| GlossaryHeading | GlossaryDetails |
| Halocarbons | Halocarbon compounds are chemicals in which one or more carbon atoms are linked by covalent bonds with one or more halogen atoms (fluorine, chlorine, bromine or iodine) resulting in the formation of organofluorine compounds, organochlorine compounds, organobromine compounds, and organoiodine compounds. Many synthetic organic compounds such as plastic polymers, and a few natural ones, contain halogen atoms; they are known as halogenated compounds or organohalogens. |
| Hazardous Air Pollutant (HAP) | An air pollutant listed under section 112 (b) of the Federal Clean Air Act as particularly hazardous to health. Emission sources of hazardous air pollutants are identified by U.S. EPA and emission standards are set accordingly. |
| Haze (Hazy) | A phenomenon that results in reduced visibility due to the scattering of light caused by aerosols. Haze is caused in large part by man-made air pollutants. |
| Health Risk Assessment (HRA) | A document that identifies the risks and quantities of possible adverse health effects that may result from exposure to emissions of toxic air contaminants. A health risk assessment cannot predict specific health effects; it only describes the increased possibility of adverse health effects based on the best scientific information available. |
| Hurricane | It is an extremely large, powerful, and destructive storm with very strong winds that occurs especially in the western part of the Atlantic Ocean. |
| Hydrocarbons | Compounds containing various combinations of hydrogen and carbon atoms. They may be emitted into the air by natural sources (e.g., trees) and as a result of fossil and vegetative fuel combustion, fuel volatilization and solvent use. Hydrocarbons are a major contributor to smog. |
| Hydrochloroflurocarbon (HCFC) | A chemical compound that would be a hydrocarbon except that one or more hydrogen atoms in each molecule is replaced by a chlorine atom and one or more hydrogen atom is replaced by a fluorine atom. Some HCFCs are implicated in the destruction of stratospheric ozone. |