Baiqing Xu

Black soot and the survival of Tibetan glaciers

We find evidence that black soot aerosols deposited on Tibetan glaciers have been a significant contributing factor to observed rapid glacier retreat. Reduced black soot emissions, in addition to reduced greenhouse gases, may be required to avoid demise of Himalayan glaciers and retain the benefits of glaciers for seasonal fresh water supplies.

Elemental and organic carbon measurements with a two-step heating-gas chromatography system in snow samples from the Tibetan Plateau

Abstract In this study, an optimized two-step heating-gas chromatography system is used to measure elemental carbon (EC) and organic carbon (OC) content in snow and ice, with the ability to quantify the elemental and organic carbon species in a snow or ice sample of 60−80 g. In this system, OC and EC are transformed into CO2 in a stream of oxygen at 340°C and 650°C, respectively. The resulting CO2 is accumulated in two molecular-sieve traps, and then put into a gas chromatograph equipped with a flame ionization detector by heating the traps to 200°C in a helium stream. Background contamination (mainly caused by impurities in the oxygen stream) and accuracy are dominated by the variability of the blank loads on the pre-cleaned filters, which are 0.50 ± 0.04 (1σ) μgC for OC, and 0.38 ± 0.04 (1σ) μgC for EC. The system is suitable for snow and ice sample measurements, with the same precision as shown for the blank tests. EC and OC concentrations have been measured in snow samples collected from different glaciers on the Tibetan Plateau. The results allow quantification for the first time of the different carbonaceous particle contents on the Tibetan Plateau and other regions. The concentrations of EC and OC particles in snow show a clearly decreasing trend from east to west and from north to south on the plateau, excluding the Pamirs region. The highest mean EC content, 79.2 ngg-1, was found in the northeast region, and the lowest, 4.3 ngg-1, was found in the western Himalaya. We note that even slight surface melting results in fresh snow getting dirtier, especially in regions with higher pollution such as seen on a glacier in the Qilian Shan. Here, the EC and OC concentrations in the fresh snow average 6.6 and 87.5 ngg-1, but after 2 days of surface melting they increased to 52.6 and 195.5 ngg-1. This suggests that surface snow melting can reduce snow albedo due to the accumulation of carbonaceous particles.

Accumulation of Perfluoroalkyl Compounds in Tibetan Mountain Snow: Temporal Patterns from 1980 to 2010

The use of snow and ice cores as recorders of environmental contamination is particularly relevant for per- and polyfluoroalky substances (PFASs) given their production history, differing source regions and varied mechanisms driving their global distribution. In a unique study perfluoroalkyl acids (PFAAs) were analyzed in dated snow-cores obtained from high mountain glaciers on the Tibetan Plateau (TP). One snow core was obtained from the Mt Muztagata glacier (accumulation period of 1980-1999), located in western Tibet and a second core from Mt. Zuoqiupo (accumulation period: 1996-2007) located in southeastern Tibet, with fresh surface snow collected near Lake Namco in 2010 (southern Tibet). The higher concentrations of ∑PFAAs were observed in the older Mt Muztagata core and dominated by perfluorooctanesulfonic acid (PFOS) (61.4-346 pg/L) and perfluorooctanoic acid (PFOA) (40.8-243 pg/L), whereas in the Mt Zuoqiupu core the concentrations were lower (e.g., PFOA: 37.8-183 pg/L) with PFOS below detection limits. These differences in PFAA concentrations and composition profile likely reflect the upwind sources affecting the respective sites (e.g., European/central Asian sources for Mt Muztagata and India sources for Mt Zuoqiupu). Perfluorobutanoic acid (PFBA) dominated the recent surface snowpack of Lake Namco which is mainly associated with India sources where the shorter chain volatile PFASs precursors predominate. The use of snow cores in different parts of Tibet provides useful recorders to examine the influence of different PFASs source regions and reflect changing PFAS production/use in the Northern Hemisphere.

The Influence of Dust on Quantitative Measurements of Black Carbon in Ice and Snow when Using a Thermal Optical Method

Accurate measurements of black carbon concentrations in snow and ice are essential to quantify its impact on glacial melting and sequential climate forcing via snow albedo. However, snow and ice contain dust that may severely bias the precision of the elemental carbon (EC) and organic carbon (OC) measurements of filters with a thermal/optical method. To evaluate the effects of dust on black carbon analysis and to optimize filtration methods, meltwater from ice core and surface snow samples with variable dust content were filtered with different methods, including filtration of the entire material (including settling) and supernatant liquid, mechanical stirring and sonication, as well as utilization of single and double quartz filters. In this research, it is shown that dust can induce an extra decrease in optical reflectance during the 250°C heating stage in the thermal/optical method and an improper OC and EC split. To address this problem, a correction procedure was suggested and used to revise the OC and EC results. The OC, EC, and TC concentration variations from different filtration methods along the ice core depth and along surface snow elevation were illustrated. These results indicate that black carbon and dust generally mix as agglomerates. The agglomerate structure will contribute to the underestimation of EC and OC in the measurement. However, carbonaceous matter can be efficiently detached from dust particles by ultrasonic agitation of the meltwater samples, which significantly improves carbon volatilization during the thermal/optical analysis. Copyright 2012 American Association for Aerosol Research

Geochemical analyses of a Himalayan snowpit profile: implications for atmospheric pollution and climate

