Xinqing Lee

Atmospheric pollution of a remote area of Tianshan Mountain: Ice core record

[1] The influence of anthropogenic pollution on the region of Tianshan Mountain, a remote area in arid central Asia, has been debated in the recent years. An ice core, covering the past 43 years, retrieved from Glacier 1 at Urumqi River head in the east Tianshan, northwest China, was analyzed to examine the problem. CH3COO- (acetate) and HCOO- (formate), the chief tropospheric carboxylates that can originate from anthropogenic pollution, average 389.4 +/- 336.3 ng g(-1) (N = 489) and 61.1 +/- 89.0 ng g(-1) (N = 541), respectively, with a mean ratio HCOO-/CH3COO- of 0.21 +/- 0.23 (N = 489). SO42-, the major inorganic anion in the core, averages 232.9 +/- 279.9 ng g(-1) (N = 542). The organic and inorganic records have covaried in the past four decades. They originate principally from anthropogenic pollution, coal combustion in particular, of the local and regional atmosphere. The pH values in the record range from 6 to 9 with an average of 6.9 +/- 0.5 (N = 541). The general trend of the pH data matches that of HCOO-, CH3COO-, and SO42-, indicating that the anthropogenic pollution has released considerable particulate material along with unsaturated hydrocarbons and SO2. As a result, the pollution has not been acidifying the environment, but making it alkaline.

Is mid-late Paleozoic ocean-water chemistry coupled with epeiric seawater isotope records?

Isotopes of epeiric sea carbonates are used to construct seawater records for modeling global changes in Paleozoic ocean chemistry, climate, and for intercontinental correlation. We present for the first time geochemical results of Paleozoic brachiopods (biogenic low-Mg calcite, bLMC) from open-ocean Permian–Carboniferous seamounts of Japan situated in the tropical mid-Panthalassic Ocean. Strontium isotope values of bLMC from the Panthalassic and Paleotethys Oceans are coupled with those of coeval specimens from epeiric seas of North America, Europe, and Russia ( p = 0.393), but not with those of epeiric sea whole rocks (matrix aragonite/calcite, mAC; p = 0.029) and conodonts (biogenic apatite, bA; p = 0.031). Oxygen isotope values of bLMC from the Panthalassic and Paleotethys exhibit mixed results with studies of counterparts from epeiric seas ( p = 0.596) reflecting overprinting of local environmental conditions on global trends. Carbon isotope values of bLMC and mAC from the Panthalassic and Paleotethys Oceans are generally dissimilar to those of coeval material from epeiric seas of North America, Europe, and Russia ( p = 0.001 and 0.002, respectively). Factors such as water mass stratification, evaporation, dilution, depth, temperature, carbon burial and/or oxidation variations, and syndepositional diagenesis within the local environment probably influenced the chemistry of the fauna and accumulating sediments. This decoupling of carbon and oxygen isotope values from the open ocean with those from epeiric seas makes questionable the use of isotope results from epeiric seas for international correlation, constructing global seawater records, determining fluxes in the global carbon cycle, and for modeling climate changes and subsequently atmospheric carbon dioxide levels.

Needle trap extraction for GC analysis of formic and acetic acids in aqueous solution

Formic and acetic acids are ubiquitous in the environment, food, and most of the natural products. Extraction of the acids from aqueous solution is required for their isotope analysis by the gas chromatography-isotope ratio mass spectrometry. To this objective, we have previously developed a purge-and-trap technique using the dynamic solid-phase microextraction technology, the NeedlEX. The extraction efficiency, however, remains unexamined. Here, we address this question using the flame ionization detector and isotope ratio mass spectrometer while comparing it with that of the CAR/PDMS fiber. The results show that the NeedlEX is applicable at a wide range of concentration through coordination of purge volume given the minimum amount 3.7 ng and 1.8 ng of formic and acetic, respectively, is extracted. The efficiency of NeedlEX was 6-7 times lower than the fiber at 1000 μg/mL depending on the analyte. It is, however, superior to the latter at 10 μg/mL or less owing to its lower detection limit. The extraction efficiency of both acids is equivalent in molar amount. This is, however, disguised by the different response of the flame ionization detector. The isotope ratio mass spectrometor overcomes this problem but is compromised by relatively large errors. These results are particularly useful for isotopic analysis of carboxylic acids.

