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Plastic pollution is fast becoming one of the most pressing global issues that we currently face. Remote areas, such as the polar regions and the Tibetan Plateau, are now also exposed to microplastic contamination. However, with the impact of global warming, the transport of microplastics within the glacier-lake basins in such regions remains unclear. In this work, the Nam Co Basin in the Tibetan Plateau was selected to study the characteristics of microplastics in the rain fallout, lake water, glacial runoff, and non-glacial runoff. Fiber and films were the most common microplastic morphologies in all water samples; a higher proportion (37%) of light-weighing polypropylene and small-size (50-300 µm, â¼30%) microplastics were found in the glacial runoff. Air mass trajectory analysis showed that microplastics could be transported through the atmosphere over a distance of up to 800 km. For microplastic loading in lakes, the atmospheric fallout was estimated to be 3.3 tons during the monsoon season, whereas the contributions of glacial runoff (â¼41 kg) and non-glacial runoff (â¼522 kg) were relatively low. For the microplastic loading in glaciers, the atmospheric deposition was â¼500 kg/yr, and the output caused by glacial melting only accounted 8% of the total atmospheric input. All these results suggested that the dominant pathway through which microplastics enter remote mountainous lake basins is atmospheric deposition, and once deposited on glaciers, microplastics will be stored for a long time. This work provides quantitative evidence elucidating the fate of microplastics in alpine lake environments.
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Microplásticos , Contaminantes Químicos del Agua , Monitoreo del Ambiente , Lagos , Plásticos , Tibet , Contaminantes Químicos del Agua/análisisRESUMEN
With global warming, the melting of glaciers can result in the release of pollutants into the environment. For remote Alpine lakes, both atmosphere-deposited anthropogenic pollutants and glacier-released pollutants can eventually sink in the sediment. To date, there has, to the best of our knowledge, been no attempt at quantifying the contributions of these processes to the accumulation of pollutants in glacial lake sediment. To fill this gap, a semi-enclosed proglacial lake located in the southern Tibetan Plateau was chosen and a 28 cm sediment core, which can be dated back to 1836, was used to explore the temporal trends of trace elements, Hg, and black carbon (BC) during the past two centuries. Geochemical indicators (Rb/Sr, Ti-Zr-Hf, and sedimentary rate) in sediment showed an overall continuous warming of the lake, while the temporal trends of fluxes of toxic elements and BC were broadly associated with their emission patterns. By using a positive matrix factorization model, the contribution of the anthropogenic source rose from <10% in the 1850s to >40% after the 1980s. However, the signal of glacial meltwater release was also distinct, and the greatest contribution of ice-snow meltwater reached up to 61% in the 1950s. Regarding the most recent two decades, 90% of pollutant deposition in the Tibetan sediment can be attributed to the combined forces of primary emissions and glacial release.
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Contaminantes Ambientales , Contaminantes Químicos del Agua , Monitoreo del Ambiente , Contaminantes Ambientales/análisis , Sedimentos Geológicos , Cubierta de Hielo , Lagos , Contaminantes Químicos del Agua/análisisRESUMEN
Nepal is abutted between the populated Indo-Gangetic Plain (IGP) and Himalayan mountains. Currently, knowledge on the country-wide distribution and cancer risks of atmospheric organic toxicants in Nepal remains limited. In this study, the concentrations, sources, and distributions of polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), and polychlorinated biphenyls (PCBs), along with their cancer risks, were investigated in Nepal by using tree bark as a passive air sampler. After transferring by a bark/air partitioning model, the averaged concentrations of ∑PAHs, ∑DDTs, ∑HCHs, HCB, ∑Endo and ∑PCBs in the atmosphere of Nepal were 3.71 × 104 pg/m3, 1.10 × 103 pg/m3, 2.92 × 102 pg/m3, 4.38 × 102 pg/m3, 4.66 pg/m3 and 65.8 pg/m3, respectively. Source diagnosis suggested that biomass burning is the major source for PAHs, while local application and long-range transport jointly contribute to the high levels of DDT and HCH in the air. The ILCR (incremental lifetime cancer risk) value was used to assess the risks of various chemicals. Adults have a higher risk than other age groups; the major exposure pathway for risk is by inhalation; and PAHs and HCHs are the dominant chemical classes that lead to risk. It was also found that, in certain hotspots in south Nepal, the carcinogenic risks caused by DDT and HCH were particularly high (>1 × 10-4). Given that illegal and disordered use of legacy POPs in south Nepal and the IGP region is common, our results highlight an urgent need for voluntary regulation of the ongoing use of pesticides.
