Particulate Carbon Concentrations Research Articles

Applicability of aethalometers for monitoring diesel particulate matter concentrations and exposure in underground mines

Occupational exposure to diesel exhaust is regulated by legislation in Europe owing to its carcinogenic effects on humans. In underground mines, exposure to diesel exhaust requires regular monitoring. In this work, we investigate the usage of aethalometer AE33 and portable micro-aethalometer MA200 to assess occupational exposure to diesel exhaust in two underground mines. These instruments provide continuous data on wavelength-dependent particle light absorption, and based on this, equivalent black carbon (eBC) particle concentrations and potential sources. Both aethalometers correlated well with the thermal-optical elemental carbon analysis. Time-resolved aethalometer data revealed work-activity-dependent eBC concentration patterns that can be beneficial for identifying work phases that are significant for occupational exposure. In particular, high eBC peak exposures were observed for workers near load haul dumping areas. The diesel soot mass absorption cross-sections determined were similar for both mines. The absorption Ångström exponent determined from the aethalometer data was suitable for detecting and assessing the contributions of other potential sources to eBC concentrations, such as tobacco smoke, which is often prevalent in work environments. Overall, the portable micro-aethalometers proved to be suitable for monitoring occupational diesel exhaust exposure and can be useful for designing targeted exposure prevention measures in mining environments.

Variation of amino acid in the sinking particulates in the northeastern Arabian Sea and the northern Bay of Bengal

Sediment traps are widely used to get insight into how particulate matter forms and settles in the water column. Earlier studies in the Northern Indian Ocean have shown that the sinking flux depends mainly on surface primary production and varies seasonally and inter-annually. In the case of the Bay of Bengal, river runoff plays a significant role in the sinking flux. As a part of the SIBER-INDIA program, a mooring consisting of sediment traps was deployed at three depths (495 m, 1205 m, and 2915 m) in the Arabian Sea (Northeastern Arabian Sea sediment trap, NEAST;16.87°N, 67.77°E) and at 580 m, 1110 m, and 1635 m in the Bay of Bengal (Bay of Bengal sediment trap, BoBST; 18.21°N, 89.63°E). We present here data on total fluxes, concentrations of particulate carbon and nitrogen, biogenic opal, and amino acid composition for the period 2017–2018 in both basins. Particle flux in the Arabian Sea was influenced by monsoon-related processes with higher flux during the northeast monsoon (NEM) and southwest monsoon (SWM) seasons, whereas the flux was higher in BoB during SWM. Particulate nitrogen (PN), particulate organic carbon (POC), and total hydrolysable amino acid (THAA) mostly decreased with depth in all traps due to the decomposition of labile organic constituents in the sinking flux. Changes in the decomposition of organic matter with depth were further reflected in the POC/PN molar ratios, which increased with depth in the Arabian Sea. A low POC/PN molar ratio associated with the higher THAA concentration in most of the shallow traps indicates the presence of fresher organic matter. Among the THAA, Glycine (Gly) was the dominant amino acid in all the samples followed by Aspartic acid (Asp), Glutamic acid (Glu), Serine (Ser), and Alanine (Ala). The amino acid-based degradation index (DI) reveals the degradation of labile organic matter with depth in the NEAST. However, the middle trap in the BoB showed a different trend with higher total and lithogenic fluxes, POC, PN, and DI values compared to the shallow trap indicating lateral advection in the bay. Monsoonal changes and mesoscale eddies make these basins distinct from one another and influence their sinking fluxes and biogeochemical settings.

