Yongfu Xu

The Flexible Global Ocean-Atmosphere-Land system model, Spectral Version 2: FGOALS-s2

The Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 (FGOALS-s2) was used to simulate realistic climates and to study anthropogenic influences on climate change. Specifically, the FGOALS-s2 was integrated with Coupled Model Intercomparison Project Phase 5 (CMIP5) to conduct coordinated experiments that will provide valuable scientific information to climate research communities. The performances of FGOALS-s2 were assessed in simulating major climate phenomena, and documented both the strengths and weaknesses of the model. The results indicate that FGOALS-s2 successfully overcomes climate drift, and realistically models global and regional climate characteristics, including SST, precipitation, and atmospheric circulation. In particular, the model accurately captures annual and semi-annual SST cycles in the equatorial Pacific Ocean, and the main characteristic features of the Asian summer monsoon, which include a low-level southwestern jet and five monsoon rainfall centers. The simulated climate variability was further examined in terms of teleconnections, leading modes of global SST (namely, ENSO), Pacific Decadal Oscillations (PDO), and changes in 19th–20th century climate. The analysis demonstrates that FGOALS-s2 realistically simulates extra-tropical teleconnection patterns of large-scale climate, and irregular ENSO periods. The model gives fairly reasonable reconstructions of spatial patterns of PDO and global monsoon changes in the 20th century. However, because the indirect effects of aerosols are not included in the model, the simulated global temperature change during the period 1850–2005 is greater than the observed warming, by 0.6°C. Some other shortcomings of the model are also noted.

Inorganic chemical composition and source signature of PM2.5 in Beijing during ACE-Asia period

Aerosol samples for PM2.5 were collected in Beijing for 38 consecutive days from March to April 2001 using an IMPROVE Sampler. Concentrations of w0 elements in PM2.5 were determined using a PIXE method. Results show that he average mineral dust concentration of PM2.5 was 14.6 μg/m3 during the observation period. On the sanddust event days of March 21 and April 10, dust PM2.5 mass concentrations were 62.4 and 54.1 μg/m3, respectively. These demonstrate that fine particle pollution by dust event in Beijing was very severe. The enrichment factors of S and Cu reached minimums on the dusty days and were high on the non-dusty days. It is considered that enrichment factors of elements in PM2.5, which are associated with human activities, can probably provide an effective method to distinguish local sources from external sources of dust. Factor analysis on the chemical composition in PM2.5 shows that sources of crustal matters, anthropogenic emission, and oil combustion contributed to PM2.5 levels in air in the springtime of 2001 in Beijing.

Effects of Relative Humidity on Ozone and Secondary Organic Aerosol Formation from the Photooxidation of Benzene and Ethylbenzene

The formation of ozone and secondary organic aerosol (SOA) from benzene–NO x and ethylbenzene–NOx irradiations was investigated under different levels of relative humidity (RH) in a smog chamber. In benzene and ethylbenzene irradiations, the intensity of the bands of O‒H, C˭O, C‒O, and C‒OH from SOA samples all greatly increased with increasing RH. The major substances in SOA were determined to be carboxylic acids and glyoxal hydrates. It was also found that SOA contained aromatic products, and NO2- and ONO2-containing products. The results show that the increase in RH can greatly reduce the maximum O3 by the transfer of NO2- and ONO2-containing products into the particle phase. During the process of evaporation, the lost substances from the collected SOA have similar structures for both benzene and ethylbenzene. This demonstrates that ethyl-containing substances are very stable and difficult to evaporate. For benzene, some of glyoxal hydrates were left to form C‒O‒C- and C˭O-containing species like hemiacetal and acetal after evaporation, whereas for ethylbenzene, glyoxal favored cross reactions with ethylglyoxal during evaporation. Only a few species in SOA were released into the gas phase during evaporation while a large part of SOA remained, which is mainly composed of carboxylic acid. It is concluded that the aqueous radical reactions and the hydration from glyoxal can be enhanced under high RH conditions, which can irreversibly enhance the formation of SOA from both benzene and ethylbenzene. Copyright 2014 American Association for Aerosol Research

Simulations of storage of anthropogenic carbon dioxide in the North Pacific using an ocean general circulation model

