Low CO2 Concentrations Research Articles

Association among polydisperse aerodynamic size of bioaerosols, biodiversity and urbanization in kindergartens

The aerodynamic sizes of bioaerosols may significantly affect their behaviors, respiratory deposition and biodiversity. The respirable bacterial size, biodiversity, and human-associated bacteria (HAB) related bioaerosols were evaluated at three kindergartens in Taiwan. Kindergartens A, B, and C were in urban, semi-urban, and rural areas, respectively. A six-stage viable Andersen cascade impactor was used to collect bioaerosols and to determine their size distributions. The geometric mean diameter (GMD), geometric standard deviation (GSD), heat maps, and uniformity were used to evaluate the association of bacteria characteristics. A BD Phoenix-100 automated interpretation system was used to identify the airborne bacteria species.The results revealed that 1425 colonies of the sampled airborne bacteria contained 63 species in 29 genera, and overall, 63.0% were HABs. The most abundant phylum was Actinobacteria (56.6 ± 22.2%) and Firmicutes (31.6 ± 22.3%), and from the taxonomic analysis, both airborne Micrococcus and the Staphylococcus aureus are the dominant genus. All the bacteria aerodynamic particle size distributions were polydisperse distributions. The heat map and uniformity analysis had revealed most of the sampled bioaerosols distributed between 1.1–3.3 μm, and most of the polydisperse airborne Streptococcus spp. had a size in the respirable range, due to urbanization, they have potentially contributed to respiratory risk in the kindergartens. The Shannon diversity index (H) and inverse Simpson diversity index (D) of the bioaerosols in urban kindergarten were negatively correlated with GMD and GSD. The Pearson correlations revealed that the kindergarten in the rural area, with a higher temperature, a lower relative humidity, and a lower CO2 concentration than the others, tended to have the largest H and D values (P < 0.05). Multiple and stepwise regression revealed that bioaerosol aerodynamic size was statistically significantly correlated with H (P = 0.001) and D values (P = 0.002). This study sheds light on the characteristics of bioaerosols and their associations with microbiome.

Dynamic breakthrough performance of low concentration CO2 adsorption in fixed-bed column with porous amino acid ionic liquid composites

Low concentration carbon dioxide (CO2) capture from air or confined spaces currently faces significant challenges, such as relatively poor dynamic adsorption breakthrough performance and cyclic stability. In our previous work, functionalized ionic liquid (IL) tetraethylammonium glycine ([N2222][Gly]) and porous molecular sieve (SBA-15) were combined to synthesize porous amino acid IL composite 60 wt% [N2222][Gly]@SBA-15 with microporous and ultra-microporous structures, which provide a new pathway for low concentration CO2 capture. In order to further obtain the dynamic CO2 adsorption breakthrough performance of this material under simulated actual working conditions, the effects of temperatures, relative humidity (RH) and CO2 concentrations on CO2 adsorption and desorption breakthrough performance of 60 wt% [N2222][Gly]@SBA-15 in a fixed-bed column were systematically studied in this work. The results indicated that CO2 adsorption capacity is up to 1.81 mmolCO2/g-adsorbent at 298.15 K, 1 bar and 0 % RH under 1 vol% CO2-containing gas mixture balanced with N2 and reaches 2.44 mmolCO2/g-adsorbent at 15 % RH due to the mechanism change of CO2 reaction with primary amine from 2: 1 under dry gas to 1: 1 stoichiometry in the presence of moisture. Moreover, the adsorbent maintains good cyclic adsorption-desorption performance. Further, CO2 adsorption breakthrough behaviors were well fitted by Avrami kinetic model, and the CO2 adsorption rate of 60 wt% [N2222][Gly]@SBA-15 was controlled by intra-particle diffusion. This work implied that IL-modified adsorbents have great potentials for low concentration CO2 capture applications.

