Redox-active quinone and nonquinone moieties represent the electron exchange capacity (EEC) of natural organic matter (NOM), playing an important role in the electron transfer link of microbes and transformation of contaminants/metal minerals. However, the corresponding transformation of quinone/phenol and their respective influence on the EECs during reduction and reoxidation remain poorly characterized. Besides, it is still controversial whether nonquinones donate or accept electrons. Herein, we demonstrated that reoxidation of NOM after reduction can form new phenolic/quinone moieties, thus increasing the EEC. The assessment for the EEC, including the electron-donating capacity (EDC) and electron-accepting capacity (EAC), of nonquinones reflects the contribution of sulfur-containing moieties with considerable EDCs and EACs. In contrast, nitrogen-containing moieties donate negligible electrons even at E h = +0.73 V. The contributions of both thiol and amine moieties to the EEC are greatly affected by adjacent functional groups. Meanwhile, aldehydes/ketones did not display an EAC during the electron transfer process of NOM. Furthermore, substantially increased EDC at E h from +0.61 to +0.73 V could not be fully explained using thiol and phenolic moieties, suggesting the contribution of unknown moieties with high oxidation potential. The overall findings suggest that the roles of new quinones/phenol (derived from the addition of oxygen to condensed aromatic/lignin-like components) during redox dynamic cycling and thiol species should be considered in assessing the electron transfer processes of NOM.

Deposition of atmospheric mercury (Hg) is the most important Hg source on the high-altitude Himalayas and Tibetan Plateau. Herein, total gaseous Hg (TGM) at an urban and a forest site on the Tibetan Plateau was collected respectively from May 2017 to October 2018, and isotopic compositions were measured to clarify the influences of landforms and monsoons on the transboundary transport of atmospheric Hg to the Tibetan Plateau. The transboundary transported anthropogenic emissions mainly originated over Indo-Gangetic Plain and carried over the Himalayas by convective storms and mid-tropospheric circulation, contributing over 50% to the TGM at the Lhasa urban site, based on the binary mixing model of isotopes. In contrast, during the transport of TGM from South Asia with low altitude, the uptake by evergreen forest in Yarlung Zangbo Grand Canyon largely decreased the TGM level and shifted isotopic compositions in TGM at the Nyingchi forest site, which are located at the highaltitude end of the canyon. Our results provided direct evidence from Hg isotopes to reveal the distinct patterns of transboundary transport to the Tibetan Plateau shaped by landforms and climates, which is critical to fully understand the biogeochemical cycling of Hg in the high-altitude regions.

Sulfate aerosols exert a net cooling effect on the earth-atmosphere system, yet their radiative forcing remains associated with largest of uncertainties in the assessment of climate change. One of the contributing factors is the poor understanding of the sulfate formation pathways, which are thought to be following mostly the mass-dependent fractionation model (i.e., Δ 33 S ~ 0). However, globally, urban sulfate aerosols exhibit significant non-zero Δ 33 S compositions (from -0.6‰ to +0.6‰), resulting in sulfur mass-independent fractionation (S-MIF) processes. The origin(s) of these S-MIF anomalies remain(s) unclear. Here, we conducted dual-isotope (Δ 33 S, δ 34 S) probing of sulfate aerosols from summertime megacity Delhi in South Asia. A shift towards concomitantly high Δ 33 S (from +0.2‰ to +0.5‰) and low δ 34 S (from +5‰ to +1‰) values was observed with the influx of mineral dust. The Fe-to-Al tracer showed significant correlations with sulfate loadings (R 2 =0.84) and Δ 33 S signatures (R 2 =0.77). As such, we postulate that the SO2 photo-oxidation on mineral dust generates S-MIF anomaly ~ +0.35±0.10‰, thereby also explaining the previously observed Δ 33 S values worldwide. Together, the findings help deconvolute S-isotope dynamics in urban regions wherein, contrary to prevailing paradigm, non-anthropogenic factor (i.e., mineral dust) is found to influence the aerosol sulfate-induced pollution affecting air quality/human health. SYNOPSISSulfate-related pollution in urban regions-affecting air quality/human health-could be linked to non-anthropogenic factor i.e., mineral dust.