Environmental Drivers of Coccolithophore Growth in the Pacific Sector of the Southern Ocean

AbstractThe Great Calcite Belt (GCB) is a band of high concentrations of suspended particulate inorganic carbon (PIC) spanning the subantarctic Southern Ocean and plays an important role in the global carbon cycle. The key limiting factors controlling coccolithophore growth supporting this high PIC have not yet been well‐characterized in the remote Pacific sector, the lowest PIC but largest area of the GCB. Here, we present in situ physical and biogeochemical measurements along 150°W from January to February 2021, where a coccolithophore bloom occurred. In both months, PIC was elevated in the Subantarctic Zone (SAZ), where nitrate was >1 μM and temperatures were ∼13°C in January and ∼14°C in February, consistent with conditions previously associated with optimal coccolithophore growth potential. The highest PIC was associated with a relatively narrow temperature range that increased about 1°C between occupations. A fresher water mass had been transported to the 150°W meridian between occupations, and altimetry‐informed Lagrangian backtracking estimates show that most of this water was likely transported from the southeast within the SAZ. Applying the observations in a coccolithophore growth model for both January and February, we show that the ∼1.7°C increase in temperature can explain the rise in PIC between occupations.

Particulate Air Pollution and Blood Pressure: Signaling by the Arachidonate Metabolism.

Short-term exposure to ambient particulate matter (PM) can raise blood pressure, but the underlying mechanisms are unclear. We explored whether arachidonate metabolites serve as biological intermediates in PM-associated prohypertensive changes. This panel study recruited 110 adults aged 50 to 65 years living in Beijing, China. The participants' blood pressure, arterial stiffness, and cardiac and endothelial function were measured up to 7 times. The serum concentrations of arachidonate metabolites were quantified by targeted lipidomics. Ambient concentrations of fine PM (PM2.5), black carbon, and accumulation mode particles were continuously monitored at a station and their associations with the health indicators were evaluated. Interquartile range increases in 25 to 96-hour-lag exposure to PM2.5, black carbon, and accumulation mode particles were associated with significant increases in systolic blood pressure (brachial: 0.8-3.2 mm Hg; central: 0.7-2.8 mm Hg) and diastolic blood pressure (brachial, 0.5-1.5 mm Hg; central, 0.5-1.6 mm Hg). At least 1 pollutant was associated with increases in augmentation pressure and heart rate and decreases in reactive hyperemia index and ejection time. The serum concentrations of arachidonate were significantly increased by 3.3% to 14.6% in association with PM exposure, which mediated 9% of the PM-associated increases in blood pressure. The levels of eicosanoids from the cytochrome P450, cyclooxygenase, and lipoxygenase pathways changed with PM exposure, and those from the cytochrome pathway significantly mediated the association between PM exposure and blood pressure. Short-term exposure to particulate air pollution was associated with a prohypertensive change in adults, which was in part mediated by alteration of arachidonate metabolism.

Observational evidence of the regional transported black carbon in high layer over Beijing

The mass concentration, size distribution and mixing state of refractory black carbon (rBC) particles, together with other pollutants and meteorological variables, were observed at a station with a height of 528 m above ground to understand source of rBC particles over Beijing. Here we present observational evidences that regional transported rBC is an important source of rBC in high layer over Beijing. In our observations, the mass concentration of rBC increased from 1.0 μg m−3 to 4.6 μg m−3 during period with strong regional transport of pollutants, but decreased to 1.8 μg m−3 when regional transport weakened. Such trend was different with local emitted NOx, but consistent with regional transported SO2. Further analyses indicated that the transported rBC particles were highly aged; the ratio of “thickly” coated rBC in total rBC (fBC) increased from 52.4% to 71.3% during period with strong regional transport, and then decreased slightly to 66.9% when regional transport weakened, likely caused by supplement of freshly emitted local BC particles. The aged rBC particles own enhanced light absorbing capacity, which may exert more important role in weakening atmospheric diffusion capacity and aggravating surface haze pollution, and hence should be concerned in future pollution mitigation.

Ambient Anthropogenic Carbons and Pediatric Respiratory Infections: A Case-Crossover Analysis in the Megacity Beijing.

