As important natural and pharmaceutical motifs,the catalytic construction of structurally diverse 3,3-disubstituted oxindoles often requires elaborate synthetic efforts on optimizations.Herein,we developed a simple an...As important natural and pharmaceutical motifs,the catalytic construction of structurally diverse 3,3-disubstituted oxindoles often requires elaborate synthetic efforts on optimizations.Herein,we developed a simple and divergent approach for constructing reverse-prenylated and prenylated oxindoles launched by Ni catalysis with bulk chemical isoprene.Using C3-unsubstituted oxindoles as starting materials,mono reverse-prenylation was demonstrated in high chemo-and regioselectivities facilitated by the combination of Ni(0)and monodentate phosphine ligand.Using the obtained reverse-prenylated oxindoles as versatile synthon,substitutions at the pseudobenzylic position with various electrophiles created vicinal quaternary centers in a concise way.With the help of additives(PPh3 and NaH),air could be directly used as green oxidant to construct prenylated and reverse-prenylatedα-hydroxy-oxindoles divergently from the same substrates.In situ esterification of prenylatedα-hydroxy-oxindoles allowed subsequent Friedel-Crafts substitutions with diverse nucleophiles to deliver prenyl substituted dimeric or spiro-oxindoles.This protocol provides a divergent synthetic approach for the construction of highly functionalized 3,3-disubstituted oxindoles,which have been otherwise difficult to access in a unified approach.展开更多
Formaldehyde(HCHO)is a high-yield product of the oxidation of volatile organic compounds(VOCs)released by anthropogenic activities,fires,and vegetations.Hence,we examined the spatiotemporal variation trends in HCHO co...Formaldehyde(HCHO)is a high-yield product of the oxidation of volatile organic compounds(VOCs)released by anthropogenic activities,fires,and vegetations.Hence,we examined the spatiotemporal variation trends in HCHO columns observed using the Ozone Monitoring Instrument(OMI)during 2005–2021 across the Fenwei Plain(FWP)and analysed the source and variability of HCHO using multi-source data,such as thermal anomalies.The spatial distribution of the annualmean HCHO in the FWP increased from northwest to southeast during 2005–2021,and the high-value aggregation areas contracted and gradually clustered,forming a belt-shaped distribution area from Xi’an to Baoji,north of the Qinling Mountains.The annual mean HCHO concentration generally showed a two-step increase over the 17 years.Fires showed a single-peak trend in March and a double-peak M-shaped trend in March and October,whereas urban thermal anomalies(UTAs)showed an inverted U-shaped trend over 17 years,with peaks occurring in May.The HCHO peaks are mainly caused by the alternating contributions of fires and UTAs.The fires and UTAs(predominantly industrial heat sources)played a role in controlling the background level of HCHO in the FWP.Precipitation and temperature were also important influencing variables for seasonal variations,and the influence of plant sources on HCHO concentrations had significant regional characteristics and contributions.In addition,the FWP has poor dispersion conditions and is an aggregated area for the long-range transport of air pollutants.展开更多
Elucidating the mutual effects between the different volatile organic compounds(VOCs)is crucial for comprehending the formation mechanism of atmospheric secondary organic aerosols(SOA).Here,the mixed VOCs experiments ...Elucidating the mutual effects between the different volatile organic compounds(VOCs)is crucial for comprehending the formation mechanism of atmospheric secondary organic aerosols(SOA).Here,the mixed VOCs experiments of isoprene and△^(3)-carene/β-caryophyllene were carried out in the presence of O_(3)using an indoor smog chamber.The suppression effect of isoprene was recognized by the scanning mobility particle sizer spectrometer,online vacuum ultraviolet free electron laser(VUV-FEL)photoionization aerosol mass spectrometry,and quantum chemical calculations.The results indicate that the suppression effect of isoprene on the ozonolysis of△^(3)-carene andβ-caryophyllene shows fluctuating and monotonous trends,respectively.The carbon content of the precursor could be themain factor for regulating the strength of the suppression effect.Plausible structures and formation mechanisms of several new products generated from the single VOC precursor and VOC-cross-reaction are proposed,which enrich the category of VOC oxidation products.Meanwhile,a new dimerization mechanism of the RO_(2)+R’O_(2)reaction is suggested,which offers an intriguing perspective on the gas phase formation process of particle phase accretion products.The present findings provide valuable insights into clarifying the pivotal roles played by isoprene in the interplay between different VOCs and understanding of SOA formation mechanisms of VOC mixtures,especially nearby the emission origins.展开更多
As a base research on intelligentized search technique in seismic ruins,we study on human odor by a portable GC-MS.Qualitative analysis experiment demonstrate that isoprene,acetone and 6-methyl-5-heptene-2-one are sym...As a base research on intelligentized search technique in seismic ruins,we study on human odor by a portable GC-MS.Qualitative analysis experiment demonstrate that isoprene,acetone and 6-methyl-5-heptene-2-one are symbol of human odor.This research give important data to search survival base on artificial olfaction technique in seismic ruins.展开更多
Abstract Two series of trans-1,4-poly（butadiene-co-isoprene） copolymers （TBIR） were prepared using the catalyst system TiCl4/MgCl2-Al（i-Bu）3 at different reaction temperatures. All dyad and triads sequence distr...Abstract Two series of trans-1,4-poly（butadiene-co-isoprene） copolymers （TBIR） were prepared using the catalyst system TiCl4/MgCl2-Al（i-Bu）3 at different reaction temperatures. All dyad and triads sequence distributions, the number-average sequence length and the sequence concentration of the copolymers were calculated according to 13C-NMR spectra. The influences of temperature and initial molar ratio of butadiene to isoprene （Bd to Ip） on the distribution of the chain segments in the TBIR copolymers were discussed. The correlation of copolymer compositions and thermal properties were also evaluated, which facilitated the understanding of controlling the degree of crystallinity and the transition tempera^re by changing Bd content and temperature.展开更多
A series of trans-1,4-butadiene/isoprene copolymers were prepared using the catalyst system TiCl4/MgCl2-Al（i- Bu）3 with bulk precipitation technology at different temperatures. Monomers reactivity ratios were calcul...A series of trans-1,4-butadiene/isoprene copolymers were prepared using the catalyst system TiCl4/MgCl2-Al（i- Bu）3 with bulk precipitation technology at different temperatures. Monomers reactivity ratios were calculated based on the Kelen-Tiid6s （K-T） method and the Mao-Huglin （M-H） method. The influence of temperature on copolymer composition and polymerization rate was discussed in detail. The increase of reaction temperature brought the decrease of butadiene reactivity ratio rBd and supplied an effective adjustment on copolymers＇ composition distribution.展开更多
