Hydroclimate variability in the North China Plain and its link with El Nino-Southern Oscillation since 1784 AD: Insights from tree-ring cellulose delta(18)O

We present here a chronology of tree-ring cellulose delta(18)O from 1784 to 2003 that is based on the individual measurements of five Larix principis-rupprechtii trees growing in the semiarid North China Plain (NCP; 34 degrees-41 degrees N, 107 degrees-120 degrees E). This chronology has a significant, negative correlation with summer precipitation, relative humidity, and the Palmer Drought Severity Index. It is representative of regional summer hydroclimate variability in the NCP by analyzing its spatial correlation patterns with CRU TS3 precipitation grid data sets. Historically, extreme climate events (drought and flood) could be detected by the high-frequency (annual) signals in the chronology. The low-frequency (11 year moving average) signals are consistent with the time series of the drought frequency and the regional dryness-wetness index derived from historical documents in the NCP. Significant spatial correlation patterns of measured precipitation and the tree-ring cellulose delta(18)O chronology from the NCP with observed sea surface temperature in the eastern equatorial Pacific during the 1954-2003 and 1854-2003 periods suggest that the summer hydroclimate of the NCP has a close link with El Nino-Southern Oscillation. Mostly extreme dry or wet years identified by the chronology follow historical El Nino or La Nina events over the past 220 years, respectively.</p

Regional hydroclimate and precipitation delta O-18 revealed in tree-ring cellulose delta O-18 from different tree species in semi-arid Northern China

Oxygen isotopic ratios (delta(18)O) of tree-ring cellulose, grown from 1954 to 2003 in semi-arid Northern China demonstrate a common inter-annual variability, despite coming from three different species in two distinct growth environments (an alpine meadow and a rocky ridge). The variability was significantly negative correlated with precipitation and relative humidity during the growing season. This suggests that the past summer hydroclimate can be inferred from tree-ring cellulose delta(18)O from various kinds of trees growing in semi-arid Northern China. In addition, we evaluated past changes in delta(18)O of precipitation from the tree-ring cellulose delta(18)O and relative humidity using the mechanistic model for tree-ring cellulose delta(18)O in Roden et al. (2000). By fixing the species-dependent exchange rate of oxygen between carbohydrate and xylem water for Larix principis-rupprechtii and Picea koraiensis, we could also reconstruct the variations in precipitation delta(18)O from the different tree species, which are similar to the observed delta(18)O of precipitation during 1985-2002. Although the reconstructed delta(18)O of precipitation does not have any significant relation to local temperature or precipitation during 1954-2003, its long-term variation pattern is similar to that of the Asian summer monsoon indices and delta(18)O of stalagmite in the Heshang cave (30 degrees 27&#39;N, 110 degrees 25&#39;E; Fig. 1), suggesting that delta(18)O of precipitation is not controlled by local meteorology but is influenced by large-scale atmospheric circulation.</p

Selected water-soluble organic compounds found in size-resolved aerosols collected from urban, mountain and marine atmospheres over East Asia

Primary (i.e. sugars and sugar-alcohols) and secondary (i.e. carboxylic acids) water-soluble organic compounds (WSOCs) in size-segregated aerosols from the urban and mountain atmosphere of China and from the marine atmosphere in the outflow region of East Asia were characterized on a molecular level. Levoglucosan is the most abundant compound among the quantified WSOCs in the urban and mountain atmosphere, whose concentration at the urban site was 1-2 orders of magnitude higher than that at the mountain and marine sites. In contrast, malic, succinic and phthalic acids were dominant among the measured WSOCs at the marine site. In the urban air, sugars except levoglucosan gave a bimodal size distribution with a large peak in fine range (&lt;2.1 mu m) and a small peak in coarse range (&gt;= 2.1 mu m) during winter, being opposite to those in spring. In contrast, these WSOCs at the mountain and marine sites dominated in the coarse range but diminished and even disappeared in the fine range. Geometric mean diameters (GMDs) of the measured WSOCs in the fine mode at the urban site were larger in winter than in spring. Levoglucosan and carboxylic acids except for azelaic and benzoic acids showed a larger GMD in the coarse mode at the marine site probably due to an increased hygroscopic growth.</p

Molecular composition and size distribution of sugars, sugar-alcohols and carboxylic acids in airborne particles during a severe urban haze event caused by wheat straw burning