Carbon loading in airway cells has shown to worsen function of antimicrobial peptides, permitting increased survival of pathogens in the respiratory tract; however, data on the impacts of carbon particles on childhood acute respiratory infection (ARI) is limited. We assembled daily health data on outpatient visits for ARI (bronchitis, pneumonia, and total upper respiratory infection [TURI]) in children aged 0-14years between 2015 and 2019 in Beijing, China. Anthropogenic carbons, including black carbon (BC) and its emission sources, and wood smoke particles (delta carbon, ultra-violet absorbing particulate matter, and brown carbon) were continuously monitored. Using a time-stratified case-crossover approach, conditional logistic regression was performed to derive risk estimates for each outcome. A total of 856,899 children were included, and a wide range of daily carbon particle concentrations was observed, with large variations for BC (0.36-20.44) and delta carbon (0.48-57.66μg/m3). Exposure to these particles were independently associated with ARI, with nearly linear exposure-response relationships. Interquartile range increases in concentrations of BC and delta carbon over prior 0-8days, we observed elevation of the odd ratio of bronchitis by 1.201 (95% confidence interval, 1.180, 1.221) and 1.048 (95% CI, 1.039, 1.057), respectively. Stronger association was observed for BC from traffic sources, which increased the odd ratio of bronchitis by 1.298 (95% CI, 1.273, 1.324). Carbon particles were also associated with elevated risks of pneumonia and TURI, and subgroup analyses indicated greater risks among children older than 6years. Our findings suggested that anthropogenic carbons in metropolitan areas may pose a significant threat to clinical manifestations of respiratory infections in vulnerable populations.

Ocean acidification increases inorganic carbon over organic carbon in shrimp's exoskeleton

Ocean acidification (OA) may either increase or have a neutral effect on the calcification in shrimp's exoskeleton. However, investigations on changes in the carbon composition of shrimp's exoskeletons under OA are lacking. We exposed juvenile Pacific white shrimps to target pHs of 8.0, 7.9, and 7.6 for 100 days to evaluate changes in carapace thickness, total carbon (TC), particulate organic carbon (POC), particulate inorganic carbon (PIC), calcium, and magnesium concentrations in their exoskeletons. The PIC: POC ratio of shrimp in pH 7.6 treatment was significantly higher by 175 % as compared to pH 8.0 treatment. Thickness and Ca% in pH 7.6 treatment were significantly higher as compared to pH 8.0 treatment (90 % and 65 %, respectively). This is the first direct evidence of an increased PIC: POC ratio in shrimp exoskeletons under OA. In the future, such changes in carbon composition may affect the shrimp population, ecosystem functions, and regional carbon cycle.

Study on the Generation of Carbon Particles in Oil and its Effect on the Breakdown Characteristics of Oil‐Paper Insulation

AbstractThe partial discharge in the converter transformer will cause the carbonization of the insulating paper. The high concentration of free carbon particles generated from the insulating paper during the operation of the converter transformer will cause partial discharge, which will aggravate the insulation performance deterioration. For the bi‐directional interaction of carbon particles and partial discharge, the mechanism of insulating paper carbonization caused by partial discharge and the effect of carbon particles on the dielectric strength of oil paper are studied. In this paper, we construct a simulation system of amorphous cellulose to study the carbonization mechanism of insulating paper from the microscopic level. Furthermore, we build a DC voltage experimental platform to carry out partial discharge damage tests of oil‐paper insulation models and to measure the changes in the breakdown voltage with different carbon particle concentrations and diameters. The results show that partial discharge speeds up the cleavage rate of cellulose, generates low molecular hydrocarbon gas and water molecules, and the carbon atoms rearrange into PAH‐like molecules with aliphatic side chains. The surface of the insulating paper will carbonize, then form free carbon particles after peeling off. Afterward, the carbon particles in insulating oil accumulate in the high electric field area and attach to the insulating paper, which will cause electric field distortion and reduce the dielectric strength of oil‐paper insulation. With the increase of carbon particle concentration and diameter, the breakdown voltage of oil‐paper insulation decreases gradually. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Investigating the growth of carbon traces in cardboard in oil-paper insulation