Determination of light carboxylic acids in snow and ice from mountain glaciers

Light carboxylic acids are major chemical species in acidic precipitation, particularly in remote areas. They play a significant part in the acidification of the environment. Because the organic acids relate closely to the biosphere in the source, their records in snow and ice provide insight into the changes of paleoenvironment and biogeochemical cycles of C, H, O and S. However, the trace concentration of the acids plus their susceptibility to contamination and the exclusiveness of an analytical procedure to a specific instrument make the determination difficult. With DX-300 ion chromatography (IC), we developed a method with AS4A-SC as a separator, TAC-2 as a pre-concentrator installed in place of the sample loop, ATC-1 as an impurity trap installed before the injection valve, and ASRS-II as the suppressor that is regenerated in 25 mM H2SO4. Using gradient elution and Na2B4O7 solution as the eluent, the method resolves and quantitates within a single run of 14 min over 10 analytes from F-, CH3COO- to PO42-, SO42- and finally to (COO)(2)(2-). The relative errors for the anions are: F-, 2.6%; CH3COO-, 4%; HCOO-, 2%; CH3COCOO2-, 6%; methane sulfonate (MSA), 16.8%; Cl-, 3%; NO2-, 4%; NO3-, 2%; Br-, 4.5%; SO42-,2%; and (COO)(2)(2-), 5.8%

Analysis of the stable carbon isotope composition of formic and acetic acids

Formic and acetic acids are ubiquitous in the environment and in many biological processes. Analysis of the stable carbon isotope composition (δ(13)C) of formic and acetic acids is important to understanding their biogeochemical cycles. However, it has been faced with poor accuracy and high detection limits due to their low carbon number, high hydrophilicity, and semi-volatility. Here we developed an analytical technique by needle trap and gas chromatography-isotope ratio mass spectrometry (GC-IRMS). The organic acids in aqueous solution were extracted using a NeedlEx needle through purge-and-trap and were analyzed by GC-IRMS for δ(13)C. The procedures incur no isotope fractionation. Defined as the point at which the mean δ(13)C is statistically the same as the given value and the analytical error starts rising, the methods detection limits are 200 and 100 mg/L for formic and acetic acids, respectively, with an uncertainty of approximately 0.5‰ in direct extraction and analysis. They were lowered to 1 mg/L with precision of 0.9‰ after samples were subjected to preconcentration. The method was successfully applied to natural samples as diverse as precipitation, vinegars, ant plasma, and vehicle exhaust, which vary considerably in concentration and matrix of the organic acids. It is applicable to the organic acids in not only aqueous solution but also gaseous phase.

Changes in chemical and isotopic properties near infiltrated cracks in an ice core from Urumqi glacier No. 1, Tien Shan, China

Abstract Ice cores recovered for paleoclimatic and/or paleoenvironmental reconstructions in the Tien Shan and Qinghai–Tibetan Plateau often encounter cracks. Although we expect that cracks opened to surface meltwater will inevitably change ice-core records, we do not know how and to what extent records are influenced. An ice core retrieved from glacier No. 1 at Ürümqi river head, Tien Shan, China, exhibits a crack nearly 2.5 m long that has admitted meltwater, forming secondary ice within the fracture. A small inclusion of the infiltrated ice in sampling is shown to reduce δ18O by an extent of Holocene vs Last Glacial Maximum while enhancing significantly the pH, conductivity and the following ionic species: CH3COO–, and CO(COO)2 2–. of the parameters increased, and HCOO– are the most affected, being enhanced nearly six-fold in the fractured section compared to the non-fractured sections, followed by CO(COO)2 2– and electrical conductivity measurement (ECM). Despite the alteration, primary fluctuations of some parameters are still recognizable. This suggests that if the infiltrated ice can be avoided in the sampling operation, ice cores with cracks may still provide authentic records. This shows the need to pay close attention to physical characteristics of ice cores in order to identify such secondary ice.

Impacts of straw biochar additions on agricultural soil quality and greenhouse gas fluxes in karst area, Southwest China

ABSTRACT Understanding and improving environmental quality by reducing soil nutrient leaching losses, sequestering carbon (C), reducing greenhouse gas (GHG) emissions, and enhancing crop productivity in highly weathered or degraded soils have always been the goals of agroecosystem researchers and producers. Biochar production and soil incorporation strategies have been recently proposed to help attain these goals. However, the effect of such approaches on soil GHG fluxes is highly uncertain and needs to be further assessed before biochar can be used on a large scale. In addition, the duration of these GHG reductions is not known and is of pivotal importance for the inclusion of biochar in climate abatement strategies. In a field trial cultivated with Chinese cabbage (Brassica campestris ssp. pekinensis) and radish (Daucus carota L. var. Sativa Hoffm), rapeseed (Brassica campestris L.) and maize (Zea mays L.) straw-derived biochar was added to the soil at rates of 0, 26, 64 and 128 t ha−1, in the whole growing season (October 2011–March 2012) to monitor the effect of treatments on soil GHG production/consumption and soil quality 16 months after biochar addition. The results showed that biochar amendment increased soil pH, nitrate nitrogen content, available phosphorus content and soil water content, but decreased soil bulk density. In biochar-treated plots, soil carbon dioxide (CO2) fluxes were from 20.1 to 87.0% higher than in the control. Soil methane (CH4) uptakes were increased significantly, by 33.2 and 80.1%, between the biochar amendment at the rate of 64 and 128 t ha−1 and the control. Soil nitrous oxide (N2O) fluxes showed no significant difference between biochar amendment and the control. Overall only the CH4 uptake-promoting effect continued into the long term, 16 months after biochar incorporation. This study demonstrates that the beneficial effects of biochar addition might first come through soil quality improvement and carbon sequestration, rather than through effects on the repression of soil C mineralization or the nitrogen cycle.

