Christian George - Academia.edu (original) (raw)
Papers by Christian George
ABSTRACT Results of recent laboratory studies [1,2] indicated that heterogeneous reactions of ozo... more ABSTRACT Results of recent laboratory studies [1,2] indicated that heterogeneous reactions of ozone and nitrogen dioxide on the surfaces of aerosol consisting of humic acids or humic like substances (HULIS) may significantly affect the chemical budget in biomass burning plumes, where HULIS is an important contributor to the aerosol composition. To achieve better understanding of potential role of these reactions in the atmosphere, we considered them together with other processes in the framework of the state- of- the- art CHIMERE chemistry transport model applied to the case of the 2010 mega fire event in western Russia. It had been shown earlier [3] that this model adequately reproduces the measured variability of the key air pollutants (O3, PM10, CO) in the Moscow region during the period when the atmospheric composition was strongly affected by numerous wildfires (e.g., up to 1 mg/m3 of daily mean PM10 concentration was detected by air pollution monitors). Using the experimental data, the heterogeneous reaction rates were parameterised as a function of actinic fluxes, reactant concentrations and relative humidity. The actinic fluxes were calculated using the on-line TUV model and aerosol optical depth data retrieved from the MODIS measurements. Results of the numerical experiments indicate that heterogeneous loss of ozone during the considered episode could be considerable (reaching several tenths of percent). They show also that although wildfires provide large reactive surface for the heterogeneous processing of ozone and nitrogen dioxide on biomass burning aerosol, at the same time they strongly inhibit these reactions by attenuating actinic fluxes through the "shielding" aerosol effect. Accordingly, the maximum impact of heterogeneous reactions on concentrations of ozone and other reactive species is estimated to be at the upper part of the boundary layer. The obtained estimates of effects of heterogeneous reactions are found to be sensitive to uncertainties in aerosol composition and reaction rate parameterisations, thus calling for new experimental and modelling studies. The study is supported by the Russian Foundation for Basic Researches.
Egs Agu Eug Joint Assembly, Apr 1, 2003
This work focuses on the measurement of Henry's Law constant of some oxygenated organic compounds... more This work focuses on the measurement of Henry's Law constant of some oxygenated organic compounds of atmospheric interest. The Henry's Law constant for acetone, methyl ethyl ketone (MEK), isobutyraldehyde and 2,3-butandione are reported as a function of temperature ranging from 274 - 293 K. One of the aims of this research is to evaluate the atmospheric fate of oxygenated species that are increasingly used as replacement solvents.
The presence of nitrous acid (HONO) in the atmosphere was first detected more than two decades ag... more The presence of nitrous acid (HONO) in the atmosphere was first detected more than two decades ago. Since then many studies have elucidated its important role as a major photochemical precursor of the hydroxyl radical- the key oxidant in the degradation of most air pollutants and a crucial intermediate in the formation of photochemical smog in the troposphere. However, the sources of HONO in the troposphere are still poorly understood, especially since recent atmospheric measurements revealed a strongly enhanced formation of HONO during daytime via an unknown mechanism. Here we show that reduction of NO2 on light-activated organics is a major source of gaseous HONO. Under atmospherically relevant conditions, this photosensitized formation of HONO is by magnitudes faster than the previously known disproportionation of NO2 on humid glass surfaces. This is the first example showing that solid surfaces containing traces of natural occurring organic matter have to be considered as photoreactive towards atmospheric oxidants and can explain the high daytime concentrations of HONO recently observed in the boundary layer, the photolysis of which accounts for up to 60% of the integrated OH radical source strengths. Thus this new photoinduced HONO source has a considerable impact on the oxidation capacity of the lower atmosphere.
Physical Chemistry Chemical Physics, 2003
Bimolecular rate coefficients for the reactions of the hydroxyl radical, OH, with methanol, ethan... more Bimolecular rate coefficients for the reactions of the hydroxyl radical, OH, with methanol, ethanol, tetrahydrofuran, dimethylmalonate [CH 3 OC (O) CH 2 C (O) OCH 3], dimethylsuccinate [CH 3 OC (O) CH 2 CH 2 C (O) OCH 3], dimethylcarbonate [CH 3 OC (O ...
