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Polycyclic aromatic hydrocarbons (PAHs) have toxic, teratogenic, mutagenic and carcinogenic effects on living organisms. Plants can function as pollutant bioindicators and bioaccumulators due to their wide surface distribution and specific responses to atmospheric pollutants. However, various plants exhibit significant differences in their capacities to accumulate PAHs. At present, research has mainly focused on the effects of leaf morphology and physiological characteristics, and few studies have evaluated the effects of the leaf surface on PAH accumulation. We aimed to assess the factors impacting the uptake and accumulation of PAHs by leaves. We selected 8 common tree species in Shanghai, China, and used supercritical fluid extraction technology to determine the content of PAHs in their leaves. Specific measurements of leaf area, width/length, wax content, and stomatal density were applied to index the morphological and physiological characteristics; surface roughness, surface free energy, polar components, and dispersion components were compiled into an adsorption performance index. Principal component analysis (PCA) and canonical correlation analysis (CCA) were used to assess the effects of different leaf characteristics on PAH accumulation. We found that the mean concentrations of ΣPAHs ranged from 300 to 2000 ng·g -1 and that the proportions of different benzene rings were significantly different among the different tree species. Leaf morphology and physiological characteristics had more significant effects compared to surface adsorption. CCA showed a significant negative correlation between leaf morphological characteristics and wax content, but had no significant correlation with surface adsorption. Low-molecular-weight PAHs were found to be mainly affected by the morphological characteristics, while medium- and high-molecular-weight PAHs were influenced by wax content and adsorption. Our conclusions provide a theoretical basis for the establishment of a reliable plant atmosphere-monitoring system and a method for screening tree species with strong PAH adsorption capacity., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Aerosol-associated non-polar organic compounds (NPOCs), including 15 polycyclic aromatic hydrocarbons (PAHs), 30 n-alkanes, 2 iso-alkanes, 5 hopanes and 5 steranes, were identified and quantified in PM2.5 samples using the thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) method. The samples were mainly collected in autumn and winter in a typical city of eastern China. The total concentrations of NPOCs were 31.7-388.7 ng m-3, and n-alkanes were the most abundant species (67.2%). The heavy-molecular-weight PAHs (four- and five-ring) contributed 67.9% of the total PAHs, and the middle-chain-length n-alkanes (C25-C34) were the most abundant (72.3%) in n-alkanes. PAHs and n-alkanes were mainly distributed in the 0.56-1.00 µm fraction, while ∑ (hopanes+steranes) were associated with the 0.32-1.00 µm fraction, suggesting condensation of combustion products was their important origin. The ratio-ratio plots indicated that NPOCs in the local area were affected by photochemical degradation. To reduce the uncertainty caused by only particle NPOC data for source apportionment, the particle and predicted gaseous-phase NPOCs, incorporated with other PM2.5 compound were used as input data for the positive matrix factorization (PMF) model. Eight factors were extracted for both cases: secondary aerosol formation, vehicle exhaust, industrial emission, coal combustion, biomass burning, ship emission, and dust and light NPOCs. These findings highlight the emissions from different aerosol-associated NPOC origins, which caused different size-specific distributions, photodegradation and gas-particle partitioning, which further affect PM2.5 source apportionment. Considering these effects on organic tracers will help us accurately identify the potential sources of aerosols and then asses the contributions from each source. [ABSTRACT FROM AUTHOR]

Airborne polycyclic aromatic hydrocarbons (PAHs) are of great concern to human health due to their potential high toxicity. Understanding the characteristics and sources of PAHs, as well as the governing factors, is therefore critical. PAHs and refractory black carbon (rBC) are both from combustion sources. This work, for the first time, investigated exclusively the rBC-bound PAH properties by using a laser-only Aerodyne soot-particle aerosol mass spectrometer (SP-AMS). This technique offers highly time-resolved PAH results that a traditional offline measurement is unable to provide. We analyzed two datasets conducted in urban Shanghai during the fall of 2018 and in suburban Nanjing during the winter of 2017, respectively. Results show that the average concentration of PAHs in Nanjing was much higher than that in Shanghai. Nanjing PAHs contained more low molecular weight components while Shanghai PAHs contained more high molecular weight ones. PAHs in Shanghai presented two peaks in early morning and evening, while Nanjing PAHs had only one significant morning peak, but remained high throughout the nighttime. A multi-linear regression algorithm combined with positive matrix factorization (PMF) analyses on sources of PAHs reveals that the industry emissions contributed the majority of PAHs in Nanjing (~80%), while traffic emissions dominated PAHs in Shanghai (~70%). We further investigated the relationships between PAHs with various factors. PAHs in both sites tended to positively correlate with primary pollutants, including primary organic aerosol (OA) factors, and gaseous pollutants of CO, NO2 and SO2, but negatively correlated with secondary OA factors and O3. This result highlights the enhancement of rBC-bound PAHs level due to primary emissions and their oxidation loss upon atmospheric aging reactions. High concentration of PAHs seemed to frequently appear under low temperature and high relative humidity conditions, especially in Shanghai. [ABSTRACT FROM AUTHOR]

