Browsing by Author "Junming Guo"

Now showing 1 - 9 of 9

Accumulation of Atmospheric Mercury in Glacier Cryoconite over Western China
(American Chemical Society, 2019) Jie Huang; Shichang Kang; Ming Ma; Junming Guo; Zhiyuan Cong; Zhiwen Dong; Runsheng Yin; Jianzhong Xu; Lekhendra Tripathee; Kirpa Ram; Feiyue Wang
Cryoconite is a granular aggregate, comprised of both mineral and biological material, and known to accumulate atmospheric contaminants. In this study, cryoconite was sampled from seven high-elevation glaciers in Western China to investigate the spatial and altitudinal patterns of atmospheric mercury (Hg) accumulation in the cryoconite. The results show that total Hg (HgT) concentrations in cryoconite were significant with relatively higher Hg accumulation in the southern glaciers (66.0 ± 29.3 ng g-1), monsoon-influenced regions, than those in the northern glaciers (42.5 ± 20.7 ng g-1), westerlies-influenced regions. The altitudinal profile indicates that HgT concentrations in the northern glaciers decrease significantly with altitude, while those in the southern glaciers generally increase toward higher elevations. Unexpectedly high accumulation of methyl-Hg (MeHg) with an average of 1.0 ± 0.4 ng g-1 was also detected in the cryoconite samples, revealing the surface of cryoconite could act as a potential site for Hg methylation in alpine environments. Our preliminary estimate suggests a storage of ?34.3 ± 17.4 and 0.65 ± 0.28 kg of HgT and MeHg from a single year of formation process in the glacier cryoconite. Therefore, glacier cryoconite could play an important role in Hg storage and transformation, which may result in downstream effects on glacier-fed ecosystems under climate warming scenario. © 2019 American Chemical Society.
Anthropogenic and natural drivers of seesaw-like spatial patterns in precipitation mercury over western China
(Elsevier Ltd, 2022) Jie Huang; Shichang Kang; Long Wang; Kaiyun Liu; Kirpa Ram; Mika Sillanpää; Wenjun Tang; Junming Guo; Qianggong Zhang; Ming Ma; Lekhendra Tripathee; Feiyue Wang
Investigation of mercury (Hg) from atmospheric precipitation is important for evaluating its ecological impacts and developing mitigation strategies. Western China, which includes the Tibetan Plateau and the Xinjiang Uyghur Autonomous Region, is one of the most remote region in the world and is understudied in regards to Hg precipitation. Here we report seesaw-like patterns in spatial variations of precipitation Hg in Western China, based on Hg speciation measurements at nine stations over this remote region. The Hg fraction analyzed included total Hg (HgT), particulate-bound Hg (HgP) and methylmercury (MeHg). Spatially, HgT concentrations and percentage of HgP in precipitation were markedly greater in the westerlies domain than those in the monsoon domain, but the higher wet HgT flux, MeHg concentration and percentage of MeHg in precipitation mainly occurred in the monsoon domain. Similar spatial patterns of wet Hg deposition were also obtained from GEOS-Chem modeling. We show that the disparity of anthropogenic and natural drivers between the two domains are mainly responsible for this seesaw-like spatial patterns of precipitation Hg in Western China. Our study may provide a baseline for assessment of environmental Hg pollution in Western China, and subsequently assist in protecting this remote alpine ecosystem. © 2022 Elsevier Ltd
Decoupling Natural and Anthropogenic Mercury and Lead Transport from South Asia to the Himalayas
(American Chemical Society, 2020) Jie Huang; Shichang Kang; Runsheng Yin; Mang Lin; Junming Guo; Kirpa Ram; Chaoliu Li; Chhatra Sharma; Lekhendra Tripathee; Shiwei Sun; Feiyue Wang
