One-box Model Research Articles

Carbon budget concept and its deviation through the pulse response lens

Abstract. The carbon budget concept states that the global mean temperature (GMT) increase is roughly linearly dependent on cumulative emissions of CO2. The proportionality is measured as the transient climate response to cumulative emissions of carbon dioxide (TCRE). In this paper, the deviations of the carbon budget from the strict linear relationship implied by the TCRE are examined through the lens of a temperature response to an emission pulse (i.e., pulse response) and its relationship with a nonlinear TCRE. Hereby, two sources of deviation are distinguished: emission scenario and climate state dependence. The former stems from the scenario choice, i.e., the specific emission pathway for a given level of cumulative emissions and the latter from the change in TCRE with changing climatic conditions. Previous literature argues for scenario independence using a stylized set of emission scenarios, and offers a way to fit a nonlinear carbon budget equation. This paper shows how the pulse response, viewed as a Green's function, gives a unifying perspective on both scenario and state dependence. Moreover, it provides an optimization program that tests the scenario independence under the full range of emission pathways for a given set of constraints. In a setup chosen in this paper, the deviations stemming from emission pathway choices are less than 10 % of the overall temperature increase and gradually diminish. Moreover, using the pulse response as a Green's function, the scenario-dependent effects of a reduced-complexity climate model were replicated to a high degree, confirming that the behavior of scenario-dependent deviations can be explained and predicted by the shape of the pulse response. Additionally, it is shown that the pulse response changes with climatic conditions, through which the carbon budget state dependency is explained. Using a pulse response as an approximation for a state-dependent TCRE, an alternative method to derive a nonlinear carbon budget equation is provided. Finally, it is shown how different calibrations of a model can lead to different degrees of carbon budget nonlinearities. The analysis is done using FaIRv2.0.0, a simple climate emulator model that includes climate feedback modifying the carbon cycle, along with a one-box model used for comparison purposes. The Green's function approach can be used to diagnose both models' carbon budget scenario dependency, paving the way for future investigations and applications with other and more complex models.

Effects of spatial scale on assessments of suspension bivalve aquaculture for productivity and environmental impacts

Proper evaluations of productivity and environmental impacts of bivalve aquaculture are necessary to achieve sustainable operations in coastal marine systems. Estimation of organic matter budgets using completely mixed one-box models provides an easy approach to help stakeholders of environmental management and aquaculture fisheries obtain an overview of the interactions between aquaculture and the environment. However, estimations and interpretations are highly dependent on the spatial scale of assessments because the distributions of aquaculture facilities and ecosystem structures are spatially heterogeneous. The objective of the present study was to examine how the spatial scale of assessments for the budgets of particulate organic matter (POM) affects the interpretation of the site-specific food supply for suspension oyster aquaculture and impacts of oyster biodeposition on local bottom environments. Based on the actual distribution of oyster farms in a temperate bay on the northeast coast of Japan, we estimated [food supply]/[food demand] (S/D) for oysters as well as the relative contribution of oyster biodeposition to the total deposition of POM (Brel) in the bay along a gradient of spatial scales l from 0.5 m to 4000 m. Although food limitation for aquaculture oysters has been reported in the study bay, S/D was greater than 1 (ranging from 16 to 154) over the spatial scale gradient. S/D tended to be relatively high and overestimated for l < 200 m and l > 1400 m due to the nature of completely mixed one-box models, but relatively lower at intermediate scales. Brel was higher in assessments at farms or smaller scales (e.g., l < 100 m) and was relatively lower at larger scales (e.g., <0.2 at the scale of >500 m). Based on our model-based calculations, the patterns of variation in S/D along the spatial scale gradient are considered to be universal; however, the scale at which S/D values are relatively low varies depending on site-specific conditions, including primary productivity and current velocity. Our findings suggest that estimated budgets of POM need to be carefully interpreted, accounting for model assumptions as well as the influence of the spatial scale of assessments.

