Fangping Yan

Characteristics and sources of polycyclic aromatic hydrocarbons in atmospheric aerosols in the Kathmandu Valley, Nepal

The Kathmandu Valley in the foothills of the Himalayas, where the capital city of Nepal is located, has one of the most serious air pollution problems in the world. In this study, total suspended particle (TSP) samples collected over a year (April 2013-March 2014) in the Kathmandu Valley were analyzed for determining the concentrations of 15 priority particle-bound polycyclic aromatic hydrocarbons (PAHs). The TSP and PAH concentrations were extremely high, with annual average concentration being 199±124μg/m(3) and 155±130ng/m(3), respectively, which are comparable to those observed in Asian cities such as Beijing and Delhi. The TSP and PAH concentrations varied considerably, with the seasonal average concentration being maximal during the post-monsoon season followed by, in descending order, the winter, pre-monsoon, and monsoon seasons. In the winter and pre-monsoon seasons, ambient TSP and PAH concentrations increased because of emissions from brick kilns and the use of numerous small generators. Moreover, in the pre-monsoon season, forest fires in the surrounding regions influenced the TSP and PAH concentrations in the valley. PAHs with 4 to 6 rings constituted a predominant proportion (92.3-93.3%) of the total PAHs throughout the year. Evaluation of diagnostic molecular ratios indicated that the atmospheric PAHs in the Kathmandu Valley originated mainly from diesel and biomass combustion. The toxic equivalent quantity (TEQ) of particle phase PAHs ranged between 2.74 and 81.5ngTEQ/m(3), which is considerably higher than those reported in other South Asian cities, and 2-80 times higher than the World Health Organization guideline (1ngTEQ/m(3)). This suggests that ambient PAH levels in the Kathmandu Valley pose a serious health risk to its approximately 3.5 million residents.

Synthesis and characterization of ZnO nanoflowers grown on AIN films by solution deposition

ZnO nanoflowers are synthesized on AlN films by solution method. The synthesized nanoflowers are composed of nanorods, which are pyramidal and grow from a central point, thus forming structures that are flower-shaped as a whole. The nanoflowers have two typical morphologies: plate-like and bush-like. The XRD spectrum corresponds to the side planes of the ZnO nanorods made up of the nanoflowers. The micro-Raman spectrum of the ZnO nanoflowers exhibits the E2 (high) mode and the second order multiple-phonon mode. The photoluminescence spectrum of the ZnO nanoflowers exhibits ultraviolet emission centred at 375 nm and a broad green emission centred at 526 nm.

Deposition and light absorption characteristics of precipitation dissolved organic carbon (DOC) at three remote stations in the Himalayas and Tibetan Plateau, China

The concentrations, depositions and optical properties of precipitation DOC at three remote stations (Nam Co, Lulang and Everest) were investigated in the Himalayas and Tibetan Plateau (HTP). The results showed that their volume-weighted mean DOC concentrations were 1.05±1.01mgCL-1, 0.83±0.85mgCL-1 and 0.86±0.91mgCL-1, respectively, close to those of other remote areas in the world and lower than those of typical polluted urban cities. Combined with precipitation amounts, the DOC depositions at these three stations were calculated to be 0.34±0.32gCm-2yr-1, 0.84±0.86gCm-2yr-1 and 0.16±0.17gCm-2yr-1, respectively. The annual DOC deposition in the HTP was approximately 0.94±0.87TgC, the highest and lowest values appeared in the southeastern and northwestern plateau, respectively. The sources of DOC in the precipitation at these three stations were remarkably different, indicating large spatial heterogeneity in the sources of precipitation DOC over the HTP. Nam Co presented combustion sources from South Asia and local residents, Lulang showed biomass combustion source from South Asia, and Everest was mainly influenced by local mineral dust. The values of the MACDOC at 365nm were 0.48±0.47m2g-1, 0.25±0.15m2g-1, and 0.64±0.49m2g-1, respectively, for the precipitation at the three stations. All of these values were significantly lower than those of corresponding near-surface aerosol samples because precipitation DOC contains more secondary organic aerosol with low light absorption abilities. Additionally, this phenomenon was also observed in seriously polluted urban areas, implying it is universal in the atmosphere. Because precipitation DOC contains information for both particle-bound and gaseous components from the near surface up to the altitude of clouds where precipitation occurs, the MACDOC of precipitation is more representative than that of near-surface aerosols for a given region.

