Reactive Polycyclic Aromatic Hydrocarbons Research Articles

Reactions of deoxyribonucleotide bases with sulfooxymethyl or halomethyl polycyclic aromatic hydrocarbons induce unwinding of DNA supercoils

Torsional stress in double-stranded DNA enables and regulates facets of chromosomal metabolism, replication, and transcription and requires regulatory enzymatic systems including topoisomerases and histone methyltransferases. As such, this machinery may be subject to deleterious effects from reactive mutagens, including ones from carcinogenic polycyclic aromatic hydrocarbon (PAH) adduct formation with DNA. Supercoiled plasmid DNA was investigated for its torsional responses to adducts formed in vitro from PAH benzylic carbocation reactive intermediates created spontaneously by release of leaving groups. PAH sulfate esters were found to (1) unwind DNA in a concentration dependent manner, and (2) provide maximum unwinding in a pattern consistent with known carcinogenicities of the parent PAHs, that is, 6-methylbenzo[a]pyrene > 7,12-methylbenz[a]anthracene > 3-methylcholanthrene > 9-methylanthracene > 7-methylbenz[a]anthracene > 1-methylpyrene. Supercoil unwinding was demonstrated to be dependent on the presence of sulfate or chloride leaving groups such that reactive carbocations were generated in situ by hydrolysis. In silico modeling of intercalative complex topology showed PAH benzylic carbocation reactive functional groups in alignment with target nucleophiles on guanine bases in a 5’-dCdG-3’ pocket in agreement with known formation of nucleotide adducts. Inhibitory or modulatory effects on PAH-induced supercoil unwinding were seen with ascorbic acid and an experimental antineoplastic agent Antineoplaston A10 in agreement with their known anticarcinogenic properties. In summary, the reactive PAH intermediates studied here undoubtedly participate in well-known mutational mechanisms such as frameshifts and apurinic site generation. However, they are also capable of random disruption of chromosomal supercoiling in a manner consistent with the known carcinogenicities of the parent compounds, and this mechanism may represent an additional detrimental motif worthy of further study for a more complete understanding of chemical carcinogenicity.

Effects of adsorbed water and hydrocarbon reactivity on the nitration of polycyclic aromatic hydrocarbons adsorbed on silica gel and Fe2O3 particles with NO2

Abstract Here, the nitration of polycyclic aromatic hydrocarbons (PAHs) adsorbed on SiO2 and Fe2O3 particles, which are abundant in PM2.5, with NO2 (9.77 ppm) was studied using a fluidized-bed column to simulate the transformation of atmospheric PAHs at night. Silica gel was used as SiO2, and anthracene, phenanthrene, pyrene, chrysene, fluoranthene, and perylene were used as PAHs. The effects of water (H2Oads) adsorbed on the substrates and the reactivity of PAHs on the transformation kinetics and mechanism were investigated. On the hydrated silica gel (H2Oads: 4.2 wt%), the most reactive PAH (perylene) was nitrated following a pseudo-first-order reaction, and moderately (anthracene and pyrene) and less reactive (chrysene) PAHs were nitrated by a H+-autocatalyzed reaction. However, on dry Fe2O3 (H2Oads: 0.02 wt%), the nitration of the moderately reactive PAHs proceeded following a pseudo-first-order reaction, and chrysene was nitrated by a H+-autocatalyzed reaction. On both substrates, the nitration of PAHs changed from pseudo-first-order to H+-autocatalyzed reactions as the reactivity of the PAHs decreased, indicating that the nitration kinetics and mechanism are affected by the concentration of H+ formed in H2Oads upon exposure to NO2. On dry Fe2O3, perylene and the moderately reactive PAHs were nitrated by NO2, while the moderately reactive PAHs and chrysene were nitrated by NO2+ on the hydrated silica gel, which would be formed via a pre-equilibrium reaction between NO2 and H+ formed by NO2 exposure and released by nitration. The formation of NO2+ is supported by the acceleration of the H+-autocatalyzed nitration on the H2SO4-adsorbed hydrated silica gel and by the detection of NO2+ on hydrated borosilicate glass.