Sulphate reduction determines the long-term effect of iron amendments on phosphorus retention in lake sediments

PurposeThis field study aimed to guide the planning of iron amendments for phosphorus retention by investigating the long-term fate of iron added to two urban lakes (Plötzensee and Groß Glienicker See) in Berlin, Germany. The contributions of iron dosing to improve lake status as well as the relevance of competing processes for management success were evaluated.MethodsSediment stratigraphy, as well as occurrence of iron minerals, and fluxes between water and sediment were examined using geochemical analyses (i.e. element composition, sequential extraction, X-ray diffraction, and pore water analyses). A one-box lake model was used to relate these fluxes to monitoring data from the water column and to sediment inventories.ResultsIn both lakes, the added iron was preserved in the sediment. Whereas phosphorus retention increased following the addition of iron to Groß Glienicker See, sulphur was retained by the excess iron in Plötzensee. This contrasting effect is attributed to significantly different sulphate reduction rates in two lakes (Wilcoxon rank sum test: W = 25, p = 0.008). According to the one-box model, sulphate reduction explained both the decrease in measured sulphate concentrations after iron application as well as the observed increase in sulphur deposition in the sediments.ConclusionManagement interventions involving iron amendments to enhance phosphorus retention must consider the competing process of iron sulphide formation during the entire management plan period, and additional iron may need to be applied to account for this effect.

Evaluation of One- and Two-Box Models as Particle Exposure Prediction Tools at Industrial Scale.

One- and two-box models have been pointed out as useful tools for modelling indoor particle exposure. However, model performance still needs further testing if they are to be implemented as trustworthy tools for exposure assessment. The objective of this work is to evaluate the performance, applicability and reproducibility of one- and two-box models on real-world industrial scenarios. A study on filling of seven materials in three filling lines with different levels of energy and mitigation strategies was used. Inhalable and respirable mass concentrations were calculated with one- and two-box models. The continuous drop and rotating drum methods were used for emission rate calculation, and ranges from a one-at-a-time methodology were applied for local exhaust ventilation efficiency and inter-zonal air flows. When using both dustiness methods, large differences were observed for modelled inhalable concentrations but not for respirable, which showed the importance to study the linkage between dustiness and processes. Higher model accuracy (ratio modelled vs. measured concentrations 0.5–5) was obtained for the two- (87%) than the one-box model (53%). Large effects on modelled concentrations were seen when local exhausts ventilation and inter-zonal variations where parametrized in the models. However, a certain degree of variation (10–20%) seems acceptable, as similar conclusions are reached.

Replication of the Arctic Ocean surface layer with horizontal variations using a box model implemented with a probability distribution function (PDF)

The 200 m-thick surface layer of the Arctic Ocean contains a lower salinity part in the Canadian Basin, receiving fresher water from the Pacific Ocean as well as rivers, and also a higher salinity part in the Eurasian Basin, receiving saltier water from the Greenland Sea. This surface layer receives atmospheric forcing, and also partially mixes with the subsurface layer. Thus, thermohaline circulation is a fundamental pattern, under the influences of mesoscale features (∼10 km) and small-scale plumes (∼1 km).The one-box model of the surface layer possesses a salinity-driven state, and also a convected state with the subsurface layer as another solution. The new modeling is proposed with a probability distribution function (PDF) on the temperature–salinity (T–S) plane, which can represent horizontal gradients and small scale features as well. The T–S distribution retains only the probabilities of different water types, while their locations are discarded. Time progressions of the PDF are calculated with mechanisms of box-mean progression, heterogeneity generation, horizontal mixing in the box and convection with the subsurface layer. As either the subsurface layer becomes fresher, or the heterogeneity is intensified, the solution near the salinity-driven state increases convection, shifting toward the convected state. The additional PDF box model is made for the Eurasian Basin, which receives fresher water from the Canadian Basin instead of the Pacific Ocean, and provides a more restricted solution with convection, mainly controlled by the fresher subsurface layer.The original PDF box model of the entire Arctic Ocean is extended to the wider horizontal variability case: i.e., the inflow from the Greenland Sea is distributed over the higher salinity portion only, and then, the lower salinity water from the Pacific Ocean is supplied to a particular T–S point, (Tp, Sp), mixing within the lower salinity portion only. The low salinity core is retained near (Tp, Sp), even though convection develops in the higher salinity portion. Thus, this advanced PDF box model is a useful tool to judge a high resolution basin-scale circulation model, whether small-scale plumes and mesoscale features play an important role on thermohaline circulation or not.

