Assessment of nitrogen fertilization for the CO2 balance during the production of poplar and rye

This study was designed to consider all nitrogen fertilizer-related effects on crop production and emission of greenhouse gases on loamy sandy soils in Germany over a period of nine years (1999–2007). In order to set up a CO₂ balance for the production of energy crops, different nitrogen pathways were investigated, such as direct N₂O emissions from the soil and indirect emissions related to NO₃ leaching and fertilizer production. Fluxes of N₂O were measured in an experimental field using closed chambers. Poplar (Populus maximowiczii × P. nigra) and rye (Secale cereale L.) as one perennial and one annual crop were fertilized at rates of 0 kg N ha^?1 yr^?1, 75 kg N ha^?1 yr^?1 and 150 kg N ha^?1 yr^?1. The mean N₂O emissions from the soil ranged between 0.5 kg N ha^?1 yr^?1 and 2.5 kg N ha^?1 yr^?1 depending on fertilization rate, crop variety and year. The CO₂ fixed in the biomass of energy crops is reduced by up to 16% if direct N₂O emissions from soil and indirect N₂O emissions from NO₃ leaching and fertilizer production are included. Taking into account the main greenhouse gas emissions, which derive from the production and the use of N fertilizer, the growth of poplar and rye may replace the global warming potential of fossil fuels by up to 17.7 t CO₂ ha^?1 yr^?1 and 12.1 t CO₂ ha^?1 yr^?1, respectively.     

Preparation and characterization of activated carbon from rubber-seed shell by physical activation with steam

The use of rubber-seed shell as a raw material for the production of activated carbon with physical activation was investigated. The produced activated carbons were characterized by Nitrogen adsorption isotherms, Scanning electron microscope, Thermo-gravimetric and Differential scanning calorimetric in order to understand the rubber-seed shell activated carbon. The results showed that rubber-seed shell is a good precursor for activated carbon. The optimal activation condition is: temperature 880 °C, steam flow 6 kg h^?1, residence time 60 min. Characteristics of activated carbon with a high yield (30.5%) are: specific surface area (S_BET) 948 m² g^?1, total volume 0.988 m³ kg^?1, iodine number of adsorbent (q_iodine) 1.326 g g^?1, amount of methylene blue adsorption of adsorbent (q_mb) 265 mg g^?1, hardness 94.7%. It is demonstrated that rubber-seed shell is an attractive source of raw material for producing high capacity activated carbon by physical activation with steam.     

Effects of volatile fatty acid concentrations on methane yield and methanogenic bacteria

Volatile fatty acids (VFAs) are important mid-products in the production of methane, and their concentrations affect the efficiency of fermentation. However, their effects on methane yield and methanogenic bacteria growth have been less extensively studied. To address these effects, acetic acid, propionic acid, butyric acid and ethanol were used as substrates and an L₉(3⁴) orthogonal table was adopted to design anaerobic digestion tests. When the highest concentrations of ethanol, acetic acid and butyric acid were 2400, 2400 and 1800 mg L^?1, respectively, there was no significant inhibition of the activity of methanogenic bacteria. However, when the propionic acid concentration was increased to 900 mg L^?1, significant inhibition appeared, the bacteria concentration decreased from 6 × 10⁷ to 0.6–1 × 10⁷ ml^?1 and their activity would not reconvert. These effects resulted in the accumulation of ethanol and VFAs, and the total methane yield consequently became very low (<321 ml). The original propionic acid concentration had a significant inhibitory effect on methanogenic bacteria growth (P < 0.01). An optimization analysis showed that ethanol, acetic acid, propionic acid and butyric acid at concentrations of 1600, 1600, 300 and 1800 mg L^?1, respectively, led to the maximum accumulative methane yield of 1620 ml and the maximum methanogenic bacteria concentration of 7.3 × 10⁸ ml^?1.     

