The sentiment that woodsmoke, being a natural substance, must be benign to humans is still sometimes heard. It is now well established, however, that wood-burning stoves and fireplaces as well as wildland and agricultural fires emit significant quantities of known health-damaging pollutants, including several carcinogenic compounds. Two of the principal gaseous pollutants in woodsmoke, CO and NOx, add to the atmospheric levels of these regulated gases emitted by other combustion sources. Health impacts of exposures to these gases and some of the other woodsmoke constituents (e.g., benzene) are well characterized in thousands of publications. As these gases are indistinguishable no matter where they come from, there is no urgent need to examine their particular health implications in woodsmoke. With this as the backdrop, this review approaches the issue of why woodsmoke may be a special case requiring separate health evaluation through two questions. The first question we address is whether woodsmoke should be regulated and/or managed separately, even though some of its separate constituents are already regulated in many jurisdictions. The second question we address is whether woodsmoke particles pose different levels of risk than other ambient particles of similar size. To address these two key questions, we examine several topics: the chemical and physical nature of woodsmoke; the exposures and epidemiology of smoke from wildland fires and agricultural burning, and related controlled human laboratory exposures to biomass smoke; the epidemiology of outdoor and indoor woodsmoke exposures from residential woodburning in developed countries; and the toxicology of woodsmoke, based on animal exposures and laboratory tests. In addition, a short summary of the exposures and health effects of biomass smoke in developing countries is provided as an additional line of evidence. In the concluding section, we return to the two key issues above to summarize (1) what is currently known about the health effects of inhaled woodsmoke at exposure levels experienced in developed countries, and (2) whether there exists sufficient reason to believe that woodsmoke particles are sufficiently different to warrant separate treatment from other regulated particles. In addition, we provide recommendations for additional woodsmoke research.

In this paper we present the synthesis and characterization of the so far largest polycyclic aromatic hydrocarbon (PAH), containing 222 carbon atoms or 37 separate benzene units. First a suitable three‐dimensional oligophenylene precursor molecule is built up by a sequence of Diels–Alder and cyclotrimerization reactions and then planarized in the final step by oxidative cyclodehydrogenation to the corresponding hexagonal PAH. Structural proof is based on isotopically resolved MALDI‐TOF mass spectra and electronic characteristics are studied by UV/Vis spectroscopy.

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The effects of the core size, the side chain length, and the number of substituents on the supramolecular organization of polycyclic aromatic hydrocarbons have been investigated by 2D wide-angle X-ray scattering experiments performed on oriented filaments prepared by extrusion. The aromatic core size of the compounds varied between the hexa-peri-hexabenzocoronene core consisting of 42 carbon atoms and the enlarged aromatic core of 132 carbon atoms, whereas the length of the side chains extended up to 20 carbon atoms per chain. It has been observed that the lateral packing characterized by the lattice constant of the 2D intercolumnar hexagonal arrangement increases with the molecular masses of the core, forming the columnar stacks, and of the side chains which fill the core periphery. A model describing the relationship between the morphological and molecular parameters for the columnar hexagonal arrangements of the discotics is suggested and indeed proven by comparison with the experimental results.

The optical absorption and charge transport properties of a series of discotic molecules consisting of peripherally alkyl-substituted polycyclic aromatic cores have been investigated for core sizes, n, of 24, 42, 60, 78, 96, and 132 carbon atoms. In dilute solution, the wavelength maximum of the first absorption band increases linearly with n according to lambda(max) = 280 + 2n and the spectral features become increasingly broadened. The two smallest core compounds display a slight red-shift and increased spectral broadening in spin-coated films. For derivatives with n = 24, 42, 60, and 96, the one-dimensional, intracolumnar charge mobility, Sigma mu(1D), was determined using the pulse-radiolysis time-resolved microwave conductivity technique. For the compounds which were crystalline solids at room temperature, Sigma mu(1D) lay within the range 0.4-1.0 cm(2)/Vs. In the discotic mesophases at ca. 100 degrees C, Sigma mu(1D) was somewhat lower and varied from 0.08 to 0.38 cm(2)/Vs. The mobility values in both phases are considerably larger than the maximum values found previously for discotic triphenylene derivatives. However, the recently proposed trend toward increasing mobility with increasing core size is not substantiated by the results on the present series of increasingly large aromatic core compounds.

Large polycyclic aromatic hydrocarbons (PAHs) can be considered as nanographenes, whose electron donating or accepting properties are controlled by their size and shape as well as functionalities in their periphery. Epitaxial thin films of them are targets for optoelectronic applications; however, large PAHs are increasingly difficult to process. Here we show that epitaxial layers of very large unsubstituted PAHs (C(42)H(18) and C(132)H(34)), as well as a mixed layer of C(42)H(18) with an electron acceptor, can be obtained by self-assembly from solution. The C(132)H(34) is by far the largest nanographene that up to now has been processed into ordered thin films; due to its size it cannot be sublimed in a vacuum. Scanning tunneling microscopy (STM) studies reveal that the interaction with the substrate induces a strong perturbation of the electronic structure of the pure donor in the first epitaxial monolayer. In a second epitaxial layer with a donor acceptor stoichiometry of 2:1 the molecules are unperturbed.

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In this study, the microstructure and oxidation behaviour of soot from the raw exhaust of a Euro IV test heavy duty (HD) diesel engine is investigated and compared to that of spark discharge soot and hexabenzocoronene (HBC, C 42 H 18 ). We find a microstructure-controlled reactivity toward oxidation of all three samples in 5% O 2 in N 2 . The spark discharge soot with its fine primary particles and fullerenoid structure has an onset temperature of 423 K for combustion, while the hexabenzocoronene with its well-ordered crystallites has a high onset temperature of 773 K. Due to an improved combustion process in the Euro IV HD diesel engine, the soot emitted consists of more fullerenoid-like or onion-like particles agglomerated in a chain-like secondary structure. The onset temperature of the Euro IV HD engine soot combustion is 573 K. Oxidation of the three samples produces only CO 2 and H 2 O. The different H 2 O production profiles can be assigned to the functionalised surface of the samples and depend on the soot structures and preparation route.