Plant leaves may emit a substantial amount of volatile organic compounds （VOCs） into the atmosphere, which include isoprene, terpene, alkanes, alkenes, alcohols, aldehydes, eters, esters and carboxylic acids. Furthe...Plant leaves may emit a substantial amount of volatile organic compounds （VOCs） into the atmosphere, which include isoprene, terpene, alkanes, alkenes, alcohols, aldehydes, eters, esters and carboxylic acids. Furthermore, most of these compounds actively participate in tropospheric chemistry. Great progresses have been made in linking emission of these compounds to climate. However, the VOCs emission function in plant is still not clear. Recently, some evidence has emerged that the production and the emission of VOCs, such as isoprene and monoterpenes, which account for 80% of total VOCs, exhibit plant protection against high temperatures. These increases in VOCs emissions could contribule in a significant way to plant thermotolerance. This perspective summarizes some latest literatures regarding the VOCs emission-dependent thermoprotection in plant species subjected to high temperature stress, presents the achievement in studies concerning plant VOCs emission-dependent thermotolerance, and then exhibits the proposed mechanisms of such plant thermotolerance. Finally open questions regarding the plant VOCs emission were shown, and the future researches were proposed.展开更多
Given the key role of biogenic volatile organic compounds(VOCs) to tropospheric chemistry and regional air quality, it is important to generate accurate VOCs emission inventories. However, only a less fraction of plan...Given the key role of biogenic volatile organic compounds(VOCs) to tropospheric chemistry and regional air quality, it is important to generate accurate VOCs emission inventories. However, only a less fraction of plant species, in temperate grassland of Inner Mongolia, has been characterized by quantitative measurements. A taxonomic methodology, which assigns VOCs measurements to unmeasured species, is an applicable and inexpensive alternation for extensive VOCs emission survey, although data are needed for additional plant families and genera to further validate the taxonomic approach in grassland vegetation. In this experiment, VOCs emission rates of 178 plant species were measured with a portable photoionization detector(PID). The results showed the most of genera and some families have consistent feature of their VOCs emission, especially for isoprene, and provide the basic premise of taxonomic methodology to develop VOCs emission inventories for temperate grassland. Then, the taxonomic methodology was introduced into assigning emission rate to other 96 species, which no measured emission rates available here. A systematical emission inventory of temperate grassland vegetation in Inner Mongolia was provided and further evidence that taxonomy relationship can serve as a useful guide for generalizing the emissions behavior of many, but not all, plant families and genera to grassland vegetation.展开更多
A series ofbutadiene-isoprene copolymers （BIR） with various compositions were synthesized with a neodymiumbased catalyst system. The microstructure, composition and sequence of copolymers were characterized by FTIR ...A series ofbutadiene-isoprene copolymers （BIR） with various compositions were synthesized with a neodymiumbased catalyst system. The microstructure, composition and sequence of copolymers were characterized by FTIR and ^13C-NMR spectroscopy. The crystallization behavior of the BIR copolymers was investigated by DSC analysis. The results demonstrate that the content of cis-1,4 configuration in both butadiene （Bd） and isoprene （Ip） units are around 98% when Bd content in feed （fBd） covering the range from 55.7 mol% to 96.0 mol%. The reactivity ratios of Bd and Ip were determined to be 1.40 and 0.48 respectively. The random copolymers of Bd and Ip show only one glass transition temperature （Tg） from -107.4℃ to -80.5℃, which is dependent on the composition and fits nicely with Fox equation. The sequence distribution followed the first-order Markov statistical model. It is found that the copolymer chains with higher Bd content contain longer polybutadiene （PBd） segments, and the sequence length of PBd segments （NBd） exhibits great influence on the crystallization behavior of the copolymer. The copolymers with NBd ≥ 11.8 could crystallize at low temperatures （-71℃ to -43℃）. The crystallization temperature and enthalpy values decreased gradually with decreasing NBd. The copolymers with NBd ≤ 7.9 are amorphous even at very low temperatures （0℃ to -150℃） due to the short PBd segments.展开更多
In order to analyze biogenic volatile organic compounds in the atmosphere, an automated gas chromatography is developed and employed at the laboratory of National Center for Atmospheric Research (NCAR) during January ...In order to analyze biogenic volatile organic compounds in the atmosphere, an automated gas chromatography is developed and employed at the laboratory of National Center for Atmospheric Research (NCAR) during January to July, 2000. A small refrigerator was used so as to remove water in the air sample from gas line, and get accurate concentrations of volatile organic compounds. At 5°C, good water removing efficiency can be obtained at controlled flow rate. Air samples were collected around the building of Mesa Lab. of NCAR and analyzed by this gas chromatography system. This paper reports this gas chromatography system and results of air samples. The experimental results show that this gas chromatography system has a good reproducibility and stability, and main interesting volatile organic compounds such as isoprene, monoterpenes have an evident diurnal variation.展开更多
Continuous observation of isoprene, β-pinene and β-pinene was carried out in a typical urban area of Beijing from March 2014 to February 2015, using an AirmoVOC online analyzer. Based on the analysis of the ambient ...Continuous observation of isoprene, β-pinene and β-pinene was carried out in a typical urban area of Beijing from March 2014 to February 2015, using an AirmoVOC online analyzer. Based on the analysis of the ambient level and variation characteristics of isoprene, β-pinene and β- pinene, the chemical reactivity was studied, and their sources were identified. Results showed that the concentrations of isoprene, α-pinene and β-pinene in the urban area of Beijing were lower than those in richly vegetated areas; the concentrations of isoprene were at a moderate level compared with those of previous studies of Beijing. Concentrations of isoprene, α-pinene and β-pinene showed different seasonal, monthly, daily and diurnal variations, and all of the three species showed higher level at night than those in the daytime as a whole, the variations of isoprene, α-pinene and β-pinene mainly influenced by emission of sources, photochemical reaction, and meteorological parameters. Isoprene was the largest contributor to the total OFP values than β-pinene and β-pinene. α-Pinene was the largest contributor to the total SOAFP values than isoprene and β-pinene in autumn, while isoprene was the largest one in other seasons. Isoprene, α-pinene and β-pinene were derived mainly from biological sources; and α- pinene level were also affected by industrial sources. To reduce the concentrations of isoprene, α-pinene and β-pinene, it is necessary to scientifically select urban green plant species, and more strict control measures should be taken to reduce the emission of β-pinene from industrial sources, such as artificial flavors and resins synthesis processes.展开更多
