Oxygenated PAHs Research Articles

Semi-volatile organic compounds in fine particulate matter on a tropical island in the South China Sea

Measurements of hazardous semi-volatile organic compounds (SVOCs) in remote tropical regions are rare. In this study, polycyclic aromatic compounds (PACs) [including polycyclic aromatic hydrocarbons (PAHs), nitrated PAHs (NPAHs), and oxygenated PAHs (OPAHs)], organophosphate esters (OPEs), and phthalic acid esters (PAEs) were measured in fine particulate matter (PM2.5) at Yongxing Island in the South China Sea (SCS). The concentrations of PACs (median = 53.5 pg/m3) were substantially low compared with previous measurements. The concentration weighted trajectory (CWT) model showed that the eastern and southern China was the main source region of PAC, occurring largely during the northeast (NE) monsoon. The PM2.5 showed remarkably high concentrations of OPEs (median = 3231 pg/m3) and moderate concentrations of PAEs (13,013 pg/m3). Some Southeast Asian countries were largely responsible for their higher concentrations, driven by the tropical SCS monsoons. We found significant atmospheric loss of the SVOCs, which is an explanation for the low concentrations of PACs. Enhanced formation of N/OPAHs originated from tropical regions was also observed. The positive matrix factorization model was applied to apportion the SVOC sources. The results, as well as correlation analyses of the SVOC concentrations, further indicate insignificant local sources and enhanced atmospheric reactions on this island.

Co-occurrence and potential ecological risk of parent and oxygenated polycyclic aromatic hydrocarbons in coastal sediments of the Taiwan Strait

Thirty-two surface sediment samples, collected from the Taiwan Strait (TWS), were investigated for the occurrence, composition profile, and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (OPAHs). PAHs were ubiquity in the TWS with a total concentration (∑PAHs, excluding naphthalene due to its high volatility) ranging from 17.8–213 ng g−1. Benzo[b] fluoranthene, fluoranthene, phenanthrene, and pyrene were the predominant PAHs. Also, eight OPAHs were detected, having a cumulative concentration range (∑OPAHs) of 10.5–118 ng g−1, predominated by anthraquinone and 6H-Benzo[c,d]Pyren-6-one. Higher concentrations of ∑PAHs and ∑OPAHs were detected at sampling sites adjacent to the mainland and in the northwest part of the TWS. The results suggested important continental input, and particle sedimentation under the specific hydrodynamic conditions of the region. Based on the measured concentrations and sediment quality guidelines, PAHs had a limited ecological impact on the area.

The chemical composition and toxicological effects of fine particulate matter (PM2.5) emitted from different cooking styles

The mass, chemical composition and toxicological properties of fine particulates (PM2.5) emitted from cooking activities in three Hong Kong based restaurants and two simulated cooking experiments were characterized. Extracts from the PM2.5 samples elicited significant biological activities [cell viability, generation of reactive oxygen species (ROS), DNA damage and inflammation effect (TNF-α)] in a dose-dependent manner. The composition of PAHs, oxygenated PAHs (OPAHs) and azaarenes (AZAs) mixtures differed between samples. The concentration ranges of the Σ30PAHs, Σ17OPAHs and Σ4AZAs and Σ7Carbonyls in the samples were 9627–23,452 pg m−3, 503–3700 pg m−3, 33–263 pg m−3 and 158 – 5328 ng m−3, respectively. Cell viability caused by extracts from the samples was positively correlated to the concentration of benzo[a]anthracene, indeno[1,2,3-cd]pyrene and 1,4-naphthoquinone in the PM2.5 extracts. Cellular ROS production (upon exposure to extracts) was positively correlated with the concentrations of PM2.5, decaldehyde, acridine, Σ17OPAHs and 7 individual OPAHs. TNF-α showed significant positive correlations with the concentrations of most chemical species (elemental carbon, 16 individual PAHs including benzo[a]pyrene, Σ30PAHs, SO42−, Ca2+, Ca, Na, K, Ti, Cr, Mn, Fe, Cu and Zn). The concentrations of Al, Ti, Mn, Σ30PAHs and 8 individual PAHs including benzo[a]pyrene in the samples were positively correlated with DNA damage caused by extracts from the samples. This study demonstrates that inhalation of PM2.5 emitted from cooking could result in adverse human health effects.

