Methods of reducing pollution. These include taxation of polluting activities and the imposition of quantitative restrictions on pollution. Quantitative restrictions may take the form of a ban on polluting activities, the imposition of pollution standards, which limit the permissible amount of pollution per unit of an activity, or the issue of a restricted number of permits to pollute, which may or may not be tradable. A ban on pollution may not be possible if there is no alternative production method available. Long-term policies to reduce pollution include research into alternative less- or non-polluting technologies.