Environmental science & technology, Jan 10, 2015
Due to its high reactivity toward tropospheric oxidants, isoprene is an important volatile organi... more Due to its high reactivity toward tropospheric oxidants, isoprene is an important volatile organic compounds emitted by biogenic sources and oceans. In the marine environment, isoprene is produced in water via various biological processes. Here we show that when H-abstraction reactions are occurring in an organic monolayer at the air/water interface, as the ubiquitous sea-surface microlayer (SML), unsaturated gaseous compounds, such as isoprene, can be emitted. The H-abstraction process is initiated by photochemically excited dissolved organic matter (DOM). This interfacial photosensitized chemistry involves only fatty acids as surfactants and dissolved organic matter as photosentitizer, both being ubiquitous in the marine environment, and may represent a significant source (up to 100 %) of isoprene in the absence of any biological sources in the marine boundary layer but in presence of a fully organic covered ocean.
ABSTRACT International @ AIR+BDA:CGO:AMM:BRM
Scientific Reports, 2015
The sea-surface microlayer (SML) has different physical, chemical and biological properties compa... more The sea-surface microlayer (SML) has different physical, chemical and biological properties compared to the subsurface water, with an enrichment of organic matter i.e., dissolved organic matter including UV absorbing humic substances, fatty acids and many others. Here we present experimental evidence that dissolved organic matter, such as humic acids, when exposed to sunlight, can photosensitize the chemical conversion of linear saturated fatty acids at the air-water interface into unsaturated functionalized gas phase products (i.e. saturated and unsaturated aldehydes and acids, alkenes and dienes,…) which are known precursors of secondary organic aerosols. These functionalized molecules have previously been thought to be of biological origin, but here we demonstrate that abiotic interfacial photochemistry has the potential to produce such molecules. As the ocean is widely covered by the SML, this new understanding will impact on our ability to describe atmospheric chemistry in the marine environment.
Comptes Rendus Chimie, 2015
The Journal of Physical Chemistry, 1994
... 1994,98, 8780-8784 Study of the Uptake of N205 by Water and NaCl Solutions Ch. George,+ JL Po... more ... 1994,98, 8780-8784 Study of the Uptake of N205 by Water and NaCl Solutions Ch. George,+ JL Ponche, and Ph. Mirabel' Facult.? ... This reaction pathway is important since it is expected to lead atomic C1. 93, 1159. (16) Ponche, JL; George, C.; Mirabel, P. J. Atmos. Chem. ...
Heterogeneous and Liquid Phase Processes, 1996
Chemical reviews, Jan 16, 2015
Atmospheric Chemistry and Physics Discussions, 2012
Organic Aerosol (OA) measurements were conducted during summer 2008 at an urban background site, ... more Organic Aerosol (OA) measurements were conducted during summer 2008 at an urban background site, in Marseille, France's second city and the largest port in the Mediterranean, an urban industrialized environment known for its active photochemistry. PM 2.5 was collected using high volume samplers and analyzed for elemental and organic car-5 bon, major ions (NH + 4 , NO − 3 and SO 2− 4 ), humic-like-substances, organic markers (i.e. primary tracers and α-pinene oxidation products), elemental composition and radiocarbon content ( 14 C). The real-time chemical characterization of submicron particles was also achieved using a compact time of flight aerosol mass spectrometer. Positive matrix factorization conducted on the organic aerosol mass spectra matrix revealed four 10 factors, including traffic emissions (hydrocarbon-like OA, HOA), industrial emissions, semi-volatile (SV-OOA) and low-volatile (LV-OOA) oxygenated organic aerosol (OOA) related to oxidation processes. The results obtained were in excellent agreement with chemical mass balance source apportionments conducted in conjunction with organic markers and elements. It appears that while primary emissions contributed only 22 % 15
Environmental science & technology, Jan 6, 2015
