Temporal Variations In Concentrations Research Articles

Statistical tools for studying the temporal variations in chlorophyll-a concentration along the Southwest Bay of Bengal waters

Multivariate statistical analysis such as Multiple Linear Regression (MLR) and Principal Component Analysis (PCA) are used to study the effect of physico-chemical parameters on chlorophyll distribution along the southwest Bay of Bengal from January 2012 to June 2014. Physical properties recorded showed clear seasonal patterns in sea surface temperature (26.2 – 32.8 °C), salinity (24 – 36 PSU), pH (7.808 to 8.428), photosynthetic photon flux (522 – 1220.4 µM m-2s-1) with the minimum and maximum values during monsoon and summer seasons, respectively. In contrast, the chemical variables such as nitrite (0.15 to 2.35 µM), nitrate (1.02 to 6.58 µM), ammonia (0.11 – 5.22 µM), total nitrogen (1.04 to 11.58 µM), inorganic phosphate (0.16 – 2.97 µM), total phosphorus (0.55 – 8.60 µM) and reactive silicate (2.00 to 23.95 µM) showed the minimum and maximum concentration during summer and monsoon seasons, respectively. The high and low chlorophyll (0.10 to 6.92 µg l-1) and dissolved oxygen (4.07 and 7.884 mg l-1) concentrations are observed during summer and pre-monsoon seasons, respectively. PCA found that nitrogenous nutrients and chlorophyll are positively loaded and Sea Surface Temperature (SST) was negatively loaded in all the seasons except during summer season. Inter-comparison of modeled and in-situ chlorophyll-a (chl-a) concentration showed a significant correlation during monsoon season by 93 % of matchup with a R2 = 0.930, N = 60 and SEE = ±0.369 compared to other seasons. Regression analysis also predicted the positive influence of nitrate and ammonia and negative influence of SST with chl-a.

Real-Time Measurements of Gas-Phase Trichloramine (NCl3) in an Indoor Aquatic Center.

NCl3 is formed as a disinfection byproduct in chlorinated swimming pools and can partition between the liquid and gas phases. Exposure to gas-phase NCl3 has been linked to asthma and can irritate the eyes and respiratory airways, thereby affecting the health and athletic performance of swimmers. This study involved an investigation of the spatiotemporal dynamics of gas-phase NCl3 in an aquatic center during a collegiate swim meet. Real-time (up to 1 Hz) measurements of gas-phase NCl3 were made via a novel on-line derivatization cavity ring-down spectrometer and a proton transfer reaction time-of-flight mass spectrometer. Significant temporal variations in gas-phase NCl3 and CO2 concentrations were observed across varying time scales, from seconds to hours. Gas-phase NCl3 concentrations increased with the number of active swimmers due to swimming-enhanced liquid-to-gas transfer of NCl3, with peak concentrations between 116 and 226 ppb. Strong correlations between concentrations of gas-phase NCl3 with concentrations of CO2 and water (relative humidity) were found and attributed to similar features in their physical transport processes in pool air. A vertical gradient in gas-phase NCl3 concentrations was periodically observed above the water surface, demonstrating that swimmers can be exposed to elevated levels of NCl3 beyond those measured in the bulk air.

A Bayesian approach to understanding the key factors influencing temporal variability in stream water quality – a case study in the Great Barrier Reef catchments

Abstract. Stream water quality is highly variable both across space and time. Water quality monitoring programmes have collected a large amount of data that provide a good basis for investigating the key drivers of spatial and temporal variability. Event-based water quality monitoring data in the Great Barrier Reef catchments in northern Australia provide an opportunity to further our understanding of water quality dynamics in subtropical and tropical regions. This study investigated nine water quality constituents, including sediments, nutrients and salinity, with the aim of (1) identifying the influential environmental drivers of temporal variation in flow event concentrations and (2) developing a modelling framework to predict the temporal variation in water quality at multiple sites simultaneously. This study used a hierarchical Bayesian model averaging framework to explore the relationship between event concentration and catchment-scale environmental variables (e.g. runoff, rainfall and groundcover conditions). Key factors affecting the temporal changes in water quality varied among constituent concentrations and between catchments. Catchment rainfall and runoff affected in-stream particulate constituents, while catchment wetness and vegetation cover had more impact on dissolved nutrient concentration and salinity. In addition, in large dry catchments, antecedent catchment soil moisture and vegetation had a large influence on dissolved nutrients, which highlights the important effect of catchment hydrological connectivity on pollutant mobilisation and delivery.