Environmental quality in sixty primary and secondary school classrooms in London

Poor environmental quality in school classrooms can have a detrimental impact on children's health, nevertheless, the association between air pollutants and physical features of classrooms is poorly understood. We monitored particulate matter (PM), carbon dioxide (CO2) and thermal comfort in sixty classrooms across ten London primary and secondary schools using similar equipment to produce a comparable dataset. The overall research objective was to understand the association of classroom air quality with occupancy levels, floor types, classroom locations, classroom volume, ventilation types and different year groups. Average in-classroom PM10 (29 ± 20), PM2.5 (10 ± 2) and PM1 (5 ± 2 μg m-3) during occupied hours were ∼150 % (PM10) and 110 % (PM2.5) higher compared to non-occupied hours. PM10 concentration was reduced by 30 % for dual (mechanical + natural) compared to natural ventilation only; the corresponding reduction was slightly lower for PM2.5 (28 %) and PM1 (20 %). PM10 almost doubled for wooden floored classrooms compared with those having carpets. During high occupancy (>26 occupants), the average CO2 (935 ± 453 ppm) was ∼140 % higher than non-occupancy. The average CO2 in classrooms occupied by younger children (reception and year one) was ∼190 % higher than those with older children (years eight and nine). 68 % of classrooms exceeded the minimum recommended levels of 40 % relative humidity. Low PM10 concentrations coincided with low CO2 concentrations in classrooms across all schools. These findings highlight the importance of simultaneously addressing both thermal comfort and the resuspension of PM10 to achieve comprehensive improvements in classroom air quality. Classroom settings where indoor environment is likely to be compromised can also be identified and addressed.

Ionic Pairs-Engineered Fluorinated Covalent Organic Frameworks Toward Direct Air Capture of CO2.

The covalent organic frameworks (COFs) possessing high crystallinity and capability to capture low-concentration CO2 (400ppm) from air are still underdeveloped. The challenge lies in simultaneously incorporating high-density active sites for CO2 insertion and maintaining the ordered structure. Herein, a structure engineering approach is developed to afford an ionic pair-functionalized crystalline and stable fluorinated COF (F-COF) skeleton. The ordered structure of the F-COF is well maintained after the integration of abundant basic fluorinated alcoholate anions, as revealed by synchrotron X-ray scattering experiments. The breakthrough test demonstrates its attractive performance in capturing (400ppm) CO2 from gas mixtures via O─C bond formation, as indicated by the in situ spectroscopy and operando nuclear magnetic resonance spectroscopy using 13C-labeled CO2 sources. Both theoretical and experimental thermodynamic studies reveal the reaction enthalpy of ≈-40kJmol-1 between CO2 and the COF scaffolds. This implies weaker interaction strength compared with state-of-the-art amine-derived sorbents, thus allowing complete CO2 release with less energy input. The structure evolution study from synchrotron X-ray scattering and small-angle neutron scattering confirms the well-maintained crystalline patterns after CO2 insertion. The as-developed proof-of-concept approach provides guidance on anchoring binding sites for direct air capture (DAC) of CO2 in crystalline scaffolds.

A Study of the Antioxidizing and Inhibiting Effects of the Alcoholic Extract of Sage Salvia Officinalis on Microorganisms