The effects of operating conditions on emissions from masonry heaters and sauna stoves

Emissions from masonry heaters and sauna stoves were studied. In the sauna stove the production of organic gaseous carbon (OGC) at 10 gC kg^?1 (per kilogram of fuel), carbon monoxide (CO) at 55 g kg^?1, fine particle mass (PM₁) at 5 g kg^?1 and number emissions (N) at 1.8 × 10¹⁵ kg^?1 was higher than in other measured appliances. In a modern technology masonry heater with a unique grate, the emissions were very low: 0.4 gC kg^?1 OGC, 14 g kg^?1 CO and 0.7 g kg^?1 PM₁. Conventional masonry heaters, using small logs, clearly produced higher emissions when compared to using large logs. Doubling the fuel load caused emission factors to increase by up to 4- times (OGC), except for the number emission, which decreased from 4.0 × 10¹⁴ to 2.0 × 10¹⁴ kg^?1. From the conventional masonry heater 90% of the PM was emitted during the firing phase. Its combustion process is different to that in stoves or conventional open fireplaces. The insufficient supply of air, due to too fast pyrolysis, and increased ash release, due to the high combustion temperature, are the main parameters which cause high particle and gas emissions in masonry heaters and sauna stoves.     

Dry matter partitioning and quality of Miscanthus,Panicum, and Saccharum genotypes in Arkansas,USA

The partitioning and quality of aboveground biomass have important ramifications for crop management and biomass conversion. In preliminary studies, Saccharum sp. × Miscanthus sp. hybrids exhibited stubble cold tolerance in west-central Arkansas, unlike Saccharum sp. × Saccharum spontaneum hybrids. The objective was to examine foliar and stem quality of the C₄ grasses Miscanthus sinensis (‘Gracillimus’), Miscanthus x giganteus (Q42641, proprietary), Panicum virgatum (‘Alamo’), and two F₁ hybrids of Saccharum sp. × Miscanthus sp. (US84-1028 and US84-1058) in a field study during 2004 (plant cane) and 2005 (first stubble) near Booneville, AR. Switchgrass produced more stems m^?2 than the other entries both years, and there was little difference in stem number among other entries. Clone US84-1028 yielded more dry mass m^?2 than other entries in plant cane, while switchgrass, US84-1028, and M. x giganteus did not differ in first stubble. Clone US84-1028 also had more stem dry mass and leaf dry mass than other entries both yr. Tissue N concentrations were low for these entries, but leaves contained about twice the N of stems (≤15.2 and 7.8 g kg^?1, respectively). Leaves represented as much as one-third of total biomass, and had large cellulose (≤482 g kg^?1) and lignin (167 g kg^?1) concentrations. The competitively high biomass yield of this small sample of sugarcane alleles should encourage the expansion of the crop beyond its current production regions. Sugarcane and M. x giganteus should be examined in higher-input temperate systems because of their bioenergy potential.     

Comparison of Arundo donax L. and Miscanthus x giganteus in a long-term field experiment in Central Italy: Analysis of productive characteristics and energy balance

Miscanthus x giganteus (miscanthus) and Arundo donax L. (giant reed) are two perennial crops which have been received particular attention during the last decade as bioenergy crops. The main aim of the present study was to compare the above-ground biomass production and the energy balance of these perennial rhizomatous grasses in a long-term field experiment. The crops were cultivated from 1992 to 2003 in the temperate climate of Central Italy with 20,000 plants ha^?1, 100–100–100 kg N, P₂O₅, K₂O per hectare, and without irrigation supply. For each year of trial, biomass was harvested in autumn to estimate biometric characteristics and productive parameters. Besides, energy analysis of biomass production was carried out determining energy output, energy input, energy efficiency (output/input) and net energy yield (output–input). Results showed high above-ground biomass yields over a period of 10 years for both species, with better productive performances in giant reed than in miscanthus (37.7 t DM ha^?1 year^?1 vs 28.7 t DM ha^?1 year^?1 averaged from 2 to 12 years of growth). Such high yields resulted positively correlated to number of stalks (miscanthus), plant height and stalk diameter (giant reed). Moreover, these perennial species are characterised by a favourable energy balance with a net energy yield of 467 and 637 GJ ha^?1 (1–12 year mean) for miscanthus and giant reed respectively.With such characteristics, both grasses could be proposed as biomass energy crops in Southern Europe with a significant and environmentally compatible contribution to energy needs.     