Direct and indirect effects of complex urban land-use types on polycyclic aromatic hydrocarbons (PAHs), including their total amount, composition, sources and sinks, were evaluated from 84 sampling points in the megacity of Shanghai. We measured the content and composition of PAHs adsorbed by the leaves of Cinnamomum camphora and established buffers of different radii at each point. The different land-use types areas were counted therewith to investigate their effects on the sources and sinks of PAHs in leaves. Results showed that the average value of PAHs in the leaves was 3014.06 ± 1879.713 ng g−1. The substance profiles were dominated by medium-molecular-weight (MMW, 54%) and high-molecular-weight (HMW, 45%) PAHs, and these fractions were much higher than that of low-molecular-weight (LMW, 1%) PAHs. Through correlation analysis, the land-use type of industry, road, business, and residential areas were initially assessed as the sources of PAHs, whereas water, farmland, and woodland areas were sinks. Lasso regression proved that road and residential areas have proven to be the main source of PAHs in Shanghai, rather than industry and business areas. Woodland was found to be a better sink for PAHs than water and farmland. Sources and sinks of PAHs with different benzene rings also differed greatly: the main sources of MMW PAHs were industrial emissions and commercial activities, with the main sinks being water and woodland; the primary sources of HMW PAHs were traffic emissions and residential activities, with the main sink being farmland. This study assessed the sources and sinks of PAHs in cities, from the perspective of varied effects of different urban land-use types on PAH composition and spatial distribution, and bridged the gap between urban PAHs alleviation and the land-use planning in megacity, with instructive significance for planning policy development. Image 1 • 1. The content of PAHs and land-use types of 84 sampling sites were calculated. • 2. PAHs in leaves were determined to characterize the content in the atmosphere. • 3. For MMW PAHs, industry served as main source, water and woodland served as sinks. • 4. The main source of HMW PAHs was road with the main sink being farmland. • 5. Land-use adjustment should be different in the urban stock land and incremental land. [ABSTRACT FROM AUTHOR]

Rapid urbanization and industrialization have precipitated the significant urban-rural gradient involving various aspects of human-related activities especially in megacities. Anthropogenic activities are the main source of polycyclic aromatic hydrocarbon (PAH) contamination, and the rising awareness concerning PAH potential toxicity to human health promotes a further understanding of its spatial distribution pattern in cities. Whether the distribution of PAH concentration and potential toxicity respond to the urban-rural gradient still requires investigation. This study applied a grid sampling method to investigate PAH concentration using Cinnamomum camphora leaves as bioindicators which were obtained from 84 sampling sites in a megacity, Shanghai. The potential toxicity of PAHs in leaves was calculated by toxicity factor equivalent method. Results revealed the patterns of PAH distribution in the city varied in concentration and potential toxicity: the total concentration of PAHs in leaves decreased along the urban–rural gradient, while the potential toxicity peaked at junction areas. The trend of PAH concentration along the distance from urban center corresponded to that of population density. The spatial distribution of potential toxicity did not correspond with the gradient but was influenced by high benzo(a)pyrene concentration originated from the industry districts nearby. Higher potential toxicity of PAHs was observed at the urban-suburban-rural junction areas of megacities, advocating health-risk attention and appropriate plan for land use of these transition areas in cities. Unlabelled Image • 84 sampling sites along the urban–rural gradient in Shanghai were studied. • PAH concentration in C. camphora leaves decreased along the urban–rural gradient. • Trend of PAH concentration corresponded to that of population density. • High PAH potential toxicity in sites resulted from adjacent industrial districts. • Urban-Suburban-rural junction areas merit more ecological risk attention. [ABSTRACT FROM AUTHOR]