Variation of Soil Organic Carbon and Its Major Constraints in East Central Asia

Variation of soil organic carbon (SOC) and its major constraints in large spatial scale are critical for estimating global SOC inventory and projecting its future at environmental changes. By analyzing SOC and its environment at 210 sites in uncultivated land along a 3020km latitudinal transect in East Central Asia, we examined the effect of environmental factors on the dynamics of SOC. We found that SOC changes dramatically with the difference as high as 5 times in north China and 17 times in Mongolia. Regardless, C:N remains consistent about 12. Path analysis indicated that temperature is the dominant factor in the variation of SOC with a direct effect much higher than the indirect one, the former breaks SOC down the year round while the latter results in its growth mainly via precipitation in the winter half year. Precipitation helps accumulate SOC, a large part of the effect, however, is taken via temperature. NH4+-N and topography also affect SOC, their roles are played primarily via climatic factors. pH correlates significantly with SOC, the effect, however, is taken only in the winter months, contributing to the decay of SOC primarily via temperature. These factors explained as much as 79% of SOC variations, especially in the summer months, representing the major constraints on the SOC stock. Soil texture gets increasingly fine southward, it does not, however, constitute an apparent factor. Our results suggested that recent global warming should have been adversely affecting SOC stock in the mid-latitude as temperature dominates other factors as the constraint.

Diurnal and spatial variations of soil NOx fluxes in the northern steppe of China

NOx emissions from biogenic sources in soils play a significant role in the gaseous loss of soil nitrogen and consequent changes in tropospheric chemistry. In order to investigate the characteristics of NOx fluxes and factors influencing these fluxes in degraded sandy grasslands in northern China, diurnal and spatial variations of NOx fluxes were measured in situ. A dynamic flux chamber method was used at eight sites with various vegetation coverages and soil types in the northern steppe of China in the summer season of 2010. Fluxes of NOx from soils with plant covers were generally higher than those in the corresponding bare vegetation-free soils, indicating that the canopy plays an important role in the exchange of NOx between soil and air. The fluxes of NOx increased in the daytime, and decreased during the nighttime, with peak emissions occurring between 12:00 and 14:00. The results of multiple linear regression analysis indicated that the diurnal variation of NOx fluxes was positively correlated with soil temperature (P<0.05) and negatively with soil moisture content (P<0.05). Based on measurement over a season, the overall variation in NOx flux was lower than that of soil nitrogen contents, suggesting that the gaseous loss of N from the grasslands of northern China was not a significant contributor to the high C/N in the northern steppe of China. The concentration of NOx emitted from soils in the region did not exceed the 1-hr National Ambient Air Quality Standard (0.25 mg/m3).

Characterization of biochars produced from seven biomasses grown in three different climate zones

The characterization of biochars produced from seven feedstocks (four crop straws: cotton stalks, wheat stalks, rape stalks and corn stalks; three hardwoods: Salix babylonica Linn, Platanus orientalis and Robinia pseudoacacia) grown in three different climate zones (arid, semiarid and humid regions) were investigated for their potential as soil amendments. The results show that ash content, K+, Ca2+, Mg2+, CEC, Cl−, pH, and salinity are generally higher in the straw biochars (STR-BCs) than the hardwood biochars (HW-BCs). However, there is no significant distinction between the two categories of biochars in terms of surface acidity, surface basicity, TC, available phosphorus (A-P) or NH4+-N. The contents of K+, Na+, Ca2+, Mg2+, EC, Cl− of all 21 biochars increase in semi-arid and arid regions in comparison to humid regions, while ash content, TC, CEC, pH, surface acidity, surface basicity, A-P and NH4+-N show no correlation to the climate. From the perspective of K+, CEC and the remediation of acidified soils, STR-BCs are preferable over HW-BCs as a soil amendment, while HW-BCs are more suitable than STR-BCs in soils with a saline problem. EC, Na+ and Cl− increase with the water stress of the climatic regions, and the high saline ions of biochar in the arid regions indicate that biochars produced from local biomass, especially from crop residues, are at a high risk of exacerbating soil salinization. The big difference in the critical chemical properties, such as the saline ions, stresses that biochar should be taken on a regional basis as well as a biomass basis, with the general assumption that whether biochar as a soil amendment is good or bad is groundless.