PM2.5 aerosol samples were collected over 12 hr and 24 hr intervals in an inland background area, Gongga Mountain National Nature Reserve（hereafter shortened to Gongga）, during the summer of 2011. Polar organic trac...PM2.5 aerosol samples were collected over 12 hr and 24 hr intervals in an inland background area, Gongga Mountain National Nature Reserve（hereafter shortened to Gongga）, during the summer of 2011. Polar organic tracers, inorganic ions and meteorological data were measured. The purpose of this work was to investigate the variation patterns, formation and sources of the secondary organic aerosol tracers in the studied atmosphere. The average concentrations of isoprene oxidation products, α-pinene oxidation products, β-caryophyllinic acid, sugars, sugar alcohols and anhydrosugars were 88.6 ± 106.1, 3.6 ± 5.7,0.13 ± 0.30, 13.6 ± 13.1, 31.9 ± 31.4 and 14.8 ± 10.7 ng/m^3 respectively in all aerosol samples.The aged α-pinene second organic aerosol（SOA） tracers（i.e., 3-hydroxyglutraric acid（3 HGA）, 3-hydroxy-2,2-dimethylglutaric acid（HDMGA）, 3-acetylpentandioic acid（APDA） and 3-methyl-1,2,3-butanetricarboxylic acid（MBTCA）） correlated significantly with each other in the 24 hr PM2.5 aerosol samples, indicating that OH· is the major factor controlling the formation of these α-pinene SOA tracers. Using the positive matrix factorization（PMF） model and the tracer-based source apportionment method, we calculated that isoprene oxidation products, α-pinene oxidation products, sesquiterpene oxidation products, biomass burning, fungi spores and anthropogenic SOA accounted for 21.9% ± 5.5%, 8.4% ± 2.1%, 3.0% ± 0.7%, 5.2% ± 5.3%, 5.0% ± 6.2% and 31.4% ± 7.8% of organic carbon respectively during the sampling period.展开更多
Neodymium chloride isopropanol complex （NdCl3.3＇prOH） activated by modified methylaluminoxane （MMAO） was examined in isoprene polymerization in hexane, with regards to Nd compounds, aluminum （Al） compounds, [Al...Neodymium chloride isopropanol complex （NdCl3.3＇prOH） activated by modified methylaluminoxane （MMAO） was examined in isoprene polymerization in hexane, with regards to Nd compounds, aluminum （Al） compounds, [Al]/[Nd] ratio, polymerization temperature and time. NdCl3＇3iprOH exhibited high activity producing polymers feasting high cis-l,4 stereospecificity （〉 96%）, very high molecular weight （Mn 〉 1.0 × 10^6） and fairly narrow molecular weight distribution （MWD, Mw/Mn 〈 2.0） simultaneously. In comparison, neodymium isopropoxide also showed high activity providing polymers with narrow MWD （Mw/Mn = 2.07）, but somewhat low cis-1,4 content （ca. 92%）, while neodymium chloride had no activity under present polymerization conditions. The Al compounds affected the polymer yield in the order of Al（i-Bu）3 〉 MMAO 〉 Al（i-Bu）2H. MMAO as cocatalyst afforded polyisoprene with high Mn over 1.0 × 10^6, whereas as stronger chain transfer agent than MMAO, AI（i-Bu）3 and AI（i-Bu）EH yielded polymers with low Mn （1.0 × 10^5-8.0 × 10^5）. NdCl3·3＇PrOH/MMAO catalyst showed a fairly good catalytic activity even at relatively low [Al]/[Nd] ratio of 30, and the produced polymer remained high cis-1,4 content of 95.8% along with high Mn over 1.0× 10^6 even at elevated temperatures up to 70℃. The polymerization rate is of the first order with respect to the concentration of isoprene. The mechanism of active species formation was discussed preliminarily.展开更多
Neodymium-based heterocyclic Schiff base complex was prepared and applied for the coordination polymerization of isoprene. This complex polymerized isoprene to afford products featuring high cis-1,4 stereospecificity ...Neodymium-based heterocyclic Schiff base complex was prepared and applied for the coordination polymerization of isoprene. This complex polymerized isoprene to afford products featuring high cis-1,4 stereospecificity （ca. 95%） and high molecular weight （ca, 10^5） in the presence of the triisobutyl aluminium （AliBu3） as cocatalyst, The microstructure of obtained polyisoprene was investigated by FTIR, 1^H NMR. Two different kinds of active centers in the catalyst system were examined by GPC method.展开更多
Terpenoids are the largest family of natural products.They are made from the building block isoprene pyrophosphate(IPP),and their bioproduction using engineered cell factories has received a great deal of attention.To...Terpenoids are the largest family of natural products.They are made from the building block isoprene pyrophosphate(IPP),and their bioproduction using engineered cell factories has received a great deal of attention.To date,the insufficient metabolic supply of IPP remains a great challenge for the efficient synthesis of terpenoids.In this work,we discover that the imbalanced metabolic flux distribution between the central metabolism and the IPP supply hinders IPP accumulation in Bacillus subtilis(B.subtilis).Therefore,we remodel the IPP metabolism using a series of genetically encoded two-input-multioutput(TIMO)circuits that are responsive to pyruvate or/and malonyl-CoA,resulting in an IPP pool that is significantly increased by up to four-fold.As a proof-of-concept validation,we design an IPP metabolism remodeling strategy to improve the production of three valuable terpenoids,including menaquinone-7(MK-7,4.1-fold),lycopene(9-fold),andβ-carotene(0.9-fold).In particular,the titer of MK-7 in a 50-L bioreactor reached 1549.6 mg·L^(-1),representing the highest titer reported so far.Thus,we propose a TIMO genetic circuits-assisted IPP metabolism remodeling framework that can be generally used for the synergistic fine-tuning of complicated metabolic modules to achieve the efficient bioproduction of terpenoids.展开更多
The first detailed inventory for volatile organic compounds(VOC) emissions from vegetation over Yunnan Province, China was presented. The spatially and temporally resolved inventory was developed based on a geographic...The first detailed inventory for volatile organic compounds(VOC) emissions from vegetation over Yunnan Province, China was presented. The spatially and temporally resolved inventory was developed based on a geographic information system(GIS), remote sensing(RS) data and field measurement data, such as digitized land-use data, normalized difference vegetation index(NDVI) and temperature data from direct real-time measurement. The inventory has a spatial resolution of 5 km×5 km and a time resolution of 1 h. Urban, agriculture, and natural land-use distributions in Yunnan Province were combined with biomass factors for each land-use category to produce a spatially resolved biomass inventory. A biogenic emission inventory was developed by combining the biomass inventory with hourly emission rates for tree, shrub and ground cover species of the study area. Correcting for environmental factors, including light intensity and temperature, a value of 1.1×10 12 gC for total annual biogenic VOC emissions from Yunnan Province, including 6.1×10 11 gC for isoprene, 2.1×10 11 gC for monoterpenes, and 2.6×10 11 gC for OVOC was obtained. The highest VOC emissions occurred in the northwestern, southwestern and north region of Yunnan Province. Some uncertainties were also discussed in this study.展开更多