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Contaminantes Atmosféricos , Hidrocarburos Clorados , Plaguicidas , Bifenilos Policlorados , Hidrocarburos Policíclicos Aromáticos , Adulto , Contaminantes Atmosféricos/análisis , Contaminantes Atmosféricos/toxicidad , Monitoreo del Ambiente , Humanos , Hidrocarburos Clorados/análisis , Hidrocarburos Clorados/toxicidad , Nepal , Plaguicidas/análisis , Plaguicidas/toxicidad , Corteza de la Planta/química , Bifenilos Policlorados/análisis , Bifenilos Policlorados/toxicidad , Hidrocarburos Policíclicos Aromáticos/análisis , Hidrocarburos Policíclicos Aromáticos/toxicidadRESUMEN
Background soils are reservoirs of persistent organic pollutants (POPs). After decades of reduced primary emissions, it is now possible that the POPs contained in these reservoirs are being remobilized because of climate warming. However, a comprehensive investigation into the remobilization of POPs from background soil on the largest and highest plateau on Earth, the Tibetan Plateau (TP), is lacking. In this study, a sampling campaign was carried out on the TP at three background sites with different land cover types (forest, meadow and desert). Field measurements of the air-soil exchange of POPs showed that previous prediction using empirical models overestimated the values of the soil-air partitioning coefficient ( KSA), especially for chemicals with KOA > 9. The direction of exchange for γ-HCH, HCB, and PCB-28 overlapped with the air-soil equilibrium range, but with a tendency for volatilization. Their emission fluxes were 720, 2935, and 538 pg m-2 day-1, respectively, and were similar in extent to those observed for background Arctic soil in Norway. Nam Co and Ngari are also permafrost regions, and most chemicals at these two sites exhibited volatilization. This is the first result showing that permafrost can also emit POPs. Seasonally, we found that chemicals tended to be re-emitted from soils to the atmosphere in winter and deposited from the air to the soil in summer. This finding is opposite to most previous results, possibly because of the higher air-soil concentration gradient caused by the prevailing transport of POPs in summer. Climate warming exerts a strong influence on air-soil exchange, with an increase of 1 °C in ambient temperature likely leading to an increase of Tibetan atmospheric inventories of POPs by 60-400%.
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Contaminantes Atmosféricos , Contaminantes Ambientales , Bifenilos Policlorados , Contaminantes del Suelo , Regiones Árticas , Monitoreo del Ambiente , Calentamiento Global , Noruega , Estaciones del Año , Suelo , TibetRESUMEN
Robust knowledge on the occurrence and distribution of persistent organic pollutants (POPs) in the atmosphere of low-latitude regions is inevitable to forecast their transportation to pristine ecosystem and assess toxicological impacts upon local biota. Despite the earlier revelation of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in soils/sediments and water bodies in Pakistan, knowledge about atmospheric levels and sources of these POPs remains limited. For the first time, a network of XAD resin-based passive air samplers (PAS) was established across megacities of Pakistan, i.e., Karachi, the coastal city, and Lahore, lying in an agricultural region. Typical geographical locations of the two cities allowed assessing the influence of source regions on the occurrence and distribution patterns of selected POPs. Average concentrations (ng/PAS) in both cities ranged as endosulfan 39-101, DDTs 63-92, HCHs 33-65, heptachlor 10-26, and PCBs 48-61. High concentrations of endosulfan and lindane as observed throughout Lahore were certainly due to their ongoing applications in surrounding agricultural fields. Lower proportions of parental DDTs as compared to their metabolites were observed in both cities, suggesting inputs of DDTs from older or secondary sources. Owing to ultimate discharge of country's agricultural/industrial waste through river streams in to Arabian Sea, the coastal region of Karachi was found potential source of weathered POPs that could be dissipated at regional/global scales by maritime advections. The study contributes to the pool of information on fate and geographical distribution of POPs in subtropical developing countries.
