scholarly journals Uptake of gaseous formaldehyde by soil surfaces: a combination of adsorption/desorption equilibrium and chemical reactions

2016 ◽  
Author(s):  
Guo Li ◽  
Hang Su ◽  
Xin Li ◽  
Uwe Kuhn ◽  
Hannah Meusel ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Chemical Reactions ◽  
High Surface ◽  
Oh Radicals ◽  
Ambient Conditions ◽  
Complex Process ◽  
Dry Conditions ◽  
Gaseous Formaldehyde ◽  
Adsorption Desorption ◽  
Over Time

Abstract. Gaseous formaldehyde (HCHO) is an important precursor of OH radicals and a key intermediate molecule in the oxidation of atmospheric volatile organic compounds (VOCs). Budget analyses reveal large discrepancies between modeled and observed HCHO concentrations in the atmosphere. Here, we investigate the interactions of gaseous HCHO with soil surfaces through coated-wall flow tube experiments applying atmospherically relevant HCHO concentrations of ~ 10 to 40 ppbv. For the determination of uptake coefficients (γ), we provide a Matlab code to account for the diffusion correction under laminar flow conditions. Under dry conditions (relative humidity = 0 %), an initial γ of (1.1 ± 0.05) × 10−4 is determined, which gradually drops to (5.5 ± 0.4) × 10−5 after 8-hour experiments. Experiments under wet conditions show a smaller γ that drops faster over time until reaching a plateau. The drop of γ with increasing relative humidity and over time can both be explained by the adsorption theory in which high surface coverage leads to a reduced uptake rate. The fact that γ stabilizes at a non-zero plateau suggests the involvement of irreversible chemical reactions. Further back-flushing experiments show that two thirds of the adsorbed HCHO can be re-emitted into the gas phase while the residual is retained by the soil. This partial reversibility confirms that HCHO uptake by soil is a complex process involving both adsorption/desorption and chemical reactions which must be considered in trace gas exchange (emission or deposition) at the atmosphere-soil interface. Our results suggest that soil and soil-derived airborne particles can either act as a source or a sink for HCHO, depending on ambient conditions and HCHO concentrations.

scholarly journals Uptake of gaseous formaldehyde by soil surfaces: a combination of adsorption/desorption equilibrium and chemical reactions

2016 ◽  
Vol 16 (15) ◽  
pp. 10299-10311 ◽  
Author(s):  
Guo Li ◽  
Hang Su ◽  
Xin Li ◽  
Uwe Kuhn ◽  
Hannah Meusel ◽  
...  
Keyword(s):  
Chemical Reactions ◽  
High Surface ◽  
Oh Radicals ◽  
Ambient Conditions ◽  
Complex Process ◽  
Dry Conditions ◽  
Gaseous Formaldehyde ◽  
Adsorption Desorption ◽  
Over Time

Abstract. Gaseous formaldehyde (HCHO) is an important precursor of OH radicals and a key intermediate molecule in the oxidation of atmospheric volatile organic compounds (VOCs). Budget analyses reveal large discrepancies between modeled and observed HCHO concentrations in the atmosphere. Here, we investigate the interactions of gaseous HCHO with soil surfaces through coated-wall flow tube experiments applying atmospherically relevant HCHO concentrations of  ∼  10 to 40 ppbv. For the determination of uptake coefficients (γ), we provide a Matlab code to account for the diffusion correction under laminar flow conditions. Under dry conditions (relative humidity  =  0 %), an initial γ of (1.1 ± 0.05)  ×  10−4 is determined, which gradually drops to (5.5 ± 0.4)  ×  10−5 after 8 h experiments. Experiments under wet conditions show a smaller γ that drops faster over time until reaching a plateau. The drop of γ with increasing relative humidity as well as the drop over time can be explained by the adsorption theory in which high surface coverage leads to a reduced uptake rate. The fact that γ stabilizes at a non-zero plateau suggests the involvement of irreversible chemical reactions. Further back-flushing experiments show that two-thirds of the adsorbed HCHO can be re-emitted into the gas phase while the residual is retained by the soil. This partial reversibility confirms that HCHO uptake by soil is a complex process involving both adsorption/desorption and chemical reactions which must be considered in trace gas exchange (emission or deposition) at the atmosphere–soil interface. Our results suggest that soil and soil-derived airborne particles can either act as a source or a sink for HCHO, depending on ambient conditions and HCHO concentrations.