A large amount of contaminants are collected on the cardboard surface of the valve-side bushing outlet of a converter transformer that has been operating for a long period, and can cause the performance of the oil–paper insulation to degrade. The analysis of their energy spectrum has shown that these contaminants contain free carbon. To investigate causes of the formation of these carbon traces, the authors of this study analyze their law of growth on the surface of the insulating paper in the presence of pure insulating oil and insulating oil containing carbon particles. We examined the influence of carbon tracks of different lengths on the breakdown voltage along the surface of the oil–paper insulation. The results showed that carbonization on the surface of the insulating paper generated carbon traces in pure insulating oil and eventually led to the formation of conductive channels. Moreover, carbon traces were generated by carbon particles deposited on the surface of the insulating paper in insulating oil containing carbon particles. The carbon traces grew from the high-voltage electrode to the ground electrode along the direction of the electric field in both types of oils. The formation of the conductive channel through the poles of the paper in insulating oil containing carbon particles required a lower voltage and a shorter discharge time than that in pure insulating oil. As the concentration of the carbon particles increased, the rate of growth of carbon traces on the surface of the insulating paper increased such that the oil–paper insulation failed earlier than otherwise. Long carbon traces were formed on the surface of the insulating paper in case of a high concentration of carbon particles under the DC pre-pressure mode, and this led to a reduction in the breakdown voltage along the surface of the oil–paper insulation.

Statistical analysis, source apportionment, and toxicity of particulate- and gaseous-phase PAHs in the urban atmosphere.

The concentrations of particulate and gaseous Polycyclic Hydrocarbons Carbon (PAHs) were determined in the urban atmosphere of Delhi in different seasons (winter, summer, and monsoon). The samples were collected using instrument air metric (particulate phase) and charcoal tube (gaseous phase) and analyzed through Gas chromatography. The principal component and correlation were used to identify the sources of particulate and gaseous PAHs during different seasons. The mean concentration of the sum of total PAHs (TPAHs) for particulate and gaseous phases at all the sites were found to be higher in the winter season (165.14 ± 50.44 ng/m3 and 65.73 ± 16.84 ng/m3) than in the summer season (134.08 ± 35.0 ng/m3 and 43.43 ± 9.59 ng/m3), whereas in the monsoon season the concentration was least (68.15 ± 18.25 ng/m3 and 37.63 1 13.62 ng/m3). The principal component analysis (PCA) results revealed that seasonal variations of PAHs accounted for over 86.9%, 84.5%, and 94.5% for the summer, monsoon, and winter seasons, respectively. The strong and positive correlation coefficients were observed between B(ghi)P and DahA (0.922), B(a)P and IcdP (0.857), and B(a)P and DahA (0.821), which indicated the common source emissions of PAHs. In addition to this, the correlation between Nap and Flu, Flu and Flt, B(a)P, and IcdP showed moderate to high correlation ranging from 0.68 to 0.75 for the particulate phase PAHs. The carcinogenic health risk values for gaseous and particulate phase PAHs at all sites were calculated to be 4.53 × 10-6, 2.36 × 10-5 for children, and 1.22 × 10-5, 6.35 × 10-5 for adults, respectively. The carcinogenic health risk for current results was found to be relatively higher than the prescribed standard of the Central Pollution Control Board, India (1.0 × 10-6).