Objectives: A study of the antioxidizing and inhibiting effects of the sage salvia officinalis on microorganisms. Methods: Chemical constituents of sage leaves the percentage of the 98% ethanol extract of sage was 5.8% prepared in concentrations of 50, 100, 150 and 200 mg/ml, Antioxidizing and inhibiting effects on microorganisms, and sensory characteristics of the sage added biscuits. Results: Scanning electron microscope images, the structure of powder sage leaves which appear as long tubes and round crystals, Hight percent concentration of minerals carbon and oxygen while low concentrations of (Zn, Al, Na, Mg, Si, K, Co, Ca, and Ce) were also found. the percentage of the moisture, protein, fat and ash (11.09, 6.89, 13.14, 9.64) % respectively, the inhibition effect of sage leaves ethanol extract prepared in concentrations of 50, 100, 150 and 200 mg/ml on three bacteria and fungi species of disc method. maximum effect on all three bacteria species Escherichia coli, Staphylococcus aureus and Pseudomonas sp. was found with the concentration 50 and 100 mg/ml. compared with 150 and 200 mg/ml. It has been found that the 150 mg/ml concentration has the most inhibition effect on the three species of fungi studied Aspergillus niger, A. carbonarius, A. flavus. All extract concentration inhibited A. flavus, it was that the antioxidant activity, iron ion bonding, reducing power and the ability capture the hydrogen peroxide of sage ethanol extract increases with high concentrations. Peroxide values decreased with increased sage added biscuits percentage (0, 0.5, 0,75 and 1) w/w% in stored for periods. However, the sensory characteristics of the sage added biscuits samples were good and close to the standard biscuit control. Conclusions: Finally, we conclude that the sage plant has medicinal and nutritional benefits due to its antioxidant and antimicrobial activity.

Woody biomass waste derivatives in decarbonised blast furnace ironmaking process

Modern ironmaking process relies significantly on fossil-related fuels, which ultimately results in the enormous CO2 emitted into the atmosphere. Biomass of plant origin, as a carbon-neutral energy source, has been considered as an alternative to fossil-based reducing agents such as coke. This study aims to investigate the potential of three woody biomass waste derivatives produced from biomass waste pyrolysis and gasification, namely charcoal, bio-oil, and bio-syngas, as the reducing agents in blast furnace. A model based on heat and mass balance and Gibbs free energy minimisation is proposed to simulate an ironmaking process with assistance of these derivatives. The effects of specific composition of biomass waste derivatives on process operation, CO2 emissions, and coke replacement are explored. Also the effects of H2-rich gas produced from biomass waste gasification on the blast furnace operation are estimated. Results indicate that reactions of woody biomass waste derivatives in blast furnace are complex and greatly dependent on composition. When charcoal has a higher carbon content, lower CO2 concentration is found from the top gas. The higher content of hydrogen in bio-oil will inhibit further reduction in CO2 emissions. Bio-syngas with H2/CO ratio of 1.3 proves to have a remarkable potential to reduce CO2 emissions. From the aspects of available biomass waste resources across the world, woody biomass waste derivatives as reducing agents are more suitable for countries with the limited pig iron production. This study provides a reference on the future of moving forward the decarbonised ironmaking by using woody biomass waste derivatives.

Assessment of Effects of Carbon Dioxide Exposure on Sleep Stability in Insomnia Using the Envelope Analysis

Objectives: Insomnia is a common sleep disorder, and various strategies have been explored for its treatment. One of the methods involves the administration of carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) at bedtime, as the CO&lt;sub&gt;2&lt;/sub&gt; increment exerts a sedative effect on the central nervous system. We aimed to assess the effect of CO&lt;sub&gt;2&lt;/sub&gt; on sleep quality in patients with insomnia using the coefficient of variation of the envelope (CVE) analysis, a novel analytical method. Methods: In this randomized, double-blind, sham-controlled crossover trial, 24 adults with sleeping difficulties underwent level 1 polysomnography. Two interventions involved exposure to either 2% low-concentration CO&lt;sub&gt;2&lt;/sub&gt; gas or room air. CVE analysis was performed to assess the stability of the delta band. Morphological variations in delta waves can be quantitatively monitored using the envelope analysis, which assesses the effect of manipulations on sleep that may otherwise elude detection. Results: Exposure to CO&lt;sub&gt;2&lt;/sub&gt; improved the total sleep time (TST) (&lt;i&gt;p&lt;/i&gt;=0.010) and total arousal index (TAI) (&lt;i&gt;p&lt;/i&gt;=0.011). The CVE analysis showed a distinct distribution between the experimental and sham-controlled groups. Moreover, correlations between the TST and CVE (r=0.41) and those between the TAI and CVE (r=0.40) were observed. Conclusions: This study is the first to evaluate the effects of CO&lt;sub&gt;2&lt;/sub&gt; exposure on sleep stability in patients with insomnia. The CVE analysis implies the possibility of sleep stabilization by CO&lt;sub&gt;2&lt;/sub&gt; administration and suggests a link between enhanced sleep maintenance and sleep stability.