Optimization of conditions for the extraction of phorbol esters from Jatropha oil

The production of Jatropha curcas seeds as a biodiesel feedstock is expected to reach 160 Mt by 2017. The present study aims at extracting phorbol esters (PEs) as a co-product from Jatropha oil before processing it to biodiesel. The conditions were optimized for extraction of PEs in organic solvents by using a magnetic stirrer and an Ultra turrax. The extent of reduction in PEs was >99.4% in methanol using any of the stirring tools. However, the extraction using Ultra turrax affected considerably the colour of the remaining oil. Therefore, further solvent:oil ratio, time and temperature were optimized using a magnetic stirrer to get PE rich fraction-I (48.4 mg PEs g^?1) and virtually PE-free oil. PEs were 14 fold higher in this fraction than the control oil. PEs, extracted in methanol from the untreated Jatropha oil, at 1 mg L^?1 produced 100% mortality in snails (Physa fontinalis). The methanol extract from virtually PE-free oil when concentrated 20 and 25 time the untreated Jatropha oil (equivalent of 20 mg L^?1 and 25 mg L^?1 PEs in the control oil) was nontoxic to snails. PE rich fraction-I, obtained as a co-product, can be used in agricultural, medicinal and pharmaceutical applications and the remaining oil can be used for biodiesel preparation. The remaining oil will be friendly to the environment and workers.     

Factorial experimental design applied to Escherichia coli disinfection by Fenton and photo-Fenton processes

The aim of this work is to apply a factorial experimental design in the disinfection of Escherichia coli present in treated urban wastewater by means of Fenton and photo-Fenton processes.As a consequence of the large number of existing variables including the matrix, irradiation (λ = 320–800 nm), and doses of H₂O₂ (20–50 mg L^?1) and Fe³⁺ (2.5–5 mg L^?1), an experimental design methodology has been used in order to study their influence. It is observed that the presence of irradiation is the variable with the greatest influence on the response factor (inactivation of E. coli), although other variables also have a significant influence. By applying photo-Fenton treatment to treated urban wastewater samples, an average value of disinfection of 2.43 log is achieved in the inactivation of E. coli. The influence of the matrix in the inactivation of E. coli is clear, with higher levels of disinfection being obtained in samples prepared by dilution of E. coli in distilled water (5.81 log).Furthermore, a reduced empirical model has been obtained taking into account the influence of variables of E. coli inactivation in treated urban wastewater. The model adequately describes the inactivation of E. coli.     

Preparation and evaluation of electrodeposited platinum nanoparticles on in situ carbon nanotubes grown carbon paper for proton exchange membrane fuel cells

Multi-walled carbon nanotubes (MWCNTs) based microporous layer on the non-woven carbon paper substrates was prepared by in situ growth in a chemical vapor deposition method. Pt with a loading of ～0.13 mg cm^?2 was electrodeposited at ?0.3, ?0.6, ?1.2, ?2.4, and ?3.6 V vs SCE in a chloroplatinic acid (60 g/L) and hydrochloric acid (10 g/L) bath using a potentiostat. Scanning electron micrographs showed that the Pt nanoparticles decorated on the MWCNTs/carbon paper are highly uniform, especially at an electrodeposition voltage of ?0.6 V vs SCE. Pt particles' size at various deposition potentials, as estimated by X-ray diffraction analysis is in nanosize range with an average diameter of 6 nm. Fuel cell performance of the Pt deposited in situ grown MWCNTs carbon paper was evaluated using Nafion-212 membrane at various operating conditions. The cathode with Pt deposition at ?0.6 V showed a power density of ～640 mW cm^?2 at 80 °C using H₂ and O₂ at 90% RH and 101 kPa.     

Anaerobic digestion of by-products of sugar beet and starch potato processing

Anaerobic digestion (AD) is a promising option for the environmentally friendly recycling of agricultural by-products. However, overloading of the digester with sugar, starch or protein might cause inhibition of the anaerobic processes. The aim of the present project was to investigate the AD of sugar beet, starch potato by-products and effect of pre-treatment by steam on methane yield of potatoes pulp. The investigated by-products have been: sugar beet pulp silage (SBP), sugar beet tail silage (SBT), potato pulp (PP), potato peel pulp (PPP) and potato fruit water (PFW). All by-products were digested in 1 l eudiometer-batch digesters at 37.5 °C during 28–38 days. The specific methane yields of SBP and SBT were 430 and 481 l_N kg^?1 volatile solids (VS), respectively. The specific methane yields of PP, PPP and PFW were 332, 377 and 323 l_N (kg VS)^?1. A steam pre-treatment significantly increased the specific methane yield of PP up to 373 l_N (kg VS)^?1.     