A Computationally Efficient Shallow Water Model for Mixed Cohesive and Non-Cohesive Sediment Transport in the Yangtze Estuary

In this paper, a computationally efficient shallow water model is developed for sediment transport in the Yangtze Estuary by considering mixed cohesive and non-cohesive sediment transport. It is firstly shown that the model is capable of reproducing tidal-hydrodynamics in the estuarine region. Secondly, it is demonstrated that the observed temporal variation of suspended sediment concentration (SSC) for mixed cohesive and non-cohesive sediments can be well-captured by the model with calibrated parameters (i.e., critical shear stresses for erosion/deposition, erosion coefficient). Numerical comparative studies indicate that: (1) consideration of multiple sediment fraction (both cohesive and non-cohesive sediments) is important for accurate modeling of SSC in the Yangtze Estuary; (2) the critical shear stress and the erosion coefficient is shown to be site-dependent, for which intensive calibration may be required; and (3) the Deepwater Navigation Channel (DNC) project may lead to enhanced current velocity and thus reduced sediment deposition in the North Passage of the Yangtze Estuary. Finally, the implementation of the hybrid local time step/global maximum time step (LTS/GMaTS) (using LTS to update the hydro-sediment module but using GMaTS to update the morphodynamic module) can lead to a reduction of as high as 90% in the computational cost for the Yangtze Estuary. This advantage, along with its well-demonstrated quantitative accuracy, indicates that the present model should find wide applications in estuarine regions.

Assessment of Home-Based and Mobility-Based Exposure to Black Carbon in an Urban Environment: A Pilot Study.

The combustion of fossil fuels is a significant source of particulate-bound black carbon (BC) in urban environments. The personal exposure (PE) of urban dwellers to BC and subsequent health impacts remain poorly understood due to a lack of observational data. In this study, we assessed and quantified the levels of PE to BC under two exposure scenarios (home-based and mobility-based exposure) in the city of Trivandrum in India. In the home-based scenario, the PE to BC was assessed in a naturally ventilated building over 24 h each day during the study period while in the mobility-based scenario, the PE to BC was monitored across diverse microenvironments (MEs) during the day using the same study protocol for consistency. Elevated BC concentrations were observed during the transport by motorcycle (26.23 ± 2.33 µg/m3) and car (17.49 ± 2.37 µg/m3). The BC concentrations observed in the MEs decreased in the following order: 16.58 ± 1.38 µg/m3 (temple), 13.78 ± 2.07 µg/m3 (restaurant), 11.44 ± 1.37 µg/m3 (bus stop), and 8.27 ± 1.88 µg/m3 (home); the standard deviations represent the temporal and spatial variations of BC concentrations. Overall, a relatively larger inhaled dose of BC in the range of 148.98–163.87 µg/day was observed for the mobility-based scenario compared to the home-based one (118.10–137.03 µg/day). This work highlights the importance of reducing PE to fossil fuel-related particulate emissions in cities for which BC is a good indicator. The study outcome could be used to formulate effective strategies to improve the urban air quality as well as public health.

Effects of input/output parameters on artificial neural network model efficiency for breakthrough contaminant prediction

Abstract Groundwater quality assessment is characterized by pollution injection rates, pollution injection locations and duration of pollution injection for identifying spatial and temporal variation. In this study, spatial variations are obtained by placing observation wells in the downstream zone. Temporal variations in contaminant concentration has been simulated during the study period. Generally, simulations are carried out using various numerical models, which are subject to the availability of all required input parameters and are necessary for the proper management of contaminated aquifers. In previous publications, artificial neural networks (ANNs) are prescribed in such situations as these modeling methods focus on available input/output datasets, thus resolving the concern of obtaining all inputs that a numerical simulator usually demands. Past studies have predicted groundwater breakthrough contaminants. But the effects of input/output variations need to be discussed. This study aims to quantify the effects of a few input/output datasets in the performance of ANN models to simulate pollutant transport in groundwater systems. The combinations of input/output scenarios have rendered these ANN models sensitive to variations, thus affecting model efficiency. These outcomes can reliably be employed for contaminant estimation and provide a paradigm in data collection that will help hydrogeologists to develop more efficient prediction models.

Study on the variation characteristics of tropospheric ozone in Northeast China.