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Contaminantes Atmosféricos/análisis , Monitoreo del Ambiente , Hidrocarburos Clorados/análisis , Insecticidas/análisis , Bifenilos Policlorados/análisis , Ciudades , PakistánRESUMEN
There have been few reports of the large-scale spatial distribution and long-term historical variations of pollutants in high-altitude forests. Tree bark and tree core samples were collected from forests in the Himalaya and Hengduan mountains to determine the spatiotemporal variations of persistent organic pollutants. The average concentrations of dichlorodiphenyl trichloroethanes (DDTs), hexachlorocyclohexanes (HCHs), hexachlorobenzene (HCB), polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in tree bark samples were 9.09, 0.10, 0.13, 0.11and 26 ng/g dry weight, respectively, and 1.30, 0.02, 0.17, 0.07 and 186 ng/g dry weight, respectively, in tree core samples. Higher levels of these pollutants were observed in the forests on the southern slopes of the Himalaya (Nepal) and the southern part of the Hengduan mountains (Yunnan, China). Lower concentrations of these pollutants were found in the interior of the Tibetan Plateau on the northern slopes of the Himalaya as a result of the blocking effect of these mountain ranges. The concentrations of DDTs and HCHs in Himalayan tree cores showed increasing trends from 1956 to 1975 when they were used as pesticide extensively worldwide, especially in India. Peak concentrations of DDTs, HCHs and PAHs in tree cores of Qamdo located in Hengduan Mountains were observed in 2013, which were consistent with the history of industrial and agricultural development in Sichuan. This study provides new insights into the impact of atmospheric pollutants in South and Southeast Asia.
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Hidrocarburos Clorados , Plaguicidas , Bifenilos Policlorados , Hidrocarburos Policíclicos Aromáticos , Hidrocarburos Policíclicos Aromáticos/análisis , Bifenilos Policlorados/análisis , Árboles , Corteza de la Planta/química , Monitoreo del Ambiente , China , Hidrocarburos Clorados/análisis , Plaguicidas/análisis , Hexaclorociclohexano/análisisRESUMEN
Nanostructures of conventional metals offer manipulation of light at the nanoscale but are largely limited to static behavior due to fixed material properties. To develop the next frontier of dynamic nano-optics and metasurfaces, this study utilizes the redox-tunable optical properties of conducting polymers, as recently shown to be capable of sustaining plasmons in their most conducting oxidized state. Electrically tunable conducting polymer nano-optical antennas are presented, using nanodisks of poly(3,4-ethylenedioxythiophene:sulfate) (PEDOT:Sulf) as a model system. In addition to repeated on/off switching of the polymeric nanoantennas, the concept enables gradual electrical tuning of the nano-optical response, which was found to be related to the modulation of both density and mobility of the mobile polaronic charge carriers in the polymer. The resonance position of the PEDOT:Sulf nanoantennas can be conveniently controlled by disk size, here reported down to a wavelength of around 1270 nm. The presented concept may be used for electrically tunable metasurfaces, with tunable farfield as well as nearfield. The work thereby opens for applications ranging from tunable flat meta-optics to adaptable smart windows.
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Energy level alignment (ELA) at donor (D) -acceptor (A) heterojunctions is essential for understanding the charge generation and recombination process in organic photovoltaic devices. However, the ELA at the D-A interfaces is largely underdetermined, resulting in debates on the fundamental operating mechanisms of high-efficiency non-fullerene organic solar cells. Here, we systematically investigate ELA and its depth-dependent variation of a range of donor/non-fullerene-acceptor interfaces by fabricating and characterizing D-A quasi bilayers and planar bilayers. In contrast to previous assumptions, we observe significant vacuum level (VL) shifts existing at the D-A interfaces, which are demonstrated to be abrupt, extending over only 1-2 layers at the heterojunctions, and are attributed to interface dipoles induced by D-A electrostatic potential differences. The VL shifts result in reduced interfacial energetic offsets and increased charge transfer (CT) state energies which reconcile the conflicting observations of large energy level offsets inferred from neat films and large CT energies of donor - non-fullerene-acceptor systems.