Here we show a study of vibrational spectroscopic identification of a few typical organic compounds which are known as the main sources of organic aerosols（OAs） particle matter in air pollution. Raman and IR spectra...Here we show a study of vibrational spectroscopic identification of a few typical organic compounds which are known as the main sources of organic aerosols（OAs） particle matter in air pollution. Raman and IR spectra of isoprene, terpenoids, pinenes and their mixture are meticulously examined, showing distinguishable intrinsic vibrational spectroscopic fingerprints for these chemicals, respectively. As a reference, first-principles calculations of Raman and infrared activities are also conducted. It is interestingly found that, the experimental spectra are peak-to-peak consistent with the DFT（Density Functional Theory）-calculated vibrational activities. Also found is that, in a certain case such as for bpinene, a dimer model, rather than an isolated single molecular model, reproduces the experimental results, indicating unneglected intermolecular interactions. Starting with this study, we are endeavoring to advocate a database of Raman/IR fingerprint spectra for OA haze identification.展开更多
FTIR spectroscopy in combination with a diamond tipped attenuated total reflectance （ATR） immersion probe was utilized to study in situ the copolymerization of butadiene （Bd） and isoprene （Ip） with neodymium-bas...FTIR spectroscopy in combination with a diamond tipped attenuated total reflectance （ATR） immersion probe was utilized to study in situ the copolymerization of butadiene （Bd） and isoprene （Ip） with neodymium-based catalyst in hexane. The relationship between the signal intensity of monomer and its concentration was investigated. The kinetic study of copolymerization of Bd and Ip was further conducted, and the monomer reactivity ratios were determined via in situ ATR FTIR. The signal band at 1010 cm^-1 was assigned to wagging vibration of Bd and its intensity was proportional to Bd concentration （[Bd]） in the range of 0.46-3.88 mol.L^-1. The signal bands at 890 and 989 cm^-1 were assigned to wagging vibration of Ip and the signal intensity was also proportional to Ip concentration （[Ip]） in the range of 0.08-4.73 mol·L^-1 at 890 cm^-1 and 0.08-7.49 mol·L^-1 at 989 cm^-1, respectively. Thus the signal band at 1010 cm^-1 was chosen to monitor Bd concentration and bands at 989 and 890 cm^-1 to monitor Ip concentration during the copolymerization, respectively. It was demonstrated that the conversions of Bd and Ip calculated from FTIR data agreed very well with those obtained gravimetrically. The poiymerization rates were first order with respect to both [Bd] and [Ip], respectively at different polymerization temperatures. The apparent propagation activation energy for Bd and Ip could be determined to be 54.4 kJ·mol^-1 and 57.7 kJ·mol^-1, respectively. The monomer reactivity ratios were calculated to be 1.08 for Bd （rBd） and 0.48 for IP （rIp） based on FTIR data. The Bd-Ip copolymer products with random sequence could be obtained with only one glass transition temperature.展开更多
A new kind of multifunctional macromolecular initiator with Sn-C bonds and polydiene arms was synthesized by living anionic polymerization. At first, polydiene-stannum chloride （PD-SnCl3） was prepared by the reactio...A new kind of multifunctional macromolecular initiator with Sn-C bonds and polydiene arms was synthesized by living anionic polymerization. At first, polydiene-stannum chloride （PD-SnCl3） was prepared by the reaction of n-butyl-Li （n-BuLi）, stannic chloride （SnCl4） and diene. Then PD-SnCl3 was used to react with the dilithium initiator to prepare the multifunctional organic macromolecular initiators. The result suggested that the initiators had a remarkable yield by GPC, nearly 90%. By using these multifunctional macromolecular initiators, styrene and butadiene were effectively polymefized via anionic polymerization, which gave birth to novel miktoarm star copolymers. The relative molecular weight and polydispersity index, microstructure contents, copolymerization components, glass transition temperature （Tg） and morphology of the miktoarm star copolymers were investigated by GPC-UV, ~H NMR, DSC and TEM, respectively. 2009 Xing Ying Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.展开更多
Isoprene emissions emitted from vegetation are one of the most important precursors for tropospheric ozone and secondary organic aerosol formation. The authors estimate the biogenic isoprene emissions in China over 20...Isoprene emissions emitted from vegetation are one of the most important precursors for tropospheric ozone and secondary organic aerosol formation. The authors estimate the biogenic isoprene emissions in China over 2006-2011 using a global chemical transport model （GEOS- Chem） driven by meteorological fields from the assimilated meteorological data from MERRA. The authors incorporate three different parameterizations of isoprene-CO2 interaction into the model, and perform three sensitivity simulations to investigate the effect of CO2 inhibition on isoprene emissions for the period 2006-2011 in China. The annual isoprene emissions rate across China is simulated to be 12.62 Tg C yr-1, averaged over 2006-2011, and decreases by about 2.7%-7.4% when the CO2 inhibition schemes are included. The CO2 inhibition effect might be significant in regions where the CO2 concentration and isoprene emissions are high. Estimates of isoprene emissions can differ depending on the scheme of CO2 inhibition. According to the results obtained from the sensitivity simulations, the authors find that the CO2 inhibition effect leads to 5.6% ±2.3% reductions in annual isoprene emissions over China. The authors also find that inclusion of CO2 inhibition can substantially alter the sensitivity of isoprene emissions to the changes in meteorological conditions during the study period.展开更多
文摘As important natural and pharmaceutical motifs,the catalytic construction of structurally diverse 3,3-disubstituted oxindoles often requires elaborate synthetic efforts on optimizations.Herein,we developed a simple and divergent approach for constructing reverse-prenylated and prenylated oxindoles launched by Ni catalysis with bulk chemical isoprene.Using C3-unsubstituted oxindoles as starting materials,mono reverse-prenylation was demonstrated in high chemo-and regioselectivities facilitated by the combination of Ni(0)and monodentate phosphine ligand.Using the obtained reverse-prenylated oxindoles as versatile synthon,substitutions at the pseudobenzylic position with various electrophiles created vicinal quaternary centers in a concise way.With the help of additives(PPh3 and NaH),air could be directly used as green oxidant to construct prenylated and reverse-prenylatedα-hydroxy-oxindoles divergently from the same substrates.In situ esterification of prenylatedα-hydroxy-oxindoles allowed subsequent Friedel-Crafts substitutions with diverse nucleophiles to deliver prenyl substituted dimeric or spiro-oxindoles.This protocol provides a divergent synthetic approach for the construction of highly functionalized 3,3-disubstituted oxindoles,which have been otherwise difficult to access in a unified approach.