N-doped Reduced Graphene Oxide nanocomposites encapsulated sodium alginate/polyvinyl alcohol microspheres for anthracene and its oxygenated-PAH removal in aqueous solution

In this work, a novel N-doped Reduced Graphene Oxide (NRGO)/sodium alginate (SA)/polyvinyl alcohol (PVA) microsphere was prepared by a simple embed method to remove anthracene and its oxygenated-PAH from aqueous solution and reduce the risk of the application of nanomaterials in the water environment. The morphology and functional groups were successfully characterized by SEM, XRD and FTIR etc. The NRGO/SA/PVA microspheres were applied as the efficient adsorbent for removal of anthracene (ANT) and its oxygenated polycyclic aromatic hydrocarbon (OPAH), 2-methylanthraquinone (2-MAQ) from aqueous solution. Batch experiments with the subject of the mass ratio of SA and PVA, the concentration of NRGO and contact time were investigated. The sorption kinetics and equilibrium data followed pseudo-second order model and the Freundlich isotherm model, respectively, indicating the chemical adsorption process. Regeneration experiments indicated that the NRGO/SA/PVA microspheres almost showed a slight loss in adsorption capacity after three cycles. This study indicated that the NRGO/SA/PVA microspheres with easy separation, environmental benignity and high reusability were proved to be a kind of potential adsorbent for PAHs and OPAHs removal from wastewater.

Differentiation of isomers of oxygenated polycyclic aromatic hydrocarbons by laser desorption laser post-ionization time-of-flight mass spectrometry

Oxygenated polycyclic aromatic hydrocarbons (OPAHs) are mutagenic and ubiquitous pollutants to both humans and environment. Routine analytical methods for differentiating their isomers still remain challenges. In this article, we present laser desorption laser post-ionization time-of-flight mass spectrometry (LDPI-TOFMS) as a new approach for the characterization of isomers of OPAHs. Herein, a pulse laser with the wavelength of 532 nm is used to desorb analytes which are post-ionized by another pulse laser with wavelength of 266 nm. A clear discrimination of quasi-molecular ion peaks and characteristic peaks among OPAHs could be observed. We have demonstrated that LDPI-TOFMS can be used to distinguish isomers quickly and clearly irrespective of the polarity and solubility of samples. Additionally, results from other four mass spectrometry (MS) based methods have also been compared, despite the fact that they were unable to distinguish the isomers or unable to obtain molecular ion peaks. These results suggested the great potential of LDPI-TOFMS platform for ascertain varieties of organic isomers which are not practically distinguished by other MS methods.

Occurrence, fates, and carcinogenic risks of substituted polycyclic aromatic hydrocarbons in two coking wastewater treatment systems

This paper reports for the first time the occurrence, fates, and carcinogenic risks of 20 substituted polycyclic aromatic hydrocarbons (SPAHs) and 16 priority PAH species in two coking wastewater treatment plants (WWTPs) (plant E and central WWTP). The measured total concentrations of PAHs and SPAHs in raw wastewater of coking plant E were 3700 and 1200 μg·L−1, respectively, with naphthalene (1400 μg·L−1), and fluoranthene (353 μg·L−1) as dominant PAH species and 2-methylnaphthalene (167 μg·L−1), anthraquinone (133 μg·L−1), and 1-methylnaphthalene (132 μg·L−1) as dominant SPAHs. For the 11 methyl-PAHs (MPAHs), 4 oxygenated-PAHs (OPAHs), and 5 nitrated-PAHs (NPAHs) investigated, the biological wastewater treatment process removed 98.6% MPAHs, 83.9% OPAHs, and 89.1% NPAHs. Mass balance analysis result revealed that transformation was the major mechanism to remove low-molecular-weight (LMW) MPAHs (59.9–77.3%), a large part of OPAHs, including anthraquinone, methylanthraquinone, and 9-fluorenone (46.7–49.6%), and some NPAHs, including 2-nitrofluorene and 9-nitroanthrancene (52.9–59.1%). Adsorption by activated sludge mainly accounted for removing high-molecular-weight (HMW) SPAHs (59.6–71.01%). The relatively high concentrations of SPAHs in excess sludge (15,000 μg·g−1) and treated effluent (104 μg·L−1) are of great concern for their potential adverse ecological impacts. SPAHS exhibited similar behaviors in central WWTP, though the influent concentrations were much lower. The concentration levels of SPAHs in the ambient air of coking plant E and central WWTP may also pose potential lung cancer risks (LCR) to the workers through inhalation, where all studied SPAHs except 3-nitrofluoranthene and 7-nitrobenz[a]anthracene exceeded the acceptable cancer risk standards (>10−6) recommended by U.S EPA. This study could help identify the ecological and healthy risks during coking wastewater treatment and provide useful information for policy-making.

