overall costs of air pollution from carbonbased sources are orders of magnitude higher than those from noncarbonbased ones and the air pollution costs of coalbased electricity are much higher than those from other carbonbased fuels see table below from until s emissions from electricity generators under the us environmental protection agency s trading programmes have thus fallen by from approximately million tonnes to mt and nox emissions by from approximately mt to mt in the same time frame in comparison road transport accounts for deaths per year the electricity sector also accounts for of nh ammonia emissions and of s sulphur dioxide emissions