Abstract Organic compounds, extracted from snow and ice from the Dasuopu glacier, on the Qinghai-Tibetan Plateau in Southwest China at an altitude of 7000 m above sea level (asl), were identified through pre-enrichment, solvent extraction and subsequent GC–MS analysis. The average concentration of the extractable organic matter reached 45.4 μg/l. C15–C33 n-alkanes, C6–C18 n-alkanoic acids, C24–C31 n-alkan-2-ones and esters were derived from subtropical higher plants, as well as marine algae and bacteria. Organic compounds, indicative of petroleum residues such as automobile and diesel exhaust were also unexpectedly identified in the glacial snow. These included n-alkanes, alkylcyclohexanes, pristane, phytane, extended C19–C29 tricyclic terpanes, a C24 tetracyclic terpane, C27–C35 αβ hopanes, and C27–C29 steranes. Their presence indicates that the remote mountainous region and, to some extent, the middle-upper troposphere are polluted by human activities. Concentrations of some organic compounds, and total extractable organic matter, display a weak seasonal variation, postulated to be related to the location of middle-upper troposphere. The C17 n-alkane abundance and some molecular ratios exhibit a stronger seasonal variation, which may signify strong climatic change.

Isotopic Signal of Earlier Summer Monsoon Onset in the Bay of Bengal

AbstractThe onset of the Asian summer monsoon is noticeably controversial, spatially and temporally. The stable oxygen isotope δ18O in precipitation has long been used to trace water vapor source, particularly to capture the summer monsoon precipitation signal. The abrupt decrease of precipitation δ18O in the Asian summer monsoon region closely corresponds to the summer monsoon onset. Two stations have therefore been set up at Guangzhou and Lulang in the East Asian summer monsoon domain to clarify the summer monsoon onset dates. Event-based precipitation δ18O during 2007/08 is much lower at Lulang than at Guangzhou and is attributable mainly to the altitude effect offset by different isotopic compositions in marine moisture sources. The earlier appearance of low δ18Owt at Lulang than at Guangzhou confirms the earlier summer monsoon onset in the Bay of Bengal. Isotopically identified summer monsoon evolutions from precipitation δ18O at both stations are verifiable with NCEP–NCAR reanalysis data, indicating...

Selected Organochlorine Pesticides and Polychlorinated Biphenyls in Urban Atmosphere of Pakistan: Concentration, Spatial Variation and Sources

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 countrys 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.

Dust concentration and flux in ice cores from the Tibetan Plateau over the past few decades

In this paper, we provide the concentrations and fluxes of dust particles (1–30μm diameter), quantitatively calculated, in several shallow ice cores recovered from the northern (Dunde), western (Muztagata), central (Tanggula) and southern (Dasuopu and Everest) parts of the Tibetan Plateau over the past few decades. Dust concentrations from the northern and western Tibetan Plateau are 2–10 times higher, and from the central Tibetan Plateau is five times higher, respectively, than in the southern part. Dust flux in ice cores is highly dependent on mass concentration, but does not necessarily correlate with accumulation. Dust flux in Dunde (about 798μg cm−2 a−1) is 10 times higher, and that in Muztagata (342μg cm−2 a−1) is four times higher, respectively, than the dust flux in the central Himalayas (77–103μg cm−2 a−1). The quantitative assessment of dust flux in ice cores accords with the aerosol optical depth, and both suggest that the general dust transport route is from northwest to southeast over the Tibetan Plateau. Our results reveal the basic properties of upper level tropospheric dust over the Tibetan Plateau, which is useful for the study of the climatic effects of this dust.

Volume-size distribution of microparticles in ice cores from the Tibetan Plateau

The volume distribution of atmospheric dust particles (microparticles) of 1-30 mm diameter in Muztagata, Dunde, Dasuopu and Everest ice cores from the Tibetan Plateau was measured and fitted as a log-normal function in order to characterize their basic size properties. Our results reveal that whether the volume distribution fits the log-normal function or not largely depends on the dust concentration and the specific dust-storm event but is independent of physiographical location and season. Our results show only high-concentration samples obey the log-normal distribution in volume, with mode sizes ranging from 3 to 16 mm. The log-normal distribution was largely attributed to the mid-sized particles between 3 and 15 mm, which contribute most (>70%) of the total volume. The volume size distribution characteristics for mineral dust particles from ice cores reveal that the coarse particles might be common in the upper-level troposphere over the Tibetan Plateau. These dust size features are useful to advance our understanding of dust effects on climate, and provide clues to better characterize atmospheric dynamics over the Tibetan Plateau that will help to improve the current models.

Massilia yuzhufengensis sp nov, isolated from an ice core

A gram-negative, rod-shaped, aerobic, motile bacterium, strain Y1243-1(T), was isolated from an ice core drilled from Yuzhufeng Glacier, Tibetan Plateau, China. Cells had polar flagella. The novel strain shared 94.7-97.6 % 16S rRNA gene sequence similarity with the type strains of species of the genus Massilia. The novel isolate is thus classified in the genus Massilia. The major fatty acids of strain Y1243-1(T) were summed feature 3 (C16 : 1ω7c and/or iso-C15 : 0 2-OH) (43.98 %), C16 : 0 (27.86 %), C10 : 0 3-OH (7.10 %), C18 : 0 (6.95 %) and C18 : 1ω7c (5.01 %). The predominant isoprenoid quinone was Q-8. The DNA G+C content of strain Y1243-1(T) was 65.7 mol% (Tm). The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol. A number of phenotypic characteristics distinguished the novel isolate from the type strains of recognized Massilia species. Furthermore, in DNA-DNA hybridization tests, strain Y1243-1(T) shared 45 % relatedness with its closest phylogenetic relative, Massilia consociata CCUG 58010(T). From the genotypic and phenotypic data, it is evident that strain Y1243-1(T) represents a novel species of the genus Massilia, for which the name Massilia yuzhufengensis sp. nov. is proposed. The type strain is Y1243-1(T) ( = KACC 16569(T) = CGMCC 1.12041(T)).