Frustrated Lewis pairs on facet-engineered CeO2 boost the conversion of low-concentration CO2 into cyclic ureas with assistance of diamine platforms

The development of efficient processes for value-added utilization of low-concentration CO2 is an on-going challenge. In this work, we present a sequential system based on diamine platforms for the direct utilization of low-concentration sources of CO2 (≤15%) in the production of cyclic ureas. Specifically, the low-concentration CO2 is captured by ethylenediamine to form ethylenediamine carbamate (EDA-CA), which subsequently undergoes the intramolecular dehydration to give ethyleneurea (EU) in the presence of frustrated Lewis pairs (FLPs) on the facet-engineered CeO2. Remarkably, the productivity of EU obtained from EDA-CA in the sequential system (9.5 mmol·gcat−1·h−1) is ∼4 times higher compared to the traditional catalytic system (2.4 mmol·gcat−1·h−1) using ethylenediamine and pure CO2 (3 MPa). Density functional theory calculations demonstrated that the FLPs on facet-engineered CeO2 significantly reduce the energy barrier for the nucleophilic attack of N-containing segment towards the carbonyl carbon in EDA-CA (rate-limiting step), ultimately optimizing the intramolecular cyclization efficiency of EDA-CA. This work not only provides an innovation tandem approach that enables the production of cyclic ureas from low-concentration CO2, but also opens up a promising avenue for the direct utilization of low-concentration CO2 for value-added applications in the future.

The study of novelty nutrients supplementary scheme and methodology on advanced carbon sequestration of microalgae

Microalgae has great potential in carbon sequestration and production of biofuel even with a low concentrations of CO2. In this paper, an Andrews based microalgae growth kinetic model and a novel and multiple nutrient supplementary scheme that significantly extends the carbon sequestration period and enhances growth rates of microalgae are proposed. First, the correlation between nutrient concentration and microalgal growth is constructed experimentally. The advanced growth kinetic model incorporating nitrogen and phosphorus consumption is developed. Then, the optimum cultivation conditions including initial nutrients concentration, nutrients supplementary interval and daily nutrients supplementary quantities are obtained in the conical flask reactor. The findings led to a novel nutrient supplementation strategy that initiates with a 0.2BC concentration, followed by a 0.3BC addition at 100 h, with subsequent supplements every 72 h. After adopting this supplementary strategy, the microalgae growth rate is increased by 42.9 % and the carbon sequestration rate is increased by 56.2 % compared with that of the original microalgae cultivation method in one cultivation cycle. Finally, the universal microalgae nutrients supplementary model is proposed in a piecewise model. It can be concluded from the model that in the first cultivation period, microalgae needs a higher affinity for nutrients and after nutrients supplementary, the sensitivity to nutrient inhibition is reduced. The paper is significantly helpful to improve the sustainability of the microalgae growth rate and the carbon sequestration rate.

Ambient carbon dioxide concentration correlates with SARS-CoV-2 aerostability and infection risk

An improved understanding of the underlying physicochemical properties of respiratory aerosol that influence viral infectivity may open new avenues to mitigate the transmission of respiratory diseases such as COVID-19. Previous studies have shown that an increase in the pH of respiratory aerosols following generation due to changes in the gas-particle partitioning of pH buffering bicarbonate ions and carbon dioxide is a significant factor in reducing SARS-CoV-2 infectivity. We show here that a significant increase in SARS-CoV-2 aerostability results from a moderate increase in the atmospheric carbon dioxide concentration (e.g. 800 ppm), an effect that is more marked than that observed for changes in relative humidity. We model the likelihood of COVID-19 transmission on the ambient concentration of CO2, concluding that even this moderate increase in CO2 concentration results in a significant increase in overall risk. These observations confirm the critical importance of ventilation and maintaining low CO2 concentrations in indoor environments for mitigating disease transmission. Moreover, the correlation of increased CO2 concentration with viral aerostability need to be better understood when considering the consequences of increases in ambient CO2 levels in our atmosphere.

