;2016;Change in per cent;Change in per cent; Since 1990;2015 - 2016; Nitrogen oxides (NOX);153;-23.4;-1.9; Sulphur dioxide (SO2);16;-70.1;-4.5; Ammonia (NH3);28;5.5;-0.4; Non-methane volatile organic compounds (NMVOC);154;-49.1;-2.9; Carbon monoxide (CO);382;-53.4;-0.7;