Mercury (Hg) and lead (Pb) accumulation since the Industrial Revolution has been generally observed to increase concurrently in lake sedimentary records around the world. Located downwind during the monsoon season from the rapidly developing South Asia, the Himalayas and the Tibetan Plateau are expected to receive direct anthropogenic Hg and Pb loadings, yet the source, pathway, and effects of such transport remain poorly known due to logistic challenges in accessing this region. When studying the sediment record from Lake Gokyo (4750 m above sea level (a.s.l.)) in the Himalayas, we find remarkably different Hg and Pb accumulation trends over the past 260 years. Although Hg accumulation has continued to increase since the Industrial Revolution, Pb accumulation peaked during that time and has been decreasing since then. Stable isotope analysis reveals that the decoupling trends between these two elements are due to different sources and pathways of Hg and Pb in the region. Both δ202Hg and Δ199Hg have been increasing since the Industrial Revolution, suggesting that anthropogenic Hg emissions from South Asia have been continuously increasing and that the Indian monsoon-driven wet deposition of atmospheric Hg is the dominant pathway for Hg accumulation in the sediments. In contrast, analysis of 206Pb/207Pb and 208Pb/207Pb ratios suggests that Pb accumulation in the sediments originates primarily from natural sources and that the decreasing trend of Pb accumulation is most likely due to a weakening input of atmospheric mineral dust by the westerlies. These decoupling trends highlight the ongoing issue of transboundary Hg transport to the Himalayas and the Tibetan Plateau that are source waters for major freshwater systems in Asia and calls for regional and international collaborations on Hg emission controls in South Asia. Copyright © 2020 American Chemical Society.
Desert dust as a significant carrier of atmospheric mercury
(Elsevier Ltd, 2020) Jie Huang; Shichang Kang; Runsheng Yin; Kirpa Ram; Xinchun Liu; Hui Lu; Junming Guo; Siyu Chen; Lekhendra Tripathee
The atmospheric circulation plays a critical role in the global transport and deposition of atmospheric pollutants such as mercury (Hg). Desert dust emissions contribute to nearly 60–95% of the global dust budget and thus, desert dust may facilitate atmospheric Hg transport and deposition to the downwind regions worldwide. The role of desert dust in biogeochemical cycling of Hg, however, has not been well recognized by the Hg research community. In this study, we measured the concentration of particulate bound Hg (HgP) in total suspended particulate (TSP) collected from China's largest desert, Taklimakan Desert, between 2013 and 2017. The results show that HgP concentrations over the Taklimakan Desert atmosphere are remarkably higher than those observed from background sites in China and are even comparable to those measured in most of the Chinese metropolitan cities. Moreover, HgP concentrations in the Taklimakan Desert exhibit a distinct seasonal pattern peaking during dust storm outbreak periods in spring and summer (March to August). A preliminary estimation demonstrates that export of total Hg associated with atmospheric dust from the Taklimakan Desert could be 59.7 ± 60.3 (1SD) Mg yr−1. The unexpectedly high HgP concentrations during duststorms, together with consistent seasonal pattern of Hg revealed from the snow/ice, clearly demonstrate that Asian desert dust could act as a significant carrier of atmospheric Hg to the cryosphere of Western China and even can have further global reach. © 2020 Elsevier Ltd
Light absorption properties of elemental carbon (EC) and water-soluble brown carbon (WS–BrC) in the Kathmandu Valley, Nepal: A 5-year study
(Elsevier Ltd, 2020) Pengfei Chen; Shichang Kang; Lekhendra Tripathee; Kirpa Ram; Maheswar Rupakheti; Arnico K. Panday; Qianggong Zhang; Junming Guo; Xiaoxiang Wang; Tao Pu; Chaoliu Li
