PAHs in Gas and Particulate Phases: Measurement and Control

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds with two to seven fused benzene rings in a linear or angular arrangement. PAHs, having ubiquitous presence, are extensively reported and have carcinogenic potential, low aqueous solubility and semi-volatile nature and have been recognized as persistent toxic substances (PTS). Therefore, they are of considerable environmental concern. Combustion of fuels of all types including wood, coke and gas is the major anthropogenic activities that produce PAHs, while forest fires and volcanic eruptions are the natural sources. PAHs with low molecular weight dominate in the gaseous phase and are considered less toxic to humans, whereas PAHs with high molecular weight due to their low vapour pressures remain in particulate phase and are carcinogenic and/or mutagenic. PAHs with low molecular weight are much more abundant and can react with other pollutants such as O3 and NOx to form highly toxic nitrated and oxy-PAH compounds. The various factors that govern the atmospheric partitioning of PAHs are ambient temperature, relative humidity, aerosol nature and its properties, interactions between the compound and the aerosol. The sources of PAHs and their quantitative contributions to a particular region are a matter of concern. In the environment, they occur as complex mixtures and not as single compounds. The two important parameters that provide a basis for identifying PAH sources are the differences in the pattern of PAH mixtures and their concentration ratios. The development of appropriate strategies for adequate and effective control measures requires identification of sources and their quantitative contributions in a region.