Hydrothermal preparation and electrochemical properties of Gd3+ and Bi3+, Sm3+, La3+, and Nd3+ codoped ceria-based electrolytes for intermediate temperature-solid oxide fuel cell

The structure, the thermal expansion coefficient, electrical conductivities of Ce_0.8Gd_0.2?xM_xO_2?δ (for M: Bi, x = 0–0.1, and for M: Sm, La, and Nd, x = 0.02) solid solutions, prepared for the first time hydrothermally, are investigated. The uniformly small particle size (28–59 nm) of the materials allows sintering of the samples into highly dense ceramic pellets at 1300–1400 °C. The maximum conductivity, σ_700 °C around 4.46 × 10^?2 S cm^?1 with E_a = 0.52 eV, is found at x = 0.1 for Bi-co-doping. Among various metal-co-dopings, for x = 0.02, the maximum conductivity, σ_700 °C around 2.88 × 10^?2 S cm^?1 with E_a = 0.67 eV, is found for Sm-co-doping. The electrolytic domain boundary (EDB) of Ce_0.8Gd_0.1Bi_0.1O_2?δ is found to be 1.2 × 10^?19 atm, which is relatively lower than that of the singly doped samples. The thermal expansion coefficients, determined from high-temperature X-ray data are 11.6 × 10^?6 K^?1 for the CeO₂, 12.1 × 10^?6 K^?1 for Ce_0.8Gd_0.2O_2?δ, and increase with co-doping to 14.2 × 10^?6 K^?1 for Ce_0.8Gd_0.18Bi_0.02O_2?δ. The maximum power densities for the single cell based on the codoped samples are higher than that of the singly doped sample. These results suggest that co-doping can further improve the electrical performance of ceria-based electrolytes.     

Cultivation of Spirulina platensis by continuous process using ammonium chloride as nitrogen source

This work is focused on the influence of dilution rate (0.08⩽D⩽0.32 d⁻¹) on the kinetics of continuous cultivation of Spirulina platensis at two different concentrations of ammonium chloride (N₀=1.0 and 10 mM) as nitrogen source. Cell productivity increased in both series of runs up to D≅0.12–0.16 d⁻¹, and then decreased. While at N₀=1.0 mM biomass washing was certainly the cause of progressive cell concentration decrease, a combination of this phenomenon with the toxic effect of excess ammonia was responsible, at N₀=10 mM and D⩾0.20 d⁻¹, for quick stop of cell growth just beyond the achievement of maximum cell productivity (92.4 mg l⁻¹ d⁻¹). Similar profile was observed for protein productivity, that achieved a maximum value of 67.0 mg l⁻¹ d⁻¹, because of the very high protein content (72.5%) of biomass produced under these conditions. The yield of nitrogen-to-biomass was much higher at the lower N₀, because of the low protein content, and reached a maximum value of 9.7 g g⁻¹ at D=0.08–0.12 d⁻¹. The yield of nitrogen-to-protein showed less marked difference, being most of the nitrogen present in the cell as proteins or free amino-acids.     

Runoff,sediment, nitrogen,and phosphorus losses from agricultural land converted to sweetgum and switchgrass bioenergy feedstock production in north Alabama

Renewable energy sources such as bioenergy crops have significant potential as alternatives to fossil fuels. Potential environmental problems arising from soil sediment and nutrient losses in runoff water from bioenergy crops need to be evaluated in order to determine the sustainability and overall feasibility of implementing bioenergy development strategies. This paper discusses runoff, sediment, N, and total P losses from agricultural land (continuous cotton (Gossypium hirsutum L.)) converted to short-rotation sweetgum (Liquidamber styraciflua L.) plantations with and without fescue (Festuca elatior L.) and switchgrass (Panicum virgatum L.) bioenergy crops, compared to corn (Zea mays L.), on a Decatur silt loam soil in north Alabama, from 1995 to 1999. Runoff volume was significantly correlated to total rainfall and sediment yield in each year, but treatment differences were not significant. Sweetgum plots produced the highest mean sediment yield of up to 800 kg ha⁻¹compared to corn and switchgrass plots, which averaged less than 200 kg ha⁻¹. Runoff NH₄⁺ N losses averaged over treatments and years for spring season (3.1 kg ha⁻¹) were three to five times those for summer, fall, and winter seasons. Runoff NO₃⁻ N for no-till corn and switchgrass plots in spring and summer were five to ten times that for sweetgum plots. No-till corn and switchgrass treatments had 2.4 and 2.1 kg ha⁻¹ average runoff total P, respectively, which were two to three times that for sweetgum treatments. Growing sweetgum with a fescue cover crop provides significantly lower risk of water pollution from sediment, runoff NH₄⁺ N, and NO₃⁻ N.     