This study presents a comprehensive analysis of organic carbon (OC), elemental carbon (EC), and particularly the light absorption characteristics of EC and water-soluble brown carbon (WS–BrC) in total suspended particles in the Kathmandu Valley from April 2013 to January 2018. The mean OC, EC, and water-soluble organic carbon (WSOC) concentrations were 34.8 ± 27.1, 9.9 ± 5.8, and 17.4 ± 12.5 μg m−3, respectively. A clear seasonal variation was observed for all carbonaceous components with higher concentrations occurring during colder months and lower concentrations in the monsoon season. The relatively low OC/EC ratio (3.6 ± 2.0) indicates fossil fuel combustion as the primary source of carbonaceous components. The optical attenuation (ATN) at 632 nm was significantly connected with EC loading (ECS) below 15 μg cm−2 but ceased as ECS increased, reflecting the increased influence of the shadowing effect. The derived average mass absorption cross-section of EC (MACEC) (7.0 ± 4.2 m2 g−1) is comparable to that of freshly emitted EC particles, further attesting that EC was mainly produced from local sources with minimal atmospheric aging processes. Relatively intensive coating with organic aerosols and/or salts (e.g., sulfate, nitrate) was probably the reason for the slightly higher MACEC during the monsoon season, whereas increased biomass burning was a major factor leading to lower MACEC in other seasons. The average MACWS-BrC at 365 nm was 1.4 ± 0.3 m2 g−1 with minimal seasonal variations. In contrast to MACEC, biomass burning was the main reason for a higher MACWS-BrC in the non-monsoon season. The relative light absorption contribution of WS-BrC to EC was 9.9% over the 300–700 nm wavelength range, with a slightly higher ratio (13.6%) in the pre-monsoon season. Therefore, both EC and WS-BrC should be considered in the study of optical properties and radiative forcing of carbonaceous aerosols in this region. © 2020 Elsevier Ltd
Microbial mercury methylation in the cryosphere: Progress and prospects
(Elsevier B.V., 2019) Prakriti Sharma Ghimire; Lekhendra Tripathee; Qianggong Zhang; Junming Guo; Kirpa Ram; Jie Huang; Chhatra Mani Sharma; Shichang Kang
Mercury (Hg) is one of the most toxic heavy metals, and its cycle is mainly controlled by oxidation–reduction reactions carried out by photochemical or microbial process under suitable conditions. The deposition and accumulation of methylmercury (MeHg) in various ecosystems, including the cryospheric components such as snow, meltwater, glaciers, and ice sheet, and subsequently in the food chain pose serious health concerns for living beings. Unlike the abundance of knowledge about the processes of MeHg production over land and oceans, little is known about the sources and production/degradation rate of MeHg in cryosphere systems. In addition, processes controlling the concentration of Hg and MeHg in the cryosphere remains poorly understood, and filling this scientific gap has been challenging. Therefore, it is essential to study and review the deposition and accumulation by biological, physical, and chemical mechanisms involved in Hg methylation in the cryosphere. This review attempts to address knowledge gaps in understanding processes, especially biotic and abiotic, applicable for Hg methylation in the cryosphere. First, we focus on the variability in Hg concentration and mechanisms of Hg methylation, including physical, chemical, microbial, and biological processes, and transportation in the cryosphere. Then, we elaborate on the mechanism of redox reactions and biotic and abiotic factors controlling Hg methylation and biogeochemistry of Hg in the cryosphere. We also present possible mechanisms of Hg methylation with an emphasis on microbial transformation and molecular function to understand variability in Hg concentration in the cryosphere. Recent advancements in the genetic and physicochemical mechanisms of Hg methylation are also presented. Finally, we summarize and propose a method to study the unsolved issues of Hg methylation in the cryosphere. © 2019 Elsevier B.V.