The goal of this study was to understand the current status of ozone pollution in Northeast China and to distinguish the main influencing factors of ozone, in order to provide a scientific basis for the future prevention and control of ozone in this region. In this study, the Ozone Monitoring Instrument data product was used as the source data, and the pixel space analysis method and grey correlation analysis method were utilized to examine the tropospheric ozone column concentration in Northeast China from 2010 to 2018. The results revealed that the ozone column concentration in Northeast China was relatively high compared to other parts of the country. The high-value areas were primarily distributed in Tahe County, Heihe City, Hegang City, and Qiqihar City. The temporal variation of the ozone column concentration in Northeast China exhibited an obvious periodicity of 9 years, and its interannual change displayed a downward trend. The maximum value occurred in 2010, and the minimum value was found in 2016. The seasonal changes manifested a relative trend of spring > winter > summer > autumn, which was contrary to the research results for other parts of China, which showed a summer maximum. Among the influencing factors, atmospheric pressure, relative humidity, sunshine hours, GDP, and primary and secondary industries exhibited the closest relationships with ozone. The high concentration of ozone in Northeast China was determined to result from the superimposed effects of long-distance atmospheric transport and anthropogenic emissions.

Investigation of atmospheric tritiated water vapor level around the Fukushima Daiichi nuclear power plant

Continuous measurement of tritium in the atmosphere is important to evaluate the environmental impact of nuclear facilities and fusion facilities as well as to elucidate tritium behavior in the environment. A passive type sampler is powerful tool to conduct long-term monitoring because this does not require any power supply. This paper demonstrated the effectiveness of the passive type sampler for continuous measurement and characterized temporal variation of atmospheric concentration of tritiated water vapor around the Fukushima Daiichi nuclear power plant. The atmospheric concentrations were successfully obtained at two sampling sites and ranged within the variation in past observation although the concentration at one of the two sites was slightly higher than that of background level in Japan. Additionally, we measured the tritium concentrations of soil pore water and free water in pine needles. These values indicated the validity of the measured atmospheric tritium concentrations.

Distribution, water quality, and health risk assessment of trace elements in three streams during the wet season, Guiyang, Southwest China

Trace element pollution derived from human activities in aquatic systems has raised widespread concerns due to its toxicity, persistence, and bioaccumulation. In this article, we presented a systematic investigation of the anthropogenic overprints on trace elements geochemistry in three streams of the human-impacted (agriculture, urban area, and abandoned mining), located at Lake Aha, Guiyang, Southwest China. Concentrations reported in the study demonstrated that the abandoned mining stream showed the highest trace elements (608.16 μg/L), followed by the urban stream (566.11 μg/L) and agricultural stream (457.51 μg/L). Nonmetric multidimensional scaling (NMDS), used to display sampling dates and trace elements, showed discernible temporal variation in trace element concentrations. Trace element concentrations in months (May, September, and October) with less rainfall were higher than in June, July, and August indicated by NMDS. Principal component analysis (PCA) had shown that As, Ba, Mo, and Zn were mainly impacted by the urbanized streams, and Fe and Sr influenced by the mine. Risk assessment of human beings to trace elements demonstrated that As may pose a detrimental health risk. The research found that trace elements were potential tracers for the presence of human activities and environmental changes.

Sand Bar Evolution Process Numerical Simulation Analyze Based on two Dimensional Numerical Model

The sand bar lies near the entrance to the sea, which is not only detrimental to the flood discharge and sediment discharge of the river, but also an important factor causing the swing the flow path to the sea. With the formation and development of the sand bar, the form of the sand bar is constantly changing, the river is expected to extend continuously, and the water level and velocity of the estuary river change within a certain range, thus affecting the estuary flood control and river management measures. It is of great significance to study the development process of sand bar and its form for flood control of estuarine rivers and to put forward reasonable control measures of the sand bar. The sediment inflow into the sea is calculated by using the validated two - dimensional numerical model of estuarine and rivers. In this paper, the variation and development process of the sediment form with time and space are analyzed from the following aspects: the process of sediment deposition thickness into the sea, the distribution chart of sediment deposition thickness along the direction of water flow into the sea, the process chart of seabed deposition height, the variation of intraday flow velocity along the sea and the analysis of the temporal and spatial variation of sediment concentration, etc. The calculated and analyzed results are consistent with the measured data.

Spatio-temporal variation of atmospheric CH4 concentration and its driving factors in monsoon Asia.

