This chapter deals with the hydrogen economy, climate change, the impact of fossil fuels on the environment, legislative acts to deal with air pollution, and energy efﬁciency and conservation.
THE HYDROGEN ECONOMY
Hydrogen is the most abundant element in the universe, making up 75 percent of its mass and 90 percent of its molecules. Hydrogen, when burned as a fuel, emits only water and heat, the cleanest source of energy by far. Though plentiful in the universe, there is no free hydrogen here on Earth. While a portion is locked away in hydrocarbons and other chemicals, most of what there is has already been burned and its product of combustion is all around and in us: water.