Energy production and use not only accounts for most of the air pollution arising from human activity, it also accounts for a very high proportion of the human-related emissions of some key pollutants. This is true of both sulfur dioxide (SO2) and nitrogen oxides (NOX), emissions of which are almost entirely attributable to energy production and use, and of some 85% of primary PM (Figure 1.3). These three categories of pollutants – SO2, NOX and primary PM – are the main focus of this report.