Humic substances (HS) acting as photosensitizers can generate a variety of reactive species, such... more Humic substances (HS) acting as photosensitizers can generate a variety of reactive species, such as OH radicals and excited triplet states ((3)HS*), promoting the degradation of organic compounds. Here, we apply compound-specific stable isotope analysis (CSIA) to characterize photosensitized mechanisms employing fuel oxygenates, such as methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE), as probes. In oxygenated aqueous media, Λ (Δδ(2)H/Δδ(13)C) values of 23 ± 3 and 21 ± 3 for ETBE obtained by photosensitization by Pahokee Peat Humic Acid (PPHA) and Suwannee River Fulvic Acid (SRFA), respectively, were in the range typical for H-abstraction by OH radicals generated by photolysis of H2O2 (Λ = 24 ± 2). However, (3)HS* may become a predominant reactive species upon the quenching of OH radicals (Λ = 14 ± 1), and this process can also play a key role in the degradation of ETBE by PPHA photosensitization in deoxygenated media (Λ = 11 ± 1). This is in agreement with a model ...
Atmospheric Chemistry and Physics Discussions, 2014
In-cloud production of sulfate modifies aerosol size distribution, with important implications fo... more In-cloud production of sulfate modifies aerosol size distribution, with important implications for the magnitude of indirect and direct aerosol cooling and the impact of SO 2 emissions on the environment. We investigate which sulfate sources dominate the in-cloud addition of sulfate to different particle classes as an air parcel passes through an orographic cloud. Sulfate aerosol, SO 2 and H 2 SO 4 were collected upwind, in-cloud and downwind of an orographic cloud for three cloud measurement events during the Hill Cap Cloud Thuringia campaign in autumn 2010 (HCCT-2010). Combined SEM and NanoSIMS analysis of single particles allowed the δ 34 S of particulate sulfate to be resolved for particle size and type.
ABSTRACT Results of recent laboratory studies [1,2] indicated that heterogeneous reactions of ozo... more ABSTRACT Results of recent laboratory studies [1,2] indicated that heterogeneous reactions of ozone and nitrogen dioxide on the surfaces of aerosol consisting of humic acids or humic like substances (HULIS) may significantly affect the chemical budget in biomass burning plumes, where HULIS is an important contributor to the aerosol composition. To achieve better understanding of potential role of these reactions in the atmosphere, we considered them together with other processes in the framework of the state- of- the- art CHIMERE chemistry transport model applied to the case of the 2010 mega fire event in western Russia. It had been shown earlier [3] that this model adequately reproduces the measured variability of the key air pollutants (O3, PM10, CO) in the Moscow region during the period when the atmospheric composition was strongly affected by numerous wildfires (e.g., up to 1 mg/m3 of daily mean PM10 concentration was detected by air pollution monitors). Using the experimental data, the heterogeneous reaction rates were parameterised as a function of actinic fluxes, reactant concentrations and relative humidity. The actinic fluxes were calculated using the on-line TUV model and aerosol optical depth data retrieved from the MODIS measurements. Results of the numerical experiments indicate that heterogeneous loss of ozone during the considered episode could be considerable (reaching several tenths of percent). They show also that although wildfires provide large reactive surface for the heterogeneous processing of ozone and nitrogen dioxide on biomass burning aerosol, at the same time they strongly inhibit these reactions by attenuating actinic fluxes through the "shielding" aerosol effect. Accordingly, the maximum impact of heterogeneous reactions on concentrations of ozone and other reactive species is estimated to be at the upper part of the boundary layer. The obtained estimates of effects of heterogeneous reactions are found to be sensitive to uncertainties in aerosol composition and reaction rate parameterisations, thus calling for new experimental and modelling studies. The study is supported by the Russian Foundation for Basic Researches.