Nitrogenous and carbonaceous aerosols in PM2.5 and TSP during pre-monsoon: Characteristics and sources in the highly polluted mountain valley
(Chinese Academy of Sciences, 2022) Hemraj Bhattarai; Lekhendra Tripathee; Shichang Kang; Pengfei Chen; Chhatra Mani Sharma; Kirpa Ram; Junming Guo; Maheswar Rupakheti
This study reports for the first time a comprehensive analysis of nitrogenous and carbonaceous aerosols in simultaneously collected PM2.5 and TSP during pre-monsoon (March–May 2018) from a highly polluted urban Kathmandu Valley (KV) of the Himalayan foothills. The mean mass concentration of PM2.5 (129.8 µg/m3) was only ~25% of TSP mass (558.7 µg/ m3) indicating the dominance of coarser mode aerosols. However, the mean concentration as well as fractional contributions of water-soluble total nitrogen (WSTN) and carbonaceous species reveal their predominance in find-mode aerosols. The mean mass concentration of WSTN was 17.43±4.70 µg/m3 (14%) in PM2.5 and 24.64±8.07 µg/m3 (5%) in TSP. Moreover, the fractional contribution of total carbonaceous aerosols (TCA) is much higher in PM2.5 (~34%) than that in TSP (~20%). The relatively low OC/EC ratio in PM2.5 (3.03 ± 1.47) and TSP (4.64 ± 1.73) suggests fossil fuel combustion as the major sources of carbonaceous aerosols with contributions from secondary organic aerosols. Five-day air mass back trajectories simulated with the HYSPLIT model, together with MODIS fire counts indicate the influence of local emissions as well as transported pollutants from the Indo-Gangetic Plain region to the south of the Himalayan foothills. Principal component analysis (PCA) also suggests a mixed contribution from other local anthropogenic, biomass burning, and crustal sources. Our results highlight that it is necessary to control local emissions as well as regional transport while designing mitigation measures to reduce the KV's air pollution. © 2021
Northward Extent of Atmospheric Mercury Transboundary Transport to the Himalayas and Tibetan Plateau Region
(John Wiley and Sons Inc, 2023) Jie Huang; Shichang Kang; Xinbin Feng; Wenjun Tang; Kirpa Ram; Junming Guo; Qianggong Zhang; Chhatra Mani Sharma; Chaoliu Li; Lekhendra Tripathee; Feiyue Wang
Indian monsoon circulation is the primary driver of the long-range transboundary mercury (Hg) pollution from South Asia to the Himalayas and Tibet Plateau region, yet the northward extent of this transport remains unknown. In this study, a strong δ202Hg signature overlapping was found between Lake Gokyo and Indian anthropogenic sources, which is an indicative of the Hg source regions from South Asia. Most of the sediment samples were characterized with relatively large positive Δ199Hg values (mean = 0.07‰–0.44‰) and small positive Δ200Hg values (mean = 0.03‰–0.08‰). Notably, the Δ199Hg values in the lake sediments progressively increased from southwest to northeast. Moreover, the Δ199Hg values peaked at Lake Tanglha (mean = 0.44‰ ± 0.04‰) before decreased at Lake Qinghai that is under the influence of the westerlies. Our results suggest that transboundary atmospheric transport could transport Hg from South Asia northwards to at least the Tanglha Mountains in the northern Himalaya-Tibet. © 2023. The Authors.
Study on mercury in PM10 at an urban site in the central indo-gangetic plain: Seasonal variability and influencing factors
(AAGR Aerosol and Air Quality Research, 2020) Junming Guo; Kirpa Ram; Lekhendra Tripathee; Shichang Kang; Jie Huang; Pengfei Chen; Prakriti Sharma Ghimire
Mercury (Hg) is among the most toxic metals possessing a major threat to human health and aquatic ecosystems over the globe. However, measurement of Hg concentrations and seasonal variability remain poorly understood over the IndoGangetic Plain (IGP) in northern India. In this study, we present one-year data of particulate-bound mercury (HgP) in aerosol samples (PM10) collected from Kanpur to understand seasonal variability and factors influencing concentration, as well as dry deposition flux. The HgP concentration exhibit a large temporal variability and ranged between 100 (on 14 June 2007) to 4340 pg m–3 (on 4 March 2007) with an annual average concentration of HgP is 776 ± 846 pg m–3. The HgP concentrations and HgP/PM10 ratios showed a marked seasonality with the highest in winter (Dec-Feb) followed by post-monsoon (Oct– Nov) and summer (April–June) seasons. HgP and HgP/PM10 were positively correlated (r2 = 0.77, p < 0.05, N = 58) during the sampling period and the estimated dry deposition flux of HgP was 104.7 µg m–2 y–1. Although this study provides a comprehensive data set on HgP in an urban atmosphere of the IGP revealing high levels of HgP, measurement of gaseous Hg is needed for estimation of the total Hg budget. Therefore, future studies should focus on identification of different sources as well as emission characteristics of all forms of Hg (organic and inorganic forms) for better mitigation strategy to prevent health risks associated with toxic Hg in the region. © The Author(s).