Cuicui Mu

Characteristics and personal exposures of carbonyl compounds in the subway stations and in-subway trains of Shanghai, China

Carbonyl compounds including their concentrations, potential sources, diurnal variations and personal exposure were investigated in six subway stations and in-subway trains in Shanghai in June 2008. The carbonyls were collected onto solid sorbent (Tenax TA) coated with pentafluorophenyl hydrazine (PFPH), followed by solvent extraction and gas chromatography (GC)/mass spectrometry (MS) analysis of the PFPH derivatives. The total carbonyl concentrations of in-subway train were about 1.4-2.5 times lower than in-subway stations. A significant correlation (R>0.5, p<0.01) between the concentrations of the low molecular-weight carbonyl compounds (<C(5)) and ozone was found in the subway stations. The diurnal variations in both the subway station and in-subway train showed that the concentrations of most carbonyls were much higher in the morning rush hour than in other sampling periods. Additionally, pronounced diurnal variations of acetaldehyde concentration before and after the evening peak hour in the subway train suggested that passengers contributed to high acetaldehyde levels. The personal exposure showed that the underground subway stations were important microenvironment for exposure to formaldehyde and acetaldehyde.

Carbon and Nitrogen Properties of Permafrost over the Eboling Mountain in the Upper Reach of Heihe River Basin, Northwestern China

Abstract The sensitivity of soil carbon and nitrogen to warming is a major uncertainty in projections of climate. However, previous studies about soil organic carbon (SOC) stocks and potential emission predominantly concentrated on the shallow soil layer in high latitude ecosystems. In this study, we analyzed the SOC, total nitrogen (TN) and soil inorganic carbon (SIC) stocks, C/N ratios, and stable carbon isotope (&dgr;13C) in the active layer and permafrost layer on the Eboling Mountain in the upper reach of Heihe River basin, northwestern China. Our results showed that the average stocks of SOC, TN, and SIC in permafrost layer above soil parent materials (71.7 kg m-2, 8.0 kg m-2, 34.7 kg m-2) were much higher than those in the active layer (44.3 kg m-2, 5.3 kg m-2, 12.2 kg m-2). The &dgr;13C pattern in the soil profiles indicated that historical drainage conditions and pedogenesis were important factors in determining soil organic matter (SOM) stocks in this permafrost region. The &dgr;13C and C/N ratios of the transient layer and some layers of permafrost implied that the degradation of SOM was different. These results highlight that carbon and nitrogen in permafrost regions with Alpine Kobresia meadow could make significant contribution to Chinas terrestrial carbon cycle.

Carbon loss and chemical changes from permafrost collapse in the northern Tibetan Plateau

Permafrost collapse, known as thermokarst, can alter soil properties and carbon emissions. However, little is known regarding the effects of permafrost collapse in upland landscapes on the biogeochemical processes that affect carbon balance. In this study, we measured soil carbon and physiochemical properties at a large thermokarst feature on a hillslope in the northeastern Tibetan Plateau. We categorized surfaces into three different microrelief patches based on type and extent of collapse (control, drape, and exposed areas). Permafrost collapse resulted in substantial decreases of surface soil carbon and nitrogen stocks, with losses of 29.64.2% and 28.93.1% for carbon and nitrogen, respectively, in the 0-10cm soil layer. Laboratory incubation experiments indicated that control soil had significantly higher CO2 production rates than that of drapes. The results from Fourier transform infrared spectroscopy analysis showed that exposed soils accumulated some organic matter due to their low position within the feature, which was accompanied by substantial changes in the chemical structure and characteristics of the soil carbon. Exposed soils had higher hydrocarbon and lignin/phenol backbone content than in control and drape soils in the 0-10cm layer. This study demonstrates that permafrost collapse can cause abundant carbon and nitrogen loss, potentially from mineralization, leaching, photodegradation, and lateral displacement. These results demonstrate that permafrost collapse redistributes the soil organic matter, changes its chemical characteristics, and leads to losses of organic carbon due to the greenhouse gas emission.

Permafrost Stores a Globally Significant Amount of Mercury

Changing climate in northern regions is causing permafrost to thaw with major implications for the global mercury (Hg) cycle. We estimated Hg in permafrost regions based on in situ measurements of ...

Permafrost collapse shifts alpine tundra to a carbon source but reduces N2O and CH4 release on the northern Qinghai‐Tibetan Plateau

Important unknowns remain about how abrupt permafrost collapse (thermokarst) affects carbon balance and greenhouse gas flux, limiting our ability to predict the magnitude and timing of the permafrost carbon feedback. We measured monthly, growing-season fluxes of CO2, CH4, and N2O at a large thermokarst feature in alpine tundra on the northern Qinghai-Tibetan Plateau (QTP). Thermokarst formation disrupted plant growth and soil hydrology, shifting the ecosystem from a growing-season carbon sink to a weak source, but decreasing feature-level CH4 and N2O flux. Temperature-corrected ecosystem respiration from decomposing permafrost soil was 2.7 to 9.5-fold higher than in similar features from Arctic and Boreal regions, suggesting that warmer and dryer conditions on the northern QTP could accelerate carbon decomposition following permafrost collapse. N2O flux was similar to the highest values reported for Arctic ecosystems, and was 60% higher from exposed mineral soil on the feature floor, confirming Arctic observations of coupled nitrification and denitrification in collapsed soils. Q10 values for respiration were typically over 4, suggesting high temperature sensitivity of thawed carbon. Taken together, these results suggest that QTP permafrost carbon in alpine tundra is highly vulnerable to mineralization following thaw, and that N2O production could be an important non-carbon permafrost climate feedback.

