A class of organic compounds known as polycyclic aromatic hydrocarbons (PAHs) is made up of molecules with two or more fused benzene rings (in a linear, cluster, or angular arrangement) or molecules with carbon and hydrogen atoms arranged in rings with five or six carbon atoms. When an alkyl or other radical is added to the ring, they are known as “PAH derivatives,” and when one carbon atom in a ring is swapped out for a nitrogen, oxygen, or sulfur atom, they are known as heterocyclic aromatic compounds (HACs). The main human-made processes that produce PAHs are incomplete combustion of organic fuels. The atmospheric distribution of PAHs is extensive. Additionally, natural events like volcanic eruptions and forest fires contribute to the ambient presence of PAHs (Suchanova et al., 2008). Both can contain PAHs. depending on their volatility, both gaseous and particulate phases. High molecular weight PAHs (HMW PAHs), with molecular weights ranging from 228 to 278g/mol and having five or more rings, are emitted in the particulate phase (ATSDR, 1995). LMW PAHs, which have two or three aromatic rings and have a molecular weight between 152 and 178g/mol, are emitted in the gaseous phase. Sulfur dioxide, nitrogen oxides, and ozone are just a few of the pollutants that can interact with PAHs in the atmosphere through photo-degradation. Due to their numerous sources and persistent nature, PAHs are found almost everywhere and are transported by the atmosphere. Despite the fact that there are hundreds of PAH compounds in the environment, PAH analysis is typically only used to identify six to sixteen compounds. Individuals are exposed to PAH mixtures in gaseous or particulate phases in ambient air. Long term exposure to high concentration of PAHs is associated with adverse health problems. Since some PAHs are

1.2. Physical and Chemical Characteristics of PAHs.

A collection of several hundred distinct organic compounds known as PAHs typically exist as complex mixtures rather than as single compounds and contain two or more aromatic rings. Depending on their structural makeup, PAHs are categorized by their melting and boiling points, vapour pressure, and water solubility. At room temperature, pure PAHs are typically colored, crystalline solids. The molecular weight and structure of PAHs affect their physical characteristics (Table1). They have very low to low water solubilities and low to moderately high vapour pressures, with the exception of naphthalene. Their relatively high octanol-water partition coefficients (Kow) suggest a potential for bioconcentration in organisms as well as relatively high potential for adsorption to suspended particles in water and the air (Sloof et al., 1989). Table 1 displays the physical and chemical

A group of several hundred individuals known as PAHs is made up of a select few of the sixteen (16) priority PAHs that the US EPA has listed. (Refer to appendix) The majority of PAHs are barely soluble in water and are soluble in non-polar organic solvents, especially as molecular weight increases (ATSDR, 1995).

The majority of PAHs in the environment are persistent organic pollutants (POPs). Many of them are inert chemically. However, under strong sunlight or ultraviolet light, PAHs can be photochemically broken down, which means that some PAHs may be lost during atmospheric sampling. Additionally, the environmental fate or circumstances of PAHs can be affected by their reactions with ozone, hydroxyl radicals, nitrogen and sulfur oxides, as well as nitric and sulfuric acids (Dennis et al., 1984; Simko, 1991).

UV absorbance spectra for PAHs have a distinctive appearance. Every ring

Each isomer has a different UV absorbance spectrum because each structure has a distinct UV spectrum. This is particularly helpful in


PAH detection is the process. The majority of PAHs are also fluorescent and, upon excitation, emit specific light wavelengths (when the molecules absorb light). In general, PAHs weakly absorb infrared light between 7 and 14 m, which is the wavelength typically absorbed by chemicals used in global warning systems (Ramanathan, 1985).

The environment contains complex mixtures of polycyclic aromatic hydrocarbons that are challenging to characterize and quantify. They are typically examined using high pressure liquid chromatography (HPLC) with ultraviolet (UV) and fluorescence dectetors or gas chromatography combined with mass spectrometry (GC-MS) (Slooff et al., 1989)


Table 1 lists the physical and chemical traits of

Some well-known PAHs


PAHs’ names

Chemical formula or structure


pressure of vapour

















Fluoranthene 3


5.0 x10-6mmHg4.90


Pyrene 4


2.5 x10-6mmHg4.88







2.5 x10-6mmHg







Benzo(a)pyrene No. 7




Eight Indeno(1,2,3-c,d)pyrene

276.3 10×10-16mmHG 6.58


Sources: (ATSDR, 1995) (ATSDR, 1995)


PAH Source and Emission

The primary human-made sources of PAHs are pyrolysis and incomplete combustion of organic matter. The toxicity and distribution of PAHs are impacted by their sources, as well as their characterization. Four categories can be used to categorize the main sources of PAH emissions: stationary sources (including domestic and industrial sources), mobile emissions, agricultural activities, and

Source and Emission of PAHs

The primary human-made sources of PAHs are pyrolysis and incomplete combustion of organic matter. The toxicity and distribution of PAHs are impacted by their sources, as well as their characterization. Four categories can be used to categorize the main sources of PAH emissions: stationary sources (such as domestic and industrial sources), mobile emissions, agricultural activities, and natural sources (Wania et al, 1996).

1.3. Stationary Sources

From point sources, some PAHs are released, and these are hardly shifted (moved) for a long time. Domestic and industrial sources are the two main categories into which stationary sources are further divided.

1.3.1. Domestic Sources

The two main sources of PAHs in the home are heating and cooking. The primary domestic sources are the burning and pyrolysis of coal, oil, gas, trash, wood, or other materials. To the overall amount of PAHs released into the environment, domestic sources contribute significantly. Large geographic variations in domestic emission are caused by varying climatic patterns and home heating systems. Because PAH emissions from these sources are so common in indoor environments, they could pose a serious health risk (Ravindra et al., 2008). More than 75% of people in China, India, and South East Asia, as well as 50% to 75% of people in some regions of South America and Africa, use combustion of solid fuel, such as wood or charcoal, for daily cooking, according to a recent World Health Organization (WHO) report.

principal indoor sources of PAH

are outdoor infiltration, heating, and cooking. Cooking-related PAH emissions make up 32.8% of all indoor PAHs (Zhu et al., 2009). LMW PAHs, which come from indoor sources, make up the majority of the total PAHs found.


in non-smoking residential air. Compared to mixtures that contain significant amounts of high molecular weight PAHs, the toxicity of PAH mixtures from indoor sources is lower. Another important source of PAHs in indoor environments is cigarette smoke. According to numerous studies, smoking homes typically have higher indoor PAH levels than non-smoking homes.

1.3.2. Industrial Sources

Sources of PAHs include emissions from commercial heat and power generation, waste incineration, rubber tire and cement manufacturing, petrochemical industries, bitumen and asphalt manufacturing, wood preservation, and primary aluminum and coke production (Fabbri and Vassura , 2006).

1.3.3. Mobile Sources

In urban areas, mobile sources account for the majority of PAH emissions. The majority of PAH emissions come from vehicles, such as cars, trains, ships, aircraft, and other motorized vehicles. Diesel, coal, gasoline, oils, and lubricant oil use are linked to PAH emissions from mobile sources. Three processes result in the formation of PAH exhaust emissions from motor vehicles: (1) synthesis from smaller molecules and aromatic compounds in fuel; (2) storage in engine deposits and fuel; and (3) pyrolysis of lubricants (Baek et al., 1991). The air-to-fuel ratio is one of the key factors that affects the production of PAHs from gasoline-powered vehicles. There have been claims that



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