Global distribution of oxygenated polycyclic aromatic hydrocarbons in mineral topsoils.

Hazardous oxygenated polycyclic aromatic hydrocarbons (OPAHs) originate from combustion (primary sources) or postemission conversion of polycyclic aromatic hydrocarbons (PAHs) (secondary sources). We evaluated the global distribution of up to 15 OPAHs in 195 mineral topsoils from 33 study sites (covering 52° N-47° S, 71° W-118 °E) to identify indications of primary or secondary sources of OPAHs. The sums of the (frequently measured 7 and 15) OPAH concentrations correlated with those of the Σ16EPA-PAHs. The relationship of the Σ16EPA-PAH concentrations with the Σ7OPAH/Σ16EPA-PAH concentration ratios (a measure of the variable OPAH sources) could be described by a power function with a negative exponent<1, leveling off at a Σ16EPA-PAH concentration of approximately 400 ng g-1 . We suggest that below this value, secondary sources contributed more to the OPAH burden in soil than above this value, where primary sources dominated the OPAH mixture. This was supported by a negative correlation of the Σ16EPA-PAH concentrations with the contribution of the more readily biologically produced highly polar OPAHs (log octanol-water partition coefficient<3) to the Σ7OPAH concentrations. We identified mean annual precipitation (Spearman ρ=.33, p<.001, n=143) and clay concentrations (ρ=.55, p<.001, n=33) as important drivers of the Σ7OPAH/Σ16EPA-PAH concentration ratios. Our results indicate that at low PAH contamination levels, secondary sources contribute considerably and to a variable extent to total OPAH concentrations, whereas at Σ16EPA-PAH contamination levels>400 ng g-1 , there was a nearly constant Σ7OPAH/Σ16EPA-PAH ratio (0.08±0.005 [SE], n=80) determined by their combustion sources.

Polycyclic aromatic compounds (PAHs, oxygenated PAHs, nitrated PAHs, and azaarenes) in air from four climate zones of China: Occurrence, gas/particle partitioning, and health risks

Polycyclic aromatic compounds (PACs) such as polycyclic aromatic hydrocarbons (PAHs) and their derivatives [oxygenated PAHs (OPAHs), nitrated PAHs (NPAHs), and azaarenes (AZAs)] are toxic and ubiquitous air pollutants. In this study, the concentrations of these PACs were determined in air obtained in spring and autumn of 2012 from urban and rural areas of the Tibetan Plateau, temperate, subtropical, and tropical climate zones in China. Average concentrations (gaseous + particulate) of ∑29PAHs, ∑15OPAHs, ∑11NPAHs, and ∑4AZAs were 928 ± 658, 54 ± 45, 5.3 ± 4.4, 14 ± 11 ng m−3 and 995 ± 635, 67 ± 38, 8.4 ± 6.1, 24 ± 16 ng m−3 in spring and autumn, respectively. Various C fractions and latitude correlated significantly with the concentrations and ratios of PACs. The slopes of the regression of gas-particle partition coefficients (Kp) of PACs on their sub-cooled liquid vapor pressures (PL0), indicated both adsorption and absorption to total suspended particles (TSP) for PAHs, OPAHs, and NPAHs in the four studied climatic zones. This result was further supported by comparing the fractions of PACs in TSP calculated from field data with those predicted by the Junge-Pankow adsorption and KOA absorption models. The concentration ratios of most OPAHs or NPAHs to their parent PAHs and of benzo[e]pyrene/benzo[a]pyrene were higher in autumn than in spring and increased with remoteness from point sources. This suggests enhanced secondary formation of PAH derivatives due to the elevated photochemical activity in autumn and longer ageing of air and associated transformation of PACs during their long-distance transport from source regions (urban sites) to rural sites. Lifetime lung cancer risk estimated from PACs ranged from 0.8 ± 0.6 to 3.1 ± 1.0 (×10−3), exceeding the value (10−5) recommended by the WHO. Gaseous PACs contributed substantially to the estimated cancer risks and their contributions increased with decreasing latitude in China.