Aged dissolved organic carbon exported from rivers of the Tibetan Plateau

The role played by river networks in regional and global carbon cycle is receiving increasing attention. Despite the potential of radiocarbon measurements (14C) to elucidate sources and cycling of different riverine carbon pools, there remain large regions such as the climate-sensitive Tibetan Plateau for which no data are available. Here we provide new 14C data on dissolved organic carbon (DOC) from three large Asian rivers (the Yellow, Yangtze and Yarlung Tsangpo Rivers) running on the Tibetan Plateau and present the carbon transportation pattern in rivers of the plateau versus other river system in the world. Despite higher discharge rates during the high flow season, the DOC yield of Tibetan Plateau rivers (0.41 gC m-2 yr-1) was lower than most other rivers due to lower concentrations. Radiocarbon ages of the DOC were older/more depleted (511±294 years before present, yr BP) in the Tibetan rivers than those in Arctic and tropical rivers. A positive correlation between radiocarbon age and permafrost watershed coverage was observed, indicating that 14C-deplted/old carbon is exported from permafrost regions of the Tibetan Plateau during periods of high flow. This is in sharp contrast to permafrost regions of the Arctic which export 14C-enriched carbon during high discharge periods.

Dissolved organic carbon fractionation accelerates glacier-melting: A case study in the northern Tibetan Plateau

In glacierized regions, melting process has a significant effect on concentrations and light absorption characteristics of dissolved organic carbon (DOC), potentially resulting in variations of its radiative forcing, which is not yet relevant research at glacier region of the Tibetan Plateau (TP). In this study, DOC fractionation and its radiative forcing change during the melting process were investigated at Laohugou glacier No. 12 (LHG glacier) in western Qilian Mts., northern TP. DOC concentrations in fresh snow, snowpit and surface ice samples were 0.38 ± 0.06, 0.22 ± 0.11 and 0.60 ± 0.21 mg L-1, respectively. Their mass absorption cross-section at 365 nm (MAC365) were 0.65 ± 0.16, 4.71 ± 3.68 and 1.44 ± 0.52 m2 g-1, respectively. The MAC365 values of snowpit samples showed a significant negative correlation with DOC concentrations, indicating DOC with high MAC365 values were likely to be kept in snow during the melting process. Topsoil samples of LHG glacierized region likely contributed a lot to snowpit DOC with high MAC365 values due to their similar absorption spectra. Spatially, the DOC concentration of surface ice samples increased from terminus to the upper part of the glacier. Correspondingly, the MAC365 value showed decreased trend. In the freezing experiment on surface ice and topsoil samples, small part of DOC with high MAC365 value was also likely to enter first frozen solid phase. In addition, the radiative forcing caused by snowpit and surface ice DOC increased around 7.64 ± 2.93 and 4.95 ± 1.19 times relative to fresh snow DOC, indicating the snow/ice melting caused by increased light-absorbing DOC needs to be considered in the future research.

Greenhouse gases emissions in rivers of the Tibetan Plateau

Greenhouse gases (GHGs) emissions from streams are important to regional biogeochemical budgets. This study is one of the first to incorporate stream GHGs (CO2, CH4 and N2O) concentrations and emissions in rivers of the Tibetan Plateau. With one-time sampling from 32 sites in rivers of the plateau, we found that most of the rivers were supersaturated with CO2, CH4 and N2O during the study period. Medians of partial pressures of CO2 (pCO2), pCH4 and pN2O were presented 864 μatm, 6.3 μatm, and 0.25 μatm respectively. Based on a scaling model of the flux of gas, the calculated fluxes of CO2, CH4 and N2O (3,452 mg-C m2 d−1, 26.7 mg-C m2 d−1 and 0.18 mg-N m2 d−1, respectively) in rivers of the Tibetan Plateau were found comparable with most other rivers in the world; and it was revealed that the evasion rates of CO2 and CH4 in tributaries of the rivers of the plateau were higher than those in the mainstream despite its high altitude. Furthermore, concentrations of GHGs in the studied rivers were related to dissolved carbon and nitrogen, indicating that riverine dissolved components could be used to scale GHGs envision in rivers of the Tibetan Plateau.

Correction: Aged dissolved organic carbon exported from rivers of the Tibetan Plateau

[This corrects the article DOI: 10.1371/journal.pone.0178166.].

