In order to better understand the pyrolysis process of cellulose, the decomposition of levoglucosan and glyceraldehyde, which are important intermediate products of cellulose, are simulated by quantum simulation. Ther...In order to better understand the pyrolysis process of cellulose, the decomposition of levoglucosan and glyceraldehyde, which are important intermediate products of cellulose, are simulated by quantum simulation. Thermodynamic analysis of four possible reaction pathways for levoglucosan is conducted by quantum chemistry.The reaction process of glyceraldehyde is checked, and the intermediates and the activation energies of the process are given. The simulation results indicate that the three well-established chemical pathways for levoglucosan in literature can spontaneously occur within the pyrolysis temperature range from 500 to 1 000 K. However, the reaction pathway involving the formation of erythrose cannot be accepted since the free energy ΔG is estimated to be above zero during the pyrolysis process. Through the analysis of glyceraldehyde decomposition by the transition state theory, decarbonylation and dehydration may be the dominant pathways for glyceraldehyde decomposition. The quantum simulation for determining the chemical pathway of glyceraldehyde and levoglucosan can give a conceptual and methodological guide for searching possible chemical pathways of cellulose pyrolysis or other macromolecules in biomass.展开更多
Expanding urbanization and agricultural intensification across neighboring South Asia and East Asia have substantially threatened atmospheric condition over the Third Pole(TP)during the past few decades.Whether the at...Expanding urbanization and agricultural intensification across neighboring South Asia and East Asia have substantially threatened atmospheric condition over the Third Pole(TP)during the past few decades.Whether the atmospheric condition over the TP is still as clean as a representative of the regional background draws great concern.In this work,great differences in levoglucosan concentration within/above the atmospheric boundary layer height are revealed.Levoglucosan results support the hypothesis that atmospheric pollutants in the mid-troposphere over the TP are mainly affected by long-range transport,although there are some local biomass burning emissions in residential areas.In addition,levoglucosan concentration in the midtroposphere over the TP is at the same magnitude as marine and polar regions,but about 2–3 magnitudes lower than neighboring densely-populated Asian regions.With insights of levoglucosan records,this work therefore proves that the high-altitude TP still has largely pristine atmospheric conditions,and is one of the cleanest remote regions on the Earth.展开更多
The environmental significance of levoglucosan(LEV) records in Tibetan glacier ice layers on sub-annual to annual scales, in particular their suitability as a specific biomarker for indicating past fire changes, is po...The environmental significance of levoglucosan(LEV) records in Tibetan glacier ice layers on sub-annual to annual scales, in particular their suitability as a specific biomarker for indicating past fire changes, is poorly understood at present. In this work, a continuous LEV record was reconstructed in a central Tibetan ice core for the period 1990–2012. The LEV record was classified into two categories based on its LEV concentrations: background levels and extreme events. Annually-resolved LEV records and background levels in the ice core were strongly correlated with satellite observations of fire occurrence frequency over the northern Indian peninsula between 2003 and 2012, especially for strong fire events during the pre-monsoon season(March–May). In addition, peaks in LEV concentrations may represent extreme fire events in regions around the Tibetan Plateau. LEV records in the ice core reflect a longterm increasing trend in fire background and also an increase in fire extreme events, across the Tibetan Plateau and its surroundings. We therefore conclude that LEV records in Tibetan ice cores can be used as a powerful tool for calibrating and reconstructing past fire changes over subtropical Asia.展开更多
The largest sugarcane-growing area in the United States is in South Florida. An estimated 7 million tons of dry sugarcane leafy biomass is removed from the fields before harvest by burning the leaves off the sugarcane...The largest sugarcane-growing area in the United States is in South Florida. An estimated 7 million tons of dry sugarcane leafy biomass is removed from the fields before harvest by burning the leaves off the sugarcane stalks. Preharvest sugarcane leaf foliage burning is a major source of airborne particulate matter (PM), polycyclic aromatic hydrocarbons (PAHs), biogenic trace elements such as K, volatile hydrocarbons and other pollutants. In one harvesting period, approximately 22 million tons of C02, a greenhouse gas, is released, 7 million tons from leaf foliage preharvest burning alone and 15 million tons from burning sugarcane bagasse in the sugar mills for power generation. In this study, PMio was collected from Belle Glade, close to the sugarcane-growing area, and from Delray Beach, an urbanized area along the East Coast of Florida. The PM samples were analyzed for trace elements and close to