Time-Related Alteration of Aqueous-Phase Anthracene and Phenanthrene Photoproducts in the Presence of TiO2 Nanoparticles.

Polycyclic aromatic hydrocarbons (PAHs) and titanium dioxide (TiO2) nanoparticles (NPs) are photoactive environmental pollutants that can contaminate aquatic environments. Aqueous-phase interactions between PAHs and TiO2-NPs are of interest due to their emerging environmental relevance, particularly with the deliberate application of TiO2-NPs to remediate pollution events (e.g., oil spills). Our objective was to investigate anthracene (ANT) and phenanthrene (PHE) photoproduct formation and transformation following ultraviolet A (UVA) irradiation in the presence and absence of TiO2-NPs. ANT and PHE solutions were prepared alone or in combination with TiO2-NPs, UVA-irradiated, and either exposed to larval zebrafish or collected for chemical analyses of diverse hydroxylated PAHs (OHPAHs) and oxygenated PAHs (OPAHs). The expression profiles of genes encoding for enzymes involved in PAH metabolism showed PAH-specific and time-dependent inductions that demonstrated changes in PAH and photoproduct bioavailability in the presence of TiO2-NPs. Chemical analyses of PAH/NP solutions in the absence of zebrafish larvae identified diverse photoproducts of differing size and ring arrangements, which suggested photodissociation, recombination, and ring re-arrangements of PAHs occurred either during or following UVA irradiation. Both ANT and PHE solutions showed heightened oxidative potential following irradiation, but TiO2-NP-related increases in oxidative potential were PAH-specific. The exploitation of multiple analytical methods provided novel insights into distinct PAH photoactivity, TiO2-NP influence on photoproduct formation in a PAH-specific manner, and the significant role time plays in photochemical processes.

Nitrated- and oxygenated-polycyclic aromatic hydrocarbon in urban soil from Nepal: Source assessment, air-soil exchange, and soil-air partitioning

In contrast to more frequently investigated priority pollutants, such as polycyclic aromatic hydrocarbons (PAHs), only little is known about the fate and distribution of nitrated- and oxygenated-PAHs (NPAHs and OPAHs) in urban soils, particularly in Indian sub-continent. Moreover, experimental data on air-soil exchange and soil-air partitioning are also lacking, which is critical in assessing the partitioning, fugacity coefficient, and secondary emission of PAH-derivatives. Hence, this article provides an insight into the fate, sources, air-soil exchange, and soil-air partitioning of PAH-derivatives on a molecular basis. Prospective health risk due to their exposure has also been discussed. The result showed that PAH-derivatives had significantly polluted all four Nepalese cities. Ʃ15NPAHs and Ʃ2OPAHs in soil were 4 and 20 times lower than their parent-PAHs, and ranged 396–2530 ng/g (median 458 ng/g) and 91.9–199 ng/g (median 94.9 ng/g), respectively. Ʃ15NPAHs was higher than a few global studies, while Ʃ2OPAHs was lower than some of the less urbanized/remote areas worldwide. The 6-Nitobenzo[a]pyrene (6-NBaP) was most abundant in soil, and accounted for 10–12% of Ʃ15NPAHs, while Benzanthrone (BZONE) exceeded among OPAHs, and represented 71–76% of Ʃ2OPAHs, respectively. Source identification study indicated that direct emissions from domestic/residential cooking and heating and secondary formations are the essential sources of derivative chemicals in soil. Fugacity fraction ratio (fratio) indicated volatilization from the soil. The soil-air partitioning study showed sorption by soil organic matter/black carbon has little role in soil-air partitioning of PAH-derivatives in Nepal's urban soil. The toxicity equivalency quotients (TEQs) of NPAHs (314 ± 102 ng/g) was estimated slightly higher than their parent-PAHs (294 ± 121 ng/g) suggesting a relatively higher risk of soil toxicity in Nepal.