Egs Agu Eug Joint Assembly, Apr 1, 2003
This work focuses on the measurement of Henry's Law constant of some oxygenated organic compounds... more This work focuses on the measurement of Henry's Law constant of some oxygenated organic compounds of atmospheric interest. The Henry's Law constant for acetone, methyl ethyl ketone (MEK), isobutyraldehyde and 2,3-butandione are reported as a function of temperature ranging from 274 - 293 K. One of the aims of this research is to evaluate the atmospheric fate of oxygenated species that are increasingly used as replacement solvents.
The presence of nitrous acid (HONO) in the atmosphere was first detected more than two decades ag... more The presence of nitrous acid (HONO) in the atmosphere was first detected more than two decades ago. Since then many studies have elucidated its important role as a major photochemical precursor of the hydroxyl radical- the key oxidant in the degradation of most air pollutants and a crucial intermediate in the formation of photochemical smog in the troposphere. However, the sources of HONO in the troposphere are still poorly understood, especially since recent atmospheric measurements revealed a strongly enhanced formation of HONO during daytime via an unknown mechanism. Here we show that reduction of NO2 on light-activated organics is a major source of gaseous HONO. Under atmospherically relevant conditions, this photosensitized formation of HONO is by magnitudes faster than the previously known disproportionation of NO2 on humid glass surfaces. This is the first example showing that solid surfaces containing traces of natural occurring organic matter have to be considered as photoreactive towards atmospheric oxidants and can explain the high daytime concentrations of HONO recently observed in the boundary layer, the photolysis of which accounts for up to 60% of the integrated OH radical source strengths. Thus this new photoinduced HONO source has a considerable impact on the oxidation capacity of the lower atmosphere.
Physical Chemistry Chemical Physics, 2003
Bimolecular rate coefficients for the reactions of the hydroxyl radical, OH, with methanol, ethan... more Bimolecular rate coefficients for the reactions of the hydroxyl radical, OH, with methanol, ethanol, tetrahydrofuran, dimethylmalonate [CH 3 OC (O) CH 2 C (O) OCH 3], dimethylsuccinate [CH 3 OC (O) CH 2 CH 2 C (O) OCH 3], dimethylcarbonate [CH 3 OC (O ...
Environmental science & technology, Jan 10, 2015
Due to its high reactivity toward tropospheric oxidants, isoprene is an important volatile organi... more Due to its high reactivity toward tropospheric oxidants, isoprene is an important volatile organic compounds emitted by biogenic sources and oceans. In the marine environment, isoprene is produced in water via various biological processes. Here we show that when H-abstraction reactions are occurring in an organic monolayer at the air/water interface, as the ubiquitous sea-surface microlayer (SML), unsaturated gaseous compounds, such as isoprene, can be emitted. The H-abstraction process is initiated by photochemically excited dissolved organic matter (DOM). This interfacial photosensitized chemistry involves only fatty acids as surfactants and dissolved organic matter as photosentitizer, both being ubiquitous in the marine environment, and may represent a significant source (up to 100 %) of isoprene in the absence of any biological sources in the marine boundary layer but in presence of a fully organic covered ocean.
ABSTRACT International @ AIR+BDA:CGO:AMM:BRM
Scientific Reports, 2015
The sea-surface microlayer (SML) has different physical, chemical and biological properties compa... more The sea-surface microlayer (SML) has different physical, chemical and biological properties compared to the subsurface water, with an enrichment of organic matter i.e., dissolved organic matter including UV absorbing humic substances, fatty acids and many others. Here we present experimental evidence that dissolved organic matter, such as humic acids, when exposed to sunlight, can photosensitize the chemical conversion of linear saturated fatty acids at the air-water interface into unsaturated functionalized gas phase products (i.e. saturated and unsaturated aldehydes and acids, alkenes and dienes,…) which are known precursors of secondary organic aerosols. These functionalized molecules have previously been thought to be of biological origin, but here we demonstrate that abiotic interfacial photochemistry has the potential to produce such molecules. As the ocean is widely covered by the SML, this new understanding will impact on our ability to describe atmospheric chemistry in the marine environment.