organic compounds. To elucidate the importance of preharvest sugarcane biomass smoke emissions on air quality, 39 trace elements, 18 PAHs, and levoglucosan were selected to apportion ambient PM constituents. Al, Ca and to a great extend also Mg are the major soil-related trace elements and key markers for fugitive soil dust emissions. Similarly, sea salt aerosol blown from the Atlantic Ocean into Florida added appreciably to PMio trace elements concentration, especially Na and Cl. Approximately half of the sea salt aerosol (PMjo -portion) by mass is removed from the atmosphere during the transport of ocean air from Delray Beach to Belle Glade. Ambient acid displacement reactions caused a substantial portion of the Cl (30%) to be liberated from the sea salt aerosol to the atmosphere during transport as gaseous HC1. The PAH concentrations at Belle Glade were high when the biomass combustion markers levoglucosan and I< also showed the highest concentrations. This indicates that during the sugarcane harvest season, when leaf foliage is burned off just before harvest, most of the ambient PAHs associated with PMio are indeed related to preharvest burning, harvesting machinery emissions, bagasse burning in sugarcane mills, and other related activities that consume biomass and/or fossil fuels for sugarcane harvesting and processing.展开更多
Pretreatment of lignocellulosic biomass is crucial for the release of biofermentable sugars for biofuels production,which could greatly alleviate the burgeoning environment and energy crisis caused by the massive usag...Pretreatment of lignocellulosic biomass is crucial for the release of biofermentable sugars for biofuels production,which could greatly alleviate the burgeoning environment and energy crisis caused by the massive usage of traditional fossil fuels.Pyrolysis is a cost-saving pretreatment process that can readily decompose biomass into levoglucosan,a promising anhydrosugar;however,many undesired toxic compounds inhibitory to downstream microbial fermentation are also generated during the pyrolysis,immensely impeding the bioconversion of levoglucosan-containing pyrolysate.Here,we took the first insight into the proteomic responses of a levoglucosan-utilizing and ethanol-producing Escherichia coli to three representative biomass-derived inhibitors,identifying large amounts of differentially expressed proteins(DEPs)that could guide the downstream metabolic engineering for the development of inhibitor-resistant strains.Fifteen up-and eight down-regulated DEPs were further identified as the biomarker stress-responsive proteins candidate for cellular tolerance to multiple inhibitors.Among these biomarker proteins,YcfR exhibiting the highest expression fold-change level was chosen as the target of overexpression to validate proteomics results and develop robust strains with enhanced inhibitor tolerance and fermentation performance.Finally,based on four plasmid-borne genes encoding the levoglucosan kinase,pyruvate decarboxylase,alcohol dehydrogenase,and protein YcfR,a new recombinant strain E.coli LGE-ycfR was successfully created,showing much higher acetic acid-,furfural-,and phenol-tolerance levels compared to the control without overexpression of ycfR.The specific growth rate,final cell density,ethanol concentration,ethanol productivity,and levoglucosan consumption rate of the recombinant were also remarkably improved.From the proteomics-guided metabolic engineering and phenotypic observations,we for the first time corroborated that YcfR is a stress-induced protein responsive to multiple biomass-derived inhibitors,and also developed an inhibitors-resistant strain that could produce bioethanol from levoglucosan in the presence of inhibitors of relatively high concentration.The newly developed E.coli LGE-ycfR strain that could eliminate the commonly-used costly detoxicification processes,is of great potential for the in situ cost-effective bioethanol production from the biomass-derived pyrolytic substrates.展开更多
基金The National High Technology Research and Development Program of China(863 Program)(No.2012AA051801)
文摘In order to better understand the pyrolysis process of cellulose, the decomposition of levoglucosan and glyceraldehyde, which are important intermediate products of cellulose, are simulated by quantum simulation. Thermodynamic analysis of four possible reaction pathways for levoglucosan is conducted by quantum chemistry.The reaction process of glyceraldehyde is checked, and the intermediates and the activation energies of the process are given. The simulation results indicate that the three well-established chemical pathways for levoglucosan in literature can spontaneously occur within the pyrolysis temperature range from 500 to 1 000 K. However, the reaction pathway involving the formation of erythrose cannot be accepted since the free energy ΔG is estimated to be above zero during the pyrolysis process. Through the analysis of glyceraldehyde decomposition by the transition state theory, decarbonylation and dehydration may be the dominant pathways for glyceraldehyde decomposition. The quantum simulation for determining the chemical pathway of glyceraldehyde and levoglucosan can give a conceptual and methodological guide for searching possible chemical pathways of cellulose pyrolysis or other macromolecules in biomass.
