The few rich countries account for the majority of the emissions of hydrocarbons, which cause acid rain and oxidant smog. As the poorer countries industrialize these problems may increase significantly. Reducing their emissions requires cross-sectoral action, as well as improving and making available environmentally friendly technologies.
Motor vehicles are major sources of hydrocarbons. Pollution levels "per vehicle" have curbed and become less polluting as a result of incorporating increasingly energy efficient engines and catalytic converters.