An Overview: Polycyclic Aromatic Hydrocarbon Emissions from the Stationary and Mobile Sources and in the Ambient Air

Abstract

Polycyclic aromatic hydrocarbons are a class of semi-volatile organic carbons that are emitted from both natural and anthropogenic sources therefore are ubiquitous in nature. Their main sources are both fossil and biomass fuels as well as other feedstocks used in chemical and combustion processes. Mostly the combustion processes are PAH depletion processes rather than PAH generating processes. PAHs are emitted from both stationary and mobile sources at varying levels depending on the operation conditions such as fuels, feedstock, and control devices in use as well as process parameters for example combustion temperatures.After emission from sources, the fates of PAHs in the atmosphere include partitioning between gas and particulate phases, particle size distribution, long range transport, dry and wet deposition on to water bodies, soil, vegetation and other receptor surfaces as well as resuspension from receptor surfaces back to the atmosphere. These processes are controlled by their physiochemical properties. Additionally, it is through these processes that human beings are exposed to PAHs via inhalation, ingestion and dermal contact.Dry deposition is the major process through which PAHs from the atmosphere are made available to receptor surfaces including the human respiratory system. From studies with cumulative fractions of dry deposition and size distribution for particulate PAHs, it is evident that the coarse particles are majorly responsible for the highest fraction of deposition fluxes. This is especially true for the high molecular weight PAHs, since the low molecular weight PAHs are majorly in the gas phase, which have lower dry deposition velocities. On the other hand, the highest risk for human being comes in the form of fine particles, whose mean aerodynamic diameter is below 2.5 µm. This is because the particle bound content results and particle size distributions of PAHs indicate that the fine particles have the most PAH content owing to their large surface areas and high organic carbon content. For the wet deposition of PAHs, more research is recommended for measurement of scavenging ratios of individual PAHs, since there is a scarcity of studies focusing on this issue.PAH mutagenic activity and exposure risk of humans can be estimated using the deposition rates, toxicity levels based on benzo(a)pyrene, or biomarkers such as urinary 1-hydroxypyrene. Other parameters that have been used to evaluate the risks of various exposure groups include inhalation exposure levels (IEL), incremental lifetime cancer risk (ILCR), and estimation of maximum consumption time (t max ). Highway toll workers, back carbon workers and food vendors in night markets are among susceptible groups identified using these biomarkers and exposure parameters.To reduce exposure to human beings, PAH emissions need to be controlled at the sources. Control and reduction of PAH emissions from various sources involves largely altering the fuel and feedstock characteristics, using air pollution control devices and/or adjustin...

Experimental Study on PCDD/Fs Adsorption onto Nano-Graphite

“…Wang et al indicated that the high affinities of polycyclic aromatic hydrocarbons (PAHs) to graphite sheets are dominated by π-π interactions. PAHs are also one class of semi-volatile organic compounds (Cheruiyot et al, 2015). Dioxin, is one of the organic compounds, which contains π electrons that can interact with π electrons of benzene rings of graphite sheets by means of π-π interaction (Wang et al, 2014b).…”

PAHs accumulation on leaves of six evergreen urban shrubs: A field experiment

“…Among the most common atmospheric semi-volatile compounds, PAHs are ubiquitous pollutants from both natural and anthropogenic sources (Cheruiyot et al, 2015). Natural sources include forest fires, volcanic eruptions and degradation of biological materials.…”

Reburning Treatment of the Froths Obtained after the Flotation of Incinerator Fly Ash

“…The principle of flotation is based on the differences in surface hydrophobicity between the particles. The hydrophobicity and lipophilicity nature of PCDD/Fs and other organic contaminants such as PAHs, CBs, CPs and PCBs makes them easy to float into the froths after flotation (Cheruiyot et al, 2015;Lee et al, 2016). The previous report indicated that the flotation process could be successfully applied to substantially decrease the amount of carbon constituents and PCDD/Fs in HSWI fly ash (Liu et al, 2013).…”

“…Due to small-scale incinerator, incomplete incineration and high chlorine content in the waste feed, some toxic persistent organic pollutants are generated such as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs), polycyclic aromatic hydrocarbons (PAHs), chlorobenzenes (CBs), chlorophenols (CPs) and polychlorinated biphenyls (PCBs), etc. (Lee et al, 2003;Chen et al, 2013;Cheruiyot et al, 2015;Lee et al, 2016). The PCDD/F emission factors of hospital solid waste incinerator (HSWI) were about 1-2 orders higher than those of municipal solid waste incinerator (MSWI) (Lee et al, 2003;Cheruiyot et al, 2016).…”