There is a large uncertainty of how much anthropogenic CO 2 has been and will be taken up by the ocean. The North Pacific is normally considered a small sink of anthropogenic CO 2 . Recently, some researchers have proposed that the North Pacific may take up more anthropogenic CO 2 than thought previously. Here we explore this issue with a basin-wide OGCM of the North Pacific. The sensitivities of ocean circulation and the redistribution of dissolved anthropogenic CO 2 in the North Pacific to the values of some mixing parameters are examined. The increase of isopycnal diffusivity generally leads to improvement of distributions of water masses. Larger isopycnal diffusivity produces larger CO 2 uptake in the subpolar region but smaller CO 2 uptake in the tropical region. Increasing thickness diffusivity reduces CO 2 uptake in both the subpolar and subtropical regions, and also reduces the inventory of CO 2 in the western subtropical region. Both smaller isopycnal and thickness diffusivities result in a large net transport of CO 2 from the North Pacific to the South Pacific. Simulated results show that the North Pacific has taken up about 23 GtC of excess carbon dioxide released by human activities between 1800 and 1997. The averaged uptake rate in the North Pacific during 1990-1997 is 0.40 GtC/year. Our model estimates the largest air-sea fluxes along the western boundary around 42°N, 150°E and in the equatorial Pacific. Our simulated inventories slightly overestimate data-based estimates in the eastern North Pacific, but exhibit less penetration of anthropogenic carbon dioxide in the western North Pacific.

Kinetic Study of the Gas-phase Ozonolysis of Propylene

Abstract Kinetics of the reaction of ozone with propylene under real atmospheric environmental conditions with an ozone concentration of ca 6.6×10−8 has been investigated in a self-made Teflon Chamber. Using Model 49C-O3 Analyzer and GC-FID, reaction rate constants at a temperature range of 282–314 K were determined by an absolute rate technique in terms of measurements of ozone concentrations. Results show that the reaction rate constant is 6.73×10−18 cm3·molecule−1·s−1 for the initial ozone concentration of 6.61×10−8 and the temperature of 282 K. According to the reaction rate constants under different temperatures, the Arrhenius equation of k2=(5.8±1.2)×10−15e(−1907±53)/T is obtained. Compared with the results reported by other researchers, although the rate constants obtained in this study are systematically underestimated and the activation energy of the reaction overestimated, the results are satisfactory. For example, the largest relative error is only 11% and 5% for the rate constant and activation energy, respectively. These demonstrate that the research equipment used in this study is reliable under real atmospheric conditions and can be used to do further studies related to ozone reactions.

Effects of relative humidity on the characterization of a photochemical smog chamber

Water vapor plays an important role in many atmospheric chemical reactions. A self-made indoor environmental smog chamber was used to investigate the effects of relative humidity (RH) on its characterization, which included the wall effects of reactive species such as 03 and NOx, and the determination of chamber-dependent OH radicals in terms of CO-NOx irradiation experiments. Results showed that the rate constant of O3 wall losses increased with increasing RH, and that their relationship was linearly significant. Although RH affected the rate constant of NOx wall losses, their relationship was not statistically significant. Background air generated a small amount of ozone at both high and low RH. When RH varied from 5% to 79%, the apparent rate constant kNO2-->HONO for the conversion of NO2 into gas phase HONO was estimated in the range of 0.70 x 10(-3)-2.5 x 10(-3) min(-1). A linear relationship between kNO2-->HONO and RH was obtained as kNO2-->HONO (10(-3) min(-1)) = -0.0255RH + 2.64, with R2 and P value being 0.978 and < 0.01. To our knowledge, this is the first report on their relationship. The generation mechanism for HONO and OH was also discussed in this work.

Sensitivity of the Simulated Distributions of Water Masses, CFCs, and Bomb 14C to Parameterizations of Mesoscale Tracer Transports in a Model of the North Pacific

Abstract A basinwide ocean general circulation model of the North Pacific Ocean is used to study the sensitivity of the simulated distributions of water masses, chlorofluorocarbons (CFCs), and bomb carbon-14 isotope (14C) to parameterizations of mesoscale tracer transports. Five simulations are conducted, including a run with the traditional horizontal mixing scheme and four runs with the isopycnal transport parameterization of Gent and McWilliams (GM). The four GM runs use different values of isopycnal and skew diffusivities. Simulated results show that the GM mixing scheme can help to form North Pacific Intermediate Water (NPIW). Greater isopycnal diffusivity enhances formation of NPIW. Although greater skew diffusivity can also generate NPIW, it makes the subsurface too fresh. Results from simulations of CFC uptake show that greater isopycnal diffusivity generates the best results relative to observations in the western North Pacific. The model generally underestimates the inventories of CFCs in the we...