Soil and Stream Water Chemistry During Spring Snowmelt

1992 ◽  
Vol 23 (1) ◽  
pp. 13-26 ◽  
Author(s):  
W. H. Hendershot ◽  
L. Mendes ◽  
H. Lalande ◽  
F. Courchesne ◽  
S. Savoie
Keyword(s):  
Stream Water ◽  
Base Cations ◽  
Stream Chemistry ◽  
Stream Water Chemistry ◽  
The Matrix ◽  
Adsorption Desorption ◽  
The Relationship ◽  
Best Fit ◽  
Spring Snowmelt ◽  
Over Time

In order to determine how water flowpath controls stream chemistry, we studied both soil and stream water during spring snowmelt, 1985. Soil solution concentrations of base cations were relatively constant over time indicating that cation exchange was controlling cation concentrations. Similarly SO4 adsorption-desorption or precipitation-dissolution reactions with the matrix were controlling its concentrations. On the other hand, NO3 appeared to be controlled by uptake by plants or microorganisms or by denitrification since their concentrations in the soil fell abruptly as snowmelt proceeded. Dissolved Al and pH varied vertically in the soil profile and their pattern in the stream indicated clearly the importance of water flowpath on stream chemistry. Although Al increased as pH decreased, the relationship does not appear to be controlled by gibbsite. The best fit of calculated dissolved inorganic Al was obtained using AlOHSO4 with a solubility less than that of pure crystalline jurbanite.

High-performance inverted planar perovskite solar cells without a hole transport layer via a solution process under ambient conditions

2015 ◽  
Vol 3 (38) ◽  
pp. 19294-19298 ◽  
Author(s):  
Xichang Bao ◽  
Qianqian Zhu ◽  
Meng Qiu ◽  
Ailing Yang ◽  
Yujin Wang ◽  
...  
Keyword(s):  
Relative Humidity ◽  
High Performance ◽  
Perovskite Solar Cells ◽  
Solution Process ◽  
Hole Transport ◽  
Transport Layer ◽  
Hole Transport Layer ◽  
Ambient Conditions ◽  
High Quality ◽  
Ito Glass

High-quality CH3NH3PbI3 perovskite films were directly prepared on simple treated ITO glass in air under a relative humidity of lower than 30%.

Texture Evaluation of Sol-Gel Derived Mesoporous Bioactive Glass

2013 ◽  
Vol 284-287 ◽  
pp. 230-234
Author(s):  
Yu Jen Chou ◽  
Chi Jen Shih ◽  
Shao Ju Shih
Keyword(s):  
Surface Area ◽  
Calcination Temperature ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Nitrogen Adsorption ◽  
Bioactive Glasses ◽  
Transmission Electron ◽  
Sol Gel Process ◽  
Adsorption Desorption

Recent years mesoporous bioactive glasses (MBGs) have become important biomaterials because of their high surface area and the superior bioactivity. Various studies have reported that when MBGs implanted in a human body, hydroxyl apatite layers, constituting the main inorganic components of human bones, will form on the MBG surfaces to increase the bioactivity. Therefore, MBGs have been widely applied in the fields of tissue regeneration and drug delivery. The sol-gel process has replaced the conventional glasses process for MBG synthesis because of the advantages of low contamination, chemical flexibility and lower calcination temperature. In the sol-gel process, several types of surfactants were mixed with MBG precursor solutions to generate micelle structures. Afterwards, these micelles decompose to form porous structures after calcination. Although calcination is significant for contamination, crystalline and surface area in MBG, to the best of the authors’ knowledge, only few systematic studies related to calcination were reported. This study correlated the calcination parameters and the microstructure of MBGs. Microstructure evaluation was characterized by transmission electron microscopy and nitrogen adsorption/desorption. The experimental results show that the surface area and the pore size of MBGs decreased with the increasing of the calcination temperature, and decreased dramatically at 800°C due to the formation of crystalline phases.

scholarly journals The dynamics of questing ticks collected for 164 consecutive months off the vegetation of two landscape zones in the Kruger National Park (1988–2002). Part II. Rhipicephalus appendiculatus and Rhipicephalus zambeziensis

2011 ◽  
Vol 78 (1) ◽  
Author(s):  
Arthur M. Spickett ◽  
Gordon J. Gallivan ◽  
Ivan G. Horak
Keyword(s):  
Population Dynamics ◽  
Relative Humidity ◽  
National Park ◽  
Rhipicephalus Appendiculatus ◽  
Kruger National Park ◽  
Large Herbivore ◽  
Questing Ticks ◽  
Over Time