Characteristics and Sources of Organic Aerosol Markers in PM2.5

ABSTRACT To investigate the molecular compositions, sources, and evolution processes of organic aerosols (OAs), PM2.5 samples in wintertime were collected in Jinan, a typically polluted city in the North China Plain (NCP). The concentrations of PM2.5, carbonaceous species, and organic components (e.g., sugars, fatty acids, polycyclic aromatic hydrocarbons (PAHs) and oxygenated-PAHs (OPAHs)) in haze episodes were 1.8–2.7 times higher than those in clean episodes. Levoglucosan was the most abundant saccharide, which exhibited significant correlations with carbonaceous species during the whole sampling period, demonstrating that biomass burning has an important effect on the concentrations of carbonaceous species in PM2.5 of Jinan during wintertime. The higher ratios of both secondary OC/OC (SOC/OC) and C18:1/C18:0 was observed during the clean days than those during haze days, implying that OAs during clean periods were more aged. The higher ratio of OPAHs/PAHs in the daytime reflected the more photochemical formation of OPAHs in the daytime. Positive matrix factorization (PMF) model proved that biomass burning was the major source of OAs during the whole sampling period. Potential source contribution function (PSCF) and concentration-weight trajectory (CWT) results indicating that Shandong Province and Beijing-Tianjing-Hebei (BTH) region made important contribution to the levels of PM2.5 in Jinan during the winter. Moreover, the CWT results showed that OAs during haze periods were largely originated from local and surrounding regions. These results confirmed that biomass burning can significantly influence the concentrations and chemical compositions of OAs, thereby they can affect human health and atmospheric chemistry.

A 150-year record of black carbon (soot and char) and polycyclic aromatic compounds deposition in Lake Phayao, north Thailand.

An improved understanding of the historical variation in the emissions and sources (biomass burning, BB vs. fossil fuel, FF combustion) of soot and char, the two components of black carbon (BC), and polycyclic aromatic compounds (PACs) may help in assessing the environmental effects of the Atmospheric Brown Cloud (ABC) in SE Asia. We therefore determined historical variations of the fluxes of soot, char, and PACs (24 polycyclic aromatic hydrocarbons (PAHs), 12 oxygenated PAHs (OPAHs), and 4 azaarenes) in a dated sediment core (covering the past ∼150 years) of Phayao Lake in Thailand. The soot fluxes have been increasing in recent times, but at a far lower rate than previously estimated based on BC emission inventories. This may be associated with a decreasing BB contribution as indicated by the decreasing char fluxes from old to young sediments. The fluxes of high- and low-molecular-weight (HMW and LMW) PAHs, OPAHs, and azaarenes all sharply increased after ∼1980, while the ΣLMW-/ΣHMW-PAHs ratios decreased, further supporting the reduction in BB contribution at the expense of increasing FF combustion emissions. We also suggest that the separate record of char and soot, which has up to now not been done in aerosol studies, is useful to assess the environmental effects of ABC because of the different light-absorbing properties of these two BC components. Our results suggest that besides the establishment of improved FF combustion technology, BB must be further reduced in the SE Asian region in order to weaken the ABC haze.

The formation and evolution of parent and oxygenated polycyclic aromatic hydrocarbons during a severe winter haze-fog event over Xi'an, China.