Copepod Feeding Responses to Changes in Coccolithophore Size and Carbon Content

Phytoplankton stoichiometry and cell size could result from both phenology and environmental change. Zooplankton graze on primary producers, and this drives both the balance of the ecosystem and the biogeochemical cycles. In this study, we performed incubations with copepods and coccolithophores including different prey sizes and particulate carbon contents by considering phytoplankton biovolume concentration instead of chlorophyll a level (Chl a) as is usually performed in such studies. The egestion of fecal pellet and ingestion rates were estimated based on a gut fluorescence method. The latter was calibrated through the relationship between prey Chl a level and the biovolume of the cell. Chl a/biovolume ratio in phytopkanton has to be considered in the copepod gut fluorescent content method. Both coccolithophore biovolume and particulate inorganic/organic carbon ratios affect the food foraging by copepods. Finally, we observed a non-linear relationship between ingestion rates and fecal pellet egestion, due to the presence of calcite inside the copepod’s gut. These results illustrate that both prey size and stoichiometry need to be considered in copepod feeding dynamics, specifically regarding the process leading to the formation of fecal pellets.

Salt‐Induced Flocculation of Dissolved Organic Matter and Iron Is Controlled by Their Concentration and Ratio in Boreal Coastal Systems

AbstractRivers and estuaries are important conduits and reactors for organic matter (OM). Despite the substantial export of terrestrial OM by rivers, only a small proportion of this material reaches the open ocean. One potentially important mechanism contributing to the removal of terrestrial dissolved OM (DOM) is flocculation; a process that transforms DOM into larger size fractions that can settle into sediment pools. Here we investigate the role of flocculation in adjacent boreal coastal systems over three consecutive seasons. Flocculation experiments, which include the artificial salting of freshwater DOM to mid (12 psu) and high salinity (25 psu), and a 1:1 mixture of freshwater DOM with their respective saline endmember, highlight a potentially important source of particulate carbon (PC) in boreal estuaries. Along with a 3.5% ± 1.0% removal of dissolved organic carbon (DOC) and 44% ± 16% dissolved iron (DFe), the potential for flocculation of these constituents significantly increased with increasing salinity from 12 to 25 psu. The particulate matter (PM) produced by salt‐induced flocculation was comparable to in situ PC concentrations (in situ PC = 27.5 μmol L−1 and flocculated PC = 15.0 μmol L−1) and stable carbon isotopic signatures (in situ PM = −28.8‰ and flocculated PM = −28.3‰). DFe:DOC and Sr were the only parameters that could significantly explain the degree of carbon and iron flocculation. This demonstrates the importance of DOC, DFe, and optical properties, and the predictive value of DFe:DOC for understanding DOM susceptibility to flocculation and its relevance and contribution to regional and global carbon budgets.

Study on the property and airflow grading of Ningxia coal gasification fine slag

Coal gasification fine slag (FS) is a solid waste of difficult-to-separate nature. In order to improve the reuse rate of coal gasification fine slag resources, so as to improve the value-added utilization and clean transformation for coal chemical industry, which is necessary to deeply study the composition characteristics and effective separation of FS. In this study, the dry pulverized coal gasification fine slag (DPFS) was divided into different particle sizes by wet screening, and the composition and structure characteristics of components with different particle sizes were investigated. Then a combined treatment method of airflow crushing and classification was used to separate DPFS. The results showed that the fixed carbon content, the ash composition, the micro morphology and the pore structure of FS were related to the particle size distribution. The fixed carbon content of particles with particle sizes ranging between 74–98 μm was the highest (about 39.98%), the particles with a size grade of 13–74 μm and larger than 98 μm was between 11.85 and 30.85%, The minimum fixed carbon content of 0–13 μm particle size is 8.69%. The microstructure of DPFS was composed of several relatively independent particle units with special morphology, including porous irregular particles, spherical particles, floccule, and the element contents of these particle units were very different. The residual carbon and ash components in the DPFS could be effectively separated and enriched in different products by airflow crushing and classification. When the grinding gas pressure was set to 0.5 MPa, the low carbon product with fixed carbon content of 4.99% and yield of 19.86% could be obtained. The mechanism of airflow crushing of FS showed that airflow crushing based on impact force and shear force could effectively separate the residual carbon and ash components, and greatly improve the separation and recovery rate of residual carbon. Therefore, the airflow crushing and classification has a good application prospect in the separation and enrichment of residual carbon of gasification fine slag.

