Quantitative regulations, often labelled as “command-and-control” measures, operate by establishing standards or limits that producers or consumers must comply with. They typically lay down maximum amounts of specified pollutants that can be emitted in given periods of time, or require that some index of pollution-concentration be kept below a prescribed limit. In extreme cases, regulations prohibit the use highly damaging inputs, or require that a pollutant emission be zero.
Alternatively, regulations may require the use of particular “clean” technologies in some production processes. In motor vehicle production, mandatory technology regulations are used widely. These include emissions standards for engine units of given sizes and for particulate emissions from diesel engines, and requirements that manufactures install catalytic converters produce engines that are operable using unleaded fuel. Standards-based approaches to pollution control have been (and remain) the main component of control programmes in the United States and Europe.