In this study, 3- or 4-h high time-resolved PM2.5 was observed during a severe winter haze-fog event (1 to 6 January 2017) to investigate the formation and evolution of parent polycyclic aromatic hydrocarbons (pPAHs) and oxygenated polycyclic aromatic hydrocarbons (OPAHs) in Xi'an, a typical city in northwestern China. Three episodes (episode I, episode II, and rainy day (EI, EII, and RD)) have been identified during this haze-fog event. Nine water-soluble ions, 8 carbonaceous fractions, 18 pPAHs, and 3 OPAHs in PM2.5 were measured. pPAHs showed two peaks at around 12:00 local standard time (LST) and 24:00 LST and two troughs at around 2:00 LST and 18:00 LST during EI. However, the OPAHs presented highest at around 18:00 LST and lowest at around 2:00 LST. During EII, pPAHs and OPAHs displayed similar diurnal variations with the highest values at noon but lowest values at around 2:00-5:00 LST.In addition, no obvious diurnal variations of pPAHs and OPAHs were observed during RDwere absent during RD. Diurnal variations of pPAH ring distributions demonstrated coal combustion, and vehicle emissions contributed to pPAHs for three episodes, which is further confirmed by diagnostic ratio results. High oxygenation (Ro) rates were found during the sampling time, which favored OPAH formation. The study herein indicates that OPAH formation through complex atmospheric reactions provides us new insights into the severe haze-fog events.

Polycyclic aromatic compounds in particulate matter and indoor dust at preschools in Stockholm, Sweden: Occurrence, sources and genotoxic potential in vitro

Children spend a significant amount of their day in preschool; thus, environmental quality at preschools may have an impact on children's health. In the present study, we analyzed polycyclic aromatic compounds (PACs), including PAHs, alkylated PAHs and oxygenated PAHs (OPAHs), in indoor and outdoor air particulate matter (PM10) and indoor dust at preschools in Stockholm, Sweden. There were significant correlations between PAC levels in outdoor and indoor PM10, with in general higher PAC levels outdoors. Fluoranthene and pyrene were detected at highest levels in all sample types, although phenanthrene and methylated phenanthrene derivatives also were found at high levels in indoor dust. In addition, the highly carcinogenic PAHs 7H-benzo[c]fluorene, 7,12-dimethylbenz[a]anthracene, benz[j]aceanthrylene, and dibenzo[a,l]pyrene were detected in some samples. Benzanthrone was the most prevalent OPAH in PM10 samples and 9,10-anthraquinone in indoor dust. Based on diagnostic ratios and Positive Matrix Factorization we identified vehicle emission and biomass burning as important PAC sources for all samples analyzed. However, poor correlation between PAC levels in indoor PM10 and indoor dust suggested additional sources for the latter. Measuring activation of DNA damage signaling in human cells exposed to organic extracts of the samples indicated substantial genotoxic potential of outdoor PM10 and indoor dust. Determination of benzo[a]pyrene equivalents demonstrated that the highly potent PAHs benz[j]aceanthrylene and dibenz[a,h]anthracene contributed more than 20% to the total carcinogenic potency of the samples. We conclude that PAC levels at Stockholm preschools are relatively low but that outdoor air quality may impact on the indoor environment.

Experimental and theoretical evidence for the temperature-determined evolution of PAH functional groups

Elucidating the chemical evolution of various functional groups in polycyclic aromatic hydrocarbons (PAH) and soot aids in understanding soot formation chemistry. In this work, the chemical evolution of various functional groups, including aromatic CH, aliphatic CH, C=O, COH and COC bonds, was experimentally investigated online, rather than with offline diagnostics. Oxidation was performed in a jet-stirred reactor (JSR), fueled with benzene/C2H2/air/N2 and benzene/phenol/C2H2/N2 for a temperature range of 600-1400 K. Kinetic modelling, including ab initio quantum chemistry calculations, reaction rate coefficient calculations and JSR simulations, were conducted to interpret the experimental data and the evolutionary chemistry of the various functional groups. Results show that the formation of functional groups on PAH and oxygenated PAH (OPAH) are highly sensitive to temperature. Aliphatic CH bonds survive mainly in the form of CCH2C, CCH2CH2C or CCH functional groups above 1200 K, and exist in the CHCH2 functional group below 1000 K. For the OPAH, the COC functional group presents stronger thermal stability than COH and C=O functional groups. Simulation results indicate that HACA-like pathway (hydrogen abstraction carbon addition), in which C2H2 attacks the O atom, followed by cyclization and H-atom elimination reactions, qualitatively describe the formation of OPAH with the CO-C functional group at different temperatures. The addition reaction involving PAH radical and C2H4 / C2H3 captures the evolution of PAH with the CHCH2 functional group, but fails to explain the formation of CCH2C and CCH2CH2C functional groups.