The study aimed to assess the long-term population dynamics of questing Rhipicephalus appendiculatus and Rhipicephalus zambeziensis in two landscape zones of the Kruger National Park (KNP). Ticks were collected by dragging the vegetation monthly in three habitats (grassland, woodland and gully) at two sites in the KNP (Nhlowa Road and Skukuza) from August 1988 to March 2002. Larvae were the most commonly collected stage of both species. More R. appendiculatus were collected at Nhlowa Road than at Skukuza, with larvae being most abundant from May to August, while nymphs were most abundant from August to December. Larvae were most commonly collected in the gullies from 1991 to 1994, but in the grassland and woodland habitats from 1998 onwards. Nymphs were most commonly collected in the grassland and woodland. More R. zambeziensis were collected at Skukuza than at Nhlowa Road, with larvae being most abundant from May to September, while nymphs were most abundant from August to November. Larvae and nymphs were most commonly collected in the woodland and gullies and least commonly in the grassland (p < 0.01). The lowest numbers of R. appendiculatus were collected in the mid-1990s after the 1991/1992 drought. Rhipicephalus zambeziensis numbers declined after 1991 and even further after 1998, dropping to their lowest levels during 2002. The changes in numbers of these two species reflected changes in rainfall and the populations of several of their large herbivore hosts, as well as differences in the relative humidity between the two sites over time.

scholarly journals Laboratory study on new particle formation from the reaction OH + SO<sub>2</sub>: influence of experimental conditions, H<sub>2</sub>O vapour, NH<sub>3</sub> and the amine tert-butylamine on the overall process

2010 ◽  
Vol 10 (3) ◽  
pp. 6447-6484 ◽  
Author(s):  
T. Berndt ◽  
F. Stratmann ◽  
M. Sipilä ◽  
J. Vanhanen ◽  
T. Petäjä ◽  
...  
Keyword(s):  
Relative Humidity ◽  
High Sensitivity ◽  
Particle Growth ◽  
Counting Efficiency ◽  
Oh Radicals ◽  
Atmospheric Conditions ◽  
Promoting Effect ◽  
Experimental Conditions ◽  
H2so4 Concentration ◽  
Tert Butylamine

Abstract. Nucleation experiments starting from the reaction of OH radicals with SO2 have been performed in the IfT-LFT flow tube under atmospheric conditions at 293±0.5 K for a relative humidity of 13–61%. The presence of different additives (H2, CO, 1,3,5-trimethylbenzene) for adjusting the OH radical concentration and resulting OH levels in the range (4–300)·105 molecule cm−3 did not influence the nucleation process itself. The number of detected particles as well as the threshold H2SO4 concentration needed for nucleation was found to be strongly dependent on the counting efficiency of the used counting devices. High-sensitivity particle counters allowed the measurement of freshly nucleated particles with diameters down to about 1.5 nm. A parameterization of the experimental data was developed using power law equations for H2SO4 and H2O vapour. The exponent for H2SO4 from different measurement series was in the range of 1.7–2.1 being in good agreement with those arising from analysis of nucleation events in the atmosphere. For increasing relative humidity, an increase of the particle number was observed. The exponent for H2O vapour was found to be 3.1 representing a first estimate. Addition of 1.2·1011 molecule cm−3 or 1.2·1012 molecule cm−3 of NH3 (range of atmospheric NH3 peak concentrations) revealed that NH3 has a measureable, promoting effect on the nucleation rate under these conditions. The promoting effect was found to be more pronounced for relatively dry conditions. NH3 showed a contribution to particle growth. Adding the amine tert-butylamine instead of NH3, the enhancing impact for nucleation and particle growth appears to be stronger.

Tetracycline Removal Enhancement With Fe-Saturated Nanoporous Montmorillonite in a Tripartite Adsorption/Desorption/Photo-Fenton Degradation Process

2021 ◽  
Author(s):  
Shiva Chahardahmasoumi ◽  
Seyed Amir Hossein Jalali ◽  
Mehdi Nasiri Sarvi
Keyword(s):  
Antimicrobial Activity ◽  
Visible Light ◽  
Fenton Reaction ◽  
Degradation Process ◽  
Oh Radicals ◽  
Desorption Process ◽  
High Tc ◽  
Modified Montmorillonite ◽  
Adsorption Desorption ◽  
First Time

