scholarly journals Contribution of dust inputs to dissolved organic carbon and water transparency in Mediterranean reservoirs

2012 ◽  
Vol 9 (7) ◽  
pp. 8307-8336
Author(s):  
I. de Vicente ◽  
E. Ortega-Retuerta ◽  
R. Morales-Baquero ◽  
I. Reche
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Organic Compounds ◽  
Western Mediterranean ◽  
Water Soluble ◽  
Water Transparency ◽  
Saharan Dust ◽  
Western Mediterranean Basin ◽  
Run Off ◽  
Atmospheric Inputs

Abstract. Mediterranean reservoirs receive frequent Saharan dust inputs with soil-derived organic compounds mostly during stratification periods, when run-off inputs are particularly limited. Here, we quantified and optically characterized the water-soluble organic carbon (WSOC) of the (dry and wet) atmospheric deposition in collectors located near three reservoirs from the Western Mediterranean Basin. In addition, we determined, during the stratification period, the WSOC contribution to the pool of dissolved organic carbon (DOC) and the influence of the chromophoric organic compounds from the dust on water transparency. We found synchrony both in the WSOC atmospheric inputs among collectors and in the DOC dynamics among the three reservoirs. DOC concentrations and WSOC atmospheric inputs were positive and significantly correlated in the two reservoirs more sensitive to atmospheric inputs: the most oligotrophic reservoir (Quentar) and the reservoir with the highest ratio of surface area to mixing water depth (Cubillas). Nevertheless, WSOC atmospheric inputs, during the stratification period, represented less than 10 % of the total DOC pool, suggesting that indirect effects of dust inputs such as primary productivity stimulation may also induce these synchronic patterns. Chromophoric compounds from dust inputs can significantly reduce water transparency to ultraviolet radiation (UVR). The depths where UVR at λ = 320 nm is reduced to ten percent of surface intensity (Z10 %) decreased 15 cm (about 24 %) in Beznar, 17 cm (about 27 %) in Cubillas, and 43 cm (about 39 %) in Quéntar due to dust inputs.

scholarly journals Contribution of dust inputs to dissolved organic carbon and water transparency in Mediterranean reservoirs

2012 ◽  
Vol 9 (12) ◽  
pp. 5049-5060 ◽  
Author(s):  
I. de Vicente ◽  
E. Ortega-Retuerta ◽  
R. Morales-Baquero ◽  
I. Reche
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Western Mediterranean ◽  
Water Soluble ◽  
Water Transparency ◽  
Saharan Dust ◽  
Organic Components ◽  
Western Mediterranean Basin ◽  
Run Off ◽  
Atmospheric Inputs

Abstract. The Mediterranean reservoirs receive frequent atmospheric Saharan dust inputs with soil-derived organic components mostly during the stratification periods, when run-off inputs are particularly limited. Here, we quantified and optically characterized the water-soluble organic carbon (WSOC) of the (dry and wet) atmospheric deposition in collectors placed near three reservoirs from the western Mediterranean Basin. In addition, we determined the WSOC contribution to the pool of dissolved organic carbon (DOC) in the reservoirs and the influence of dust-derived chromophoric organic components on the water transparency during their stratification periods. We found synchronous dynamics in the WSOC atmospheric inputs among the three collectors and in the DOC concentrations among the three reservoirs. The DOC concentrations and the WSOC atmospheric inputs were positive and significantly correlated in the most oligotrophic reservoir (Quéntar) and in the reservoir with the highest ratio of surface area to mixing water depth (Cubillas). Despite these correlations, WSOC atmospheric inputs represented less than 10% of the total DOC pool, suggesting that indirect effects of dust inputs on reservoir DOC may also promote these synchronous patterns observed in the reservoirs. Chromophoric components from dust inputs can significantly reduce the water transparency to the ultraviolet radiation (UVR). The depths where UVR at λ = 320 nm was reduced to ten percent of surface intensity (Z10%) decreased 27 cm in Béznar, 49 cm in Cubillas, and 69 cm in Quéntar due to the dust inputs. Therefore, the increasing dust export to the atmosphere may have consequences for the water transparency of aquatic ecosystems located under the influence of the global dust belt.