Atmospheric degradation of chrysene initiated by OH radical: A quantum chemical investigation

Chrysene, a four-ring polycyclic aromatic hydrocarbon (PAH), is recalcitrant to biodegradation and persistent in the environment due to its low water solubility. Here, we investigated the atmospheric degradation process of chrysene initiated by OH radical in the presence of O2 and NOX using quantum chemical calculations. The reaction mechanisms were elucidated by density functional theory (DFT) at M06–2X/6–311++G(3df,2p)//M06–2X/6-311+G(d,p) level, and the kinetics calculations were conducted with Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The results show that the oxidation products of atmospheric chrysene are oxygenated PAHs (OPAHs) and nitro-PAHs (NPAHs), including nitro-chrysene, hydroxychrysene, hydroxychrysenone, 11-benzo[a]fluorenone and dialdehydes. Most of the products have deleterious effects on the environment and human beings due to their acute toxicity, carcinogenicity and mutagenicity. The overall rate constant for the reaction of chrysene with OH radical is 4.48 × 10−11 cm3 molecule−1 s−1 and the atmospheric lifetime of chrysene determined by OH radical is 6.4 h. The present work provided a comprehensive understanding on the degradation mechanisms and kinetics of chrysene, which could help to clarify its atmospheric fate and environmental risks.

Atmospheric oxidation mechanism of acenaphthene initiated by OH radicals

Gas-phase oxidation of PAHs can result in formation of oxygenated PAHs (OPAHs) and nitro-PAH (NPAHs) as well as a series of secondary pollutants which contribute to formation of SOA. Acenaphthene (ACE) is one of the PAHs with three rings which exists mainly as gaseous form in the atmosphere, where the oxidation is mainly initiated by reaction with OH radical. In this study, the atmospheric oxidation mechanism of ACE initiated by OH radical is investigated using high level quantum chemistry (at the ROCBS-QB3 level) and kinetic calculations, and the overall rate coefficient obtained here is in good agreement with previous experimental values. The reaction starts with OH radical additions to the C3-, C5-site and H atom abstraction from C1/C2 of ACE, and the fates of main adducts formed as ACE-n-OH (ACE3 and ACE5 in short) and R2 are further considered. ACE3 and ACE5 would react with O2 at different sites, of which all the additions are reversible. An overall effective removal rate of ~9 s−1 for ACE5 with O2 are calculated here using steady state approximately, which allows their reaction with NO2 to a relative significant extent in the atmosphere. We predicted significant 4-NACE formation from ACE5. Reaction of ACE3 with O2 is fast enough of ~107 s−1 that 9-NACE is expected to form in smaller quantities. Additionally, a number of cyclic OPAHs and multifunctional compounds are formed in the oxidation of ACE3, ACE5 and R2 under the high/low NOx concentration as observed in previous investigations.

Characteristics of indoor and personal exposure to particulate organic compounds emitted from domestic solid fuel combustion in rural areas of northwest China

Household solid fuel combustion for heating in winter is a substantial source of air pollution in rural areas of northwest China. The present study investigated the concentration characteristics and health risks of particulate matter (PM) and its organic compounds, including polycyclic aromatic hydrocarbons (PAHs), oxygenated PAHs (OPAHs), and phthalate esters (PAEs). Indoor air and housewives' personal exposure (PE) samples were collected in Guanzhong Basin, among rural households relying on various solid fuels for heating in winter. Indoor PM primarily comprised fine PM (PM2.5, 76%), and its organic compounds were identified in particular abundance in households that used coal as the only domestic fuel (Group C, 96% in PM2.5). The mean concentration of PE to PM2.5 was 307 ± 120 μg·m−3, which was 2.4-times higher than the indoor concentration (130 ± 103 μg·m−3) because of the housewives' short-term exposure to high-concentration pollution emitted by solid fuel combustion. Organic compounds exhibited the same pattern, with PE samples having a 44% higher concentration than indoor samples. The correlation of PM2.5-bound organics between indoor and PE samples in Group C (R2 = 0.9) was higher than that in the group using coal and biomass (Group M, R2 = 0.6), indicating the stronger correlation of single-fuel heating method. The PE/indoor ratio of high molecular weight (HMW) PAHs in Group C (2.5) was higher than that of the other organic compounds (1.3) because HMW PAHs emitted through coal combustion had a larger effect on PE. This further led to higher incremental lifetime cancer risks (ICLRs) via inhalation pathway among housewives in Group C (2.4- and 1.2-times higher risk for PAHs and PAEs, respectively) than among those in Group M. However, inhalational ILCR values of Group M were still 2.1–340-times higher than the international safety standard (10−6). Therefore, the upgradation of domestic fuels and heating ways is urgently needed in rural area of northwest China to reduce indoor air pollution and health risks.

