Polycyclic Aromatic Hydrocarbons and Combustion

Abstract

The polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in any incomplete combustion; that is, one that does not generate only water and carbon dioxide. A huge variety of PAHs can be produced in combustion; the unsubstituted forms differ in ring number, ring isomerization, degree of condensation, and whether there are only six‐member carbon rings or some with five carbons. Substitution can be as simple as alkylation limited only to methylation. Various conditions can produce hydroxyl, carboxyl, and nitro substitutions. This chapter will mainly focus on the unsubstituted PAHs, as they are the prevalent type found in combustion products. This variety depends on combustion conditions such as the fuel and its concentration, residence time, and combustion temperature. Numerous reactions are involved that involve a multitude of production pathways, and to understand this complexity modern analytical tools must be used. Such tools include gas chromatography‐mass spectrometry and liquid chromatography with UV spectral detection, and are used to differentiate and identify specific PAHs. How these techniques work, and what types of information they provide, will be highlighted.

Seasonal Deposition Fluxes and Removal Efficiency of Atmospheric Polybrominated Diphenyl Ethers in a Large Urban Center: Importance of Natural and Anthropogenic Factors

“…Similar seasonal and spatial patterns were also observed for PAHs . This similarity between PBDEs and PAHs probably suggested strong atmospheric convective mixing in Guangzhou, as these two groups of contaminants are mainly derived from completely different sources, i.e., volatilization from electronic products for PBDEs and incomplete combustion of fossil fuel and biomass for PAHs. , …”

“…3 This similarity between PBDEs and PAHs probably suggested strong atmospheric convective mixing in Guangzhou, 24 as these two groups of contaminants are mainly derived from completely different sources, i.e., volatilization from electronic products for PBDEs and incomplete combustion of fossil fuel and biomass for PAHs. 4,8 Key Factors Controlling the Occurrence of PBDEs in Wet Deposition. Detailed CIT results for ΣPBDE and BDE-209 are shown in Figure 2, whereas those for individual BDE congeners are displayed in SI Figure S2.…”

“…We found that wet deposition was an important mechanism to remove PAHs and PM from the atmosphere and the related removal rates in November 2010 would have been higher without artificial rain intervention. It is well-known that PAHs are mainly derived from incomplete combustion of fossil fuel and biomass, and automobile exhausts may be the major contributor of PAHs in urban areas in this context. , As a result, administrative policy limiting the usage of motored vehicles during a certain period of time may work well for PAHs, but not so for other pollutants of different sources. To test this hypothesis and provide further insights into the efficacy of the implemented pollution control measures, we analyzed the same samples for polybrominated diphenyl ethers (PBDEs) and calculated their deposition fluxes and removal efficiencies by wet deposition.…”

Interconversion of Methyltropyl and Xylyl Radicals: A Pathway Unavailable to the Benzyl–Tropyl Rearrangement

“…Polycyclic aromatic hydrocarbons play crucial roles in many chemical processes, ranging from combustion, , to atmospheric pollution, − to the molecular evolution of cosmic carbon . Although different mechanisms for their assembly and growth have been proposed, including hydrogen abstraction–acetylene addition and Diels–Alder reactions, many gaps in our knowledge persist.…”

Coating Polycyclic Aromatic Hydrocarbon Cations with Helium Clusters: Snowballs and Slush

“…Detailed experiments ,,− and calculations ,− concurred to show that the interaction between the helium atoms and the molecular substrate is highly anisotropic, especially in electronic excited states, giving rise to equally anisotropic delocalization and confinement manifested by specific spectral features such as so-called zero-phonon lines and zero-phonon wings. Polycylic aromatic hydrocarbons (PAHs) have recently gained a lot of attention from the physical chemistry community because of their relevance as combustion products and in astrochemistry as possible carriers of specific infrared bands in the emission spectra of interstellar clouds . Such rather large molecular compounds could be synthesized upon electron irradiation of smaller aromatics in helium droplets .…”