A relationship between phages and organic carbon in wastewater treatment plant effluents

With stringent effluent requirements and the implementation of new processes for micropollutant removal, it is increasingly important for wastewater treatment plants (WWTPs) to understand the factors affecting effluent quality. Phages (viruses infecting prokaryotes) are abundant in the biological treatment processes. They can contribute to organic carbon in the treated effluent both because they are organic in nature and occur in the effluent and because they cause lysis of microorganisms. Today very little is known about the effects of phages on effluent quality. The goal of this study was, therefore, to determine the relationship between phages and organic carbon in WWTP effluents. We also examined the diversity, taxonomy, and host-association of DNA phages using metagenomics. Effluent samples were collected from four WWTPs treating municipal wastewater. Significant differences in both organic carbon and virus-like particle concentrations were observed between the plants and there was a linear relationship between the two parameters. The phage communities were diverse with many members being taxonomically unclassified. Putative hosts were dominated by bacteria known to be abundant in activated sludge systems such as Comamonadaceae. The composition of phages differed between the WWTPs, suggesting that local conditions shape the communities. Overall, our findings suggest that the abundance and composition of phages are related to effluent quality. Thus, there is a need for further research clarifying the association between phage dynamics and WWTP function.

Design of a low-cost wireless emission monitoring system for solid-fuel heat sources

INTRODUCTION: The study presents a conceptual and detailed design methodology overview of a wireless sensor network (WSN) aimed to evaluate the SmartCity air quality in real-time. The aim of the article is to provide low-cost, reliable, and accurate emission data at remote locations, assisting the 2050 Climate-Neutral target set by the European Commission. The sensor devices shall monitor emission parameters such as ozone, carbon dioxide concentration and particle concentrations, specifically concentrations PM2,5 and PM10.OBJECTIVES: The overall objective of the article is to demonstrate the use of a modern home-made air quality device within the market of boilers, fireplaces or other heating devices.METHODS: The methodology consists of reverse engineering of used professional portable emission analyzers, determining the detailed parts, building a model of how the device's internal systems operate. The paper later explains a series of future experiments including the setup, the necessary components and specific aim. Two numerical models shall be constructed in MATLAB Simscape and Simulink, specifically a telecommunication model, assisting the design of the telecommunication module, and thermal numerical model, that aids in verifying the system temperature and cooling.RESULTS: The study presents a large potential in increasing the accuracy and spectrum of modern air quality data and decreasing emission levels.CONCLUSION: In the conclusion of the paper, the functional requirements of the data processing are stated, along with schematic illustration of the user interface of measured emissions.

Detrital Carbonate Minerals in Earth's Element Cycles.

We investigate if the commonly neglected riverine detrital carbonate fluxes might reconciliate several chemical mass balances of the global ocean. Particulate inorganic carbon (PIC) concentrations in riverine suspended sediments, that is, carbon contained by these detrital carbonate minerals, were quantified at the basin and global scale. Our approach is based on globally representative data sets of riverine suspended sediment composition, catchment properties, and a two‐step regression procedure. The present‐day global riverine PIC flux is estimated at 3.1 ± 0.3 Tmol C/y (13% of total inorganic carbon export and 4% of total carbon export) with a flux‐weighted mean concentration of 0.26 ± 0.03 wt%. The flux prior to damming was 4.1 ± 0.5 Tmol C/y. PIC fluxes are concentrated in limestone‐rich, rather dry and mountainous catchments of large rivers near Arabia, South East Asia, and Europe with 2.2 Tmol C/y (67.6%) discharged between 15°N and 45°N. Greenlandic and Antarctic meltwater discharge and ice‐rafting additionally contribute 0.8 ± 0.3 Tmol C/y. This amount of detrital carbonate minerals annually discharged into the ocean implies a significant contribution of calcium (∼4.75 Tmol Ca/y) and alkalinity fluxes (∼10 Tmol (eq)/y) to marine mass balances and moderate inputs of strontium (∼5 Gmol Sr/y) based on undisturbed riverine and cryospheric inputs and a dolomite/calcite ratio of 0.1. Magnesium fluxes (∼0.25 Tmol Mg/y), mostly hosted by less‐soluble dolomite, are rather negligible. These unaccounted fluxes help in elucidating respective marine mass balances and potentially alter conclusions based on these budgets.