Heavy near-surface PM2.5 pollution in Lhasa, China during a relatively static winter period

Fairly high near-surface PM2.5 concentrations were found during relatively static winter conditions within Lhasa - a Tibetan Plateau city normally considered to have a clean atmosphere. The average daily PM2.5 concentration reached 118 ± 60 μg m-3 during the study period, was approximately 3.4 times the United States Environmental Protection Agency 24-h standard. PM2.5 concentration of Lhasa increased from 20:00 until 23:00, which was probably caused by space heating, waste incineration activities and decreased boundary layer at night. Furthermore, we found traditional religious butter lamp lighting of local Tibetan residents during festivals could cause PM2.5 concentration to reach an alarmingly high level, 240 ± 30 μg m-3. Therefore, to protect the atmosphere of Lhasa, the government may wish to conduct more complete monitoring and find ways to encourage clean heating and cooking fuels, enforce the supervision on illegal emission activities such as waste incineration, and guide residents to transfer to more environmentally friendly activities during festivals.

Fossil Fuel Combustion Emission From South Asia Influences Precipitation Dissolved Organic Carbon Reaching the Remote Tibetan Plateau: Isotopic and Molecular Evidence

The dissolved organic carbon in precipitation (water-soluble organic carbon, WSOC) can provide a carbon subsidy to receiving ecosystems. The concentrations, isotopic signatures (δC/ΔC), and molecular signatures (transform ion cyclotron mass spectrometry) of WSOC being delivered to Nam Co—a remote site on the inland Tibetan Plateau (TP)—were compared to those of WSOC in the snowpack, and in wet deposition from urban cities fringing the TP. The averageWSOC concentration at Nam Co (1.0 ± 0.9 mg C L ) was lower than for the large cities (1.6 to 2.3 mg C L ) but higher than in the snowpack samples (0.26 ± 0.09 mg C L ). Based upon radiocarbon data, it is estimated that 15 ± 6% of Nam Co WSOC was fossil derived, increasing to 20 ± 8% for snowpack WSOC, 29 ± 4% for Lhasa WSOC, and 34 ± 8% for the three cities. Transform ion cyclotron mass spectrometry results revealed that the abundance of dissolved black carbon and sulfur-containing molecules of WSOC increased in the order Nam Co < snow pack < urban. The enrichment in C and depletion in dissolved black carbon and sulfurous organic molecules of Nam CoWSOC was suggestive of low, but still detectable inputs of fossil-derived organics to WSOC on the remote TP. Backward air mass trajectories for the precipitation events at Nam Co suggested that the fossil fuel contributions to WSOC in Nam Co region originated mainly from South Asia. This study provides novel radiocarbon age, chemistry, and source evidence that anthropogenic WSOC is delivered to the remote TP, one of the most remote regions on Earth.

Lakes on the Tibetan Plateau as Conduits of Greenhouse Gases to the Atmosphere

Lakes play an important role in the global carbon cycle, and littoral zones of lakes are potential hotspots of greenhouse gas production. In this study, we measured the partial pressures of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in the littoral zones of 17 lakes on the Tibetan Plateau. The littoral zones of lakes on the Tibetan Plateau were supersaturated and acted as sources of CO2, CH4, and N2O to the atmosphere. The average partial pressures of CO2, CH4, and N2O in the surface lake water were 664.8 ± 182.5, 139.8 ± 335.6, and 0.3 ± 0.1 μatm, respectively. The average diffusive fluxes (and uncentainty intervals) of these three gases were 73.7 (0.9–295.3) mmol · m 2 · day , 5.2 (0.0008–45.9) mmol · m 2 · day , and 6.5 (0.07–20.9) μmol · m 2 · day , respectively. The diffusive fluxes of CO2 in lakes were significantly correlated with dissolved organic carbon, dissolved organic nitrogen, salinity, and water temperature. The diffusive fluxes of N2O were significantly correlated with lake water depth. However, no relationships were found between environmental factors and the CH4 diffusive flux at the scale of this study. CO2 exchange with the atmosphere from saline lakes was found to be higher than from freshwater lakes with equivalent CO2 concentrations by a factor of 2.5 due to chemical enhancement of the gas transfer velocity. Therefore, further study with enhanced spatiotemporal resolution and breadth is needed to better understand the important role played by lakes on the Tibetan Plateau in both regional and global carbon cycles.