Isolation Of Element Carbon And Chemical Structure,Absorbance And Cytotoxicity Of Aerosol Organic Carbon

Atmospheric carbonaceous aerosols are the important components of atmospheric aerosols and have become a hot topic of concern worldwide due to their significant climate and human health effects.Carbonaceous aerosols are generally classified into Elemental Carbon?EC?and Organic Carbon?OC?.Radiocarbon isotope(¹⁴C)is a powerful tool for tracing carbonaceous aerosol sources,but the main factor limiting the application of this technology to carbonaceous aerosol research is the complete separation of OC and EC.In addition,the organic carbon?OC?component is a very important chemical component in atmospheric aerosols.Because it contains thousands of compounds,the composition of the components is highly complex,so the understanding of its molecular composition characteristics is still limited;and the understanding of the relationship between molecular composition and absorbance characteristics and early health effects is more limited.In view of the difficult problems in the separation of carbonaceous aerosols and the important scientific issues such as the relationship between the composition characteristics of OC molecules and the characteristics of light absorption and cytotoxicity,in this study,hydropyrolysis,Nuclear Magnetic Resonance?NMR?,Fourier Transform Ion Cyclotron Resonance Mass Spectrometry?FT-ICR MS?,absorbance properties and cytotoxicity were determined to study typical carbonaceous aerosol samples.In the first part of the study,a hydropyrolysis separation EC method for carbon isotope analysis of carbonaceous aerosols was established,and several common EC methods were evaluated using typical carbonaceous aerosol formulations.First,seven typical carbonaceous aerosol samples,such as bio-combustion,coal-fired and motor vehicle emissions samples,and Beijing and Guangzhou ash aerosol samples were used to explore the experimental conditions of hydropyrolysis.The hydropyrolysis products of different conditions were characterized by solid state nuclear magnetic resonance?NMR?and elemental analysis and isotope techniques.It was finally determined that the hydropyrolysis method can effectively remove non-EC organic matter in aerosol samples under the conditions of 15MPa hydrogen pressure and 550°C temperature.This method is a stable and effective separation EC for ¹⁴C analysis method.Then,several common EC separation methods were evaluated using different ratiometric samples of typical carbonaceous aerosols.The results showed that the order of EC/TC ratios of the hydropyrolysis method,the two-step heating method CTO-375,the thermo-optic method?S?and the thermal-optical method after water-extracted?HS?is EC/TC?CTO-375?<EC/TC?S?<EC/TC?HS?<EC/TC?hypy?and EC/TC?TOT?,and EC/TC?TOT?value is not significantly different?p>0.05?from the EC/TC?hypy?value.The EC/TC%of the hydropyrolysis sample and its NIOSH870-TOT method EC/TC?TOT?%trend line slope reached 0.9881,indicating that the hydropyrolysis method as a quantitative carbonaceous aerosol EC method is in good agreement with the NIOSH870-TOT method.The results of thermochemical analysis show that the thermochemical properties of EC separated by the same method are similar,and there are great differences between different methods.The carbon content of the aerobic high temperature zone?550?C-870?C,PC+EC1-6?is used to characterize the fire resistance component.It can be concluded that the thermal stability of the separated EC is CTO-375.EC?17%-48%?<thermo-optic method?S and SH?EC?72%-82%?<catalytic hydrogenation method EC?90.5%-94.6%?.The results of FTIR comparison showed that the CTO-375 method separated EC had the highest proportion of aliphatic hydrocarbons,while the HS method separated EC had the lowest proportion of aliphatic hydrocarbons.The other two methods were in the middle.Pearson correlation analysis was performed using FTIR?A and XY factors?and thermochemical properties?the ratio of each carbon component?.The results show that the thermochemical properties of the separated EC samples by each method are peaked at OC3+OC4?anaerobic high temperature stage?,indicating that its aliphatic hydrocarbon/aromatic hydrocarbon ratio is larger,and it can be said that the aliphatic hydrocarbon content is higher.Samples with peaks in the EC fraction?aerobic high temperature stage?indicate a higher aromatic hydrocarbon/aliphatic hydrocarbon ratio and higher aromatic hydrocarbon content.The results of stable carbon isotope analysis of the samples indicate that the?¹³C results of the EC by hydropyrolysis are not significantly different from the theoretical calculations?p>0.05?.The results of ¹⁴C analysis showed that the thermal-optical method after water-extracted?HS?were the closest to the theoretical calculations.And if the hydropyrolysis method changed corn stalks to pine,there was no significant difference from the theoretical calculation?p>0.05?.A comprehensive analysis of the experimental results of carbon isotope(¹³C and ¹⁴C)in each experimental method,we recommend hydropyrolysis method and the thermal-optical method after water-extracted?HS?separation of EC for carbon isotope analysis,both methods have their own advantages and disadvantages.The advantage of the thermal-optical method after water-extracted?HS?is that the operation is simple,and the disadvantage is that the result is susceptible to the sample matrix,the operator and the environmental conditions.The hydropyrolysis method,on the other hand,has the advantages of being more stable and reliable,and the disadvantage is that the operation is cumbersome and the equipment and methods need to be more perfect.In the second part of the paper,13 typical combustion sources including bio-combustion?non-fossil source?,coal combustion and motor vehicle emissions?fossil source?were analyzed using NMR,FT-ICR MS and soluble component absorbance characteristics and inflammatory effect analysis techniques.The molecular