基金the Youth Innovation Promotion Association CAS(2020071)Chinese Academy of Sciences(YIPA-2020071,XDA20060200)+1 种基金the National Natural Science Foundation of China(41701078,41805127)the Second Tibetan Plateau Scientific Expedition and Research(2019QZKK0201).
文摘Expanding urbanization and agricultural intensification across neighboring South Asia and East Asia have substantially threatened atmospheric condition over the Third Pole(TP)during the past few decades.Whether the atmospheric condition over the TP is still as clean as a representative of the regional background draws great concern.In this work,great differences in levoglucosan concentration within/above the atmospheric boundary layer height are revealed.Levoglucosan results support the hypothesis that atmospheric pollutants in the mid-troposphere over the TP are mainly affected by long-range transport,although there are some local biomass burning emissions in residential areas.In addition,levoglucosan concentration in the midtroposphere over the TP is at the same magnitude as marine and polar regions,but about 2–3 magnitudes lower than neighboring densely-populated Asian regions.With insights of levoglucosan records,this work therefore proves that the high-altitude TP still has largely pristine atmospheric conditions,and is one of the cleanest remote regions on the Earth.
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences(XDA20100000)the National Natural Science Foundation of China(41701078,41805127)+1 种基金International Partnership Program of Chinese Academy of Sciences(GJHZ1674)the Second Comprehensive Scientific Expedition on Tibetan Plateau
文摘The environmental significance of levoglucosan(LEV) records in Tibetan glacier ice layers on sub-annual to annual scales, in particular their suitability as a specific biomarker for indicating past fire changes, is poorly understood at present. In this work, a continuous LEV record was reconstructed in a central Tibetan ice core for the period 1990–2012. The LEV record was classified into two categories based on its LEV concentrations: background levels and extreme events. Annually-resolved LEV records and background levels in the ice core were strongly correlated with satellite observations of fire occurrence frequency over the northern Indian peninsula between 2003 and 2012, especially for strong fire events during the pre-monsoon season(March–May). In addition, peaks in LEV concentrations may represent extreme fire events in regions around the Tibetan Plateau. LEV records in the ice core reflect a longterm increasing trend in fire background and also an increase in fire extreme events, across the Tibetan Plateau and its surroundings. We therefore conclude that LEV records in Tibetan ice cores can be used as a powerful tool for calibrating and reconstructing past fire changes over subtropical Asia.