The role of reactive PAH dimerization in reducing soot nucleation reversibility

Abstract Nucleation of incipient soot or carbon black nanoparticles has significant scientific and industrial importance because it influences the particle size distribution, morphology and composition, hence its health and environmental impact as well as functional properties. R eversible P olycyclic Aromatic Hydrocarbon (PAH) C lustering (RPC) with van der Waals forces (vdW) was proposed recently as opposed to I rreversible P AH C lustering (IPC) for soot nucleation (Eaves et al., Proc. Combust. Inst, 35 (2015) 1787) to relax the assumption of stable dimer formation with physical bonds at flame temperatures. Here, the necessity of considering chemical bond formation between PAHs in a dimer for reducing soot nucleation reversibility in ethylene coflow diffusion flames with a wide range of nitrogen dilution ratios is demonstrated. An RPC model with C hemical B ond F ormation (RPC CBF) is developed and its performance is compared to those of RPC and IPC models. Only the RPC CBF model with low reversibility for PAH addition on the surface of soot primary particles can predict soot volume fraction, average primary particle diameter, primary particle number density and the bimodal size distribution of soot agglomerates on the flame centerline within experimental uncertainty. While the IPC model overpredicts soot concentrations by a factor of five with increased dilution, the RPC model underpredicts it by more than two orders of magnitude for the flame with 68% nitrogen dilution. The RPC model fails to predict the observed bimodality of agglomerate particle size distribution in flames with low dilution because its predicted nucleation rate is much weaker compared to that of growth. Accounting for chemical bond formation for dimers is essential to form enough nuclei with increasing dilution and temperature. Also, low reversibility for PAH addition is required to predict the balance between nucleation and surface growth, hence the average size of soot primary particles.

Correction: Reactive polycyclic aromatic hydrocarbon dimerization drives soot nucleation

Correction for 'Reactive polycyclic aromatic hydrocarbon dimerization drives soot nucleation' by M. R. Kholghy et al., Phys. Chem. Chem. Phys., 2018, 20, 10926-10938.

Stability of polycyclic aromatic compounds in polyurethane foam-type passive air samplers upon O3 exposure

Stability of polycyclic aromatic compounds (PACs) in polyurethane foam (PUF) disks upon O3 exposure was studied in a flow tube. A wide range of PACs was evaluated by spiking PUF disks with PACs and exposing to O3 at concentrations that were equivalent to two months exposure, a typical deployment period for these passive air samplers. Ambient concentrations of O3 (∼50 ppb) at 0% and 50% relative humidity (RH) were applied. At 0% RH, 23 of 68 PACs yielded more than 50% loss after exposure. The mean percent loss was 30% with perylene and 9,10-dimethylanthracene the most reactive polycyclic aromatic hydrocarbons (PAHs) and alkylated PAHs, respectively. At 50% RH, 77% of the studied PACs was stable upon O3 exposure (PACexposed/PACunexposed > 0.7). The mean percent loss was 17% and only 7 of 68 PACs yielded greater than 50% loss. In general, the reactivity of most of the PACs decreased at higher RH, except for the reactive PAHs (acenaphthylene, 2,3-dimethylanthracene, 9,10-dimethylanthracene, dibenzothiophene, and 2-methyldibenzothiophene) which demonstrated lower RH dependence. The experimental conditions in this study represent a worst case scenario for the stability of PACs sorbed to PUF. In reality, the sampling of PACs in ambient air represents an ‘aged’ component of PACs where the most reactive species have already partially been removed. Also, PACs in ambient air will be associated with the particle phase to varying extents that will help to enhance their stability. Therefore, under regular operating conditions, over a 2-month exposure, we expect a minimal error in the measurement of total concentration of PACs in air using the PUF disk passive sampler.

