Analytical methodologies for oxidized organic compounds in the atmosphere (original) (raw)
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Environmental Science & Technology, 2015
Very recent studies have reported the existence of highly oxidized multifunctional organic compounds (HOMs) with O/C ratios greater than 0.7. Because of their low vapor pressure, these compounds are often referred as extremely low-volatile organic compounds (ELVOCs), and thus, they are able to contribute significantly to organic mass in tropospheric particles. While HOMs have been successfully detected in the gas phase, their fate after uptake into particles remains unclear to date. Hence, the present study was designed to detect HOMs and related oxidation products in the particle phase and, thus, to shed light on their fate after phase transfer. To this end, aerosol chamber investigations of α-pinene ozonolysis were conducted under near environmental precursor concentrations (2.4 ppb) in a continuous flow reactor. The chemical characterization shows three classes of particle constituents: (1) intact HOMs that contain a carbonyl group, (2) particle-phase decomposition products, and (3) highly oxidized organosulfates (suggested to be addressed as HOOS). Besides chamber studies, HOM formation was also investigated during a measurement campaign conducted in summer 2013 at the TROPOS research station Melpitz. During this field campaign, gas-phase HOM formation was found to be correlated with an increase in the oxidation state of the organic aerosol.
Atmospheric Chemistry and Physics, 2015
Field observations over the past decade indicate that a significant fraction of organic aerosol in remote areas may contain highly oxidized molecules. Aerosol processing or further oxidation (aging) of organic aerosol has been suggested to be responsible for their formation through heterogeneous reaction with oxidants and multigenerational oxidation of vapours by OH radicals. In this study we investigated the influence of several aging processes on the molecular composition of secondary organic aerosols (SOA) using direct infusion and liquid chromatography high-resolution mass spectrometry. SOA was formed in simulation chamber experiments from ozonolysis of a mixture of four biogenic volatile organic compounds (BVOC): α-pinene, β-pinene, 3 -carene and isoprene. The SOA was subsequently aged under three different sets of conditions: in the dark in the presence of residual ozone, with UV irradiation and OH radicals, and using UV light only. Among all studied conditions, only OH radical-initiated aging was found to influence the molecular composition of the aerosol and showed an increase in carbon oxidation state (OS C ) and elemental O / C ratios of the SOA components. None of the aging processes produced an observable effect on the oligomers formed from ozonolysis of the BVOC mixture, which were found to be equally abundant in both "fresh" and "aged" SOA. Additional experiments using α-pinene as the sole precursor demonstrated that oligomers are an important group of compounds in SOA produced from both ozonolysis and OH radical-initiated oxidation processes; however, a completely different set of oligomers is formed under these two oxidation regimes. SOA from the OH-initiated oxidation of α-pinene had a significantly higher overall OS C and O / C compared to that from pure ozonolysis experiments confirming that the OH radical reaction is more likely to be responsible for the occurrence of highly oxidized species in ambient biogenic SOA.
Atmospheric Chemistry and Physics Discussions, 2015
Field observations over the past decade indicate that a significant fraction of organic aerosol in remote areas may contain highly oxidised molecules. Aerosol processing or further oxidation (ageing) of organic aerosol has been suggested to be responsible for their formation through heterogeneous uptake of oxidants and multigenerational oxida-5 tion of vapours by OH radicals. In this study we investigated the influence of several ageing processes on the molecular composition of secondary organic aerosols (SOA) using direct infusion and liquid chromatography ultrahigh resolution mass spectrometry. SOA was formed in simulation chamber experiments from ozonolysis of a mixture of four biogenic volatile organic compounds (BVOC): α-pinene, β-pinene, ∆ 3 -carene and 10 isoprene. The SOA was subsequently aged under three different sets of conditions: in the dark in the presence of residual ozone, with UV irradiation and OH radicals, and using UV light only. Among all studied conditions, only OH radical-initiated ageing was found to influence the molecular composition of the aerosol and showed an increase in carbon oxidation state (OS C ) and elemental O/C ratios of the SOA components.