Based on the ground-based observations from seven atmospheric background stations during 2009 to 2018 in monsoon Asia (including BKT station in Indonesia, LLN and WLG stations in China, RYO and YON stations in Japan, TAP station in Republic of Korea, and UUM station in Mongolia), we analyzed the temporal and spatial variation of atmospheric CH4 concentration and its driving factors using harmonic model and maximal information-based nonparametric exploration. The results showed that the CH4 concentration in monsoon Asia varied from 1853.04 to 1935.61 nmol·mol-1, higher than that in Mauna Loa (MLO) station (1838.33 nmol·mol-1) in Hawaii, USA. The CH4 concentration decreased from north to south, with the highest value in TAP station (1935.61 nmol·mol-1) in Republic of Korea and RYO station (1907.19 nmol·mol-1) in Japan. The average seasonal amplitude at YON station in Japan was the largest (108.20 nmol·mol-1); while that at WLG station in China was the smallest (29.48 nmol·mol-1). The seasonal amplitude of TAP station in Republic of Korea changed faster at the rate of 4.49 nmol·mol-1·a-1. Except for WLG and TAP stations, CH4 concentrations were low in summer and high in winter. From the long-term perspective, the CH4 concentration at LLN (7.68 nmol·mol-1·a-1) and WLG (7.56 nmol·mol-1·a-1) stations in China exhibited the most obvious growth trend. Compared with wind speed, temperature and precipitation had greater impact on CH4 concentration, which were negatively associated with CH4 concentration. Local CH4 emission at some stations had a significant positive effect on CH4 concentration.

Spatial and temporal variations in indoor radon concentrations in Pennsylvania, USA from 1988 to 2018

Indoor radon poses one of the most significant environmental threats to public health as it is the second leading cause of lung cancer in the United States. Developing a more thorough understanding of the factors that affect radon concentrations is key for developing risk maps, identifying where testing should be a priority, and education about indoor radon exposure. The objectives of this study are to investigate seasonal and annual variation of indoor radon concentrations in Pennsylvania, USA from 1988 to 2018, to explore the hotspot areas for high indoor radon concentrations, and to analyze the association with various factors such as weather conditions, housing types, and floor levels. Based on a total of 1,808,294 radon tests conducted from 1988 to 2018, we found that 61% of the area (by zip codes), 557,869 tests conducted in the basement and 49,141 tests conducted on the ground floor in homes in Pennsylvania had higher radon levels than the U.S. EPA action level concentration of 148 Bq/m3 (equivalent to 4 pCi/L). Winter and fall had significantly higher indoor radon concentrations than summer and spring. Case studies conducted in Pittsburgh, Philadelphia, and Harrisburg showed that there was no significant correlation of daily temperature, precipitation, or relative humidity with indoor radon concentration on the day a radon test occurred.

Impacts of traffic on roadside particle variations in varied temporal scales

Traffic is a significant pollution source in cities and has caused various health and environmental concerns worldwide. Therefore, the improved understanding of traffic impacts on particle concentrations could help mitigate air pollution. In this study, field measurements were conducted beside an arterial road in Shanghai, China, to obtain the fine-scale temporal variations in traffic volumes, meteorological parameters, and size-resolved particle concentrations. The generalized additive model was developed to reveal their associations under different analysis intervals (time scales). Results indicate that on-road traffic greatly increased the concentration and variability of roadside particles. Variations of roadside fine particles (<1 μm, having high homogeneity) closely followed those at the background point, but background variations of coarse particles (having high heterogeneity) were negligible compared with the roadside point. Roadside particles showed high variability on the 10-s scale and presented frequent stochastic spikes above the background level. The particle variability was greatly reduced on the 60-min scale, exhibiting stable variations. The association between traffic and roadside particle variations was weak on a fine temporal scale (5-min scale). However, the association showed a pronounced increase when the analysis interval was increased (60-min scale). This is because extending the analysis interval could reduce the influence of random factors (sample randomness) and emission lagging effects on the results. Moreover, with the increase of the analysis interval, the improvement of associations between variables can be well characterized by exponential curves, which could help determine the optimal analysis interval. Additionally, heavy-duty vehicles showed a lot more significant influence on particle variations compared with that of light-duty vehicles, and should be regarded as the key governance target for on-road pollution control. These findings broaden the knowledge of traffic impacts on particle concentrations, which could provide implications in air pollution abatement.

Rare Earth Element in Bivalves' Soft Tissues of French Metropolitan Coasts: Spatial and Temporal Distribution.

