Polycyclic aromatic hydrocarbon

Polycyclic aromatic hydrocarbon
Name	Polycyclic aromatic hydrocarbon
Formula	Variable (CnHm)
Molar mass	Variable
Appearance	Colorless to pale yellow solids or liquids
Density	Variable
Melting point	Variable
Boiling point	Variable
Solubility	Low in water; soluble in organic solvents

Polycyclic aromatic hydrocarbon Polycyclic aromatic hydrocarbons are a class of organic compounds composed of multiple fused aromatic rings. They occur widely in the environment as products of incomplete combustion and are of concern because of their persistence, potential for long-range transport, and diverse toxicological properties. Research on these compounds spans industrial chemistry, environmental science, public health, and regulatory policy.

Introduction

PAH chemistry entered the literature alongside developments in organic synthesis during the 19th century and has been studied in contexts such as industrial smelting at Industrial Revolution sites, fuel combustion in London smogs, and petrochemical production at facilities like Standard Oil refineries. Interest from regulatory bodies such as the United States Environmental Protection Agency and the European Chemicals Agency increased after associations were made with occupational exposures in settings like coking plant operations and urban pollution monitored by agencies including National Aeronautics and Space Administration research programs and municipal public health departments in cities such as New York City and Beijing.

Structure and Classification

PAHs are defined by fused benzene rings forming planar, conjugated pi systems; canonical examples include structures first characterized by chemists in institutions such as the University of Cambridge and École Polytechnique. Classification schemes often reference parent hydrocarbons like naphthalene, anthracene, and phenanthrene, which were subjects in early studies at places like Royal Society meetings and laboratories led by figures associated with Royal Institution. Heteroatom analogs and substituted derivatives extend the class toward topics covered by scholars at Massachusetts Institute of Technology and Max Planck Society research groups. Nomenclature conventions are reflected in compendia by organizations like the International Union of Pure and Applied Chemistry.

Sources and Occurrence

Primary anthropogenic sources include combustion of fossil fuels at sites such as Chevron and ExxonMobil refineries, vehicle emissions regulated under policies like the Clean Air Act, residential wood burning in regions such as Scandinavia, and pyrolysis in industrial processes at companies akin to ArcelorMittal steelworks. Natural sources include wildfire events studied by teams from Pacific Northwest National Laboratory and seeps near petroleum fields such as those exploited by Royal Dutch Shell and BP. PAHs have been detected in media investigated by researchers affiliated with institutions like Smithsonian Institution and Scripps Institution of Oceanography, from urban air in Los Angeles to sediments in the Gulf of Mexico.

Environmental Fate and Transport

Once released, PAHs undergo processes assessed by environmental groups including World Health Organization and modeled in studies from Intergovernmental Panel on Climate Change. Photochemical reactions driven by sunlight in the upper layers of the atmosphere have been simulated in laboratories at Lawrence Berkeley National Laboratory and Argonne National Laboratory. Partitioning between air, water, and soil is influenced by sorption to organic matter observed in river systems such as the Mississippi River and coastal zones like the Chesapeake Bay. Long-range transport events documented by monitoring networks operated by European Environment Agency show deposition patterns that intersect with assessments by United Nations Environment Programme.

Health Effects and Toxicology

Epidemiological links between PAH exposure and health outcomes have been explored in cohorts studied in cities like London and Beijing and by research teams at universities such as Johns Hopkins University and Harvard University. Toxicological studies implicate specific PAHs in mutagenesis and carcinogenesis with mechanisms investigated in laboratories at National Institutes of Health and Centers for Disease Control and Prevention. Occupational exposure cases documented in histories of industries like coke production and mining prompted workplace regulations enforced by agencies such as Occupational Safety and Health Administration. Vulnerable populations highlighted in public health reports from World Health Organization include residents near contaminated sites remediated under programs like the Superfund.

Analysis and Detection Methods

Analytical chemistry approaches for PAH quantification were advanced by instrumentation from manufacturers such as Agilent Technologies and Thermo Fisher Scientific and validated in laboratories at institutions including Rensselaer Polytechnic Institute and École Normale Supérieure. Gas chromatography coupled with mass spectrometry, liquid chromatography with fluorescence detection, and high-resolution mass spectrometry used in studies by teams at Oak Ridge National Laboratory provide compound-specific identification. Passive air sampling networks coordinated by organizations like the Global Atmospheric Watch complement sediment and biota monitoring programs run by museums such as the Natural History Museum, London.

Regulation and Mitigation

Regulatory frameworks addressing PAHs are enacted through instruments like the Clean Water Act, the European Union REACH regulation, and municipal ordinances in jurisdictions such as California. Mitigation strategies include source control at utilities managed by entities like General Electric and emissions reductions from transportation fleets overseen by departments akin to the California Air Resources Board. Remediation technologies applied at contaminated sites have been developed by firms with ties to research at University of California, Berkeley and Stanford University, employing approaches such as bioremediation piloted in projects funded by agencies like the National Science Foundation.

Category:Environmental chemistry