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Record power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have been obtained with the organic hole transporter 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9'-spirobifluorene (spiro-OMeTAD). Conventional doping of spiro-OMeTAD with hygroscopic lithium salts and volatile 4-tert-butylpyridine is a time-consuming process and also leads to poor device stability. We developed a new doping strategy for spiro-OMeTAD that avoids post-oxidation by using stable organic radicals as the dopant and ionic salts as the doping modulator (referred to as ion-modulated radical doping). We achieved PCEs of >25% and much-improved device stability under harsh conditions. The radicals provide hole polarons that instantly increase the conductivity and work function (WF), and ionic salts further modulate the WF by affecting the energetics of the hole polarons. This organic semiconductor doping strategy, which decouples conductivity and WF tunability, could inspire further optimization in other optoelectronic devices.
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Atmospheric wet deposition is an important process for the occurrence of perfluoroalkyl substances (PFASs) in polar/remote mountain regions; however, there are limited data on PFASs in precipitation from the Tibetan Plateau (TP). Precipitation (rain from May to October 2017) was therefore collected across the TP to investigate the concentrations, composition profiles, sources, and fluxes of perfluoroalkyl acids (PFAAs). The average ∑PFAA concentrations ranged from 212.3 pg L-1 to 547.7 pg L-1, and perfluoroalkyl carboxylic acids (PFCAs) accounted for 87% of the measured PFAAs (mean value). Significant positive associations (p < 0.05) were found for most PFCAs in the southeast TP, indicating that they may come from similar sources. The monthly PFAA deposition flux ranged from 12.6 to 68.9 ng m-2 month-1, decreasing from east to west. As climate of the eastern TP is controlled mainly by the Indian monsoon, indicating that the Indian monsoon plays an important role in delivering PFAAs to the TP. PCA (principal component analysis) combined with back-trajectory analysis was used to estimate the atmospheric transport pathways, and the PSCF (potential source contribution function) model was applied to define the potential source regions of individual PFAAs. The results suggested that northeast India, Bangladesh, and southern Nepal are the potential sources of C4-C7 PFCAs; C8-C10 PFCAs are more influenced by emissions from southern Nepal and Bhutan; while the source regions of long-chain PFCAs (C11-C12) can be attributed to northern India and Pakistan. Specifically, PFOS (perfluorooctane sulfonic acid) has a local contribution from the central TP.
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Ácidos Alcanesulfónicos , Fluorocarburos , Contaminantes Químicos del Agua , Ácidos Alcanesulfónicos/análisis , Monitoreo del Ambiente , Fluorocarburos/análisis , Estaciones del Año , Tibet , Contaminantes Químicos del Agua/análisisRESUMEN
Limited studies have been carried out on the historical variations of atmospheric polycyclic aromatic hydrocarbons (PAHs), especially in remote regions of the world. In this study, century-long record of PAHs (1916-2018) were reconstructed from tree rings in the remote southeastern Tibetan Plateau (TP). The total concentrations of 15 PAHs varied from 27.5 to 6.05 × 102 ng/g dry weight (dw), with a mean value of 1.40 × 102 ng/g dw. Higher levels of PAHs were observed during World War â ¡ and the Peaceful Liberation of Tibet, and increasing trends were observed starting from rapid industrialization in India. Both the isomer ratios and the positive matrix factorization model results indicated biomass and coal combustion were the dominant sources of PAHs. The carcinogenic risk of PAHs to local residents was assessed, which might have been negligible in most past periods and lower than in other regions of the world. Nevertheless, since the beginning of the 21st century, the cancer risk has been increasing year by year, indicating more actions are needed to reduce emissions of PAHs. This study provides an idea for reconstructing the pollution history of PAHs at the global scale.