composition characteristics?NMR and FT-ICR MS?,absorbance characteristics?MAE and AAE?and cytotoxicity data?ROS,IL-6 and IL-8?of typical carbonaceous aerosol samples were obtained.Further,the relationship between molecular composition characteristics,light absorption characteristics and cytotoxicity data was analyzed.The following results were obtained:The results of NMR analysis indicated that the composition of biomass samples in the methanol-soluble components of the three types of typical emission source aerosols was the most complex,and the content of polar components such as oxygen-saturated aliphatic protons was higher;motor vehicle emissions have high aliphatic protons,mainly small polar hydrocarbon components;coal-fired samples are mainly composed of aromatic ring structure and aliphatic carbon connected to unsaturated.Among the water-soluble organic components,the composition of biomass samples is the most complicated,and the content of protons and aromatic ring protons in the saturated oxygen is higher;motor vehicles emit high levels of aliphatic protons and low levels of aryl ring protons;coal-fired samples have a high content of unsaturated protons linked to aliphatic protons and a small amount of aromatic ring protons.The results of FT-ICR MS analysis indicate that biomass burning,motor vehicle and coal-fired emissions are important potential sources of soluble organic matter in atmospheric aerosols,while fossil source emissions?motor vehicles and coal-fired?are very important source of nitrogen-containing and sulfur-containing compounds.These nitrogen and sulfur containing compounds may be composed of aromatic organic sulfates and nitrogen oxide organic sulfates.The main CHO,CHON,and CHOS types of typical soluble organic matter samples of typical carbonaceous aerosols are further subdivided according to the number of heteroatoms?O,N,S?.The results show that there are large differences in the various types of compounds of methanol soluble organic matter?M?and water soluble organic matter?H?.The main difference is that the methanol soluble organic matter?M?has a higher hypoxia component,possibly because the higher the oxygen content,the greater the polarity,so the content is higher in the water-soluble organic matter.The results of light absorption characteristics?MAE and AAE?showed that the order of methanol extracted organic matter MAE of three types of samples was coal combustion>biomass burning>motor vehicle emission products;the MAE values of water-soluble organic matter of biomass burning and coal-fired emissions were similar.Both are greater than the vehicle emissions.The AAE comparison between the three types of samples is not much different;the overall comparison is that the AAE value of the water-soluble organic matter is greater than the methanol soluble organic matter AAE value.The results of correlation between the absorbance characteristics?MAE and AAE?and their molecular composition characteristics?NMR and FT-ICR MS?show that the typical carbonaceous aerosol soluble organic matter absorbance characteristics MAE value and double bond index?DBEw?,aromatic index?AImod?are positive related?[r=0.64,p<0.01,95%CI,0-0.83]and[r=0.61,p<0.01,95%CI,0.08⁰.79]?,but negatively correlated with OM/OCw.This indicates that the higher the sample aromaticity?AImod?,the larger the MAE value.The regression equation for MAE and NMR?aliphatic hydrogen/aromatic hydrogen?is y=1.341x^-0.341.This equation also requires a large number of actual sample verification and improvement.The AAE value of soluble organic matter was positively correlated with NMR?1.9-3.2?ppm,negatively correlated with NMR?0.7-1.9??r=0.81,p<0.01,95%CI,0.68-0.91?,positively correlated with O/Cw and CHOS%,and negatively correlated with molecular weight MWw.The soluble organic AAE value may be related to the unsaturated atom containing O,S and other heteroatoms.The higher the content of CHOS compound,the larger the AAE value;the larger the molecular weight,the smaller the AAE value.The results of cytotoxicity?ROS,IL-6 and IL-8?showed that the order of inflammatory effects of the same quality soluble organic matter in the three types of samples is coal combustion>motor vehicle>biomass combustion emission products.Inflammation response of fossil fuel combustion are 1.5 to 3 or more times that of biomass burning emissions.The ROS value of methanol-extracted organic matter in motor vehicle emission products is the largest among the three types of samples.According to the comprehensive analysis,the cytotoxicity of typical carbonaceous aerosol soluble organic matter are fossil source samples>biomass samples,and the basic order is consistent with coal combustion>motor vehicle>biomass combustion emission products.The correlation between cytotoxicity?ROS,IL-6 and IL-8?and their molecular composition characteristics?NMR and FT-ICR MS?showed that the typical carbonaceous aerosols in methanol soluble and water-soluble organic matter caused ROS mainly CHON compounds?r=0.57,p<0.01,95%CI,0.13-0.81?.Especially from N2O4 to N2O10 compounds,as well as S1O3 compounds in CHOS.The inflammatory factors?IL-6 and IL-8?that cause early health effects are mainly CHOS compounds,especially S1O4 and S1O3 compounds.In addition,the inflammatory effects?IL-6 and IL-8?are positively correlated with to the aromaticity index?AImod??[r=0.64,p<0.01,95%CI,0.19-0.82]and[r=0.72,p<0.01,95%CI,0.37⁰.86]?,but negatively correlated with the values of H/C?[r=-0.47,p<0.05,95%CI,-0.72^-0.05]and[r=-0.55,p<0.01,95%CI,-0.74^-0.18]?and O/C?[r=-0.76,p<0.01,95%CI,-0.89^-0.58]and[r=-0.72,p<0.01,95%CI,-0.85^-0.54]?.In other words,the higher the degree of aromaticity?AImod?,the greater the inflammatory effect;the higher the degree of oxidation,the smaller the inflammatory effect.It is speculated that the main soluble organic substances that cause inflammation in aerosols are organic sulfur-containing and nitrogen-containing compounds,especially those with low oxidation and high unsaturation.