文摘The largest sugarcane-growing area in the United States is in South Florida. An estimated 7 million tons of dry sugarcane leafy biomass is removed from the fields before harvest by burning the leaves off the sugarcane stalks. Preharvest sugarcane leaf foliage burning is a major source of airborne particulate matter (PM), polycyclic aromatic hydrocarbons (PAHs), biogenic trace elements such as K, volatile hydrocarbons and other pollutants. In one harvesting period, approximately 22 million tons of C02, a greenhouse gas, is released, 7 million tons from leaf foliage preharvest burning alone and 15 million tons from burning sugarcane bagasse in the sugar mills for power generation. In this study, PMio was collected from Belle Glade, close to the sugarcane-growing area, and from Delray Beach, an urbanized area along the East Coast of Florida. The PM samples were analyzed for trace elements and close to organic compounds. To elucidate the importance of preharvest sugarcane biomass smoke emissions on air quality, 39 trace elements, 18 PAHs, and levoglucosan were selected to apportion ambient PM constituents. Al, Ca and to a great extend also Mg are the major soil-related trace elements and key markers for fugitive soil dust emissions. Similarly, sea salt aerosol blown from the Atlantic Ocean into Florida added appreciably to PMio trace elements concentration, especially Na and Cl. Approximately half of the sea salt aerosol (PMjo -portion) by mass is removed from the atmosphere during the transport of ocean air from Delray Beach to Belle Glade. Ambient acid displacement reactions caused a substantial portion of the Cl (30%) to be liberated from the sea salt aerosol to the atmosphere during transport as gaseous HC1. The PAH concentrations at Belle Glade were high when the biomass combustion markers levoglucosan and I< also showed the highest concentrations. This indicates that during the sugarcane harvest season, when leaf foliage is burned off just before harvest, most of the ambient PAHs associated with PMio are indeed related to preharvest burning, harvesting machinery emissions, bagasse burning in sugarcane mills, and other related activities that consume biomass and/or fossil fuels for sugarcane harvesting and processing.
基金The authors gratefully acknowledge the financial support of the National Natural Science Foundation of China(Grants NO.21978287)the Fundamental Research Funds for the Central Universities(Y954035XX2).
文摘Pretreatment of lignocellulosic biomass is crucial for the release of biofermentable sugars for biofuels production,which could greatly alleviate the burgeoning environment and energy crisis caused by the massive usage of traditional fossil fuels.Pyrolysis is a cost-saving pretreatment process that can readily decompose biomass into levoglucosan,a promising anhydrosugar;however,many undesired toxic compounds inhibitory to downstream microbial fermentation are also generated during the pyrolysis,immensely impeding the bioconversion of levoglucosan-containing pyrolysate.Here,we took the first insight into the proteomic responses of a levoglucosan-utilizing and ethanol-producing Escherichia coli to three representative biomass-derived inhibitors,identifying large amounts of differentially expressed proteins(DEPs)that could guide the downstream metabolic engineering for the development of inhibitor-resistant strains.Fifteen up-and eight down-regulated DEPs were further identified as the biomarker stress-responsive proteins candidate for cellular tolerance to multiple inhibitors.Among these biomarker proteins,YcfR exhibiting the highest expression fold-change level was chosen as the target of overexpression to validate proteomics results and develop robust strains with enhanced inhibitor tolerance and fermentation performance.Finally,based on four plasmid-borne genes encoding the levoglucosan kinase,pyruvate decarboxylase,alcohol dehydrogenase,and protein YcfR,a new recombinant strain E.coli LGE-ycfR was successfully created,showing much higher acetic acid-,furfural-,and phenol-tolerance levels compared to the control without overexpression of ycfR.The specific growth rate,final cell density,ethanol concentration,ethanol productivity,and levoglucosan consumption rate of the recombinant were also remarkably improved.From the proteomics-guided metabolic engineering and phenotypic observations,we for the first time corroborated that YcfR is a stress-induced protein responsive to multiple biomass-derived inhibitors,and also developed an inhibitors-resistant strain that could produce bioethanol from levoglucosan in the presence of inhibitors of relatively high concentration.The newly developed E.coli LGE-ycfR strain that could eliminate the commonly-used costly detoxicification processes,is of great potential for the in situ cost-effective bioethanol production from the biomass-derived pyrolytic substrates.