Occurrence mode and molecular structure model of unburned carbon in coal gasification fine slags

Coal gasification fine slag (CGFS) is a kind of solid waste produced in the process of coal gasification, in which unburned carbon (UC) severely restricts its resource utilization. The study of physical/chemical properties, occurrence state and molecular structure of UC is of great significance to the utilization of CGFS. The characterization results show that the carbon content of particles increases with the increase of particle size, which is enriched to concentrate in particle size above 125 μm. UC is loose and porous, which leads to the wrapping and covering with inorganic ash particles. The molecular formula of the UC is determined to be C178H73O46N1S1, with a molecular weight of 2991. The average macromolecular structure model of UC is established by computer simulation. It is basically consistent with the infrared results of the simulation experiment. From the perspective of structure, UC has a high degree of aromatization and abundant oxygen-containing functional groups, which may increase the difficulty of decarbonization by enhancing hydrophilicity. This work provides a comprehensive understanding of UC structure at the atomic level, which is conducive to the efficient decarbonization of CGFS.

Temporal dynamics of total microbial biomass and particulate detritus at Station ALOHA

Particulate adenosine-5′-triphosphate (P-ATP) and particulate carbon (PC) concentrations were measured on approximately monthly intervals throughout the upper water column (0–1000 m) over a 30-yr (1989–2018) period at Station ALOHA to track the seasonal-to-decadal variability in total microbial biomass and the dynamics of living-to-nonliving particulate organic matter pools. On selected cruises, samples were also collected to a depth of ∼4800 m. P-ATP concentrations were relatively uniform (27–34 ng l−1) throughout the upper euphotic zone (0–100 m) with a distinct peak at 45 m. P-ATP concentrations were significantly higher (p < 0.001) in summer (Jun-Aug) than in winter (Dec-Feb), especially between 45 and 100 m where the seasonal differences averaged 28%. Below 100 m, P-ATP concentrations decreased rapidly with depth to a 30-yr mean value of 3.5 ng ATP l−1 at 250 m, and then decreased more gradually to a 30-yr mean value of 0.9 ng ATP l−1 at 1000 m. Between 125 and 175 m, the seasonal peak in P-ATP shifted to spring (Mar-May), with minima in fall (Sep-Nov) and winter (Dec-Feb). No consistent seasonal variations in P-ATP were detected at depths >175 m, suggesting a temporally stable habitat. Assuming a PC:P-ATP ratio of 250:1 (g g−1), the 0–100 m, 100–250 m, and 250–1000 m depth-integrated microbial biomass estimates were 775, 425, and 350 mg C m−2, respectively. Bathypelagic zone (>1000 m) P-ATP concentrations, based on a more limited data set than the upper portions of the water column, were low (0.4–0.7 ng ATP l−1). However, when integrated over the entire deep water habitat (1000–4800 m), bathypelagic zone microbial biomass was substantial (425 mg C m−2). Expressed as a percentage of total PC, microbial biomass ranged from ∼30% in the upper euphotic zone to ∼3% at depths >3000 m, emphasizing the preponderance of detrital PC throughout the entire water column. The total water column inventory of microbial biomass at Station ALOHA was 2 g C m−2 compared to ∼18 g C m−2 for total suspended PC; approximately 50% of the total microbial biomass is resident in the aphotic zone (>175 m). Although daily gross primary production at Station ALOHA is on par with the total euphotic zone (0–175 m)-integrated microbial biomass (∼1 g C m−2 d−1 and ∼1 g C m−2, respectively), the sources of C and energy fueling the substantial aphotic zone microbial biomass (∼1 g m−2) are not well understood at the present time.

