3. Regulations

3.1 General

Given the harmful effects of compounds such as nitrogen oxides on humans and the natural environment, and the damage they can cause to our heritage, public authorities have gradually been led to set maximum concentration limits for these substances in the gases they emit, in order to preserve ambient air quality. These emission standards have evolved considerably over time in our industrialized countries, becoming increasingly stringent as knowledge of the effects of pollutants and advances in off-gas treatment techniques have progressed. As a result, the European Union is drawing up increasingly stringent directives, based in particular on the concept of "best available technology (BAT) that does not entail excessive costs", a restriction designed not to jeopardize the...