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Hidrocarburos Policíclicos Aromáticos , China , Carbón Mineral , Monitoreo del Ambiente , India , Hidrocarburos Policíclicos Aromáticos/análisis , TibetRESUMEN
Atmospheric dry deposition is a major pathway for removal of polycyclic aromatic hydrocarbons (PAHs) from the atmosphere. Despite its significance in the atmospheric environment, measurements of the dry deposition velocity (VDD) and deposition fluxes (FDD) of PAHs are relatively limited. In this study, a passive dry deposition (PAS-DD) collector was co-deployed with passive air sampler polyurethane foam (PAS-PUF) from November 2015 to November 2016 in two major cities (Kathmandu and Pokhara), Nepal, to investigate the VDD and FDD of PAHs. The VDD of PAHs ranged from 0.25 to 0.5 cm s-1 and the annual average was recorded as 0.37 ± 0.08 cm s-1. On the basis of measured VDD, the FDD of ∑15PAHs in Kathmandu and Pokhara were estimated as 66 and 5 kg yr-1 respectively. According to the measured VDD of Kathmandu and Pokhara in this study, and the previously published VDD data of Toronto, Canada, where the same PAS-DD collector was used, a significant multi-linear correlation (r2 = 0.79, p < 0.05) was found between VDD of higher molecular weight (HMW with MW ≥ 228.3 and ≥ 4 rings) PAHs and meteorological parameters (precipitation and wind speed) and vapor pressure of PAHs. To the best of our knowledge, this enabled the development of an empirical model that can exhibit the combined effects of meteorological conditions on the VDD of HMW PAHs. The model was used to estimate the VDD values for major cities in the Indo-Gangetic Plain (IGP) region and the maximum estimated proportion of HMW PAHs deposited by dry deposition reached up to 60% of total emissions. Although PAH emissions in the IGP region pose global risks, the results of this study highlight the considerable risk for local IGP residents, due to the large dry deposition proportion of HMW PAHs.
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Contaminantes Atmosféricos/análisis , Hidrocarburos Policíclicos Aromáticos/análisis , Canadá , Monitoreo del Ambiente , Nepal , Clima TropicalRESUMEN
Being able to dynamically shape light at the nanoscale is one of the ultimate goals in nano-optics1. Resonant light-matter interaction can be achieved using conventional plasmonics based on metal nanostructures, but their tunability is highly limited due to a fixed permittivity2. Materials with switchable states and methods for dynamic control of light-matter interaction at the nanoscale are therefore desired. Here we show that nanodisks of a conductive polymer can support localized surface plasmon resonances in the near-infrared and function as dynamic nano-optical antennas, with their resonance behaviour tunable by chemical redox reactions. These plasmons originate from the mobile polaronic charge carriers of a poly(3,4-ethylenedioxythiophene:sulfate) (PEDOT:Sulf) polymer network. We demonstrate complete and reversible switching of the optical response of the nanoantennas by chemical tuning of their redox state, which modulates the material permittivity between plasmonic and dielectric regimes via non-volatile changes in the mobile charge carrier density. Further research may study different conductive polymers and nanostructures and explore their use in various applications, such as dynamic meta-optics and reflective displays.
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Snow is an efficient scavenger for the deposition of contaminants. Atmospheric transport and snow deposition jointly control the distribution of pollutants in remote mountain/polar regions. But can the contaminants contained within snow be used to reflect the interactions of air circulation patterns? The physicochemical properties of perfluoroalkyl substances (PFASs) are unique because of their high water solubilities. Taking advantage of this, 15 surface-snow and 3 snow-pit samples were collected across a vast area of western China (spanning 20° of latitude and 25° of longitude), to investigate the concentrations, composition profiles (fingerprints), and deposition fluxes of PFASs. Both a high concentration (3974â¯pg/L) and deposition flux (4.0⯵g/m2/yr) for a total of 16 PFASs were found in the snow at Yulong, the most southern sample site, possibly because of its close proximity to source regions of pollutants in South Asia and high rate of snow deposition. Perfluorobutanoic acid was the most commonly found chemical in snow, but in general the PFAS composition in the snow of western China showed large spatial differences, with long-chain (Câ¯>â¯10) PFASs being relatively dominant in the north and west of the region and short-chain (Câ¯<â¯6) PFASs in the south and east. On the basis of the different compositions of PFASs in the snow of western China and the previously reported features of pollutant sources in Europe and India, we found that PFASs in snow can be used as an atmospheric tracer for tracking the interactions between westerly winds and the Indian Monsoon. The belt along 33°N is a key location where both the Indian Monsoon and westerly winds can arrive/interact; however, the contribution of the monsoon was found to be above 70%, while that of the westerly winds can be lower than 30%. The western part of the 33°N belt was found to be more vulnerable to the Indian Monsoon, and could be grouped into the monsoon domain, while the influence of the westerly winds increased from west to east along the belt. This finding is opposite to previous results, which reported that the western part of the 33°N belt was mainly under the influence of the westerly winds, and for the first time quantifies the relative contribution of westerly winds and the Indian Monsoon to the atmospheric transport of chemicals.