基金supported by the National Natural Science Foundation of China(No.41571062)the Fundamental Research Funds for the Central Universities(No.2021TS014)the Natural Science Basic Research Plan in Shaanxi Province of China(No.2023-JC-YB-259).
文摘Formaldehyde(HCHO)is a high-yield product of the oxidation of volatile organic compounds(VOCs)released by anthropogenic activities,fires,and vegetations.Hence,we examined the spatiotemporal variation trends in HCHO columns observed using the Ozone Monitoring Instrument(OMI)during 2005–2021 across the Fenwei Plain(FWP)and analysed the source and variability of HCHO using multi-source data,such as thermal anomalies.The spatial distribution of the annualmean HCHO in the FWP increased from northwest to southeast during 2005–2021,and the high-value aggregation areas contracted and gradually clustered,forming a belt-shaped distribution area from Xi’an to Baoji,north of the Qinling Mountains.The annual mean HCHO concentration generally showed a two-step increase over the 17 years.Fires showed a single-peak trend in March and a double-peak M-shaped trend in March and October,whereas urban thermal anomalies(UTAs)showed an inverted U-shaped trend over 17 years,with peaks occurring in May.The HCHO peaks are mainly caused by the alternating contributions of fires and UTAs.The fires and UTAs(predominantly industrial heat sources)played a role in controlling the background level of HCHO in the FWP.Precipitation and temperature were also important influencing variables for seasonal variations,and the influence of plant sources on HCHO concentrations had significant regional characteristics and contributions.In addition,the FWP has poor dispersion conditions and is an aggregated area for the long-range transport of air pollutants.
基金supported by the National Natural Science Foundation of China(Nos.92361302,22125303,92061203,and 22288201)the National Key Research and Development Program of China(No.2021YFA1400501)+2 种基金the Innovation Program for Quantum Science and Technology(No.2021ZD0303304)Dalian Institute of Chemical Physics(No.DICP DCLS201702)Chinese Academy of Sciences(No.GJJSTD20220001).
文摘Elucidating the mutual effects between the different volatile organic compounds(VOCs)is crucial for comprehending the formation mechanism of atmospheric secondary organic aerosols(SOA).Here,the mixed VOCs experiments of isoprene and△^(3)-carene/β-caryophyllene were carried out in the presence of O_(3)using an indoor smog chamber.The suppression effect of isoprene was recognized by the scanning mobility particle sizer spectrometer,online vacuum ultraviolet free electron laser(VUV-FEL)photoionization aerosol mass spectrometry,and quantum chemical calculations.The results indicate that the suppression effect of isoprene on the ozonolysis of△^(3)-carene andβ-caryophyllene shows fluctuating and monotonous trends,respectively.The carbon content of the precursor could be themain factor for regulating the strength of the suppression effect.Plausible structures and formation mechanisms of several new products generated from the single VOC precursor and VOC-cross-reaction are proposed,which enrich the category of VOC oxidation products.Meanwhile,a new dimerization mechanism of the RO_(2)+R’O_(2)reaction is suggested,which offers an intriguing perspective on the gas phase formation process of particle phase accretion products.The present findings provide valuable insights into clarifying the pivotal roles played by isoprene in the interplay between different VOCs and understanding of SOA formation mechanisms of VOC mixtures,especially nearby the emission origins.
文摘As a base research on intelligentized search technique in seismic ruins,we study on human odor by a portable GC-MS.Qualitative analysis experiment demonstrate that isoprene,acetone and 6-methyl-5-heptene-2-one are symbol of human odor.This research give important data to search survival base on artificial olfaction technique in seismic ruins.
基金financially supported by the National Basic Research Program of China(No.2015CB654700(2015CB654706))Shandong Province Natural Science Fund for Distinguished Young Scholars(No.JQ201213)the National Natural Science Foundation of China(No.51473083)
文摘Abstract Two series of trans-1,4-poly（butadiene-co-isoprene） copolymers （TBIR） were prepared using the catalyst system TiCl4/MgCl2-Al（i-Bu）3 at different reaction temperatures. All dyad and triads sequence distributions, the number-average sequence length and the sequence concentration of the copolymers were calculated according to 13C-NMR spectra. The influences of temperature and initial molar ratio of butadiene to isoprene （Bd to Ip） on the distribution of the chain segments in the TBIR copolymers were discussed. The correlation of copolymer compositions and thermal properties were also evaluated, which facilitated the understanding of controlling the degree of crystallinity and the transition tempera^re by changing Bd content and temperature.
基金financially supported by the National Key Technology R&D Program of China(No.2011BAE26B05)the Shandong Province Natural Science Fund for Distinguished Young Scholars(No.JQ201213)+2 种基金National Natural Science Foundation of China(No.21174074)Shandong Province Science and Technology Development Plan(No.2012GGA05042)the Major Projects of Independent Innovation Achievements Transformation in Shandong Province(No.2013ZHZX1A0207)
文摘A series of trans-1,4-butadiene/isoprene copolymers were prepared using the catalyst system TiCl4/MgCl2-Al（i- Bu）3 with bulk precipitation technology at different temperatures. Monomers reactivity ratios were calculated based on the Kelen-Tiid6s （K-T） method and the Mao-Huglin （M-H） method. The influence of temperature on copolymer composition and polymerization rate was discussed in detail. The increase of reaction temperature brought the decrease of butadiene reactivity ratio rBd and supplied an effective adjustment on copolymers＇ composition distribution.