scholarly journals Molecular characterization of gaseous and particulate oxygenated compounds at a remote site in Cape Corsica in the western Mediterranean Basin

2021 ◽  
Vol 21 (10) ◽  
pp. 8067-8088
Author(s):  
Vincent Michoud ◽  
Elise Hallemans ◽  
Laura Chiappini ◽  
Eva Leoz-Garziandia ◽  
Aurélie Colomb ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Carboxylic Acids ◽  
Organic Aerosol ◽  
Western Mediterranean ◽  
Water Soluble ◽  
Molecular Composition ◽  
Particle Phase ◽  
Western Mediterranean Basin ◽  
Partitioning Coefficients

Abstract. The characterization of the molecular composition of organic carbon in both gaseous and aerosol is key to understanding the processes involved in the formation and aging of secondary organic aerosol. Therefore a technique using active sampling on cartridges and filters and derivatization followed by analysis using a thermal desorption–gas chromatography–mass spectrometer (TD–GC–MS) has been used. It is aimed at studying the molecular composition of organic carbon in both gaseous and aerosol phases (PM2.5) during an intensive field campaign which took place in Corsica (France) during the summer of 2013: the ChArMEx (Chemistry and Aerosol Mediterranean Experiment) SOP1b (Special Observation Period 1B) campaign. These measurements led to the identification of 51 oxygenated (carbonyl and or hydroxyl) compounds in the gaseous phase with concentrations between 21 and 3900 ng m−3 and of 85 compounds in the particulate phase with concentrations between 0.3 and 277 ng m−3. Comparisons of these measurements with collocated data using other techniques have been conducted, showing fair agreement in general for most species except for glyoxal in the gas phase and malonic, tartaric, malic and succinic acids in the particle phase, with disagreements that can reach up to a factor of 8 and 20 on average, respectively, for the latter two acids. Comparison between the sum of all compounds identified by TD–GC–MS in the particle phase and the total organic matter (OM) mass reveals that on average 18 % of the total OM mass can be explained by the compounds measured by TD–GC–MS. This number increases to 24 % of the total water-soluble OM (WSOM) measured by coupling the Particle Into Liquid Sampler (PILS)-TOC (total organic carbon) if we consider only the sum of the soluble compounds measured by TD–GC–MS. This highlights the important fraction of the OM mass identified by these measurements but also the relative important fraction of OM mass remaining unidentified during the campaign and therefore the complexity of characterizing exhaustively the organic aerosol (OA) molecular chemical composition. The fraction of OM measured by TD–GC–MS is largely dominated by di-carboxylic acids, which represent 49 % of the PM2.5 content detected and quantified by this technique. Other contributions to PM2.5 composition measured by TD–GC–MS are then represented by tri-carboxylic acids (15 %), alcohols (13 %), aldehydes (10 %), di-hydroxy-carboxylic acids (5 %), monocarboxylic acids and ketones (3 % each), and hydroxyl-carboxylic acids (2 %). These results highlight the importance of polyfunctionalized carboxylic acids for OM, while the chemical processes responsible for their formation in both phases remain uncertain. While not measured by the TD–GC–MS technique, humic-like substances (HULISs) represent the most abundant identified species in the aerosol, contributing for 59 % of the total OM mass on average during the campaign. A total of 14 compounds were detected and quantified in both phases, allowing the calculation of experimental partitioning coefficients for these species. The comparison of these experimental partitioning coefficients with theoretical ones, estimated by three different models, reveals large discrepancies varying from 2 to 7 orders of magnitude. These results suggest that the supposed instantaneous equilibrium being established between gaseous and particulate phases assuming a homogeneous non-viscous particle phase is questionable.

scholarly journals Molecular characterization of gaseous and particulate oxygenated compounds at a remote site in Cape Corsica in the western Mediterranean basin

2020 ◽  
Author(s):  
Vincent Michoud ◽  
Elise Hallemans ◽  
Laura Chiappini ◽  
Eva Leoz-Garziandia ◽  
Aurélie Colomb ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Carboxylic Acids ◽  
Organic Aerosol ◽  
Western Mediterranean ◽  
Water Soluble ◽  
Molecular Composition ◽  
Particle Phase ◽  
Western Mediterranean Basin ◽  
Hydroxyl Compounds