Modeling of High Nanoparticle Exposure in an Indoor Industrial Scenario with a One-Box Model.

Mass balance models have proved to be effective tools for exposure prediction in occupational settings. However, they are still not extensively tested in real-world scenarios, or for particle number concentrations. An industrial scenario characterized by high emissions of unintentionally-generated nanoparticles (NP) was selected to assess the performance of a one-box model. Worker exposure to NPs due to thermal spraying was monitored, and two methods were used to calculate emission rates: the convolution theorem, and the cyclic steady state equation. Monitored concentrations ranged between 4.2 × 104–2.5 × 105 cm−3. Estimated emission rates were comparable with both methods: 1.4 × 1011–1.2 × 1013 min−1 (convolution) and 1.3 × 1012–1.4 × 1013 min−1 (cyclic steady state). Modeled concentrations were 1.4-6 × 104 cm−3 (convolution) and 1.7–7.1 × 104 cm−3 (cyclic steady state). Results indicated a clear underestimation of measured particle concentrations, with ratios modeled/measured between 0.2–0.7. While both model parametrizations provided similar results on average, using convolution emission rates improved performance on a case-by-case basis. Thus, using cyclic steady state emission rates would be advisable for preliminary risk assessment, while for more precise results, the convolution theorem would be a better option. Results show that one-box models may be useful tools for preliminary risk assessment in occupational settings when room air is well mixed.

On the future role of the most parsimonious climate module in integrated assessment

Abstract. In the following, we test the validity of a one-box climate model as an emulator for atmosphere–ocean general circulation models (AOGCMs). The one-box climate model is currently employed in the integrated assessment models FUND, MIND, and PAGE, widely used in policy making. Our findings are twofold. Firstly, when directly prescribing AOGCMs' respective equilibrium climate sensitivities (ECSs) and transient climate responses (TCRs) to the one-box model, global mean temperature (GMT) projections are generically too high by 0.5 K at peak temperature for peak-and-decline forcing scenarios, resulting in a maximum global warming of approximately 2 K. Accordingly, corresponding integrated assessment studies might tend to overestimate mitigation needs and costs. We semi-analytically explain this discrepancy as resulting from the information loss resulting from the reduction of complexity. Secondly, the one-box model offers a good emulator of these AOGCMs (accurate to within 0.1 K for Representative Concentration Pathways, RCPs, namely RCP2.6, RCP4.5, and RCP6.0), provided the AOGCM's ECS and TCR values are universally mapped onto effective one-box counterparts and a certain time horizon (on the order of the time to peak radiative forcing) is not exceeded. Results that are based on the one-box model and have already been published are still just as informative as intended by their respective authors; however, they should be reinterpreted as being influenced by a larger climate response to forcing than intended.