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Monitoreo del Ambiente , Contaminantes Ambientales/análisis , Nieve/química , Viento , China , Tormentas Ciclónicas , Monitoreo del Ambiente/métodos , Fluorocarburos/análisisRESUMEN
Due to their low temperatures, the Arctic, Antarctic and Tibetan Plateau are known as the three polar regions of the Earth. As the most remote regions of the globe, the occurrence of persistent organic pollutants (POPs) in these polar regions arouses global concern. In this paper, we review the literatures on POPs involving these three polar regions. Overall, concentrations of POPs in the environment (air, water, soil and biota) have been extensively reported, with higher levels of dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) detected on the Tibetan Plateau. The spatial distribution of POPs in air, water and soil in the three polar regions broadly reflects their distances away from source regions. Based on long-term data, decreasing trends have been observed for most "legacy POPs". Observations of transport processes of POPs among multiple media have also been carried out, including air-water gas exchange, air-soil gas exchange, emissions from melting glaciers, bioaccumulations along food chains, and exposure risks. The impact of climate change on these processes possibly enhances the re-emission processes of POPs out of water, soil and glaciers, and reduces the bioaccumulation of POPs in food chains. Global POPs transport model have shown the Arctic receives a relatively small fraction of POPs, but that climate change will likely increase the total mass of all compounds in this polar region. Considering the impact of climate change on POPs is still unclear, long-term monitoring data and global/regional models are required, especially in the Antarctic and on the Tibetan Plateau, and the fate of POPs in all three polar regions needs to be comprehensively studied and compared to yield a better understanding of the mechanisms involved in the global cycling of POPs.
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Monitoreo del Ambiente , Contaminantes Ambientales/análisis , Contaminantes Atmosféricos/análisis , Regiones Antárticas , Regiones Árticas , Cambio Climático , Clima Frío , DDT , Cadena Alimentaria , Predicción , Hexaclorociclohexano , Hidrocarburos Clorados , Suelo , TibetRESUMEN
The morphology of the active layer plays a crucial role in determining device performance and stability for organic solar cells. All-polymer solar cells (All-PSCs), showing robust and stable morphologies, have been proven to give better thermal stability than their fullerene counterparts. However, outstanding thermal stability is not always the case for polymer blends, and the limiting factors responsible for the poor thermal stability in some All-PSCs, and how to obtain higher efficiency without losing stability, still remain unclear. By studying the morphology of poly [2,3-bis (3-octyloxyphenyl) quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl](TQ1)/poly[4,8-bis[5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b']dithiophene-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl]] (PCE10)/PNDI-T10 blend systems, we found that the rearranged molecular packing structure and phase separation were mainly responsible for the poor thermal stability in devices containing PCE10. The TQ1/PNDI-T10 devices exhibited an improved PCE with a decreased π-π stacking distance after thermal annealing; PCE10/PNDI-T10 devices showed a better pristine PCE, however, thermal annealing induced the increased π-π stacking distance and thus inferior hole conductivity, leading to a decreased PCE. Thus, a maximum PCE could be achieved in a TQ1/PCE10/PNDI-T10 (1/1/1) ternary system after thermal annealing resulting from their favorable molecular interaction and the trade-off of molecular packing structure variations between TQ1 and PCE10. This indicates that a route to efficient and thermal stable All-PSCs can be achieved in a ternary blend by using material with excellent pristine efficiency, combined with another material showing improved efficiency under thermal annealing.