Summary of Recent Climate Change Studies on the Carbon and Nitrogen Cycles in the Terrestrial Ecosystem and Ocean in China

This article reviews recent advances over the past 4 years in the study of the carbon-nitrogen cycling and their relationship to climate change in China. The net carbon sink in the Chinese terrestrial ecosystem was 0.19–0.26 Pg C yr−1 for the 1980s and 1990s. Both natural wetlands and the rice-paddy regions emitted 1.76 Tg and 6.62 Tg of CH4 per year for the periods 1995–2004 and 2005–2009, respectively. China emitted ∼1.1 Tg N2O-N yr−1 to the atmosphere in 2004. Land soil contained ∼8.3 Pg N. The excess nitrogen stored in farmland of the Yangtze River basin reached 1.51 Tg N and 2.67 Tg N in 1980 and 1990, respectively. The outer Yangtze Estuary served as a moderate or significant sink of atmospheric CO2 except in autumn. Phytoplankton could take up carbon at a rate of 6.4×1011 kg yr−1 in the China Sea. The global ocean absorbed anthropogenic CO2 at the rates of 1.64 and 1.73 Pg C yr−1 for two simulations in the 1990s. Land net ecosystem production in China would increase until the mid-21st century then would decrease gradually under future climate change scenarios. This research should be strengthened in the future, including collection of more observation data, measurement of the soil organic carbon (SOC) loss and sequestration, evaluation of changes in SOC in deep soil layers, and the impacts of grassland management, carbon-nitrogen coupled effects, and development and improvement of various component models and of the coupled carbon cycle-climate model.

A global ocean biogeochemistry general circulation model and its simulations

An ocean biogeochemistry model was developed and incorporated into a global ocean general circulation model (LICOM) to form an ocean biogeochemistry general circulation model (OBGCM). The model was used to study the natural carbon cycle and the uptake and storage of anthropogenic CO2 in the ocean. A global export production of 12.5 Pg C yr−1 was obtained. The model estimated that in the pre-industrial era the global equatorial region within ±15° of the equator released 0.97 Pg C yr−1 to the atmosphere, which was balanced by the gain of CO2 in other regions. The post-industrial air-sea CO2 flux indicated the oceanic uptake of CO2 emitted by human activities. An increase of 20–50 μmol kg−1 for surface dissolved inorganic carbon (DIC) concentrations in the 1990s relative to pre-industrial times was obtained in the simulation, which was consistent with data-based estimates. The model generated a total anthropogenic carbon inventory of 105 Pg C as of 1994, which was within the range of estimates by other researchers. Various transports of both natural and anthropogenic DIC as well as labile dissolved organic carbon (LDOC) were estimated from the simulation. It was realized that the Southern Ocean and the high-latitude region of the North Pacific are important export regions where accumulative air-sea CO2 fluxes are larger than the DIC inventory, whereas the subtropical regions are acceptance regions. The interhemispheric transport of total natural carbon (DIC+LDOC) was found to be northward (0.11 Pg C yr−1), which was just balanced by the gain of carbon from the atmosphere in the Southern Hemisphere.

Influences of climate change on the uptake and storage of anthropogenic CO2 in the global ocean

A global ocean general circulation model, called LASG/IAP Climate system ocean model (LICOM), is employed to study the influence of climate change on the uptake and storage of anthropogenic CO2 in the global ocean. Two simulations were made: the control run (RUN1) with the climatological daily mean forcing data, and the climate change run (RUN2) with the interannually varying daily mean forcing data from the NCEP (National Centers for Environmental Prediction) of the US. The results show that the simulated distributions and storages of anthropogenic dissolved inorganic carbon (anDIC) from both runs are consistent with the data-based results. Compared with the data-based results, the simulations generate higher anDIC concentrations in the upper layer and lower storage amount of anDIC between the subsurface and 1000-m depth, especially in RUN1. A comparison of the two runs shows that the interannually varying forcing can enhance the transport of main water masses, so the rate of interior transport of anDIC is increased. The higher transfer rate of anDIC in RUN2 decreases its high concentration in the upper layer and increases its storage amount below the subsurface, which leads to closer distributions of anDIC in RUN2 to the data-based results than in RUN1. The higher transfer rate in RUN2 also induces larger exchange flux than in RUN1. It is estimated that the global oceanic anthropogenic CO2 uptake was 1.83 and 2.16 Pg C yr−1 in the two runs in 1995, respectively, and as of 1994, the global ocean contained 99 Pg C in RUN1 and 107 Pg C in RUN2 of anDIC, indicating that the model under the interannually varying forcing could take up 8.1% more anthropogenic carbon than the model under the climatological forcing. These values are within the range of other estimates based on observation and model simulation, while the estimates in RUN1 are near the low bound of other works. It is estimated that the variability of root mean square of the global air-sea anthropogenic carbon flux from the simulated monthly mean results of RUN2 with its seasonal cycle and long-term trend removed is 0.1 Pg C yr−1. The most distinct anomalies appear to be in the tropical Pacific Ocean and the Southern Ocean.