Abstract. Organic atmospheric aerosols in the Hindu Kush–Himalayas–Tibetan Plateau region are still poorly characterized. To better understand the chemical characteristics and sources of organic aerosols in the foothill region of the central Himalaya, the atmospheric aerosol samples were collected in Bode, a suburban site of the Kathmandu Valley (KV) over a 1-year period from April 2013 to April 2014. Various molecular tracers from specific sources of primary organic aerosols (POAs) and secondary organic aerosols (SOAs) were determined. Tracer-based estimation methods were employed to apportion contributions from each source. The concentrations of organic carbon (OC) and elemental carbon (EC) increased during winter with a maximum monthly average in January. Levoglucosan (a molecular tracer for biomass burning, BB) was observed as the dominant species among all the analyzed organic tracers and its annual average concentration was 788±685 ng m−3 (ranging from 58.8 to 3079 ng m−3). Isoprene-SOA (I-SOA) represented a high concentration among biogenic-SOA tracers. For the seasonality, anhydrosugars, phenolic compounds, resin acid, and aromatic SOA tracer showed similar seasonal variations with OC and EC while monosaccharides, sugar alcohols, and I-SOA tracers showed lower levels during winter. BB contributed a significant fraction to OC, averaging 24.9 %±10.4 % during the whole year, and up to 36.3 %±10.4 % in the post-monsoon season. On an annual average basis, anthropogenic toluene-derived secondary OC accounted for 8.8 % and biogenic secondary OC contributed 6.2 % to total OC. The annual contribution of fungal spores to OC was 3.2 % with a maximum during the monsoon season (5.9 %). For plant debris, it accounted for 1.4 % of OC during the monsoon. Therefore, OC is mainly associated with BB and other anthropogenic activity in the KV. Our findings are conducive to designing effective measures to mitigate the heavy air pollution and its impacts in the KV and surrounding area.

While there is a lack of information about the trophic transfer of short-chain per- and polyfluoroalkyl substances (PFASs) in the terrestrial ecosystem, this study focused on the occurrence and trophic transfer of both legacy and short-chain PFASs in a terrestrial food chain composed of the plants, plateau pikas, and eagles of the Tibetan Plateau. Total PFAS concentrations were in the range of 0.130–1.507, 0.406–1.085, 0.601–8.293, and 5.021–76.482 ng/g dw in soils, plants, pika muscles, and eagle muscles, respectively, among which perfluorooctanesulfonic acid (PFOS) and perfluorobutanoic acid (PFBA) were predominant in all sample types. Levels of PFASs in eagle feathers were significantly correlated with those in eagle muscles (r = 0.73), implying feathers could be used as an indicator of exposure of raptors to PFASs. Trophic magnification factors of PFOS (5.75), perfluorohexanesulfonic acid (2.43), C10–C12 perfluorocarboxylic acids (1.84–4.65), PFBA (5.11), and perfluorobutanesulfonic acid (5.96) along the plant–pika–eagle food chain were all significantly greater than 1. The short-chain PFASs may be biomagnified in air-breathing animals because of the nonvolatility of their charged forms and recalcitrance (not biotransformed). The results suggest that the ecological risks of these short-chain substitutions warrant further investigation.

To investigate the atmospheric aerosols of the Himalayas and Tibetan Plateau (HTP), an observation network was established within the region’s various ecosystems, including at the Ngari, Qomolangma (QOMS), Nam Co, and Southeastern Tibetan (SET) stations. In this paper we illustrate aerosol mass loadings by integrating <i>in situ</i> measurements with satellite and ground-based remote sensing datasets for the 2011&amp;ndash;2013 period, on both local and large scales. Mass concentrations of these surface atmospheric aerosols were relatively low and varied with land cover, showing a general tendency of Ngari and QOMS (barren sites) > Nam Co (grassland site) > SET (forest site). Daily averages of online PM_2.5 (particulates with aerodynamic diameters below 2.5&amp;thinsp;μm) at these sites were sequentially 18.2&amp;thinsp;±&amp;thinsp;8.9, 14.5&amp;thinsp;±&amp;thinsp;7.4, 11.9&amp;thinsp;±&amp;thinsp;4.9 and 11.7&amp;thinsp;±&amp;thinsp;4.7&amp;thinsp;μg&amp;thinsp;m^&amp;minus;3. Correspondingly, the ratios of PM_2.5 to total suspended particles (TSP) were 27.4&amp;thinsp;±&amp;thinsp;6.65&amp;thinsp;%, 22.3&amp;thinsp;±&amp;thinsp;10.9&amp;thinsp;%, 37.3&amp;thinsp;±&amp;thinsp;11.1&amp;thinsp;% and 54.4&amp;thinsp;±&amp;thinsp;6.72&amp;thinsp;%. Bimodal mass distributions of size-segregated particles were found at all sites, with a relatively small peak in accumulation mode and a more notable peak in coarse mode. Diurnal variations in fine aerosol masses generally displayed a bi-peak pattern at the QOMS, Nam Co and SET stations and a single-peak pattern at the Ngari station, controlled by the effects of local geomorphology, mountain-valley breeze circulation and aerosol emissions. Mineral content in PM_2.1 samples gave fractions of 26&amp;thinsp;% at the Ngari station and 29&amp;thinsp;% at the QOMS station, or ~&amp;thinsp;2&amp;ndash;3 times that of reported results at human-influenced sites. Furthermore, observed evidence confirmed the existence of the aerodynamic conditions necessary for the uplift of fine particles from a barren land surface. Combining surface aerosol data and atmospheric-column aerosol optical properties, the TSP mass and aerosol optical depth (AOD) of the Multi-angle Imaging Spectroradiometer (MISR) generally decreased as land cover changed from barren to forest, in inverse relation to the PM_2.5 ratios. The seasonality of aerosol mass parameters was land-cover dependent. Over forest and grassland areas, TSP mass, PM_2.5 mass, MISR-AOD and fine-mode AOD were higher in spring and summer, followed by relatively lower values in autumn and winter. At the barren site (the QOMS station), there were inconsistent seasonal variations between surface TSP mass (PM_2.5 mass) and atmospheric column AOD (fine-mode AOD). Our findings implicate that, HTP aerosol masses (especially their regional characteristics and fine particle emissions) need to be treated sensitively in relation to any assessments of their climatic effect and potential role as cloud condensation nuclei and ice nuclei.