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Long-term monitoring in remote regions is essential for revealing pollution trends at the global scale but relevant studies remain limited. In the present study, a six-year continuous monitoring of atmospheric persistent organic pollutants (POPs) and polycyclic aromatic hydrocarbons (PAHs) was carried out at Lulang in the southeastern Tibetan Plateau (TP). Average concentrations of hexachlorocyclohexanes (HCHs), hexachlorobenzene (HCB), dichlorodiphenyltrichloroethanes (DDTs), polychlorinated biphenyls (PCBs) and PAHs were 13.5, 8.9, 41.7, 1.8pg/m3 and 6.2ng/m3, respectively. Obvious seasonality was found for all the target compounds. HCHs, DDTs and PCBs had their highest concentrations in summer (monsoon season) and lowest in winter, which is consistent with the fluctuation of the Indian monsoon. Meanwhile, HCB and 5-6-ring PAHs showed opposite variations, possibly induced by local sources and the westerly flow in winter. Declining trends were observed for most of the chemicals, except o,p'-DDE, HCB and PCBs. A declining trend in the α/γ-HCH ratio indicated a shift from technical HCHs to lindane. An increasing trend in the o,p'/p,p'-DDT ratio suggested a likely shift from technical DDTs to dicofol. For PAHs, the contribution from high-temperature combustion has increased recently. The half-lives of α-HCH, γ-HCH, o,p'-DDT, p,p'-DDT were 6.1, 108, 77.6 and 14.2years, respectively. The half-lives of γ-HCH, o,p'-DDT and p,p'-DDT were higher than those in the Arctic, indicating these compounds will persist in the TP for a longer period. The temporal trends in atmospheric POPs were possibly induced by emissions in India and likely driven by wind speed in Lulang. This study contributes toward a better understanding of the behavior and transport of POPs in the TP region.
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Atmospheric polycyclic aromatic hydrocarbons (PAHs) in urban areas have always been a global concern, as these areas are considered to be the source region. Despite studies on the concentrations of PAHs in water, soils and sediments, knowledge of the distribution patterns, seasonality and sources of PAHs in urban areas of Nepal remains limited. In this study, polyurethane foam passive air samplers were used to measure gas-phase PAH concentrations over different land types in three major cities of Nepal-namely, Kathmandu (the capital) and Pokhara (both densely populated cities), and Hetauda (an agricultural city). The average concentrations of ∑15PAHs in ng/m3 were 16.1±7.0 (6.4-28.6), 14.1±6.2 (6.8-29.4) and 11.1±9.0 (4.1-38.0) in Kathmandu, Pokhara and Hetauda, respectively. Molecular diagnostic ratio analysis suggested that fossil fuel combustion was a common PAH source for all three cities. In addition to this, coal combustion in Kathmandu, vehicle emissions in Pokhara, and grass/wood combustion in Hetauda were also possible sources of PAHs. In terms of cancer risk from PAH inhalation, a religious site with intense incense burning, a brick production area where extensive coal combustion is common, and a market place with heavy traffic emission, were associated with a higher risk than other areas. There were no clear seasonal trends in atmospheric PAHs. The estimated cancer risk due to inhalation of gas-phase PAHs exceeded the USEPA standard at >90% of the sites.
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Contaminación del Aire/estadística & datos numéricos , Atmósfera/química , Exposición a Riesgos Ambientales/estadística & datos numéricos , Neoplasias/epidemiología , Hidrocarburos Policíclicos Aromáticos/análisis , Nepal/epidemiologíaRESUMEN
Brown carbon (BrC), a carbonaceous aerosol which absorbs solar radiation over a broad range of wavelengths, is beginning to be seen as an important contributor to global warming. BrC absorbs both inorganic and organic pollutants, leading to serious effects on human health. We review the fundamental features of BrC, including its sources, chemical composition, optical properties and radiative forcing effects. We detail the importance of including photochemical processes related to BrC in the GEOS-Chem transport model for the estimation of aerosol radiative forcing. Calculation methods for BrC emission factors are examined, including the problems and limitations of current measurement methods. We provide some insight into existing publications and recommend areas for future research, such as further investigations into the reaction mechanisms of the aging of secondary BrC, calculations of the emission factors for BrC from different sources, the absorption of large and long-lived BrC molecules and the construction of an enhanced model for the simulation of radiative forcing. This review will improve our understanding of the climatic and environmental effects of BrC.