Utilization of summer legumes as bioenergy feedstocks

Sunn hemp (Crotolaria juncea), is a fast growing, high biomass yielding tropical legume that may be a possible southeastern bioenergy crop. When comparing this legume to a commonly grown summer legume – cowpeas (Vigna unguiculata), sunn hemp was superior in biomass yield (kg ha^?1) and subsequent energy yield (GJ ha^?1). In one year of the study after 12 weeks of growth, sunn hemp had 10.7 Mg ha^?1 of biomass with an energy content of 19.0 Mg ha^?1. This resulted in an energy yield of 204 GJ ha^?1. The energy content was 6% greater than that of cowpeas. Eventhough sunn hemp had a greater amount of ash, plant mineral concentrations were lower in some cases of minerals (K, Ca, Mg, S) known to reduce thermochemical conversion process efficiency. Pyrolytic degradation of both legumes revealed that sunn hemp began to degrade at higher temperatures as well as release greater amounts of volatile matter at a faster rate.     

Electrochemical behavior of polyamides with cyclic disulfide structure and their application to positive active material for lithium secondary battery

Polyamides (DTA-I, DTA-II, and DTA-III) containing cyclic disulfide structure were prepared by condensation between 1,2-dithiane-3,6-dicarboxylic acid (DTA) and alkyl diamine, NH₂–(CH₂)_n–NH₂ (DTA-I; n=4, DTA-II; n=6, DTA-III; n=8) and their application to positive active material for lithium secondary batteries was investigated. Cyclic voltammetry (CV) measurements under slow sweep rate (0.5 mV s⁻¹) with a carbon paste electrode containing the polyamide (DTA-I, DTA-II, or DTA-III) were performed. The results indicated that the polyamides were electroactive in the organic electrolyte solution (propylene carbonate (PC)-1,2-dimethoxyethane (DME), 1:1 by volume containing lithium salt, such as LiClO₄). The responses based on the redox of the disulfide bonds in the polyamide were observed.Test cells, Li/PC-DME (1:1. by volume) with 1 mol dm⁻³ LiClO₄/the polyamide cathode, were constructed and their performance was tested under constant current charge/discharge condition. The average capacity of the test cells with the DTA-III cathode was 64.3 Ah kg⁻¹ of cathode (135 Wh kg⁻¹ of cathode, capacity (Ah kg⁻¹) of the cathode×average cell voltage (2.10 V)). Performance of the cell with linear polyamide containing disulfide bond (–CO–(CH₂)₂–S–S–(CH₂)₂–CONH–(CH₂)₈–NH–, GTA-III) was also investigated and the average capacity was 56.8 Ah kg⁻¹ of cathode (100 Wh kg⁻¹ of cathode, capacity (Ah kg⁻¹) of the cathode×average cell voltage (1.76 V)). Cycle efficiency of the test cell with the DTA-III cathode was higher than that with the GTA-III cathode.     

Developing solar cells with recycled materials and household chemicals for drinking water chlorination by communities with limited resources

Ferric tannate-sensitized n-(ZnO, SnO₂)/Cu photoelectrochemical cells were constructed for drinking water chlorination using recycled waste materials and household chemicals and utilising Fe²⁺–Fe³⁺ and Cu²⁺–Cu redox couples for charge transfer. The solar cells, which were constructed in recycled clear plastic tubing and drinking straws in a home environment, produced an open-circuit voltages of 0.4–0.6 V and a short-circuit current densities of 1–2.5 mA cm^?2. Chlorine was produced at a rate of 4 mg h^?1 from a 1% salt solution using an array of cells with a combined voltage of 5 V and a current of 200 mA. This study has demonstrated that it is possible to construct viable solar cells for drinking water chlorination using waste materials and readily available chemicals. Further studies are needed to determine how practicable this would be in regions with drinking water quality and sanitation problems.     