Atmospheric behaviors of polycyclic aromatic hydrocarbons at a Japanese remote background site, Noto peninsula, from 2004 to 2014

Total suspended particulates were collected at a Japanese remote background site (Noto Air Monitoring Station; NAMS) on the Noto Peninsula from September 2004 to June 2014. Nine polycyclic aromatic hydrocarbons (PAHs) in the particulates (fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, benzo[ghi]perylene and indeno[1,2,3-cd]pyrene) were determined by HPLC with fluorescence detection. The mean total concentrations of the nine PAHs in the cold season (November to May for the years 2004–2014) was 670 pg m−3 (range 37–4100 pg m−3). The mean total concentration in the warm season (June to October for the same period) was 170 pg m−3 (range 31–960 pg m−3). The atmospheric PAH level at NAMS decreased in recent years, although no significant change was found in the warm season. An analysis of meteorological conditions showed that the atmospheric PAHs at NAMS were long range transported from Northeast China in the cold seasons and were contributed to by Japanese domestic sources in the warm seasons. Lower concentration ratios of reactive PAHs to their isomers at NAMS also supported these results. Activities associated with the Beijing Olympic and Paralympic Games in 2008 and reconstruction after the 2007 Noto Hanto earthquake may have contributed to the yearly variations of atmospheric PAH levels at NAMS during the period 2007–2009. Source control measures implemented by the Chinese and Japanese governments appear to have been effective in decreasing the atmospheric PAH levels at NAMS in recent years.

Reactivity of polycyclic aromatic compounds (PAHs, NPAHs and OPAHs) adsorbed on natural aerosol particles exposed to atmospheric oxidants

Reactivity of polycyclic aromatic compounds (PACs) adsorbed on natural aerosol particles exposed to different atmospheric oxidants (O3, OH and NO2/O3 mixture) was studied. Decay of polycyclic aromatic hydrocarbons (PAHs) and formation/decay of oxygenated PAHs (OPAHs) and nitrated PAHs (NPAHs) were monitored. Overall, benzo[a]pyrene appeared to be the most reactive PAH (degradation of 50%). Only its nitrated derivative, 6-nitrobenzo[a]pyrene, was significantly formed explaining just 0.4% of reacted benzo[a]pyrene. No other nitrated or oxygenated benzo[a]pyrene derivatives were detected. Interestingly, B[e]P and In[1,2,3,c,d]P, which are usually considered as quite stable PAHs, also underwent decay in all experiments. In presence of O3, ketones were significantly formed but their amount was not totally explained by decay of parent PAH. These results suggest that PAH derivatives could be formed from the reaction of other compounds than their direct parent PAHs and raise the question to know if the oxidation of methyl-PAHs, identified in vehicle-exhausts, could constitute this missing source of OPAHs. NPAHs were significantly formed in presence of O3/NO2 and OH. Surprisingly, NPAH formation was clearly observed during O3 experiments. Nitrated species, already associated with aerosol particles (NO3−, NO2−) or formed by ozonation of particulate nitrogen organic matter, could react with PAHs to form NPAHs. Heterogeneous formation of 2-nitropyrene from pyrene oxidation was for the first time observed, questioning its use as an indicator of NPAH formation in gaseous phase. Equally, formation of 2-nitrofluoranthene by heterogeneous reaction of fluoranthene with O3/NO2 was clearly shown, while only its formation by homogeneous processes (gaseous phase) is reported in the literature. Finally, results obtained highlighted the dependence of heterogeneous PAH reactivity with the substrate nature and the importance to focus reactivity studies on natural particles, whatever the quality of the models previously studied.

Evaluation of the noncovalent binding interactions between polycyclic aromatic hydrocarbon metabolites and human p53 cDNA

The binding of reactive polycyclic aromatic hydrocarbon (PAH) metabolites, formed enzymatically, to DNA is a crucial step in PAH carcinogenesis in vivo. We investigated the noncovalent binding interactions between 11 PAH metabolites and human p53 complementary DNA ( p53 cDNA) using the fluorescence displacement method and molecular docking analysis. All of the examined metabolites predominantly interacted with p53 cDNA by intercalation instead of groove binding. The dissociation constants ranged from 0.02 to 12.34 μM. Of the metabolites tested, 1-hydroxypyrene and 3-hydroxybenzo[a]pyrene showed the strongest binding affinities to DNA, while 2-naphthol was the weakest DNA intercalator. The intercalation of the metabolites was stabilized by stacking the PAH phenyl rings with the DNA base pairs and the formation of hydrogen bonds between the oxide or hydroxyl groups on the metabolites, and DNA bases or backbones. The binding of the metabolites to DNA showed some sequence selectivity. The binding affinities and hydrogen bonds for 3-hydroxybenzo[a]pyrene, benzo[a]pyrene-4,5-dihydroepoxide (BPE) and benzo[a]pyrene-r-7,t-8-dihydrodiol-t-9,10-epoxide (BPDE) differed. It seems that the functional groups on the periphery of the PAH aromatic ring play crucial roles in regulating its binding affinity with DNA. Although it was difficult to determine the correlation between DNA noncovalent binding affinity and carcinogenicity for some of the PAH metabolites, the present study improved our understanding of the formation of PAH metabolite-DNA adducts.

