Over 2002-12, PM emissions from mobile sources declined by about 45%. Transport-related NOx emissions decreased by 13% thanks to better performance of the passenger car fleet (Figure 1.9), yet NOx emissions from heavy trucks increased by roughly 25% (MMA, 2014a). The law obliges the states to monitor air quality and produce annual air quality reports, but only 12 of the 27 states (including the Federal District) had some type of monitoring system installed by 2012, and few of them provide consistent, accessible data (IEMA, 2012).