&lt;p&gt;&lt;strong&gt;Abstract.&lt;/strong&gt; The long-term temporal-spatial variations of aerosol optical properties in Tibetan Plateau (TP) and the potential long-range transport from surrounding areas to TP were analyzed in this work, by using multiple years of sunphotometer measurements (CE318) at five stations in TP, satellite aerosol productions from Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), back-trajectory analysis from the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) and model simulation of the Goddard Earth Observing System (GEOS)-Chem chemistry transport model. The results from ground-based observations show that the annual aerosol optical depth (AOD) at most TP sites increased in the past decades with trends of 0.001&amp;#8201;&amp;#177;&amp;#8201;0.003/year at Lhasa, 0.013&amp;#8201;&amp;#177;&amp;#8201;0.003/year at Mt_WLG, 0.002&amp;#8201;&amp;#177;&amp;#8201;0.002/year at NAM_CO, and 0.000&amp;#8201;&amp;#177;&amp;#8201;0.002/year at QOMS_CAS. The increasing trend is also found for the aerosol Extinction &amp;#197;ngstrom exponent (EAE) at most sites, except for Mt_WLG sites with an obvious decreasing trend. Spatially, the AOD observed from MODIS shows negative trends in the northwest edge closed to the Taklimakan Desert and east of the Qaidam Basin and slightly positive trends in most of the other area of TP. Different aerosol types and sources contribute to the polluted day (with CE318 AOD at 440&amp;#8201;nm&amp;#8201;&gt;&amp;#8201;0.4) in the five sites of TP: dust dominant in Lhasa, Mt_WLG and Muztagh with sources from the Taklimakan Desert but fine aerosol pollution dominant at NAM_CO and QOMS_CAS with the transport from South Asia. A case of aerosol pollution at Lhasa, NAM_CO and QOMS_CAS during 28 April&amp;#8211;3 May 2016 reveals that the smoke aerosols in South Asia were lifted up to 10&amp;#8201;km and transported to TP, while the dust from Taklimakan Desert could climb the north slope of TP and then be transported to center TP. The long-range transport thereby seriously impact aerosol loading over the TP.&lt;/p&gt;

Abstract. The Tibetan Plateau and its surroundings, also known as the Third Pole, play an important role in the global and regional climate and hydrological cycle. Carbonaceous aerosols (CAs), including black carbon (BC) and organic carbon (OC), can directly or indirectly absorb and scatter solar radiation and change the energy balance on the Earth. CAs, along with the other atmospheric pollutants (e.g., mercury), can be frequently transported over long distances into the inland Tibetan Plateau. During the last decades, a coordinated monitoring network and research program named “Atmospheric Pollution and Cryospheric Changes” (APCC) has been gradually set up and continuously operated within the Third Pole regions to investigate the linkage between atmospheric pollutants and cryospheric changes. This paper presents a systematic dataset of BC, OC, water-soluble organic carbon (WSOC), and water-insoluble organic carbon (WIOC) from aerosols (20 stations), glaciers (17 glaciers, including samples from surface snow and ice, snow pits, and 2 ice cores), snow cover (2 stations continuously observed and 138 locations surveyed once), precipitation (6 stations), and lake sediment cores (7 lakes) collected across the Third Pole, based on the APCC program. These data were created based on online (in situ) and laboratory measurements. High-resolution (daily scale) atmospheric-equivalent BC concentrations were obtained by using an Aethalometer (AE-33) in the Mt. Everest (Qomolangma) region, which can provide new insight into the mechanism of BC transportation over the Himalayas. Spatial distributions of BC, OC, WSOC, and WIOC from aerosols, glaciers, snow cover, and precipitation indicated different features among the different regions of the Third Pole, which were mostly influenced by emission sources, transport pathways, and deposition processes. Historical records of BC from ice cores and lake sediment cores revealed the strength of the impacts of human activity since the Industrial Revolution. BC isotopes from glaciers and aerosols identified the relative contributions of biomass and fossil fuel combustion to BC deposition on the Third Pole. Mass absorption cross sections of BC and WSOC from aerosol, glaciers, snow cover, and precipitation samples were also provided. This updated dataset is released to the scientific communities focusing on atmospheric science, cryospheric science, hydrology, climatology, and environmental science. The related datasets are presented in the form of excel files. BC and OC datasets over the Third Pole are available to download from the National Cryosphere Desert Data Center (https://doi.org/10.12072/ncdc.NIEER.db0114.2021; Kang and Zhang, 2021).