Both replication bypass fidelity and repair efficiency influence the yield of mutations per target dose in intact mammalian cells induced by benzo[a]pyrene-diol-epoxide and dibenzo[a,l]pyrene-diol-epoxide

Mutations induced by polycyclic aromatic hydrocarbons (PAH) are expected to be produced when error-prone DNA replication occurs across unrepaired DNA lesions formed by reactive PAH metabolites such as diol epoxides. The mutagenicity of the two PAH-diol epoxides (+)-anti-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) and (±)-anti-11,12-dihydroxy-13,14-epoxy-11,12,13,14-tetrahydrodibenzo[a,l]pyrene (DBPDE) was compared in nucleotide excision repair (NER) proficient and deficient hamster cell lines. We applied the 32P-postlabelling assay to analyze adduct levels and the hprt gene mutation assay for monitoring mutations. It was found that the mutagenicity per target dose was 4 times higher for DBPDE compared to BPDE in NER proficient cells while in NER deficient cells, the mutagenicity per target dose was 1.4 times higher for BPDE. In order to investigate to what extent the mutagenicity of the different adducts in NER proficient cells was influenced by repair or replication bypass, we measured the overall NER incision rate, the rate of adduct removal, the rate of replication bypass and the frequency of induced recombination in the hprt gene. The results suggest that NER of BPDE lesions are 5 times more efficient than for DBPDE lesions, in NER proficient cells. However, DBPDE adducts block replication more efficiently and also induce 6 times more recombination events in the hprt gene than adducts of BPDE, suggesting that DBPDE adducts are, to a larger extent, bypassed by homologous recombination. The results obtained here indicate that the mutagenicity of PAH is influenced not only by NER, but also by replication bypass fidelity. This has been postulated earlier based on results using in vitro enzyme assays, but is now also being recognized in terms of forward mutations in intact mammalian cells.

Persistent organic pollutants in soil density fractions: distribution and sorption strength

The sorption strength of persistent organic pollutants in soils may vary among different soil organic matter (SOM) pools. We hypothesized that polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were unevenly distributed and had different soil organic carbon (SOC)–water partition coefficients ( K OC) among soil density fractions. We determined the concentrations and K OC values of 20 PAHs and 12 PCBs in bulk samples and three density fractions (light, <2.0, medium, 2.0–2.4, and heavy, >2.4 g cm −3) of 11 urban topsoils (0–5 cm) from Bayreuth, Germany. The K OC values were determined using sequential extraction with methanol–water mixtures (35% and 65% methanol) at 60 °C. The sum of 20 PAH concentrations in bulk soil ranged 0.4–186 mg kg −1, and that of 12 PCB concentrations 1.2–158 μg kg −1. The concentrations of all PAHs and PCBs decreased in the order light > medium > heavy fraction. When normalized to the SOC concentrations, PAH concentrations were significantly higher in the heavy than in the other density fractions. The K OC values of the PAHs in density fractions were 3–20 times higher than those of the PCBs with similar octanol–water partition coefficients ( K OW). The K OC values of individual PAHs and PCBs varied up to a factor of 1000 among the studied soils and density fractions. The K OC values of 5- and 6-ring PAHs tended to be highest in the heavy fraction, coinciding with their enrichment in this fraction. For the other PAHs and all PCBs, the K OC values did not differ among the density fractions. Thus, there is no relationship between sorption strength and distribution among density fractions, indicating that density fractionation is not a suitable tool to distinguish among differently reactive PAH and PCB pools in soils.