Abstract The adsorption and photo-Fenton degradation of tetracycline (TC) over Fe saturated nanoporous montmorillonite was analyzed. The synthesized samples were characterized using XRD, FTIR, SEM, and XRF analysis, and the adsorption and desorption of TC onto these samples as well as the antimicrobial activity of TC during these processes were analyzed at different pH. The results indicated that the montmorillonite is a great adsorbent for the separation of the TC from aqueous solutions, however, after increasing the amount of TC adsorbed, the desorption process started, and up to 50% of TC adsorbed onto non-modified montmorillonite was released back to the solution with almost no changes in its antimicrobial activity. After acid treatment (for creation of nanoporous layers) and Fe saturation of the montmorillonite, almost similar great separation was achieved compared to non-modified montmorillonite. In addition, the desorption of TC from modified montmorillonite was still high up to 40% of adsorbed TC. However, simultaneous adsorption and photodegradation of TC were detected and almost no antimicrobial activity was detected after 180 min of visible light irradiation, which could be due to the photo-Fenton degradation of TC on the modified montmorillonite surface. In the porous structures of modified montmorillonite high ˙OH radicals were created in the photo-Fenton reaction and were measured using the Coumarin technique. The ˙OH radicals help the degradation of TC as proposed in an oxidation process. Surprisingly, more than 90 % of antimicrobial activity of the TC decreased under visible light (after 180 min) when desorbed from nanoporous Fe-saturated montmorillonite compared to natural montmorillonite. To the best of our knowledge, this is the first time that such a high TC desorption rate from an adsorbent with the least remained antimicrobial activity is reported which makes nanoporous Fe-saturated montmorillonite a perfect separation substance of TC from the environment.

Secondary organica aerosol formation from the reactions of 2,5-dimethylfuran with OH radicals and ozone

2021 ◽  
Author(s):  
Ana Rodriguez Cervantes ◽  
Mercedes Tajuelo Diaz-Pavón ◽  
Diana Rodriguez Rodriguez ◽  
Alba Escalona Verbo ◽  
Gabriela Viteri Tovar ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Lignocellulosic Biomass ◽  
Low Cost ◽  
Fine Particulate Matter ◽  
Simulation Models ◽  
Pollutant Emissions ◽  
Oh Radicals ◽  
Aerosol Formation ◽  
Furan Derivatives ◽  
Seed Particles

&lt;p&gt;Biomass is a significant renewable energy source and is expected to grow in importance in the transition away from fossil energy sources at a relatively low cost. Lignocellulosic biomass, which is the most abundant biomass, has critical importance as sustainable production of chemicals and fuels. Catalytic production methods of converting lignocellulosic biomass into furan derivatives have been improved significantly. One of these furan derivatives, 2,5-dimethylfuran (2,5-DMF), has attracted interest as a potential biofuel due to its physicochemical properties, in some aspects better than gasoline and ethanol, such as the low pollutant emissions in its combustion. However, before 2,5-DMF can be accepted as an alternative transport fuel, some outstanding problems, as its atmospheric fate, must be resolved.&lt;/p&gt;&lt;p&gt;2,5-DMF can be degraded by the main tropospheric oxidants, resulting in furan derivatives such as furanones which are efficient precursors of SOA. To this end, the present study had the aim of analyzing the OH radical photooxidation and ozonolysis of 2,5-DMF, characterizing the conditions that lead to the formation and growth of new particles. Factors such as relative humidity (RH), NOx and SO&lt;sub&gt;2&lt;/sub&gt; level and pre-existing inorganic seed particles, which could influence in SOA formation, has been assessed. The study was carried out in two different chambers at (296&amp;#177;1) K and atmospheric pressure. Results for OH-photooxidation indicate that SOA yields decrease (from 6.2 to 0.4%) with the rise of 2,5-DMF concentration (from10 to 1000 ppb). In the absence of NOx and under high relative humidity (RH) conditions (60%), higher aerosol yields are favored. SOA formation is dependent on the initial seed surface for two kinds of inorganic seed particles ((NH&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt; and CaCl&lt;sub&gt;2&lt;/sub&gt;), being the effect slightly greater for CaCl&lt;sub&gt;2&lt;/sub&gt;. The ozonolysis only generates particles in the presence of SO&lt;sub&gt;2&lt;/sub&gt; and the increase of relative humidity from 0 to 15% lowers the particle number and particle mass concentrations. The water-to-SO&lt;sub&gt;2&lt;/sub&gt; rate constant ratio of the Criegee intermediate was derived from the SOA yield in experiments with different relative humidity values.&lt;/p&gt;&lt;p&gt;The obtained results provide detailed daytime chemistry about SOA formation from 2,5-DMF oxidation and improves our understanding of the chemical evolution of biomass burning plumes. Moreover, these results could be integrated into air quality simulation models, especially in developing countries which are suffering severe fine particulate matter pollution.&lt;/p&gt;

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