Rare earth elements (REE) are becoming an environmental pollutant of emerging concern, linked to their use in various anthropic processes. Because REE bioconcentrate in marine organisms throughout their food webs, a better understanding of biogeochemical processes leading to REE concentrations found in coastal species is necessary. This study was designed to assess REEs concentrations in various common bivalves from the French coastline to identify possible geographic, taxonomic, or temporal variations of concentrations. Based on the French Mussel Watch program, three species of bivalves (oyster Crassostrea gigas and mussels Mytilus edulis and Mytilus galloprovincialis) were collected all along the French metropolitan coast and soft tissues were analyzed forREEconcentrations. Results have shown higher REE concentrations in bivalve soft tissues near estuaries without taxonomic nor national geographic differences. The highest levels have been observed in the Gironde estuary with total REE concentrations (∑REE) in oysters up to 10.94µgg-1 d.w. The REE distribution pattern in both mussel species described a particle-like (inverse V-shape) pattern, whereas C. gigas REE distribution pattern changes from a particle-like to a dissolved-like pattern with a heavy REE (HREE) enrichment. However, no environmental parameter could be linked to these pattern changes. Finally, neither Gd anomalies nor an evolution of REE concentrations over a 30-year period have been detected in bivalves' soft tissues.

Temporal variation of sulfate concentration in PM2.5 and major factors enhancing sulfate concentration in the atmosphere of Seoul, Korea

Despite frequent observations of high particulate matter (PM) concentrations in Seoul, Korea, the sulfate (SO42−) concentrations in PM with an aerodynamic diameter below or equal to 2.5 μm (PM2.5) in Seoul have been reduced during the 1990s. However, there has been no decreasing trend during the 2000s. Despite the very low ambient SO2 concentrations, high SO42− concentration episodes frequently occur in Seoul; however, the reasons for this remain poorly understood. In the present study, we sought to determine the major factors that enhance sulfur oxidation in Seoul by analyzing measurement data from an intensive air quality monitoring station in the Seoul metropolitan area acquired in 2015. Additionally, we aimed to distinguish the contributions of local sources and long-range transport to the elevated SO42− concentrations in PM2.5 in Seoul. In some cases in March and October 2015, the molar ratio of SO42− to SO2, which reflects sulfur partitioning between the particle and gas phases, showed an exponential increase with an increase of relative humidity (RH). However, despite the fact that the RH was high during August 2015, no statistically significant relationship was observed between RH and the molar ratio of SO42− to SO2 during this month. In August 2015, the molar ratio of SO42− to SO2 showed an exponential increase with increasing O3 concentration. Therefore, under sufficient RH, the concentrations of radical oxidants might be the most important factor that underlies the increase in ambient SO42− concentrations. No significant relationship was observed between the molar ratio of SO42− to SO2 and O3 in October. Furthermore, using Potential Source Density Function (PSDF) and backward trajectory analysis, the high SO42− concentrations in March 2015 were found to be caused by the transportation of air pollutants from China and local sources around Seoul. The high SO42− concentrations in August 2015 are concluded to have been greatly affected by these power plant emissions in the Taean area on the west coast of Korea. The high SO42− concentrations in October 2015 appear to have been caused by the transportation of air pollutants from North Korea. In summary, the high SO42− concentration in Seoul is affected by long-range transport from China and by the emissions from around the Seoul metropolitan area, such as Taean or North Korea.

Influence of agricultural system transition on trace element contamination in salt marsh and seagrass sediments from a coastal Ramsar site

Vegetated coastal ecosystems have an important role as contaminant filters. Temporal variations in concentrations, enrichment factors (EF), and fluxes of trace elements (As, Cd, Co, Cr, Cu, Ni, Pb, V, and Zn) were evaluated in 210Pb-dated sediment cores from salt marsh and seagrass ecosystems at San Quintín Bay (Mexican northern Pacific). Trace element contamination was negligible in seagrass sediments, but minor to severe, depending on the element, in salt marsh cores, owing to higher organic carbon and fine sediment contents. EF temporal variation in salt marsh cores was attributed to agriculture technology changes (e.g. installation of greenhouses, and improved irrigation and fertilization systems). Trace element flux ratios increased during the past 100 years, likely caused by steadily increasing sediment accumulation rates promoted by land-use changes in the catchment. The conservation of salt marsh areas is important to preserve their function as contaminants biofilters and the health of adjacent ecosystems.

Factors influencing temporal variations of radon concentration in high-rise buildings

Long-term radon time series were analyzed in 14 rooms and offices to search factors influencing indoor radon concentration in high-rise buildings. Radon entry to living rooms is determined both by diffusion from building materials and advection from adjoined low-ventilated spaces. Humans affect on seasonal and diurnal radon concentration changes in high-rise buildings by activating ventilation system. Indoor-outdoor temperature difference significantly influence on the air exchange rate under uncontrolled ventilation, which is especially important in new energy efficient buildings.