An assessment of natural methane fluxes simulated by the CLASS-CTEM model

Abstract. Natural methane emissions from wetlands and fire, and soil uptake of methane, simulated using the Canadian Land Surface Scheme and Canadian Terrestrial Ecosystem (CLASS-CTEM) modelling framework, over the historical 1850–2008 period, are assessed by using a one-box model of atmospheric methane burden. This one-box model also requires anthropogenic emissions and the methane sink in the atmosphere to simulate the historical evolution of global methane burden. For this purpose, global anthropogenic methane emissions for the period 1850–2008 were reconstructed based on the harmonized representative concentration pathway (RCP) and Emission Database for Global Atmospheric Research (EDGAR) data sets. The methane sink in the atmosphere is represented using bias-corrected methane lifetimes from the Canadian Middle Atmosphere Model (CMAM). The resulting evolution of atmospheric methane concentration over the historical period compares reasonably well with observation-based estimates (correlation = 0.99, root mean square error = 35 ppb). The modelled natural emissions are also assessed using an inverse procedure where the methane lifetimes required to reproduce the observed year-to-year increase in atmospheric methane burden are calculated based upon the specified global anthropogenic and modelled natural emissions that we have used here. These calculated methane lifetimes over the historical period fall within the uncertainty range of observation-based estimates. The present-day (2000–2008) values of modelled methane emissions from wetlands (169 Tg CH4 yr−1) and fire (27 Tg CH4 yr−1), methane uptake by soil (29 Tg CH4 yr−1), and the budget terms associated with overall anthropogenic and natural emissions are consistent with estimates reported in a recent global methane budget that is based on top-down approaches constrained by observed atmospheric methane burden. The modelled wetland emissions increase over the historical period in response to both increases in precipitation and in atmospheric CO2 concentration. This increase in wetland emissions over the historical period yields evolution of the atmospheric methane concentration that compares better with observation-based values than the case when wetland emissions are held constant over the historical period.

Modelling traffic-induced multicomponent ultrafine particles in urban street canyon compartments: Factors that inhibit mixing

This study implements a two-box model coupled with ultrafine particle (UFP) multicomponent microphysics for a compartmentalised street canyon. Canyon compartmentalisation can be described parsimoniously by three parameters relating to the features of the canyon and the atmospheric state outside the canyon, i.e. the heterogeneity coefficient, the vortex-to-vortex exchange velocity, and the box height ratio. The quasi-steady solutions for the two compartments represent a balance among emissions, microphysical aerosol dynamics (i.e. evaporation/condensation of semi-volatiles, SVOCs), and exchange processes, none of which is negligible. This coupled two-box model can capture significant contrasts in UFP number concentrations and a measure of the volatility of the multi-SVOC-particles in the lower and upper canyon. Modelled ground-level UFP number concentrations vary across nucleation, Aitken, and accumulation particle modes as well-defined monotonic functions of canyon compartmentalisation parameters. Compared with the two-box model, a classic one-box model (without canyon compartmentalisation) leads to underestimation of UFP number concentrations by several tens of percent typically. By quantifying the effects of canyon compartmentalisation, this study provides a framework for understanding how canyon geometry and the presence of street trees, street furniture, and architectural features interact with the large-scale atmospheric flow to determine ground-level pollutant concentrations.

Theoretical foundations of emergent constraints: relationships between climate sensitivity and global temperature variability in conceptual models

There is as yet no theoretical framework to guide the search for emergent constraints. As a result, there are significant risks that indiscriminate data-mining of the multidimensional outputs from GCMs could lead to spurious correlations and less than robust constraints on future changes. To mitigate against this risk, Cox et al (hereafter CHW18) proposed a theory-motivated emergent constraint, using the one-box Hasselmann model to identify a linear relationship between ECS and a metric of global temperature variability involving both temperature standard deviation and autocorrelation ($\Psi$). A number of doubts have been raised about this approach, some concerning the theory and the application of the one-box model to understand relationships in complex GCMs which are known to have more than the single characteristic timescale. We illustrate theory driven testing of emergent constraints using this as an example, namely we demonstrate that the linear $\Psi$-ECS proportionality is not an artifact of the one-box model and rigorously features to a good approximation in more realistic, yet still analytically soluble conceptual models, namely the two-box and diffusion models. Each of the conceptual models predict different power spectra with only the diffusion model's pink spectrum being compatible with observations and the complex CMIP5 GCMs. We also show that the theoretically predicted $\Psi$-ECS relationship exists in the \texttt{piControl} as well as \texttt{historical} CMIP5 experiments and that the differing gradients of the proportionality are inversely related to the effective forcing in that experiment.

Historical phosphorus dynamics in Lake of the Woods (USA–Canada) — does legacy phosphorus still affect the southern basin?