New developments on emerging organic pollutants in the atmosphere
Environmental Science and Pollution Research, 2012
Background The continuous progress in analytical techniques has improved the capability of detecting chemicals and recognizing new substances and extended the list of detectable contaminants widespread in all environmental compartments by human activities. Most concern is focused on water contamination by emerging compounds. By contrast, scarce attention is paid to the atmospheric sector, which in most cases represents the pathway of diffusion at local or global scale. Information concerning a list of organic pollutants is provided in this paper. Methods The volatile methyl tert-butyl ether and siloxanes are taken as examples of information insufficient with regard to the potential risk induced by diffusion in the atmosphere. Illicit drugs, whose presence in the air was ascertained although by far unexpected, are considered to stress the needs of investigating not solely the environmental compartments where toxic substances are suspected to display their major influence. Finally, the identification of two recognized emerging contaminants, i.e., tris(2-chloroisopropyl) phosphate and N,N-diethyl-m-toluamide, in aerosols originally run to characterize other target compounds is presented with the purpose of underlining the wide diffusion of the organic emerging contaminants in the environment.
Aerosol Science and Technology, 2013
Spectrophotometric methods were developed to quantify carbonyl, hydroxyl, carboxyl, and ester groups in samples with composition typical of oxidized atmospheric organic aerosol. The methods employ derivatizing agents to convert functional groups to characteristic colored derivatives that are quantified by spectrophotometry. Effects of molecular structure on quantification have been evaluated by measuring calibration curves for a variety of monofunctional and multifunctional compounds. In addition, potential interferences from compounds containing nontarget functional groups have been determined and methods developed to eliminate these interferences. Detection limits are approximately 0.01, 0.02, 0.03, and 0.1 µmoles for carbonyl, hydroxyl, carboxyl, and ester groups, respectively. The use of these methods for analysis of secondary organic aerosol (SOA) composed of a complex mixture of oxidized compounds is also demonstrated.
Secondary organic compounds in atmospheric aerosols: speciation and formation mechanisms
Journal of The Brazilian Chemical Society, 2005
Atendendo às características fotoquímicas atmosféricas, as áreas florestadas dos países mediterrânicos constituem um ambiente apropriado para investigar os aerossóis orgânicos secundários. Este estudo visa estudar in situ a composição dos aerossóis, em particular os produtos resultantes da foto-oxidação de compostos orgânicos voláteis biogênicos, considerando simultaneamente a contribuição antropogênica, e explicar como estes compostos surgem nos aerossóis. As amostragens de matéria particulada atmosférica ocorreram em dois locais: uma floresta de Abies boressi na Grécia central e numa localidade rural próxima da costa, no centro de Portugal. A matéria orgânica presente nos aerossóis foi extraída com solventes e analisada por cromatografia gasosa e espectrometria de massa. Detectaram-se vários produtos resultantes da foto-oxidação de compostos orgânicos voláteis emitidos pela vegetação ou de precursores antropogênicos. Estes constituintes secundários incluem derivados de alcenos, ácidos oxo-, di-e monocarboxílicos, compostos aromáticos oxigenados, azaarenos, tio-arenos e muitos produtos da foto-oxidação dos terpenos. Esta experiência in situ possibilitou a confirmação da presença de constituintes secundários, os quais haviam sido estudados quase exclusivamente em atmosferas simuladas através de ensaios laboratoriais. Alguns mecanismos reacionais que explicam a formação de compostos na fase particulada a partir de precursores são aqui apresentados.
Talanta, 2013
A method for quantifying secondary organic aerosol compounds (SOA) and water soluble secondary organic aerosol compounds (WSOA) produced from photo-oxidation of complex mixtures of volatile organic compounds (VOCs) in smog chambers by gas chromatography/mass spectrometry (GC/MS) has been developed. This method employs a double extraction with water and methanol jointly to a double derivatization with N,O-bis (trimethylsilil) trifluoroacetamide (BSTFA) and O-(2,3,4,5,6)-pentafluorobenzyl-hydroxylamine hydrochloride (PFBHA) followed by an analysis performed by GC/MS. The analytical procedure complements other methodologies because it can analyze SOA and WSOA compounds simultaneously at trace levels. As application, the methodology was employed to quantify the organic composition of aerosols formed in a smog chamber as a result of photo-oxidation of two different mixtures of volatile organic compounds: an anthropogenic mixture and a biogenic mixture. The analytical method allowed us to quantify up to 17 SOA compounds at levels higher than 20 ng m À 3 with reasonable recovery and a precision below 11%. Values found for applicability, selectivity, linearity, precision, recovery, detection limit, quantification limit and sensitivity demonstrated that the methodology can be satisfactorily applied to quantify SOA and WSOA.