Carbonation of Recycled Concrete Aggregates for New Concrete and Concrete Fines to Make Cement-Free Hollow Blocks

Mineral carbonation provides a way to increase the recycling of concrete waste in added-value products, and contributes to the principles of the circular economy. At present, most concrete waste is still downcycled. The high water absorption of recycled concrete aggregates, among other factors, impedes their recycling in the concrete industry. The quality of coarse recycled concrete aggregates (RCA) can, however, be enhanced by carbonation. Even when starting with high-grade RCA obtained from a selective demolition process, the carbonation process can decrease the water absorption of the RCA to as low as 3.0%. Concrete with a 50% replacement rate of carbonated RCA can be produced without a significant compressive strength reduction. The research further shows that carbonation can be performed at atmospheric pressure and low CO2 concentrations (e.g., 10%). The recycled concrete fines (RCF, 0–4 mm) in combination with 25% stainless steel slag were used to make zero-cement hollow blocks (39 × 19 × 9 cm) by carbonation curing without using any hydraulic binder. The hollow blocks have a compressive strength of 15.4 MPa at the lab scale. Both technologies were demonstrated on a pilot scale. In both processes, CO2 is immobilized in the resulting construction product. The developed production processes use less primary raw materials and cause less greenhouse-gas emissions than the production of traditional concrete products.

Multiscale effects of radial mixing on mixotrophic microalgal growth and macromolecular synthesis in tubular bubble-column photobioreactors

Extremophillic microalga Chlorella sorokiniana is grown mixotrophically in a 5 L externally-illuminated tubular bubble-column photobioreactor with an external light intensity of 10,500 lx (≈195 μmol-photons.m−2.s−1) at atmospheric (0.04 %), 1 %, 2 %, 3 %, 4 %, and 5 % CO2 concentrations, with acetic acid and urea as the organic carbon and nitrogen sources, respectively, for 6–8 days. Two different setups are employed: one permits axial air flow, and another promotes radial mixing of algal particles, dissolved CO2 and nutrients along with axial sparging. We show that radial mixing increases biomass yields by reducing both photo-limitation and photo-inhibition up to CO2 concentrations <3 %, above which substrate (CO2) inhibition necessitates lower reactor mixing. Radial mixing increases the lipid yield from 1.06 and 1.61 g/L to 1.27 and 1.78 g/L at 2 % and 3 % CO2, respectively, in nitrogen-limited cases, resulting in a 10–20 % increase. We show that complete reactor mixing, facilitated by the dual effects of branched (radial) and axial sparger, is preferred only in the absence of substrate (CO2) inhibition. Subsequently, we stratify the tubular photobioreactor design strategy into two regimes based on CO2 inlet concentrations. In one regime (for inlet CO2 < 3 %), we recommend the deployment of branched sparger to facilitate both radial and axial mixing simultaneously, thereby creating a well-mixed reactor at lower CO2 concentrations. In the other regime (for inlet CO2 > 3 %), axial sparging alone is recommended since complete mixing of CO2 increases substrate inhibition by reducing the reactor pH below 7.5.