ABSTRACT Edlund MB, Schottler SP, Reavie ED, Engstrom DR, Baratono NG, Leavitt PR, Heathcote AJ, Wilson B, Paterson AM. 2017. Historical phosphorus dynamics in Lake of the Woods (USA–Canada) — does legacy phosphorus still affect the southern basin? Lake Reserv Manage. 33:386–402. A historical phosphorus (P) budget was constructed for southern Lake of the Woods. Sediment cores from 7 bays were radioisotopically dated and analyzed for loss-on-ignition, P, Si, diatoms, and pigments. Geochemical records for cores were combined using focusing factors for whole-basin estimates of sediment, total P, and P fraction accumulation. Although historical monitoring shows that external P loads decreased since the 1950s, sediment P has continued to increase since the mid-20th century. Much sediment P is labile and may be mobile within the sediments and/or available for internal loading and resuspension. Two mass-balance models were used to explore historical P loading scenarios and in-lake dynamics, a static one-box model and a dynamic multi-box model. The one-box model predicts presettlement external loads were slightly less than modern loads. The dynamic model shows that water-column P was higher in the 1950s–1970s than today, that the lake is sensitive to external loads because P losses from burial and outflow are high, and that the lake is moving to a new steady state with respect to water-column P and size of the active sediment P pool. The active sediment pool built up in the mid-20th century has been depleted through outflow and burial, such that its legacy effects are now minimal. Comparison of historical nutrient dynamics and sediment records of algal production showed a counterintuitive increase in production after external P loads decreased, suggesting other drivers may now regulate modern limnoecology, including seasonality of P loading, shifting nutrient limitation, and climate warming.

Linearization of a Highly Nonlinear Envelope Tracking Power Amplifier Targeting Maximum Efficiency

This letter presents a linearization algorithm designed for envelope tracking transmitters with an optimal highly efficient envelope shaping function. Targeting high efficiency at all power regions of the PA results in a severe nonlinear input-output response, and broadening of the PA output spectrum compared with a fixed voltage, or other envelope shaping functions. A two-box modeling approach is used, where a static nonlinearity function focuses on reducing the nonlinearity of the transmitter, and a memory polynomial model is used in cascade to reduce remaining distortions. The results show a definite improvement over traditional one-box models, and is suitable for PAs exhibiting unique nonlinear responses, especially for ET applications.

Modelling photochemical pollutants in a deep urban street canyon: Application of a coupled two-box model approximation

Air pollution associated with road transport is a major environmental issue in urban areas. Buildings in urban areas are the artificial obstacles to atmospheric flow and cause reduced ventilation for street canyons. For a deep street canyon, there is evidence of the formation of multiple segregated vortices, which generate flow regimes such that pollutants exhibit a significant contrast between these vortices. This results in poor air ventilation conditions at pedestrian level, thereby leading to elevated pollutant levels and potential breaches of air quality limits. The hypothesis of a well-mixed deep street canyon in the practical one-box model approach is shown to be inappropriate. This study implements a simplified simulation of the canyon volume: a coupled two-box model with a reduced chemical scheme to represent the key photochemical processes with timescales similar to and smaller than the turbulent mixing timescale. The two-box model captures the significant pollutant contrast between the lower and upper parts of a deep street canyon, particularly for NO2. Core important parameters (i.e. heterogeneity coefficient, exchange velocity and box height ratio) in the two-box model approach were investigated through sensitivity tests. The two-box model results identify the emission regimes and the meteorological conditions under which NO2 in the lower canyon (i.e. the region of interest for the assessment of human health effects) is in breach of air quality standards. Higher NO2 levels were observed for the cases with higher heterogeneity coefficients (the two boxes are more segregated), with lower exchange velocities (worse ventilation conditions), or with smaller box height ratios (reduced dilution possibly due to secondary smaller eddies in the lower canyon). The performance of a one-box model using the same chemical scheme is also evaluated against the two-box model. The one-box model was found to systematically underestimate NO2 levels compared with those in the lower box of the two-box model for all test scenarios. This underestimation generally tends to worsen for higher heterogeneity coefficients, lower exchange velocities or smaller box height ratios. This study highlights the limitation of the assumption of homogeneity in single box models for street canyon simulation, and the inherent uncertainties that must be borne in mind to appropriately interpret such model output (in particular, that a single-box treatment will systematically underestimate NO2 as experienced at street level).