Molecular compositions and size distributions of water-soluble organic compounds (WSOC, i.e., sugars, sugar-alcohols and carboxylic acids) in particles from urban air of Nanjing, China during a severe haze event caused by field burning of wheat straw were characterized and compared with those in the summer and autumn non-haze periods. During the haze event levoglucosan (4030 ng m(-3)) was the most abundant compound among the measured WSOC, followed by succinic acid, malic acid, glycerol, arabitol and glucose, being different from those in the non-haze samples, in which sucrose or azelaic acid showed a second highest concentration, although levoglucosan was the highest. The measured WSOC in the haze event were 2-20 times more than those in the non-hazy days. Size distribution results showed that there was no significant change in the compound peaks in coarse mode (&gt;2.1 mu m) with respect to the haze and non-haze samples, but a large difference in the fine fraction (&lt;2.1 mu m) was found with a sharp increase during the hazy days mostly due to the increased emissions of wheat straw burning. Molecular compositions of organic compounds in the fresh smoke particles from wheat straw burning demonstrate that sharply increased concentrations of glycerol and succinic and malic acids in the fine particles during the haze event were mainly derived from the field burning of wheat straw, although the sources of glucose and related sugar-alcohols whose concentrations significantly increased in the fine haze samples are unclear. Compared to that in the fresh smoke particles of wheat straw burning an increase in relative abundance of succinic acid to levoglucosan during the haze event suggests a significant production of secondary organic aerosols during transport of the smoke plumes.</p

Plant-wax hydrogen isotopic evidence for postglacial variations in delivery of precipitation in the monsoon domain of China

The Asian monsoon is a key component of the Earth&#39;s climate system that directly affects the livelihood of 60% of the world population. Reliable reconstruction of changes in monsoon precipitation during the Holocene is required to better understand the present climate conditions and to predict future climate processes in the Asian monsoon domain. Reconstruction of changes in Holocene monsoon precipitation has been done in various regions of this domain using a variety of paleoclimate proxies. However, different proxies have yielded different paleoclimate records of long-term monsoon rainfall variability. We apply compound-specific stable hydrogen isotope compositions of the plant wax n-alkanes isolated from the Hongyuan peat sequence in eastern Tibet to reevaluate the regional carbonate oxygen isotopic and lake-level records. The D/H ratios of the n-alkanes resolve the apparent discrepancy among the different paleoclimate proxies. Our result indicates that lake-level fluctuation is a reliable recorder of changes in the amount of summer monsoonal precipitation while long-term isotope records largely reflect large-scale changes in the source of water vapor rather than a local precipitation signal. Combining lake-level, biomarker, and carbonate isotopic records, we conclude that the early Holocene monsoon precipitation in southwest China has been greatly influenced by the Indian monsoon.</p

Molecular Distribution and Stable Carbon Isotopic Composition of Dicarboxylic Acids, Ketocarboxylic Acids, and alpha-Dicarbonyls in Size-Resolved Atmospheric Particles From Xi'an City, China

Size-resolved airborne particles (9-stages) in urban Xi&#39;an, China, during summer and winter were measured for molecular distributions and stable carbon isotopic compositions of dicarboxylic acids, ketocarboxylic acids, and alpha-dicarbonyls. To our best knowledge, we report for the first time the size-resolved differences in stable carbon isotopic compositions of diacids and related compounds in continental organic aerosols. High ambient concentrations of terephthalic (tPh, 379 +/- 200 ng m(-3)) and glyoxylic acids (omega C-2, 235 +/- 134 ng m(-3)) in Xi&#39;an aerosols during winter compared to those in other Chinese cities suggest significant emissions from plastic waste burning and coal combustions. Most of the target compounds are enriched in the fine mode (&lt;2.1 mu m) in both seasons peaking at 0.7-2.1 mu m. However, summertime concentrations of malonic (C-3), succinic (C-4), azelaic (C-9), phthalic (Ph), pyruvic (Pyr), 4-oxobutanoic (omega C-4), and 9-oxononanoic (omega C-9) acids, and glyoxal (Gly) in the coarse mode (&gt;2.1 mu m) are comparable to and even higher than those in the fine mode (&lt;2.1 mu m). Stable carbon isotopic compositions of the major organics are higher in winter than in summer, except oxalic acid (C-2), omega C-4, and Ph. delta C-13 of C-2 showed a clear difference in sizes during summer, with higher values in fine mode (ranging from -22.8 parts per thousand to -21.9 parts per thousand) and lower values in coarse mode (-27.1 parts per thousand to -23.6 parts per thousand). The lower delta C-13 of C-2 in coarse particles indicate that coarse mode of the compound originates from evaporation from fine mode and subsequent condensation/adsorption onto pre-existing coarse particles. Positive linear correlations of C-2, sulfate and omega C-2 and their delta C-13 values suggest that omega C-2 is a key intermediate, which is formed in aqueous-phase via photooxidation of precursors (e.g., Gly and Pyr), followed by a further oxidation to produce C-2.</p