Noble gas tracers in gas streams at Norwegian CO2 capture plants

Carbon capture and storage (CCS) may play a significant role in reducing greenhouse gas emissions. Noble gases are potential tracers to monitor subsurface CO2 storage sites and verify their containment. Naturally occurring noble gases have been used successfully to refute alleged CO2 leakage in the past.We present results from several sampling campaigns at two Norwegian CO2 capture facilities, the demonstration plant Technology Centre Mongstad (TCM) and the natural gas processing plant with CO2 capture and storage on Melkøya. The gas streams in the capture plants were monitored with a combination of on-site mass spectrometry and subsequently analysed discrete samples. This allows us to define the factors controlling noble gas concentrations in captured CO2, to monitor temporal variation of noble gas concentrations and finally evaluate the potential to use noble gases as inherent environmental tracers for labelling CO2 in storage reservoirs.At both sites, CO2 is captured using amine gas treatment. Noble gas concentrations in the gas streams were observed to decrease by several orders of magnitude during the processing. Isotopic ratios are air-like for CO2 captured after natural gas combustion at TCM and natural gas-like for CO2 captured from natural gas processing on Melkøya. Further, we detected a solubility trend caused by the amine solvent at TCM with higher solubility for heavier noble gases.We find that the relative concentrations of noble gases in the captured CO2 are defined by the gas from which the CO2 is captured and the design of the amine gas treatment process. Both factors were observed to cause temporal variation in the captured CO2.Using mixing and noble gas partitioning calculations we show that the significant depletion in noble gas concentrations, together with degassing of noble gas enriched formation water, means that the injected CO2 will inherit the noble gas signature of the storage formation, even following the injection of significant CO2 volumes. Any CO2 leaked from the storage formation is thus likely to have a crustal noble gas signature, characteristic of the storage site, which can be targeted for monitoring.

Natural and anthropogenic effects on microplastic distribution in a hypersaline lagoon

Information on the transport and distribution of microplastics in coastal lagoons is scarce. This study provides the first evaluation of microplastic distribution in a hypersaline coastal lagoon and explores natural and anthropogenic factors that drive their location and transport. The study combines different field strategies: spatial distribution of microplastics in sediments, for September 2017 (wet season and peak use of the lagoon) and February 2018 (winter season, characterized by intense Northerly winds and least use of the lagoon); spatial distribution of microplastics in the water column in the winter season; ocean-lagoon exchanges of water and microplastics at the lagoon entrance during tidal cycles. Also, one-year records of water level variations along the lagoon provide connections between local pressure gradients and water fluxes. Statistical analyses indicate relationships between temporal variations of microplastic concentrations and human activities. Results show marked seasonality in sources and transport agents. During the summer, microplastics concentration was related to human activities. After this season, the accumulated precipitation in the continental karst region leads to an increase in the water level at the head of the lagoon. The resulting pressure gradient promotes seaward flushing of hypersaline water and of microplastics. At tidal (diurnal) time scales, measurements at the mouth of the lagoon revealed that more particles were collected in ebb than in flood. This variability underscores the need to resolve tidal variability for microplastic sampling in coastal lagoons and estuaries.

Interaction of Bulk Nanobubbles (Ultrafine Bubbles) with a Solid Surface.

The experimental results [Kanematsu, W. Chem. Eng. Sci. 2020, 219, 115594] on the temporal variations of number concentrations of bulk nanobubbles (ultrafine bubbles) in contact with polymer materials are theoretically analyzed based on the dynamic equilibrium model of bulk nanobubbles partly covered with hydrophobic materials (impurities). It is suggested that bulk nanobubbles are adsorbed on a polymer surface by attractive hydrophobic interaction between a polymer surface and a hydrophobic material partly covering the bubble surface, overcoming the repulsive double-layer interaction. There are two mysteries. One is that the maximum surface number concentration of bulk nanobubbles of about 70 nm in diameter adsorbed on a hydrophobic polymer surface is more than an order of magnitude lower than the typical value for colloid particles of a similar or larger size. The other is that the experimental adsorption rate of bulk nanobubbles on hydrophobic polymer surface is several orders of magnitude lower than the theoretically estimated one. The mysteries are resolved if many of the bulk nanobubbles adsorbed on a hydrophobic polymer surface change to surface nanobubbles with a footprint diameter of about 1 μm.