Abstract. The characterization of the molecular composition of organic carbon in both gaseous and aerosol is key to understand the processes involved in the formation and aging of secondary organic aerosol. Therefore a technique using active sampling on cartridges and filters and derivatization followed by analysis using a Thermal Desorption-Gas Chromatography/mass spectrometer (TD-GC/MS) has been used to study the molecular composition of organic carbon in both gaseous and aerosol phases during an intensive field campaign which took place in Corsica during the summer 2013: the ChArMEx (Chemistry and Aerosol Mediterranean Experiment) SOP1b (Special Observation Period 1B) campaign. These measurements led to the identification of 51 oxygenated (carbonyl and or hydroxyl) compounds in the gaseous phase with concentrations comprised between 21 ng m−3 and 3900 ng m−3 and of 85 compounds in the particulate phase with concentrations comprised between 0.3 and 277 ng m−3. Comparisons of these measurements with collocated data using other techniques have been conducted showing fair agreement in general for most species except for glyoxal in the gas phase and malonic, tartaric, malic and succinic acids in the particle phase with disagreements that can reach up to a factor of 8 and 20 on average, respectively for the latter two acids. Comparison between the sum of all compounds identified by TD-GC/MS in particle phase with the total Organic Matter (OM) mass reveal that 18 % of the total OM mass can be explained by the compounds measured by TD-GC/MS for the whole campaign. This number increase to 24 % of the total Water Soluble OM (WSOM) measured by PILS-TOC if we consider only the sum of the soluble compounds measured by TD-GC/MS. This highlights the non-negligible fraction of the OM mass identified by these measurements but also the relative important fraction of OM mass remaining unidentified during the campaign and therefore the complexity of characterizing exhaustively the Organic Aerosol (OA) molecular chemical composition. The fraction of OM measured by TD-GC/MS is largely dominated by di-carboxylic acids which represents 49 % of the PM2.5 content detected and quantified by this technique. Other contributions to PM2.5 composition measured by TD-GC/MS are then represented by tri-carboxylic acids (15 %), alcohols (13 %), aldehydes (10 %), di-hydroxy-carboxylic acids (5 %), monocarboxylic acids and ketones (3 % each) and hydroxyl-carboxylic acids (2 %). These results highlight the importance of poly functionalized carboxylic acids for OM while the chemical processes responsible for their formation in both phases remain uncertain. While not measured by TD-GC/MS technique, HUmic-LIke Substances (HULIS) represent the most abundant identified species in the aerosol, contributing for 59 % of the total identified OM mass on average during the campaign. 14 compounds were detected and quantified in both phases allowing the calculation of experimental partitioning coefficient for these species. The comparison of these experimental partitioning coefficients with theoretical ones, estimated by three different models, reveals large discrepancies varying from 2 to 7 orders of magnitude. These results suggest that the supposed instantaneous equilibrium being established between gaseous and particulate phases assuming a homogeneous non-viscous particle phase is questionable.

scholarly journals Photooxidants from Brown Carbon and Other Chromophores in Illuminated Particle Extracts

2018 ◽  
Author(s):  
Richie Kaur ◽  
Jacqueline R. Labins ◽  
Scarlett S. Helbock ◽  
Wenqing Jiang ◽  
Keith Bein ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Organic Compounds ◽  
Excited States ◽  
Liquid Water ◽  
Light Absorption ◽  
Singlet Molecular Oxygen ◽  
Brown Carbon ◽  
Aggregate Rate ◽  
Triplet Excited States