Carbon dioxide fixation by microalgae cultivated in open bioreactors

The biofixation of carbon dioxide (CO₂) by microalgae has been proven to be an efficient and economical method, mainly due to the photosynthetic ability of these microorganisms to use this gas as a source of nutrients for their development. The aim of this work was to study the growth of Spirulina LEB18 and Chlorella kessleri microalgae, exposed to controlled and non-controlled conditions, with the injection of different concentrations of CO₂. The cultures was carried out in 6 L open raceway ponds, under controlled conditions at 30 °C and 39 μE m^?2 s^?1 and under non-controlled conditions, protected by a tunnel of transparent film. The experiments were subjected to CO₂ injections at concentrations of 0.038, 6, 12 and 18% (v/v). The highest concentration of biomass (4.95 g L^?1) and maximum daily fixation (0.21 g g^?1 d^?1) were obtained for Spirulina LEB18 in culture that was prepared in non-controlled conditions with an injection of 6% (v/v) of CO₂. C. kessleri had maximum (p < 0.0008) specific growth rate (0.84 d^?1) when grown with 18% (v/v) of CO₂ in non-controlled conditions of cultivation.     

Development of high energy density small flat spiral cells and battery pack based on lithium/carbon monofluoride (Li/CFx)

Small spiral-wound lithium–carbon monofluoride (Li/CF_x) cells, which were discharged at the C/40 rate, had a nominal capacity of 300 mAh and a gravimetric energy density of about 464 Wh kg⁻¹. These cells delivered pulse current loads (>22 mA) with good capacity (>200 mAh) if they were subjected to a pre-discharge step. A 17 V, 2.2 kW battery based on Li/CF_x flat cell technology has also been fabricated and tested. The battery had gravimetric and volumetric energy densities of 360 Wh kg⁻¹ and 700 Wh dm⁻³, respectively. This compares with a value of 330 Wh kg⁻¹ and 522 Wh dm⁻³ for an equivalent battery based on Li/SOCl₂.     

Evaluating renewable carbon sources as substrates for single cell oil production by Cunninghamella echinulata and Mortierella isabellina

The biochemical behavior (biomass production, accumulation of total lipid, substrate uptake, fatty acid composition of fungal oil) of two oleaginous Mucorales strains, namely Mortierella isabellina ATHUM 2935 and Cunninghamella echinulata ATHUM 4411, was studied when the aforementioned microorganisms were cultivated on xylose, raw glycerol and glucose under nitrogen-limited conditions. Significant differences in the process of lipid accumulation as related to the carbon sources used were observed for both microorganisms. These differences were attributed to the different metabolic pathways involved in the assimilation of the above substrates. Therefore, the various carbon sources were channeled, at different extent, to storage lipid or to lipid-free biomass formation. Although glucose containing media favored the production of mycelial mass (15 g L^?1 of total biomass in the case of C. echinulata and 27 g L^?1 in the case of M. isabellina), the accumulated lipid in dry matter was 46.0% for C. echinulata and 44.6% for M. isabellina. Lipid accumulation was induced on xylose containing media (M. isabellina accumulated 65.5% and C. echinulata 57.7% of lipid, wt wt^?1, in dry mycelial mass). In these conditions, lipids of C. echinulata contained significant quantities of γ-linolenic acid (GLA). This fungus, when cultivated on xylose, produced 6.7 g L^?1 of single cell oil and 1119 mg L^?1 of GLA. Finally, the growth of both C. echinulata and M. isabellina on raw glycerol resulted in lower yields in terms of both biomass and oil produced than the growth on xylose.     

History recovery and source identification of multiple gaseous contaminants releasing with thermal effects in an indoor environment

Thermal transport and transient dispersion of pollutants emitted from two discrete strips within the displacement ventilation enclosure have been modeled numerically. Following the full numerical simulation of turbulent air flows, the inverse determinations of multiple pollutant sources were conducted by the use of quasi reversibility methodology. Direct simulation together with the turbulent streamlines and turbulent heatlines demonstrate that the enclosure flow pattern, enclosure air thermal level and heat transfer potential will depend on the interactions of external forced flow and thermal buoyancy driven flows, i.e., Reynolds number (2 × 10³ ? Re ? 10⁴) and Grashof number (10⁶ ? Gr ? 10¹⁰). In subsequent forward time and backward time modeling of airborne pollutant transports, temporal evolutions of enclosure average concentration and pollutant exhaust are shown to depend on the supplying velocity (Re), thermal plume (Gr), pollutant diffusivity (0.1 ? Sc ? 2), and the pitch between both sources (0.2H ? d_PSL = d_PSR ? 0.7H). Reverse time modeling of airborne spread has demonstrated that increasing the spread rate and the concentration sensitivity of airborne pollutants will facilitate the identification of pollutant sources.