Mass Spectrometric Analysis of Organic Aerosol Composition: Laboratory and Ambient
2012
Organic compounds contribute a significant mass fraction of ambient aerosol and play a role in determining the physiochemical properties of ambient aerosol. A significant fraction of organic aerosol is secondary organic aerosol (SOA), which is produced when the volatile organic compounds (VOCs) originated from various anthropogenic and biogenic sources react with atmospheric oxidants such as ozone, hydroxyl radicals, and nitrate radicals to form lower volatility organic compounds, which subsequently partition into the particle phase. Understanding the composition of ambient aerosol is crucial for identifying their sources and formation mechanisms and predicting their properties and effects on various ambient processes. This thesis focuses on investigating the composition of laboratory–generated SOA formed from the oxidation of biogenic VOCs of atmospheric importance (isoprene and β–caryophyllene) and ambient aerosol collected in the field campaigns using advanced mass spectrometric ...
Volatile organic compounds in the polluted atmosphere: The 3rd ACCENT Barnsdale Expert Meeting
2007
Volatile organic compounds (VOC) play a central role in air pollution; they react with nitrogen oxides in the presence of sunlight to generate ozone and other photo-oxidants; they also, in the course of their various reactions, can form higher molecular weight organic compounds which condense to produce "secondary" organic aerosol (SOA). While their general role in tropospheric chemistry is appreciated, the number of VOC and the complexity of the reactions which chemically degrade and oxidise them, means that there are many large uncertainties associated with VOC. These uncertainties feed into the chemical transport models used to describe the tropospheric environment, and so reduce their reliability in understanding, forecasting and assessing the troposphere. SOA is formed from the less volatile products of the oxidation of VOC. These may condense on aerosol nuclei forming aerosol particles, and the compounds are partitioned between the gas phase and the liquid/solid phase on the particle. The importance of SOA has grown in recent years with the realisation that they may have effects on human health. By their very nature, the detailed chemical composition of SOA is seldom known and the aerosol is very difficult to characterise and quantify. The 3 rd ACCENT expert workshop was initiated to try to address some of the many uncertainties with respect to VOC and SOA, and to indicate research paths, by which the uncertainties could be reduced. The workshop was held under the auspices of seven ACCENT groups: Transport and Transformation of Pollutants (T&TP), Remote Sensing from Space (AT2), Access to Emissions; Access to Laboratory Data, Aerosols, BIAFLUX and Modelling. The meeting was held at the Barnsdale Hall Hotel in Rutland on Monday, Tuesday and Wednesday 30 th , 31 st October and the 1 st November 2007; some forty nine experts attended (Appendix A). The meeting was organised around three discussion groups, addressing the major areas of concern. There was a mixture of plenary talks and discussion sessions (Appendix B). All the speakers, chairs, rapporteurs and participants received detailed instructions to try to ensure that the discussions were as productive as possible (Appendix C). The following conclusions and recommendations emerged from the three discussion groups. These were seen and commented upon by the workshop as a whole. 1.1. Emissions of VOC General conclusions Uncertainties in VOC emissions The huge uncertainties in VOC emissions, particularly biogenic VOC and OVOC (oxygenated VOC), need to be addressed and current accuracy and precision of emission inventories need to be drastically improved. Characterisation of VOC emissions Adequate characterization of VOC emission variability (diurnal, weekend, seasonal, etc.) was identified as being crucial to our understanding of current and future emissions. New and existing platforms are required to make high quality long-term measurements with their scope based on science (rather than policy-based) criteria. * Light and temperature alone are not sufficient to predict the response of emissions to global change. There is a need to include seasonality, ecophysiology, water availability, etc. Circadian controls may also be important for how plants react to change. * Journals should be encouraged to mandate that references to data files, secured in a recognised archive, accompany any articles that are published. * Satellite measurements should be developed and used to extend the scale of measurement stations. * Priority species should be defined, including satellite products and global change compounds. One could build on recommendations for specific gases to measure from the recent WMO/GAW workshop. Glyoxal and supporting tracers such as * Which processes are most relevant for SOA removal (i.e. dry deposition, wet deposition, SOA volatilisation)? * Studies of the optical, chemical and hygroscopic properties of SOA, and of SOA yields under low NO x and low VOC precursor concentrations. Attempts should be made to answer the question: can the concentration dependence observed for d-pinene be generalized to other VOC? Volatile Organic Compounds in the Polluted Atmosphere 3. Emissions of VOC-anthropogenic and biogenic