文摘Plant leaves may emit a substantial amount of volatile organic compounds （VOCs） into the atmosphere, which include isoprene, terpene, alkanes, alkenes, alcohols, aldehydes, eters, esters and carboxylic acids. Furthermore, most of these compounds actively participate in tropospheric chemistry. Great progresses have been made in linking emission of these compounds to climate. However, the VOCs emission function in plant is still not clear. Recently, some evidence has emerged that the production and the emission of VOCs, such as isoprene and monoterpenes, which account for 80% of total VOCs, exhibit plant protection against high temperatures. These increases in VOCs emissions could contribule in a significant way to plant thermotolerance. This perspective summarizes some latest literatures regarding the VOCs emission-dependent thermoprotection in plant species subjected to high temperature stress, presents the achievement in studies concerning plant VOCs emission-dependent thermotolerance, and then exhibits the proposed mechanisms of such plant thermotolerance. Finally open questions regarding the plant VOCs emission were shown, and the future researches were proposed.
文摘Given the key role of biogenic volatile organic compounds(VOCs) to tropospheric chemistry and regional air quality, it is important to generate accurate VOCs emission inventories. However, only a less fraction of plant species, in temperate grassland of Inner Mongolia, has been characterized by quantitative measurements. A taxonomic methodology, which assigns VOCs measurements to unmeasured species, is an applicable and inexpensive alternation for extensive VOCs emission survey, although data are needed for additional plant families and genera to further validate the taxonomic approach in grassland vegetation. In this experiment, VOCs emission rates of 178 plant species were measured with a portable photoionization detector(PID). The results showed the most of genera and some families have consistent feature of their VOCs emission, especially for isoprene, and provide the basic premise of taxonomic methodology to develop VOCs emission inventories for temperate grassland. Then, the taxonomic methodology was introduced into assigning emission rate to other 96 species, which no measured emission rates available here. A systematical emission inventory of temperate grassland vegetation in Inner Mongolia was provided and further evidence that taxonomy relationship can serve as a useful guide for generalizing the emissions behavior of many, but not all, plant families and genera to grassland vegetation.
基金supported by the National 863 program(No.2006AA03Z552)China Petroleum Chemical Corp. (SINOPEC) and Program for Changjiang Scholars and Innovative Research Teams in Universities(IRT0706)
文摘A series ofbutadiene-isoprene copolymers （BIR） with various compositions were synthesized with a neodymiumbased catalyst system. The microstructure, composition and sequence of copolymers were characterized by FTIR and ^13C-NMR spectroscopy. The crystallization behavior of the BIR copolymers was investigated by DSC analysis. The results demonstrate that the content of cis-1,4 configuration in both butadiene （Bd） and isoprene （Ip） units are around 98% when Bd content in feed （fBd） covering the range from 55.7 mol% to 96.0 mol%. The reactivity ratios of Bd and Ip were determined to be 1.40 and 0.48 respectively. The random copolymers of Bd and Ip show only one glass transition temperature （Tg） from -107.4℃ to -80.5℃, which is dependent on the composition and fits nicely with Fox equation. The sequence distribution followed the first-order Markov statistical model. It is found that the copolymer chains with higher Bd content contain longer polybutadiene （PBd） segments, and the sequence length of PBd segments （NBd） exhibits great influence on the crystallization behavior of the copolymer. The copolymers with NBd ≥ 11.8 could crystallize at low temperatures （-71℃ to -43℃）. The crystallization temperature and enthalpy values decreased gradually with decreasing NBd. The copolymers with NBd ≤ 7.9 are amorphous even at very low temperatures （0℃ to -150℃） due to the short PBd segments.
基金This work is supported by Knowledge Creative Project (KZCX2-204) of Chinese Academy of Sci-ences and the National Natural Scienc
文摘In order to analyze biogenic volatile organic compounds in the atmosphere, an automated gas chromatography is developed and employed at the laboratory of National Center for Atmospheric Research (NCAR) during January to July, 2000. A small refrigerator was used so as to remove water in the air sample from gas line, and get accurate concentrations of volatile organic compounds. At 5°C, good water removing efficiency can be obtained at controlled flow rate. Air samples were collected around the building of Mesa Lab. of NCAR and analyzed by this gas chromatography system. This paper reports this gas chromatography system and results of air samples. The experimental results show that this gas chromatography system has a good reproducibility and stability, and main interesting volatile organic compounds such as isoprene, monoterpenes have an evident diurnal variation.
基金supported by the Project of China National Science and Technology Support Plan (Grant No. 2014BAC23B01)the Project of China Environmental Protection Public Science and Technology Research Fund (Grant No. 201409005 and No. 201509002)the Strategic Pilot Science and Technology Project of the Chinese Academy of Sciences (Class B) (Grant No. XDB05010200)
文摘Continuous observation of isoprene, β-pinene and β-pinene was carried out in a typical urban area of Beijing from March 2014 to February 2015, using an AirmoVOC online analyzer. Based on the analysis of the ambient level and variation characteristics of isoprene, β-pinene and β- pinene, the chemical reactivity was studied, and their sources were identified. Results showed that the concentrations of isoprene, α-pinene and β-pinene in the urban area of Beijing were lower than those in richly vegetated areas; the concentrations of isoprene were at a moderate level compared with those of previous studies of Beijing. Concentrations of isoprene, α-pinene and β-pinene showed different seasonal, monthly, daily and diurnal variations, and all of the three species showed higher level at night than those in the daytime as a whole, the variations of isoprene, α-pinene and β-pinene mainly influenced by emission of sources, photochemical reaction, and meteorological parameters. Isoprene was the largest contributor to the total OFP values than β-pinene and β-pinene. α-Pinene was the largest contributor to the total SOAFP values than isoprene and β-pinene in autumn, while isoprene was the largest one in other seasons. Isoprene, α-pinene and β-pinene were derived mainly from biological sources; and α- pinene level were also affected by industrial sources. To reduce the concentrations of isoprene, α-pinene and β-pinene, it is necessary to scientifically select urban green plant species, and more strict control measures should be taken to reduce the emission of β-pinene from industrial sources, such as artificial flavors and resins synthesis processes.