Comptes Rendus Chimie, 2015
The Journal of Physical Chemistry, 1994
... 1994,98, 8780-8784 Study of the Uptake of N205 by Water and NaCl Solutions Ch. George,+ JL Po... more ... 1994,98, 8780-8784 Study of the Uptake of N205 by Water and NaCl Solutions Ch. George,+ JL Ponche, and Ph. Mirabel' Facult.? ... This reaction pathway is important since it is expected to lead atomic C1. 93, 1159. (16) Ponche, JL; George, C.; Mirabel, P. J. Atmos. Chem. ...
Heterogeneous and Liquid Phase Processes, 1996
Chemical reviews, Jan 16, 2015
Atmospheric Chemistry and Physics Discussions, 2012
Organic Aerosol (OA) measurements were conducted during summer 2008 at an urban background site, ... more Organic Aerosol (OA) measurements were conducted during summer 2008 at an urban background site, in Marseille, France's second city and the largest port in the Mediterranean, an urban industrialized environment known for its active photochemistry. PM 2.5 was collected using high volume samplers and analyzed for elemental and organic car-5 bon, major ions (NH + 4 , NO − 3 and SO 2− 4 ), humic-like-substances, organic markers (i.e. primary tracers and α-pinene oxidation products), elemental composition and radiocarbon content ( 14 C). The real-time chemical characterization of submicron particles was also achieved using a compact time of flight aerosol mass spectrometer. Positive matrix factorization conducted on the organic aerosol mass spectra matrix revealed four 10 factors, including traffic emissions (hydrocarbon-like OA, HOA), industrial emissions, semi-volatile (SV-OOA) and low-volatile (LV-OOA) oxygenated organic aerosol (OOA) related to oxidation processes. The results obtained were in excellent agreement with chemical mass balance source apportionments conducted in conjunction with organic markers and elements. It appears that while primary emissions contributed only 22 % 15
Environmental science & technology, Jan 6, 2015
Humic substances (HS) acting as photosensitizers can generate a variety of reactive species, such... more Humic substances (HS) acting as photosensitizers can generate a variety of reactive species, such as OH radicals and excited triplet states ((3)HS*), promoting the degradation of organic compounds. Here, we apply compound-specific stable isotope analysis (CSIA) to characterize photosensitized mechanisms employing fuel oxygenates, such as methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE), as probes. In oxygenated aqueous media, Λ (Δδ(2)H/Δδ(13)C) values of 23 ± 3 and 21 ± 3 for ETBE obtained by photosensitization by Pahokee Peat Humic Acid (PPHA) and Suwannee River Fulvic Acid (SRFA), respectively, were in the range typical for H-abstraction by OH radicals generated by photolysis of H2O2 (Λ = 24 ± 2). However, (3)HS* may become a predominant reactive species upon the quenching of OH radicals (Λ = 14 ± 1), and this process can also play a key role in the degradation of ETBE by PPHA photosensitization in deoxygenated media (Λ = 11 ± 1). This is in agreement with a model ...
Atmospheric Chemistry and Physics Discussions, 2014
In-cloud production of sulfate modifies aerosol size distribution, with important implications fo... more In-cloud production of sulfate modifies aerosol size distribution, with important implications for the magnitude of indirect and direct aerosol cooling and the impact of SO 2 emissions on the environment. We investigate which sulfate sources dominate the in-cloud addition of sulfate to different particle classes as an air parcel passes through an orographic cloud. Sulfate aerosol, SO 2 and H 2 SO 4 were collected upwind, in-cloud and downwind of an orographic cloud for three cloud measurement events during the Hill Cap Cloud Thuringia campaign in autumn 2010 (HCCT-2010). Combined SEM and NanoSIMS analysis of single particles allowed the δ 34 S of particulate sulfate to be resolved for particle size and type.