Investigation of the indoor CO2 removal efficiency and fresh air energy savings of living walls in office spaces

Elevated indoor CO2 levels might have adverse effects on human health. However, conventional physical and chemical methods for indoor CO2 removal face the challenges of high energy consumption, low efficiency at low CO2 concentrations, and high costs. Furthermore, the introduction of outdoor air to lower indoor CO2 concentrations results in significant HVAC energy consumption. Aligning with office hours and the natural light cycle, the utilization of photosynthesis in living walls (LWs) offers an energy-efficient and sustainable solution for the mitigation of high CO2 levels in office spaces. This study experimentally investigates the impacts of the carbon fixation pathways, light flux density, and substrate moisture content on the CO2 removal rate of LWs in two identical rooms. The findings provide practical suggestions for plant species selection, lighting design, and irrigation management in office spaces to enhance the CO2 removal efficiency of LWs. Additionally, the fresh air energy-saving effects of LWs under different scenarios are accurately simulated in EnergyPlus. The results demonstrate that choosing C3 plants over CAM plants in LWs yields higher CO2 removal efficiency. The activation of artificial lighting is recommended when the surface light flux density of LWs drops below the light compensation point (LCP), ensuring favorable conditions for growth. In a 30-m2 office room accommodating two and three occupants, LWs can respectively reduce the demand for fresh air by 13.9 %–38.5 % and decrease fresh air energy consumption by 11.2 %–28.2 %.

Effects of sodium aluminate on fleeting semi-dry carbonation and properties of steel slag powders in low concentration CO2 atmosphere

Accelerated carbonation suffers from the limitation of low efficiency when CO2 supply is inadequate. This study aims at proposing a carbonation accelerator of sodium aluminate (SA) to stimulate the reaction between steel slag and CO2. Additionally, a fleeting semi-dry carbonation is proposed and mixed gas with 20 vol% CO2 was used to simulate the CO2 concentration of flue gas. According to the MGC results, with only 0.07 wt% of SA added, steel slag obtained 3.55 wt% of CO2 uptake after 10 min carbonation under 20 vol% CO2 atmosphere, which is 36.02 % higher than that of the carbonated control steel slag. As a result of elevated carbonation efficiency, f-CaO (free calcium oxide) in SA incorporated steel slag (SA-SS) is decreased more substantially than that of the control steel slag after carbonation. According to autoclaving test, cement paste cast with carbonated SA-SS showed less expansion than the one cast with carbonated control steel slag. Mortar cast with carbonated SA-SS obtained a competitive compressive strength of 40.63 MPa at 28 d. SA plays the role as a pH buffer that slows down the alkalinity decrease during the fleeting carbonation and hence enables more CO2 to dissolve in water. With enhanced carbonation efficiency, CaCO3 particles in carbonated SA-SS are big cubes which is opposed to the small, shapeless grains in carbonated control steel slag.

Effect of Microwave Pretreatment on the Properties and Microstructure of Low-Concentration Carbon Dioxide Early Cured Cement-Based Materials

The utilization of microwave drying technology has expanded across various sectors due to its rapid processing speed, reduced operation time, lower sample temperatures, and consistent heating. In this research, microwave pretreatment was implemented prior to carbonation curing with low concentrations, and an array of tests including moisture content, compressive strength, carbonation depth, CO2 absorptivity, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) were utilized to investigate the effect of microwave pretreatment on the properties and microstructure of cementitious materials under early carbonation curing with low CO2 concentrations. The findings reveal that microwave pretreatment significantly decreases the moisture content within the test specimens, expediting the ingress of CO2 and improving the compressive strength of the specimens. At the same time, the effectiveness of microwave pretreatment in reducing moisture content diminishes as the pretreatment time increases. The absorption of CO2 is relatively rapid in the early stage of carbonation curing, with over 50% of the CO2 absorption occurring within the 0–6 h period of carbonation curing. The hydration products and microstructure of the uncarbonated part inside the specimens are generally consistent with the normal curing state. The formation of CaCO3 contributed to the densification of the specimen by infilling its internal voids, thereby enhancing its compressive strength. Although carbonation curing enlarges the average pore size of the samples, it also serves a filling function, making the samples more compact and reducing the porosity.

Resembling Graphene/Polymer Aerogel Morphology for Advancing the CO2/N2 Selectivity of the Postcombustion CO2 Capture Process.