基金supported by the National Natural Science Foundation of China(No.41073101)the Youth Fund of Education Department of Sichuan Province(No.11ZB065)the Open Fund of State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex(SCAPC)of Tsinghua University(No.110001122)
文摘PM2.5 aerosol samples were collected over 12 hr and 24 hr intervals in an inland background area, Gongga Mountain National Nature Reserve（hereafter shortened to Gongga）, during the summer of 2011. Polar organic tracers, inorganic ions and meteorological data were measured. The purpose of this work was to investigate the variation patterns, formation and sources of the secondary organic aerosol tracers in the studied atmosphere. The average concentrations of isoprene oxidation products, α-pinene oxidation products, β-caryophyllinic acid, sugars, sugar alcohols and anhydrosugars were 88.6 ± 106.1, 3.6 ± 5.7,0.13 ± 0.30, 13.6 ± 13.1, 31.9 ± 31.4 and 14.8 ± 10.7 ng/m^3 respectively in all aerosol samples.The aged α-pinene second organic aerosol（SOA） tracers（i.e., 3-hydroxyglutraric acid（3 HGA）, 3-hydroxy-2,2-dimethylglutaric acid（HDMGA）, 3-acetylpentandioic acid（APDA） and 3-methyl-1,2,3-butanetricarboxylic acid（MBTCA）） correlated significantly with each other in the 24 hr PM2.5 aerosol samples, indicating that OH· is the major factor controlling the formation of these α-pinene SOA tracers. Using the positive matrix factorization（PMF） model and the tracer-based source apportionment method, we calculated that isoprene oxidation products, α-pinene oxidation products, sesquiterpene oxidation products, biomass burning, fungi spores and anthropogenic SOA accounted for 21.9% ± 5.5%, 8.4% ± 2.1%, 3.0% ± 0.7%, 5.2% ± 5.3%, 5.0% ± 6.2% and 31.4% ± 7.8% of organic carbon respectively during the sampling period.
基金supported by the Administration of Science and Technology of Jilin Province,China (No.200505254)
文摘Neodymium chloride isopropanol complex （NdCl3.3＇prOH） activated by modified methylaluminoxane （MMAO） was examined in isoprene polymerization in hexane, with regards to Nd compounds, aluminum （Al） compounds, [Al]/[Nd] ratio, polymerization temperature and time. NdCl3＇3iprOH exhibited high activity producing polymers feasting high cis-l,4 stereospecificity （〉 96%）, very high molecular weight （Mn 〉 1.0 × 10^6） and fairly narrow molecular weight distribution （MWD, Mw/Mn 〈 2.0） simultaneously. In comparison, neodymium isopropoxide also showed high activity providing polymers with narrow MWD （Mw/Mn = 2.07）, but somewhat low cis-1,4 content （ca. 92%）, while neodymium chloride had no activity under present polymerization conditions. The Al compounds affected the polymer yield in the order of Al（i-Bu）3 〉 MMAO 〉 Al（i-Bu）2H. MMAO as cocatalyst afforded polyisoprene with high Mn over 1.0 × 10^6, whereas as stronger chain transfer agent than MMAO, AI（i-Bu）3 and AI（i-Bu）EH yielded polymers with low Mn （1.0 × 10^5-8.0 × 10^5）. NdCl3·3＇PrOH/MMAO catalyst showed a fairly good catalytic activity even at relatively low [Al]/[Nd] ratio of 30, and the produced polymer remained high cis-1,4 content of 95.8% along with high Mn over 1.0× 10^6 even at elevated temperatures up to 70℃. The polymerization rate is of the first order with respect to the concentration of isoprene. The mechanism of active species formation was discussed preliminarily.
基金The authors are indebted to the financial supports of the National Natural Science Foundation of China （No.20774078 and the Key Program No.20434020）；the Special Funds for Major Basic Research Projects （G2005CB623802）.
文摘Neodymium-based heterocyclic Schiff base complex was prepared and applied for the coordination polymerization of isoprene. This complex polymerized isoprene to afford products featuring high cis-1,4 stereospecificity （ca. 95%） and high molecular weight （ca, 10^5） in the presence of the triisobutyl aluminium （AliBu3） as cocatalyst, The microstructure of obtained polyisoprene was investigated by FTIR, 1^H NMR. Two different kinds of active centers in the catalyst system were examined by GPC method.
基金financially supported by the National Natural Science Foundation of China(32070085,32200050,31871784,and 32021005)the Natural Science Foundation of Jiangsu Province(BK20221079)+4 种基金National Postdoctoral Program for Innovative Talents(BX20220136)the Jiangsu Funding Program for Excellent Postdoctoral Talent(2022ZB498)the Fundamental Research Funds for the Central Universities(JUSRP52019A,JUSRP121010 and JUSRP221013)National Key Research and Development Program of China(2020YFA0908300)Postgraduate Research&Practice Innovation Program of Jiangsu Provence(KYCX18_1797)。
文摘Terpenoids are the largest family of natural products.They are made from the building block isoprene pyrophosphate(IPP),and their bioproduction using engineered cell factories has received a great deal of attention.To date,the insufficient metabolic supply of IPP remains a great challenge for the efficient synthesis of terpenoids.In this work,we discover that the imbalanced metabolic flux distribution between the central metabolism and the IPP supply hinders IPP accumulation in Bacillus subtilis(B.subtilis).Therefore,we remodel the IPP metabolism using a series of genetically encoded two-input-multioutput(TIMO)circuits that are responsive to pyruvate or/and malonyl-CoA,resulting in an IPP pool that is significantly increased by up to four-fold.As a proof-of-concept validation,we design an IPP metabolism remodeling strategy to improve the production of three valuable terpenoids,including menaquinone-7(MK-7,4.1-fold),lycopene(9-fold),andβ-carotene(0.9-fold).In particular,the titer of MK-7 in a 50-L bioreactor reached 1549.6 mg·L^(-1),representing the highest titer reported so far.Thus,we propose a TIMO genetic circuits-assisted IPP metabolism remodeling framework that can be generally used for the synergistic fine-tuning of complicated metabolic modules to achieve the efficient bioproduction of terpenoids.