Atmospheric oxidation of indene initiated by OH radical in the presence of O2 and NO: A mechanistic and kinetic study

The atmospheric degradation of polycyclic aromatic hydrocarbons (PAHs) can generate organic pollutants that contribute to the formation of secondary organic aerosols (SOAs) and exacerbate their carcinogenicity. Indene is an example of styrene-like bicyclic hydrocarbons that are not fully aromatic. The OH-initiated atmospheric oxidation of indene in the presence of O2 and NO was investigated using quantum chemical methods at M06–2X/6–311++G(3df,2p)//M06–2X/6-311+G(d,p) level. The oxidation products are oxygenated polycyclic aromatic hydrocarbons (OPAHs) containing hydroxyindene, indenone, dialdehydes and 2-(formylmethyl)benzaldehyde. Calculation results showed that 7-indene radical, which is the precursor of various PAHs, has a high production ratio that is 35.29% in the initial reaction, indicating that the OH-initiated oxidation increase the environmental risks of indene in the atmosphere. The rate constants for the crucial elementary reactions were calculated based on Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The overall rate constant of the initial reaction is calculated to be 1.04 × 10−10 cm3 molecule−1 s−1 and the atmospheric lifetime of indene is determined as 2.74 h. This work provides a comprehensive understanding on the oxidation mechanisms of indene and the findings could help to clarify the fate of indene in the atmosphere.

The occurrence and levels of polycyclic aromatic hydrocarbons (PAHs) in African environments-a systematic review.

In the African continent, several studies have been conducted to determine PAH pollution levels with their associated health risks in the environment. However, these studies are very much disconnected. The objective of this study is to conduct a systematic review that serves as a comprehensive report on the PAH-related studies conducted in the African continent. Data sources are from Google Scholar and PubMed. English language studies that reported on PAH levels in smoked fish and meat, soils and dust, aquatic environments, indoor and outdoor air, and ready-to-eat food items were selected. Specific PAHs included the following: 33 PAHs comprising ofthe 16 USEPA PAHs, non-alkylated PAHs, non-alkylated PAHs, oxygenated PAHs (OPAHs), and azaarenes (AZAs). Study appraisal and synthesis methods: The Newcastle-Ottawa Scale (NOS) was adapted to assess the quality of the selected studies basing on their sampling methods, analytical techniques, and results. A total of 121 studies were reviewed, with the majority (56) being from Nigeria. PAH levels in smoked fish and meat, soils and dust, aquatic environments, indoor and outdoor air, and ready-to-eat food items recorded total concentrations of PAHs ranging from 5 to 3585 μg/kg, BDL to 6,950,000 μg/kg, 0 to 10,469,000 μg/kg, 0 to 7.82 ± 0.85 μg/m3, and 2.5 to 7889 ± 730 μg/kg respectively. Carcinogenic risk assessment for children and adults ranged from very low to very high levels when compared to the ILCR range (10-6 to 10-4) defined by the USEPA. Out of 54 African countries, only 19 were represented. The majority of selected studies failed to apply any standard protocols for sample collection and analysis. The low to very high PAH levels reported in studies calls for effective actions on environmental health. Similar systematic reviews are expected to be performed in other continents for a global assessment of PAH pollution.