Organic tracer compounds, as well as organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and stable carbon isotope ratios (δ13C) of total carbon (TC) have been investigated in aerosol samples collected during early and late periods of the Mount Tai eXperiment 2006 (MTX2006) field campaign in the North China Plain. Total solvent-extractable fractions were investigated by gas chromatography/mass spectrometry. More than 130 organic compounds were detected in the aerosol samples. They were grouped into twelve organic compound classes, including biomass burning tracers, biogenic primary sugars, biogenic secondary organic aerosol (SOA) tracers, and anthropogenic tracers such as phthalates, hopanes and polycyclic aromatic hydrocarbons (PAHs). In early June when the field burning activities of wheat straws in the North China Plain were very active, the total identified organics (2090 ± 1170 ng m^[-3]) were double those in late June (926 ± 574 ng m^[-3]). All the compound classes were more abundant in early June than in late June, except phthalate esters, which were higher in late June. Levoglucosan (88-1210 ng m^[-3], mean 403 ng m^[-3]) was found as the most abundant single compound in early June, while diisobutyl phthalate was the predominant species in late June. During the biomass-burning period in early June, the diurnal trends of most of the primary and secondary organic aerosol tracers were characterized by the concentration peaks observed at mid-night or in early morning, while in late June most of the organic species peaked in late afternoon. This suggests that smoke plumes from biomass burning can uplift the aerosol particulate matter to a certain altitude, which could be further transported to and encountered the summit of Mt. Tai during nighttime. On the basis of the tracer-based method for the estimation of biomass-burning OC, fungal-spore OC and biogenic secondary organic carbon (SOC), we estimate that an average of 24% (up to 64 %) of the OC in the Mt. Tai aerosols was due to biomass burning in early June, followed by the contribution of isoprene SOC (mean 4.3 %). In contrast, isoprene SOC was the main contributor (6.6 %) to OC, and only 3.0% of the OC was due to biomass burning in late June. In early June, δ13C of TC (-26.6 to -23.2 ‰, mean -25.0 ‰) were lower than those (-23.9 to -21.9 ‰, mean -22.9 ‰) in late June. In addition, a strong anti-correlation was found between levoglucosan and δ13C values. This study demonstrates that crop-residue burning activities can significantly enhance the organic aerosol loading and alter the organic composition and stable carbon isotopic composition of aerosol particles in the troposphere over the North China Plain

In this paper we present an estimate of net ecosystem CO 2 exchange over China for the years 2001-2010 using the CarbonTracker Data Assimilation System for CO 2 (CTDAS). Additional Chinese and Asian CO 2 observations are used in CTDAS to improve our estimate. We found that the combined terrestrial ecosystems in China absorbed about À0.33 Pg C yr À1 during 2001-2010. The uncertainty on Chinese terrestrial carbon exchange estimates as derived from a set of sensitivity experiments suggests a range of À0.29 to À0.64 Pg C yr À1 . This total Chinese terrestrial CO 2 sink is attributed to the three major biomes (forests, croplands, and grass/shrublands) with estimated CO 2 fluxes of À0.12 Pg C yr À1 (range from À0.09 to À0.19 Pg C yr À1 ), À0.12 Pg C yr À1 (range from À0.09 to À0.26 Pg C yr À1 ), and À0.09 Pg C yr À1 (range from À0.09 to À0.17 Pg C yr À1 ), respectively. The peak-to-peak amplitude of interannual variability of the Chinese terrestrial ecosystem carbon flux is 0.21 Pg C yr À1 (~64% of mean annual average), with the smallest CO 2 sink (À0.19 Pg C yr À1 ) in 2003 and the largest CO 2 sink (À0.40 Pg C yr À1 ) in 2007. We stress that our estimate of terrestrial ecosystem CO 2 uptake based on inverse modeling strongly depends on a limited number of atmospheric CO 2 observations used. More observations in China specifically and in Asia in general are needed to improve the accuracy of terrestrial carbon budgeting for this region.

Evapotranspiration (ET) plays an important role in both energy and water balances. Determining changes in the different types of ET and their influencing factors under climate change is crucial to fully understand the mechanisms controlling ET and regional water cycles. Based on ET and meteorological data measured during 1998–2005 at the Yucheng Comprehensive Experimental Station of the Chinese Academy of Sciences, the variation of reference ET (ET0), pan evaporation (Epan), and lysimeter ET (the actual ET, Elys) were estimated. Together with a Mann‐Kendall trend test, correlation and sensitivity analyses were conducted to determine the effects of climatic factors, crop coefficients (Kc), and leaf area index (LAI) on different types of ET. During 1998–2005, precipitation presented an upward trend at all time scales, and average temperature (Ta), minimum temperature (Tmin), relative humidity, Epan, and ET0 exhibited downward trends. Elys displayed a downward trend at the daily scale and an upward trend at monthly and annual scales. The correlation analysis indicated that Epan and Elys were significantly positively correlated with all climatic factors except precipitation and relative humidity. The sensitivity analysis revealed that except for relative humidity, the influence of the other climatic factors on ET0 was positive. The highest sensitivity was found for relative humidity, followed by Ta, maximum temperature (Tmax), and Tmin. An analysis of the influence of Kc and LAI on the actual ET indicated that with an increase of Kc and LAI, the actual water demand of crops also displayed an upward trend.