Emission inventory and sources of polycyclic aromatic hydrocarbons in the atmosphere at a suburban area in Taiwan

The application of a chemical mass balance air pollution model to ambient measurements of polycyclic aromatic hydrocarbons (PAHs) is presented. Sixteen air samples were collected at seven sites in a suburban area in Taiwan and analyzed for the concentration of 21 compounds between July 2001 and September 2001. Each ambient sample was evaluated for the PAH contribution from six sources (heavy oil combustion, natural gas combustion, coal combustion, diesel combustion, vehicles and municipal solid waste incinerator). Average predictions agree well with the emission inventory. By this method, the average contributions are 49%, 14%, 22%, 12%, and 2% from vehicles, heavy oil combustion, natural gas combustion, coal combustion and diesel combustion at these seven receptors. By far, vehicles are the major PAH emission sources and municipal solid waste incinerator is a minor contributor. The calculated result of particulate PAHs is compared with that of total (gaseous and particulate) PAHs. The estimate based on total PAHs is better than the estimate based on particulate PAHs only. Contributions of eight low reactive PAHs for the same emission sources and receptors were calculated. Atmospheric reactivity seems not a problem for source apportionment in this study.

Alteration in Phase I and II Enzyme Activities andPolycyclic Aromatic Hydrocarbons-DNA Adduct Formationby Plant Phenolics in Mouse Epidermis

Several naturally occurring plant phenols were shown to inhibit the mutagenicity and/or tumorigenicity of chemical carcinogens, including polycyclic aromatic hydrocarbons (PAHs). In this study, the effect of the topical application of three structurally diverse phenolic acids and trihydroxystilbene, resveratrol, on epidermal aryl hydrocarbon hydroxylase (AHH), phase II enzymes, as well as the binding of benzo[a]pyrene (B[a]P) and 7,12-dimethylbenz[a]anthracene (DMBA) to epidermal DNA were compared. The single, topical application of 8 and 16 μmol of protocatechuic or chlorogenic acid increased the activity of AHH by 10-30%, whereas resveratrol in a dose of 16 μmol almost completely (99%) inhibited the enzyme activity. Phenolic acids also increased the activities of phase II enzymes. Resveratrol did not affect the glutathione S-transferase activity but induced UDP glucuronosyltransferase (by ~100-150%) and to a lesser extent NAD(P)H:quinone oxidoreductase. In a dose of 16 μmol all phenolic acids afforded 40-50% inhibition of covalent benzo[a]pyrene-diol-epoxide (B[a]PDE) binding to DNA. Resveratrol had no effect on B[a]PDE adduct formation but reduced the levels of all the major DMBA adducts. Phenolic acids, particularly tannic acid, mostly affected the formation of syn- and anti-DMBADE dAdo adducts. These results indicate that both the modulation of carcinogen activating enzymes and the prevention of their ultimate metabolites binding to DNA by naturally occurring phenolics are involved in the antitumorigenic activity of these compounds. For phenolic acids, however, their interactions with reactive PAH metabolites and/or blocking of a specific binding site in a genome seem more important. Derivatives of stilbene, such as resveratrol, affect DNA adduct formation and thus the initiation of tumorigenesis through the interaction with the Ah receptor rather than the scavenging active metabolites.

Collection of gas and particle semi-volatile organic compounds: use of an oxidant denuder to minimize polycyclic aromatic hydrocarbons degradation during high-volume air sampling

The decomposition of polycyclic aromatic hydrocarbons (PAHs) by ozone in gas and particles, under high-volume sampling, was studied by using in parallel a conventional device and a device protected with an oxidant denuder. Three different sampling regimes—short and long sampling under high-ozone concentration and long sampling under low-ozone concentration—were selected at three representative sampling sites—a boreal forest, an urban site and a background marine station. The results of our study suggest that most PAHs are susceptible to ozone degradation under high ozone atmospheric concentrations (>50 ppbv) and long sampling times (>24 h). The highest concentration ratio of total PAHs between the two sampling systems was observed under collection conditions of long sampling and high ozone concentration, especially for the gaseous PAHs (up to 2.10). Conversely, long sampling time under low ozone concentration did not affect the concentration of collected PAHs in the gas or particle phase. The most reactive PAHs collected on filters and polyurethane foam were cyclopentane[cd]pyrene and pyrene, respectively. The use of an oxidant denuder did not affect the PAH gas–particle distribution study. The slopes mr and the intercepts br of the regression between the log Kp and logPL0 did not substantially deviate between the two sampling devices.