Does the Budyko curve reflect a maximum-power state of hydrological systems? A backward analysis

Abstract. Almost all catchments plot within a small envelope around the Budyko curve. This apparent behaviour suggests that organizing principles may play a role in the evolution of catchments. In this paper we applied the thermodynamic principle of maximum power as the organizing principle. In a top-down approach we derived mathematical formulations of the relation between relative wetness and gradients driving run-off and evaporation for a simple one-box model. We did this in an inverse manner such that, when the conductances are optimized with the maximum-power principle, the steady-state behaviour of the model leads exactly to a point on the asymptotes of the Budyko curve. Subsequently, we added dynamics in forcing and actual evaporation, causing the Budyko curve to deviate from the asymptotes. Despite the simplicity of the model, catchment observations compare reasonably well with the Budyko curves subject to observed dynamics in rainfall and actual evaporation. Thus by constraining the model that has been optimized with the maximum-power principle with the asymptotes of the Budyko curve, we were able to derive more realistic values of the aridity and evaporation index without any parameter calibration. Future work should focus on better representing the boundary conditions of real catchments and eventually adding more complexity to the model.

Long-term efficiency of lake restoration by chemical phosphorus precipitation: Scenario analysis with a phosphorus balance model

An artificial increase of phosphorus (P) retention in lakes with a long residence time and/or a large mobile sediment P pool by adding P binding chemicals can drastically shorten the time these lakes require to reach water quality targets. Suitable tools to optimize timing and extent of external and internal measures are lacking. The one-box model, a mass balance tool for predicting the P trend in the water under different management options was applied to highly eutrophic Lake Arendsee (a = 5.14 km2, zmax = 49 m), Germany. Mass developments of blue green algae and increasing hypolimnetic oxygen deficiencies are urgent reasons for restoring Lake Arendsee. Detailed studies of P cycling and scenario analyses with the one-box model led to the following conclusions: i) immediate improvement of the trophic state is only possible by in-lake P inactivation because of the long water residence time (56 years); ii) a gradual external P load reduction, even if the effect is delayed, will assure the sustainability of the scheduled Al application beyond one decade; iii) a twofold precipitation reduces the risk of failure compared to a singular application with an overdose related to the relevant internal P pools.

First observations of the fourth generation synthetic halocarbons HFC-1234yf, HFC-1234ze(E), and HCFC-1233zd(E) in the atmosphere.

Halogenated alkenes are a class of anthropogenic substances, which replace ozone-depleting substances and long-lived greenhouse gases in the foam-blowing, refrigeration, and solvent sectors. We report the first multiyear atmospheric measurements of the hydrofluorocarbons HFC-1234yf (2,3,3,3-tetrafluoroprop-1-ene, CF3CF═CH2), and HFC-1234ze(E) (E-1,3,3,3-tetrafluoroprop-1-ene trans-CF3CH═CHF), and the hydrochlorofluorocarbon HCFC-1233zd(E) (E-1-chloro-3,3,3-trifluoroprop-1-ene trans-CF3CH═CHCl) from the high altitude observatory at Jungfraujoch and from urban Dubendorf (Switzerland). When observations started in 2011 HFC-1234yf was undetectable at Jungfraujoch (mole fractions <0.003 ppt, parts-per-trillion, 10(-12)) but since then the percentage of measurements with detectable mole fractions has steadily increased to 4.5% in 2014. By contrast, in 2014 HFC-1234ze(E) was detectable in half of our samples at Jungfraujoch and in all samples at Dubendorf demonstrating the wide use of this compound within the air mass footprints of the stations. Our back trajectory analysis for the Jungfraujoch observations suggests high emission strength of HFC-1234ze(E) in the Belgium/Netherlands region. HCFC-1233zd(E) is present at very low mole fractions (typically <0.03 ppt) at both stations, and features pronounced seasonality and a general absence of pollution events during our 2013-2014 measurements. This is indicative of the presence of significant emissions from source locations outside the footprints of the two stations. Based on a simple one-box model calculation we estimate globally increasing HCFC-1233zd(E) emissions from 0.2 Gg yr(-1) in 2013 to 0.5 Gg yr(-1) for 2014.