Thaw Depth Determines Dissolved Organic Carbon Concentration and Biodegradability on the Northern Qinghai‐Tibetan Plateau

The response of dissolved organic carbon (DOC) flux to permafrost degradation is one of the major sources of uncertainty in predicting the permafrost carbon feedback. We investigated DOC export and properties over two complete flow seasons in a catchment on the northern Qinghai-Tibetan Plateau. DOC concentration and biodegradability decreased systematically as thaw depth increased through the season, attributable to changing carbon sources and degree of microbial processing. Increasing DOC aromaticity and δ13C-DOC indicated shifts towards more recalcitrant carbon sources and greater residence time in soils prior to reaching the stream network. These strong and consistent seasonal trends suggest that gradual active layer deepening may decrease DOC export and biodegradability from permafrost catchments. Because these patterns are opposite observations from areas experiencing abrupt permafrost collapse (thermokarst), the overall impact of permafrost degradation on DOC flux and biodegradability may depend on the proportion of the landscape experiencing gradual thaw versus thermokarst.

Influence of temperature on methane hydrate formation

During gas hydrate formation process, a phase transition of liquid water exists naturally, implying that temperature has an important influence on hydrate formation. In this study, methane hydrate was formed within the same media. The experimental system was kept at 1.45, 6.49, and 12.91 °C respectively, and then different pressurization modes were applied in steps. We proposed a new indicator, namely the slope of the gas flow rates against time (dνg/dt), to represent the intrinsic driving force for hydrate formation. The driving force was calculated as a fixed value at the different stages of formation, including initial nucleation/growth, secondary nucleation/growth, and decay. The amounts of gas consumed at each stage were also calculated. The results show that the driving force during each stage follows an inverse relation with temperature, whereas the amount of consumed gas is proportional to temperature. This opposite trend indicates that the influences of temperature on the specific formation processes and final amounts of gas contained in hydrate should be considered separately. Our results also suggest that the specific ambient temperature under which hydrate is formed should be taken into consideration, when explaining the formation of different configurations and saturations of gas hydrates in natural reservoirs.

Soil organic carbon stabilization by iron in permafrost regions of the Qinghai‐Tibet Plateau

A close relationship exists between soil organic carbon (SOC) and reactive iron; however, little is known about the role of iron in SOC preservation in permafrost regions. We determined the amount of SOC associated with reactive iron phases (OC-Fe) in the permafrost regions of the Qinghai-Tibetan Plateau (QTP). The results showed that the percentage of OC-Fe ranged between 0.9% and 59.5% in the upper 30 cm of soil and that the OC-Fe represented 19.5 ± 12.3% of the total SOC pool. No clear vertical distribution pattern in OC-Fe was present in the upper 1 m of soil. Throughout the year, the OC-Fe accounted for relatively stable proportions of the total SOC pool. This study suggests that approximately 20% of SOC is a potential rusty OC pool in the permafrost regions of the QTP. Biogeochemical processes related to the reaction of iron may play important roles in soil carbon cycles in permafrost regions.

Nucleation Mechanisms of CO 2 Hydrate Reflected by Gas Solubility

The concentration of gas has been confirmed as a key factor dominating hydrate nucleation. In this study, CO2 hydrates were formed in pure water and a sodium dodecyl sulphate (SDS) solution using a temperature reduction method under constant pressure at different temperatures. The dissolving properties of CO2 throughout the whole induction period were investigated in detail. The experimental results showed that the ‘memory effect’ of hydrate might not be attributed to residual water structures after hydrate dissociation. Instead, residual gas molecules in the aqueous phase should receive more attention. Hydrate nucleation was confirmed to be a type of chain reaction. Low temperature was a significant factor that promoted hydrate nucleation. As a result, these two factors enhanced the stochastic features of the CO2 hydrate nucleation reaction. Even under the same conditions, critical gas concentrations beyond the threshold that hydrates can spontaneously nucleate were not fixed, but they still exhibited linear relations regarding a set temperature. Taking the significant influences of temperature into account, a new nucleation mechanism for CO2 hydrates was established based on the potential of the reaction system. Therefore, this study sheds new light when explaining the reason for the formation of gas hydrates in natural reservoirs.

Greenhouse gas released from the deep permafrost in the northern Qinghai-Tibetan Plateau

Deep carbon pool in permafrost regions is an important component of the global terrestrial carbon cycle. However, the greenhouse gas production from deep permafrost soils is not well understood. Here, using soils collected from 5-m deep permafrost cores from meadow and wet meadow on the northern Qinghai-Tibetan Plateau (QTP), we investigated the effects of temperature on CO2 and N2O production under aerobic incubations and CH4 production under anaerobic incubations. After a 35-day incubation, the CO2, N2O and CH4 production at −2 °C to 10 °C were 0.44~2.12 mg C-CO2/g soil C, 0.0027~0.097 mg N-N2O/g soil N, and 0.14~5.88 μg C-CH4/g soil C, respectively. Greenhouse gas production in deep permafrost is related to the C:N ratio and stable isotopes of soil organic carbon (SOC), whereas depth plays a less important role. The temperature sensitivity (Q10) values of the CO2, N2O and CH4 production were 1.67–4.15, 3.26–5.60 and 5.22–10.85, without significant differences among different depths. These results indicated that climate warming likely has similar effects on gas production in deep permafrost and surface soils. Our results suggest that greenhouse gas emissions from both the deep permafrost and surface soils to the air will increase under future climate change.