Mutational spectra for polycyclic aromatic hydrocarbons in the supF target gene

An SV40-based shuttle vector system was used to identify the types of mutational changes and the sites of mutation within the supF DNA sequence generated by the four stereoisomers of benzo[ c]phenanthrene 3,4-dihydrodiol 1,2-epoxide (B[ c]PhDE), by racemic mixtures of bay or fjord region dihydrodiol epoxides (DE) of 5-methylchrysene, of 5,6-dimethylchrysene, of benzo[ g]chrysene and of 7-methylbenz[ a]anthracene and by two direct acting polycyclic aromatic hydrocarbon carcinogens, 7-bromomethylbenz[ a]anthracene (7-BrMeBA) and 7-bromomethyl-12-methylbenz[ a]anthracene (7-BrMe-12-MeBA). The results of these studies demonstrated that the predominant type of mutation induced by these compounds is the base substitution. The chemical preference for reaction at deoxyadenosine (dAdo) or deoxyguanosine (dGuo) residues in DNA, which is in general correlated with the spatial structure (planar or non-planar) of the reactive polycyclic aromatic hydrocarbon, is reflected in the preference for mutation at A⋅T or G⋅C pairs. In addition, if the ability to react with DNA in vivo is taken into account, the relative mutagenic potencies of the B[ c]PhDE stereoisomers are consistent with the higher tumorigenic activity associated with non-planar polycyclic aromatic hydrocarbons and their extensive reaction with dAdo residues in DNA. Comparison of the types of mutations generated by polycyclic aromatic hydrocarbons and other bulky carcinogens in this shuttle vector system suggests that all bulky lesions may be processed by a similar mechanism related to that involved in replication past apurinic sites. However, inspection of the distribution of mutations over the target gene induced by the different compounds demonstrated that individual polycyclic aromatic hydrocarbons induce unique patterns of mutational hotspots within the target gene. A polymerase arrest assay was used to determine the sequence specificity of the interaction of reactive polycyclic aromatic hydrocarbons with the shuttle vector DNA. The results of these assays revealed a divergence between mutational hotspots and polymerase arrest sites for all compounds investigated, i.e., sites of mutational hotspots do not correspond to sites where high levels of adduct formation occur, and suggested that some association between specific adducts and sequence context may be required to constitute a premutagenic lesion. A site-specific mutagenesis system employing a single-stranded vector (M13mp7L2) was used to investigate the mutational events a single benzo[ a]pyrene or benzo[ c]phenanthrene dihydrodiol epoxide–DNA adduct elicits within specific sequence contexts. These studies showed that sequence context can cause striking differences in mutagenic frequencies for given adducts. In addition, these sequence context effects do not originate only from nucleotides immediately adjacent to the adduct, but are also modulated by more distal nucleotides. The implications of these results for mechanisms of polycyclic aromatic hydrocarbon-induced mutagenesis and carcinogenesis are discussed.

Why are some polycyclic aromatic hydrocarbons extremely reactive?

Higher members of the polyacene series are extremely reactive although they are aromatic in nature. This aspect of aromatic chemistry can be explained using conventional indices of kinetic stability, such as a localization energy and a HOMO–LUMO energy separation. Large polyacene molecules have smaller localization energies and smaller HOMO–LUMO energy separations than their respective polyene references defined using matching polynomials. These molecules are presumed to be thermodynamically more stable but kinetically less stable than non-aromatic polyolefins. The same situation is sometimes observed in other groups of polycyclic aromatic hydrocarbons (PAHs). Such highly reactive PAH molecules were found to be substructures of metallic one-dimensional benzenoid polymers.