Screening for potentially hazardous PRTR chemicals in the Lake Biwa-Yodo River basin of Japan using a one-box multimedia model.

A system is needed to predict the behavior, fate, and occurrence of environmental pollutants for effective environmental monitoring. Available monitoring data and computational modeling were used to develop a one-box multimedia model based on the mass balance of the emitted chemicals. Eight physiochemical phenomena in the atmosphere, soil, water, and sediment were considered in this model. This study was carried out in the Lake Biwa-Yodo River basin which provides multiple land uses and also the natural water resource for nearly 13 million of population in the region. Annual emissions for 214 nonmetallic compounds were calculated using the chemical emission data on Japanese pollutant release and transfer registry and used for executing the model simulations for 1997, 2002, and 2008 as input data. The calculated chemical concentrations by the model for all the environmental media were analyzed to determine trends in concentration over this study span. The majority of the chemicals decreased in concentration over time. Among the 214 nonmetallic chemical pollutants, 36 chemicals did not decrease in concentration and were in the top 10 % for concentration on average. Of these 36 pollutants, 7 occur in all 4 environmental media and pose a potential health risk at humans in the Lake Biwa-Yodo River basin.

Evaluation of mercury concentration in the lake biwa-yodo river basin by a one-box multimedia model and model sensitivity on the experimentally determined water-sediment partition coefficient

Abstract Considering the environmental damage caused by mercury, evaluating mercury concentrations in four environmental media, namely the atmosphere, water, soil, and sediment, is necessary. Available data on mercury emissions and

Groundwater as a Source of Hydrogen Sulfide in Indoor Air in Central and South Florida

Groundwater in Central and South Florida is known to contain high levels of sulfide. A series of shower tests were designed to evaluate hydrogen sulfide (H2S) emissions from sulfide-containing groundwater in residential houses. To our knowledge, indoor H2S levels resulting from regular household usage of water containing sulfide have never been studied or compared to that generated by other sources, such as defective drywall. Our objectives were to determine the factors controlling H2S emissions during a shower; to evaluate indoor H2S levels associated with regular household water usage; and to apply a one-box model to predict indoor steady-state H2S concentration. Shower tests conducted under controlled conditions indicated that pH has a significant impact on emission rate, whereas temperature does not. Both pH and temperature significantly impacted emission percentage. Flow rate and total sulfide concentration in water significantly impacted emission rate, but not emission percentage. Shower tests conducted at six residential houses located in five cities indicated that H2S in the air increased linearly with time during the shower-testing period. A 3- to 20-min shower—using water with total sulfide concentrations ranging from 0.20 to 2.45 mg/L—raised H2S concentrations in the bathroom air to 300–2250 parts per billion by volume. The indoor steady-state H2S concentration caused by regular household water usage can be predicted with a one-box model. Our study suggested that, without proper treatment, groundwater containing high concentrations of sulfide can be a significant source of H2S in indoor air.

Application of a simple genetic algorithm for the calibration of aquatic ecosystem model of an agricultural pond

In this study, we aim to construct and apply a simple genetic algorithm (SGA) to optimize a large number of parameters of an one-box ecosystem model. The ecosystem model was used to simulate the water quality over a 6-month period based on the new observation data in an agricultural pond which was strongly influenced by a green algal bloom. Of the 54 parameters in this model, 10 important parameters were initially selected for the optimization, with one other parameter being subsequently added. The SGA program was used for three purposes, namely (1) to narrow the search space for the 10 parameters, (2) to assess the influence of the additional parameter on the optimization results, and (3) to observe the distribution and convergence of the optimized values for the 10 selected parameters. In the next step, new ranges for these 10 important parameters were assigned and the SGA was applied to all 54 model parameters to seek the optimum value for each parameter. The modeling approach and the results presented here provide valuable and reliable evidences of the optimum parameters for further simulations to clarify the mechanisms of the biochemical processes in the water.