The separation of CO2 from N2 remains a highly challenging task in postcombustion CO2 capture processes, primarily due to the relatively low CO2 content (3-15%) compared to that of N2 (70%). This challenge is particularly prominent for carbon-based adsorbents that exhibit relatively low selectivity. In this study, we present a successfully implemented strategy to enhance the selectivity of composite aerogels made of reduced graphene oxide (rGO) and functionalized polymer particles. Considering that the CO2/N2 selectivity of the aerogels is affected on the one hand by the surface chemistry (offering more sites for CO2 capture) and fine-tuned microporosity (offering molecular sieve effect), both of these parameters were affected in situ during the synthesis process. The resulting aerogels exhibit improved CO2 adsorption capacity and a significant reduction in N2 adsorption at a temperature of 25 °C and 1 atm, leading to a more than 10-fold increase in selectivity compared to the reference material. This achievement represents the highest selectivity reported thus far for carbon-based adsorbents. Detailed characterization of the aerogel surfaces has revealed an increase in the quantity of surface oxygen functional groups, as well as an augmentation in the fractions of micropores (<2 nm) and small mesopores (<5 nm) as a result of the modified synthesis methodology. Additionally, it was found that the surface morphology of the aerogels has undergone important changes. The reference materials feature a surface rich in curved wrinkles with an approximate diameter of 100 nm, resulting in a selectivity range of 50-100. In contrast, the novel aerogels exhibit a higher degree of oxidation, rendering them stiffer and less elastic, resembling crumpled paper morphology. This transformation, along with the improved functionalization and augmented microporosity in the altered aerogels, has rendered the aerogels almost completely N2-phobic, with selectivity values ranging from 470 to 621. This finding provides experimental evidence for the theoretically predicted relationship between the elasticity of graphene-based adsorbents and their CO2/N2 selectivity performance. It introduces a new perspective on the issue of N2-phobicity. The outstanding performance achieved, including a CO2 adsorption capacity of nearly 2 mmol/g and the highest selectivity of 620, positions these composites as highly promising materials in the field of carbon capture and sequestration (CCS) postcombustion technology.

Size-dependent dynamics of the internal carbon pool drive isotopic vital effects in calcifying phytoplankton

Isotopic offsets in biogenic calcite from equilibrium values can provide unique insights into the physiology and mechanisms of carbon regulation in calcifying phytoplankton. This study examines the impact of varying CO2 (controlled via pH) on five coccolithophore species chosen for varied cell sizes, physiology, and calcification. The study investigates isotopic offsets in coccolith calcite and organic matter, in relation to carbon demand and supply (µ/CO2). Species-specific CO2 and/or pH optima for growth (µopt) were derived from variations in growth rates with varying CO2 concentrations. Growth rates for all species declined with rising CO2 (decreasing pH) due to H+-driven inhibition. C. braarudii and C. leptoporus exhibited µopt at high CO2 concentrations (suggesting high carbon-demand) and limited growth under low CO2 (high pH) suggesting carbon limitation. Under low CO2 supply, when growth rates were CO2-limited, both species exhibited coincident isotopic depletion in calcite and organic matter as a consequence of CO2 diffusion into the cell that experienced no equilibration as a result of a highly depleted internal carbon pool. In these two species, isotopic values in calcite remained unaffected by growth rates and CO2 concentration (µ/CO2) when CO2 was sufficient for optimal growth. G. huxleyi and G. oceanica displayed optima for growth (µopt) at low CO2 concentrations and showed no growth limitation under low CO2 (indicating low carbon-demand). Both species experienced depleted (negative) vital effects caused by an excess of CO2 diffusioninto the small internal carbon pool of the cell when diffusive carbon supply outpaced low demand (low µ/CO2). Enriched (positive) vital effects were observed under low carbon supply and high demand, likely due to increased HCO3– uptake and diffusive CO2 loss from the intracellular carbon pooldue to a lower intracellular pH than the seawater pH. C. carterae exhibited a µopt at intermediate CO2 concentrations and isotopically equilibrated intracellular carbon pool such that δ13C values in calcite and organic matter suggested a shared carbon pool. This study illustrates that pH and CO2 driven vital effects and fractionation into organic matter indicate the residence time for carbon in the intracellular carbon pool, where the size of the pool is proportional to cell size. Due to the increased buffering afforded by a larger pool, C. leptoporus and C. carterae may have elevated intracellular pH which minimises CO2 leakage, whereas vital effects in G. huxleyi and G. oceanica are caused by CO2 diffusion in or out of their small internal carbon pool with limited buffering capacity owing to its small size.