Abstract. While photooxidants are important in atmospheric condensed phases, there are very few measurements in particulate matter (PM). Here we measure light absorption and the concentrations of three photooxidants – hydroxyl radical (•OH), singlet molecular oxygen (1O2*) and oxidizing triplet excited states of organic matter (3C*) – in illuminated aqueous extracts of wintertime particles from Davis, California. 1O2* and 3C*, which are formed from photoexcitation of brown carbon (BrC), have not been previously measured in PM. In the extracts, mass absorption coefficients for dissolved organic compounds (MACDOC) at 300 nm range between 13,000–30,000 cm2 g–C–1 and are approximately twice as high as previous values in Davis fogs. The average (± 1σ) •OH steady-state concentration in particle extracts is 4.7 (± 1.9) × 10−16 M, which is very similar to previous values in fog, cloud and rain: although our particle extracts are more concentrated, the resulting enhancement in the rate of •OH photoproduction is essentially cancelled out by a corresponding enhancement in concentrations of natural sinks for •OH. In contrast, concentrations of the two oxidants formed primarily from brown carbon (i.e., 1O2* and 3C*) are both enhanced in the particle extracts compared to Davis fogs, a result of higher concentrations of dissolved organic carbon and faster rates of light absorption in the extracts. The average 1O2* concentration in the PM extracts is 1.6 (± 0.5) × 10−12 M, seven times higher than past fog measurements, while the average concentration of oxidizing triplets is 1.0 (± 0.4) × 10−13 M, nearly double the average Davis fog value. Additionally, the rates of 1O2* and 3C* photoproduction are both well correlated with the rate of sunlight absorption. While concentrations of 1O2* and 3C* are higher in our PM extracts compared to fog, the extracts are approximately 1000 times more dilute than water-containing ambient PM. Since we cannot experimentally measure photooxidants under these ambient conditions, we measured the effect of PM dilution on oxidant concentrations and then extrapolated to ambient particle conditions. As the particle mass concentration in the extracts increases, measured concentrations of •OH remain relatively unchanged, 1O2* increases linearly, and 3C* concentrations increase less than linearly, likely due to quenching by dissolved organics. Based on our measurements, and accounting for additional sources and sinks that should be important under PM conditions, we estimate that [•OH] in particles is essentially the same as in fog waters, [3C*] is higher in PM by nearly a factor of 3, and [1O2*] is enhanced by a factor of roughly 600. Because of these enhancements in 1O2* and 3C* concentrations, the lifetimes of some highly soluble organics appear to be much shorter in particle liquid water than under foggy/cloudy conditions. Based on our extrapolated rates of formation, BrC-derived singlet molecular oxygen and triplet excited states are the dominant sinks for organic compounds in particle liquid water, with an aggregate rate of reaction for each oxidant that is approximately 200–300 times higher than the aggregate rate of reactions for organics with •OH. For individual, highly soluble reactive organic compounds it appears that 1O2* is the major sink in particle water. Triplet excited states are likely also important in the fate of individual particulate organics, but assessing this requires additional measurements of triplet interactions with dissolved organic carbon in natural samples.

scholarly journals On the implications of aerosol liquid water and phase separation for organic aerosol mass

2017 ◽  
Vol 17 (1) ◽  
pp. 343-369 ◽  
Author(s):  
Havala O. T. Pye ◽  
Benjamin N. Murphy ◽  
Lu Xu ◽  
Nga L. Ng ◽  
Annmarie G. Carlton ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Organic Compounds ◽  
Water Uptake ◽  
Liquid Water ◽  
Transport Model ◽  
Organic Aerosol ◽  
Water Soluble ◽  
Organic Nitrates ◽  
Monitoring Networks ◽  
Chemical Transport Model

Abstract. Organic compounds and liquid water are major aerosol constituents in the southeast United States (SE US). Water associated with inorganic constituents (inorganic water) can contribute to the partitioning medium for organic aerosol when relative humidities or organic matter to organic carbon (OM ∕ OC) ratios are high such that separation relative humidities (SRH) are below the ambient relative humidity (RH). As OM ∕ OC ratios in the SE US are often between 1.8 and 2.2, organic aerosol experiences both mixing with inorganic water and separation from it. Regional chemical transport model simulations including inorganic water (but excluding water uptake by organic compounds) in the partitioning medium for secondary organic aerosol (SOA) when RH  >  SRH led to increased SOA concentrations, particularly at night. Water uptake to the organic phase resulted in even greater SOA concentrations as a result of a positive feedback in which water uptake increased SOA, which further increased aerosol water and organic aerosol. Aerosol properties, such as the OM ∕ OC and hygroscopicity parameter (κorg), were captured well by the model compared with measurements during the Southern Oxidant and Aerosol Study (SOAS) 2013. Organic nitrates from monoterpene oxidation were predicted to be the least water-soluble semivolatile species in the model, but most biogenically derived semivolatile species in the Community Multiscale Air Quality (CMAQ) model were highly water soluble and expected to contribute to water-soluble organic carbon (WSOC). Organic aerosol and SOA precursors were abundant at night, but additional improvements in daytime organic aerosol are needed to close the model–measurement gap. When taking into account deviations from ideality, including both inorganic (when RH  >  SRH) and organic water in the organic partitioning medium reduced the mean bias in SOA for routine monitoring networks and improved model performance compared to observations from SOAS. Property updates from this work will be released in CMAQ v5.2.

