg/m³).hours. The AOT60 was not incorporated into the current European Ambient Air Quality Directive, but is a better indicator to quantify the excess burden on public health. This indicator was also incorporated into the Flemish MINA-4 plan (2011-2015) to illustrate the plan objectives.