Low Concentration CO Gas Sensor Based on Pulsed-Heating and Wafer-Level Fabricated MEMS Hotplate

Low Concentration CO Gas Sensor Based on Pulsed-Heating and Wafer-Level Fabricated MEMS Hotplate

Carboxysomes: Green Solutions for Sustainable Agriculture and Renewable Energy

Carboxyomes are emerging as potential tools in the sustainable agriculture and biofuel production. They are proteinaceous organelles that are distributed in different species of photosynthetic bacteria and archaea and are significantly involved in carbon fixation. They enable the organisms to thrive in diverse environmental conditions and enhance the efficacy of photosynthesis. They have shown promising potential to address challenging regarding global food security, climate change and renewable energy. These nanocompartments encapsulate Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), an enzyme that catalyzes the first step of the Calvin-Benson-Bassham cycle that is a key pathway in carbon fixation. These specialized structures concentrate CO2 around RuBisCO ad shield it from the competing oxygen, thereby optimizing the efficiency of photosynthetic process and minimize wasteful photorespiration. The photosynthetic organisms having carboxysomes are therefore ideal candidates for sustainable agriculture as they are able to thrive in the harsh conditions such as low CO2 concentrations, water scarcity and high temperatures. They are recently being studied for enhancing the productivity and yield of crops. Efforts are being exerted to introduce carboxysome shell proteins and RuBisCO enzymes into crop genomes. Researchers are aiming to create plants with the ability to efficiently capture and utilize CO2 for photosynthesis. These genetically modified crops can potentially increase crop yields, improve water and nutrient efficiency significantly. Moreover, these carboxysomal transgenes are also able to enhance the resilience of GM plants to different environmental stressors such as drought and heat, and ultimately contribute to global food security and sustainable agriculture. In addition to their applications in agriculture, carboxysomes hold promise for biofuel production as well, as they are capable of carbon fixation. They have enabled researchers to engineer photosynthetic organisms to produce renewable fuels such as ethanol, biodiesel and hydrogen. Furthermore, nanobioreactors that are based on carboxysomes can contribute protectively against climate change as they have the potential to mitigate greenhouse gas emissions by capturing CO2 from industrial emissions and converting it into valuable bioproducts. This approach represents a promising avenue to address global challenges of food insecurity, climate crisis and rapidly declining non-renewable energy sources. If leveraged appropriately, these nanocompartments can significantly contribute in paving a way for more sustainable and resilient future.

Effect of airflow rate on CO2 concentration in downflow indoor ventilation

We perform direct numerical simulations to study the effect of increasing airflow rate on CO2 concentration in downflow and displacement ventilation in a room with one occupant. Often, CO2 concentration is used as a proxy for the concentration of bio-aerosols of respiratory droplets, and therefore, tracking the CO2 concentration in ventilation strategies can be useful to understand and quantify the risk of spread of communicable respiratory illnesses. At low to moderate airflow rates, the flow in the downflow setup is not mixed, but stratified. The CO2 concentration in the upper and lower layers is determined by the strength of the thermal plume originating from the occupant. We provide a simple theoretical model to predict the height of the stratified interface, the volumetric flux of the ascending plume, and the CO2 concentration in the lower and upper layers. At very high airflow rates, the flow is well-mixed and the average CO2 concentration in the room can be predicted with the mixing ventilation assumption. We demonstrate that at low to moderate airflow rates, displacement ventilation more effectively maintains lower CO2 concentrations in the lower layer compared to downflow ventilation.