scholarly journals Dissolved organic carbon (DOC) and select aldehydes in cloud and fog water: the role of the aqueous phase in impacting trace gas budgets

2013 ◽  
Vol 13 (10) ◽  
pp. 5117-5135 ◽  
Author(s):  
B. Ervens ◽  
Y. Wang ◽  
J. Eagar ◽  
W. R. Leaitch ◽  
A. M. Macdonald ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Gas Phase ◽  
Aqueous Phase ◽  
Water Soluble ◽  
Box Model ◽  
High Solubility ◽  
Fog Water ◽  
Air Masses ◽  
Order Of Magnitude

Abstract. Cloud and fog droplets efficiently scavenge and process water-soluble compounds and, thus, modify the chemical composition of the gas and particle phases. The concentrations of dissolved organic carbon (DOC) in the aqueous phase reach concentrations on the order of ~ 10 mgC L−1 which is typically on the same order of magnitude as the sum of inorganic anions. Aldehydes and carboxylic acids typically comprise a large fraction of DOC because of their high solubility. The dissolution of species in the aqueous phase can lead to (i) the removal of species from the gas phase preventing their processing by gas phase reactions (e.g., photolysis of aldehydes) and (ii) the formation of unique products that do not have any efficient gas phase sources (e.g., dicarboxylic acids). We present measurements of DOC and select aldehydes in fog water at high elevation and intercepted clouds at a biogenically-impacted location (Whistler, Canada) and in fog water in a more polluted area (Davis, CA). Concentrations of formaldehyde, glyoxal and methylglyoxal were in the micromolar range and comprised ≤ 2% each individually of the DOC. Comparison of the DOC and aldehyde concentrations to those at other locations shows good agreement and reveals highest levels for both in anthropogenically impacted regions. Based on this overview, we conclude that the fraction of organic carbon (dissolved and insoluble inclusions) in the aqueous phase of clouds or fogs, respectively, comprises 2–~ 40% of total organic carbon. Higher values are observed to be associated with aged air masses where organics are expected to be more highly oxidised and, thus, more soluble. Accordingly, the aqueous/gas partitioning ratio expressed here as an effective Henry's law constant for DOC (KH*DOC) increases by an order of magnitude from 7 × 103 M atm−1 to 7 × 104 M atm−1 during the ageing of air masses. The measurements are accompanied by photochemical box model simulations. These simulations are used to contrast two scenarios, i.e., an anthropogenically vs. a more biogenically impacted one as being representative for Davis and Whistler, respectively. Since the simplicity of the box model prevents a fully quantitative prediction of the observed aldehyde concentrations, we rather use the model results to compare trends in aldehyde partitioning and ratios. They suggest that the scavenging of aldehydes by the aqueous phase can reduce HO2 gas phase levels significantly by two orders of magnitude due to a weaker net source of HO2 production from aldehyde photolysis in the gas phase. Despite the high solubility of dicarbonyl compounds (glyoxal, methylglyoxal), their impact on the HO2 budget by scavenging is < 10% of that of formaldehyde. The overview of DOC and aldehyde measurements presented here reveals that clouds and fogs can be efficient sinks for organics, with increasing importance in aged air masses. Even though aldehydes, specifically formaldehyde, only comprise ~ 1% of DOC, their scavenging and processing in the aqueous phase might translate into significant effects in the oxidation capacity of the atmosphere.

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