PAH Profiles of Charbroiled Hamburgers: Pyrene/B[a]P Ratios and Presence of Reactive PAH

Abstract Analysis of the polycyclic aromatic hydrocarbons (PAH) in charbroiled hamburgers, used in an earlier study of BaP-DNA adducts in peripheral white blood cells, has been accomplished using HPLC with UV diode array detection. The concentration data for one of these PAH, benzo[a]pyrene (BaP), are in excellent agreement with data obtained using a thin-layer chromatography (TLC)/fluorescence technique. There is significant interest in pyrene/BaP ratios in these samples and other sources of human exposure to PAH since urinary metabolites of both compounds have been used as biomarkers of exposure. In the food samples examined, this ratio is roughly 5. However, differences in cooking procedures between different studies suggest that this value can only be used semi-quantitatively. The BaP concentrations themselves vary by a factor of almost twenty in hamburgers prepared under very similar conditions. Some unstable PAH, including cyclopenteno[cd]pyrene and methylated PAH are found in the hamburger. This po...

Factors influencing the reactivity of polycyclic aromatic hydrocarbons adsorbed on filters and ambient POM with ozone

Five polycyclic aromatic hydrocarbons (PAH), pyrene (PY), fluoranthene (FL), benz(a)anthracene (BaA), benzo(a)pyrene (BaP), and benzo(e)pyrene (BeP) adsorbed on glass fiber (GF) and Teflon impregnated glass fiber (TIGF) filters and on ambient particulate organic matter (POM) were exposed to ozone (50–300 ppb) passively in a 360-liter Teflon chamber and actively in a flow system. The influence of ozone concentration, exposure time and relative humidity (RH) on the degree of degradation of these PAH was established. The most reactive PAH both on filters and in ambient POM were PY, BaA and BaP. Up to 50–80% of these PAH degraded in 3-hr exposures to 200 ppb of ozone at ∼1% RH; in a flow system, most of the degradation occurred within the first 10 minutes of exposure. With the exception of BaP, the degradation of the PAH tested on GF and TIGF filters were much lower at 50% RH than at 1% RH, whether they were exposed to ozone in an active or passive mode. Interestingly, RH did not significantly affect the reactivity of PAH present in ambient POM passively exposed to ozone. Our results show that PAH are susceptible to ozone degradation under many typical atmospheric conditions.

Transformation of reactive PAH on particles by exposure to oxidized nitrogen compounds and ozone

In order to study the conditions for atmospheric transformation of reactive polycyclic aromatic hydrocarbons (PAH) on particles by exposure to nitrogen dioxide (NO 2), nitrous acid (HNO 2), nitric acid (HNO 3) and ozone (O 3), a set of experiments has been carried out in a flow reactor. Soot and PAH were generated in a smoke gas generator and collected on a glass fiber filter. The filter was attached to the Teflon coated wall in the reactor tube and the reactive gas was added to the purified and humidified air pumped through the reactor. After exposure, the filter was soxhlet-extracted with methylene chloride or acetone and fractionated on a silica gel column into five fractions with increasing polarity. The results indicate that reactive PAH are transformed when exposed to NO 2 and O 3, while HNO 2 and HNO 3 have no effect. The decrease of the concentration of PAH is dependent on the NO 2 and O 3 concentration, the time of exposure, and the relative humidity. The presence of hydrochloric acid (HCl) or sulphur trioxide (SO 3) increased the reactivity. So far, only a few transformation products have been identified. The formation of oxy derivatives and above all, even more polar compounds are dominating. Only when SO 3 is introduced during the generation of PAH/soot, the formation of nitron derivatives is favoured.

The effect of nitrogen dioxide and ozone on the decomposition of particle-associated polycyclic aromatic hydrocarbons during sampling from the atmosphere

The effects of NO 2 and O 3 exposure on the degradation of polycyclic aromatic hydrocarbons (PAH) during high-volume sampling of airborne particulate matter were studied. Addition of 1 ppm NO 2 during ambient air sampling caused degradation of pyrene, benz(a)anthracene and benzo(a)pyrene, most probably due to nitration. Acid particles seem to enhance the reaction. The results indicate that NO 2 concentrations within the range normally formed in urban air may cause degradation of some reactive PAH. Addition of 200 ppb O 3 caused degradation in one of the three experiments only.