oceans). Fund pollutants are not destroyed, but rather converted into less harmful substances, or diluted/dispersed to non-harmful concentrations. Specific groups of pollutants Many pollutants are within the following notable groups: Environmental persistent pharmaceutical pollutants (EPPP) Greenhouse gases (GHGs) Particulate matter (PM) Persistent organic pollutants (POPs) Polycyclic aromatic hydrocarbons (PAHs) Volatile organic compounds (VOCs) Light pollutant Light pollution is the impact that anthropogenic light has on the visibility of the night sky. It also encompasses ecological light pollution which describes the effect of artificial light on individual organisms and on the structure of ecosystems as a whole. Zones of influence Pollutants can also be defined by their zones of influence, both horizontally and vertically. Horizontal zone The horizontal zone refers to the area that is damaged by a pollutant. Local pollutants cause damage near the emission source. Regional pollutants cause damage further from the emission source. Vertical zone The vertical zone refers to whether the damage is ground-level or atmospheric. Surface pollutants cause damage by accumulating near the Earth's surface. Global pollutants cause damage by concentrating on the atmosphere. Measuring concentration Regulation International Pollutants can cross international borders and therefore international regulations are needed for their control. The Stockholm Convention on Persistent Organic Pollutants, which entered into force in 2004, is an international legally binding agreement for the control of persistent organic pollutants. Pollutant Release and Transfer Registers (PRTR) are systems to collect and disseminate information on environmental releases and transfers of toxic chemicals from industrial and other facilities. European Union The European Pollutant Emission Register is a type of PRTR providing access to information on the annual emissions of industrial facilities in the Member States of the European Union, as well as Norway. United States Clean Air Act standards. Under the Clean Air Act, the National Ambient Air Quality Standards (NAAQS) are developed by the Environmental Protection Agency (EPA) for six common air pollutants, also called "criteria pollutants": particulates; smog and ground-level ozone; carbon monoxide; sulfur oxides; nitrogen oxides; and lead. The National Emissions Standards for Hazardous Air Pollutants are additional emission standards that are set by EPA for toxic air pollutants. Clean Water Act standards. Under the Clean Water Act, EPA promulgated national standards for municipal sewage treatment plants, also called publicly owned treatment works, in the Secondary Treatment Regulation. National standards for industrial dischargers are called Effluent guidelines (for existing sources) and New Source Performance Standards, and currently