Arthur Pigou was the economist who developed the study of externalities. In particular, he thought seriously about the problems resultant from negative externalities. Negative externalities manifest when the production or consumption of a good or service harms an unrelated third party. Pollution is an example; chronic air pollution increases the mortality rate and health risks of those in the surrounding area. His solution was a tax on the participants of the harmful activities. The tax should be in proportion to the harms of those sources. For car emissions, the tax would vary depending on the impact of each car. The government charges the producer of the externality. In this sense, the London emissions charge is a crude Pigouvian tax.
The benefit of such a tax is that it discourages those behaviours that negatively impact the commons or uninvolved third parties. The taxes incentivise greater efficiencies in the economy.
An unavoidable issue with such a tax is that the harms can prove onerous to measure - this often results in regressive Pigouvian taxes, such as the aforementioned emissions charge, which are flat-rate taxes. These flat rates take a greater percentage of the income from low-income people.