基金The National Natural Science Foundation of China(No. 40075027 40375038)
文摘The first detailed inventory for volatile organic compounds(VOC) emissions from vegetation over Yunnan Province, China was presented. The spatially and temporally resolved inventory was developed based on a geographic information system(GIS), remote sensing(RS) data and field measurement data, such as digitized land-use data, normalized difference vegetation index(NDVI) and temperature data from direct real-time measurement. The inventory has a spatial resolution of 5 km×5 km and a time resolution of 1 h. Urban, agriculture, and natural land-use distributions in Yunnan Province were combined with biomass factors for each land-use category to produce a spatially resolved biomass inventory. A biogenic emission inventory was developed by combining the biomass inventory with hourly emission rates for tree, shrub and ground cover species of the study area. Correcting for environmental factors, including light intensity and temperature, a value of 1.1×10 12 gC for total annual biogenic VOC emissions from Yunnan Province, including 6.1×10 11 gC for isoprene, 2.1×10 11 gC for monoterpenes, and 2.6×10 11 gC for OVOC was obtained. The highest VOC emissions occurred in the northwestern, southwestern and north region of Yunnan Province. Some uncertainties were also discussed in this study.
基金supported by Young Professionals Program in Institute of Chemistry,Chinese Academy of Sciences (No. Y3297B1261)financial support from CAS project (Nos. Y31M0112C1 and Y5294512C1)
文摘Here we show a study of vibrational spectroscopic identification of a few typical organic compounds which are known as the main sources of organic aerosols（OAs） particle matter in air pollution. Raman and IR spectra of isoprene, terpenoids, pinenes and their mixture are meticulously examined, showing distinguishable intrinsic vibrational spectroscopic fingerprints for these chemicals, respectively. As a reference, first-principles calculations of Raman and infrared activities are also conducted. It is interestingly found that, the experimental spectra are peak-to-peak consistent with the DFT（Density Functional Theory）-calculated vibrational activities. Also found is that, in a certain case such as for bpinene, a dimer model, rather than an isolated single molecular model, reproduces the experimental results, indicating unneglected intermolecular interactions. Starting with this study, we are endeavoring to advocate a database of Raman/IR fingerprint spectra for OA haze identification.
基金supported by the National 863 program(No.2006AA03Z552)the National Natural Science Foundation of China(No.50903003)China Petroleum Chemical Corp.(SINOPEC)and Program for Changjiang Scholars and Innovative Research Teams in Universities(IRT0706)
文摘FTIR spectroscopy in combination with a diamond tipped attenuated total reflectance （ATR） immersion probe was utilized to study in situ the copolymerization of butadiene （Bd） and isoprene （Ip） with neodymium-based catalyst in hexane. The relationship between the signal intensity of monomer and its concentration was investigated. The kinetic study of copolymerization of Bd and Ip was further conducted, and the monomer reactivity ratios were determined via in situ ATR FTIR. The signal band at 1010 cm^-1 was assigned to wagging vibration of Bd and its intensity was proportional to Bd concentration （[Bd]） in the range of 0.46-3.88 mol.L^-1. The signal bands at 890 and 989 cm^-1 were assigned to wagging vibration of Ip and the signal intensity was also proportional to Ip concentration （[Ip]） in the range of 0.08-4.73 mol·L^-1 at 890 cm^-1 and 0.08-7.49 mol·L^-1 at 989 cm^-1, respectively. Thus the signal band at 1010 cm^-1 was chosen to monitor Bd concentration and bands at 989 and 890 cm^-1 to monitor Ip concentration during the copolymerization, respectively. It was demonstrated that the conversions of Bd and Ip calculated from FTIR data agreed very well with those obtained gravimetrically. The poiymerization rates were first order with respect to both [Bd] and [Ip], respectively at different polymerization temperatures. The apparent propagation activation energy for Bd and Ip could be determined to be 54.4 kJ·mol^-1 and 57.7 kJ·mol^-1, respectively. The monomer reactivity ratios were calculated to be 1.08 for Bd （rBd） and 0.48 for IP （rIp） based on FTIR data. The Bd-Ip copolymer products with random sequence could be obtained with only one glass transition temperature.
基金supported by National Natural Science Foundation of China(No.50573005)
文摘A new kind of multifunctional macromolecular initiator with Sn-C bonds and polydiene arms was synthesized by living anionic polymerization. At first, polydiene-stannum chloride （PD-SnCl3） was prepared by the reaction of n-butyl-Li （n-BuLi）, stannic chloride （SnCl4） and diene. Then PD-SnCl3 was used to react with the dilithium initiator to prepare the multifunctional organic macromolecular initiators. The result suggested that the initiators had a remarkable yield by GPC, nearly 90%. By using these multifunctional macromolecular initiators, styrene and butadiene were effectively polymefized via anionic polymerization, which gave birth to novel miktoarm star copolymers. The relative molecular weight and polydispersity index, microstructure contents, copolymerization components, glass transition temperature （Tg） and morphology of the miktoarm star copolymers were investigated by GPC-UV, ~H NMR, DSC and TEM, respectively. 2009 Xing Ying Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
基金supported by the National Natural Science Foundation of China[grant number 41405138]the National High Technology Research and Development Program of China[grant number 2013AA122002]
文摘Isoprene emissions emitted from vegetation are one of the most important precursors for tropospheric ozone and secondary organic aerosol formation. The authors estimate the biogenic isoprene emissions in China over 2006-2011 using a global chemical transport model （GEOS- Chem） driven by meteorological fields from the assimilated meteorological data from MERRA. The authors incorporate three different parameterizations of isoprene-CO2 interaction into the model, and perform three sensitivity simulations to investigate the effect of CO2 inhibition on isoprene emissions for the period 2006-2011 in China. The annual isoprene emissions rate across China is simulated to be 12.62 Tg C yr-1, averaged over 2006-2011, and decreases by about 2.7%-7.4% when the CO2 inhibition schemes are included. The CO2 inhibition effect might be significant in regions where the CO2 concentration and isoprene emissions are high. Estimates of isoprene emissions can differ depending on the scheme of CO2 inhibition. According to the results obtained from the sensitivity simulations, the authors find that the CO2 inhibition effect leads to 5.6% ±2.3% reductions in annual isoprene emissions over China. The authors also find that inclusion of CO2 inhibition can substantially alter the sensitivity of isoprene emissions to the changes in meteorological conditions during the study period.