Toward Cleaner Transport Alternatives: Reduction in Exposure to Air Pollutants in a Mass Public Transport.

Commuters are often exposed to higher concentrations of air pollutants due to its proximity to mobile sources. Despite recent trends in urban transport toward zero- and low-tailpipe emission alternatives, the assessments of the impact of these transformations on commuter exposure are limited by the low frequency of such studies. In this work, we use a unique data set of personal exposure concentration measurements collected over the span of 5 years to analyze changes due to the introduction of a new fleet for Bogotá's Bus Rapid Transit System. In that system, over a thousand Euro-II and -III diesel-powered buses were replaced with Euro-VI compressed natural gas and filter-equipped Euro-V diesel buses. We measured personal exposure concentrations of equivalent black carbon (eBC), fine particulate (PM2.5), and ultra fine particles (UFP) during and after the retirement of old buses and the introduction of new ones. Observations collected prior to the fleet renewal were used as baseline and later compared to data collected over two follow-up campaigns in 2019 and 2020. Significant reductions in the concentration of PM2.5 and eBC were observed during the 2019 campaign, with a 48% decrease for mean in-bus eBC (89.9 to 46.4 μg m-3) and PM2.5 (180.7 to 95.4 μg m-3) concentrations. Further reductions were observed during the 2020 follow-up, when the fleet renovation was completed, with mean in-bus eBC decreasing to 17.7 μg m-3 and PM2.5 to 42.3 μg m-3. These observations imply nearly a 5-fold reduction in eBC exposure and a 4-fold decrease in PM2.5. There was a much smaller reduction of in-bus UFP concentration between 2019 and 2020, indicating a persistent presence of high particle number concentrations in the near-road environment despite the fleet renovation process. In-bus UFP concentrations ranged between 65 000 and 104 500 cm-3 during the follow-up campaigns. The results in this work illustrate the immediate benefits of reducing personal exposure through the adoption of vehicles with more stringent emission standards.

Characterizations of MWCNTs Nanofluids on the Effect of Surface Oxidative Treatments.

In this study, multi-walled carbon nanotubes (MWCNTs) were chemically modified using three acid treatment methods to introduce the surface oxygen functional group (SOFG). The presence of SOFG on the MWCNTs has been characterized by Fourier Transform Infrared (FTIR) spectroscopy. Morphology, structural and thermal properties were performed using Field Emission Scanning Electron Microscopy (FESEM), Raman spectroscopy, and Thermogravimetric analysis (TGA), respectively. The result shows that the modification with acid treatment significantly affects the degree of defects and surface group functionality of surface oxidized MWCNTs from method B. The preparation of nanofluids using MWCNTs produced from method B (MWCNT-MB) was prepared using two different parameters: with and without polyvinylpyrrolidone (PVP) as surfactant. The experiment was conducted by setting variable carbon particle concentration from 0.1 wt.% to 1.0 wt.%, and the amount of PVP is 10% of carbon particles at different temperatures (6 °C, 25 °C, 40 °C). Based on visual observation, the dispersion of carbon particles was enhanced by the presence of PVP as the stabilizing agent. The thermal conductivity performance of nanofluids revealed that the surface oxidized MWCNTs with PVP show enhanced thermal conductivity compared to the nanofluid containing MWCNTs without PVP. The improvement contributes to this in terms of stability and homogenization of nanoparticles. Hence the improved distribution of MWCNTs in water-based media improves thermal conductivity. These promising properties of MWCNTs in water-based fluids would enable the nanofluids to be used in heat transfer fluid and cooling applications.