The MERMAID study: indoor and outdoor average pollutant concentrations in 10 low‐energy school buildings in France

Indoor air quality was characterized in 10 recently built energy‐efficient French schools during two periods of 4.5 days. Carbon dioxide time‐resolved measurements during occupancy clearly highlight the key role of the ventilation rate (scheduled or occupancy indexed), especially in this type of building, which was tightly sealed and equipped with a dual‐flow ventilation system to provide air refreshment. Volatile organic compounds (VOCs) and inorganic gases (ozone and NO₂) were measured indoors and outdoors by passive techniques during the occupied and the unoccupied periods. Over 150 VOC species were identified. Among them, 27 species were selected for quantification, based on their occurrence. High concentrations were found for acetone, 2‐butanone, formaldehyde, toluene, and hexaldehyde. However, these concentrations are lower than those previously observed in conventional school buildings. The indoor/outdoor and unoccupied/occupied ratios are informative regarding emission sources. Except for benzene, ozone, and NO₂, all the pollutants in these buildings have an indoor source. Occupancy is associated with increased levels of acetone, 2‐butanone, pentanal, butyl acetate, and alkanes.     

Surface neutralization and H₂S oxidation at early stages of sewer corrosion: influence of temperature, relative humidity and H₂S concentration

While the involvement of a range of environmental factors in sewer corrosion is known, a comprehensive understanding of the processes involved and the exact role of individual environmental factors in sewer corrosion is still lacking. The corrosion of concrete in sewer systems is reported to be initiated through chemical reactions (involving H₂S and CO₂) that lower the surface pH to a level then conducive for biological activity. However, the specific influence of environmental variables, such as H₂S level, temperature, and relative humidity etc. remains unclear; although, they are expected to control these initial surface reactions of the concrete sewer pipe. We examined changes in the surface chemistry of concrete during the early stages of corrosion by exposing concrete coupons to thirty-six independent conditions in well-controlled laboratory chambers that simulated conditions typically found in various sewer environments across Australia. The conditions employed were combinations of six H₂S levels, three gas-phase temperatures and two relative humidity levels. Our results indicate that the role of CO₂ on initial surface pH reduction is insignificant when compared to the influence of H₂S. Within the first 12 months, a decrease in surface pH by 4.8 units was observed for coupons exposed to 30 °C and 50 ppm H₂S, while significantly lower pH reductions of 3.5 and 1.8 units were detected for coupons exposed to 25 °C and 18 °C respectively, and 50 ppm H₂S. Elemental sulphur was found to be the major oxidation product of H₂S and elevated concentrations were detected at the higher levels of H₂S, temperature and relative humidity. More significantly, the data obtained from the controlled chamber experiments correlated with those obtained from the field-exposed coupons. Hence, these findings can be extended to real sewer corrosion processes.     

Biological and environmental exposure monitoring of volatile organic compounds among nail technicians in the Greater Boston area

Nail technicians are exposed to volatile organic compounds (VOCs) from nail products, but no studies have previously measured VOC biomarkers for these workers. This study of 10 nail technicians aimed to identify VOCs in nail salons and explore relationships between air concentrations and biomarkers. Personal and area air samples were collected using thermal desorption tubes during a work shift and analyzed using gas chromatography/mass spectrometry (GC/MS) for 71 VOCs. Whole blood samples were collected pre‐shift and post‐shift, and analyzed using GC/MS for 43 VOCs. Ventilation rates were determined using continuous CO₂ measurements. Predominant air VOC levels were ethyl methacrylate (median 240 µg/m³), methyl methacrylate (median 205 µg/m³), toluene (median 100 µg/m³), and ethyl acetate (median 639 µg/m³). Blood levels were significantly higher post‐shift than pre‐shift for toluene (median pre‐shift 0.158 µg/L and post‐shift 0.360 µg/L) and ethyl acetate (median pre‐shift <0.158 µg/L and post‐shift 0.510 µg/L); methacrylates were not measured in blood because of their instability. Based on VOCs measured in these seven nail salons, we estimated that emissions from Greater Boston area nail salons may contribute to ambient VOCs. Ventilation rates did not always meet the ASHRAE guideline for nail salons. There is a need for changes in nail product formulation and better ventilation to reduce VOC occupational exposures.     

Impact of water boundary layer diffusion on the nitrification rate of submerged biofilter elements from a recirculating aquaculture system

Total ammonia nitrogen (TAN) removal by microbial nitrification is an essential process in recirculating aquaculture systems (RAS). In order to protect the aquatic environment and fish health, it is important to be able to predict the nitrification rates in RAS's. The aim of this study was to determine the impact of hydraulic film diffusion on the nitrification rate in a submerged biofilter. Using an experimental batch reactor setup with recirculation, active nitrifying biofilter units from a RAS were exposed to a range of hydraulic flow velocities. Corresponding nitrification rates were measured following ammonium chloride, NH₄Cl, spikes and the impact of hydraulic film diffusion was quantified.The nitrification performance of the tested biofilter could be significantly increased by increasing the hydraulic flow velocity in the filter. Area based first order nitrification rate constants ranged from 0.065 m d⁻¹ to 0.192 m d⁻¹ for flow velocities between 2.5 m h⁻¹ and 40 m h⁻¹ (18 °C). This study documents that hydraulic film diffusion may have a significant impact on the nitrification rate in fixed film biofilters with geometry and hydraulic flows corresponding to our experimental RAS biofilters. The results may thus have practical implications in relation to the design, operational strategy of RAS biofilters and how to optimize TAN removal in fixed film biofilter systems.     

Investigation of volatile organic compounds in office buildings in Bangkok,Thailand: Concentrations,sources, and occupant symptoms

To conserve energy, office buildings with air-conditioning systems in Thailand are operated with a tight thermal envelope. This leads to low fresh-air ventilation rates and is thought to be partly responsible for the sick building syndrome symptoms reported by occupants. The objectives of this study are to measure concentrations and to determine sources of 13 volatile organic compounds (VOCs) in office buildings with air-conditioning systems in the business area of Bangkok. Indoor and outdoor air samples from 17 buildings were collected on Tenax-TA^™ sorbent tubes and analyzed for individual VOCs by thermal desorption-gas chromatography/mass spectrometry (TD–GC/MS). Building ventilation was measured with a constant injection technique using hexafluorobenzene as a tracer gas. The results show that the VOC concentrations varied significantly among the studied buildings. The two most dominant VOCs were toluene and limonene with average concentrations of 110 and 60.5 μg m⁻³, respectively. A Wilcoxon sum rank test indicated that the indoor concentrations of aromatic compounds and limonene were statistically higher than outdoor concentrations at the 0.05 level, while the indoor concentrations of chlorinated compounds were not. Indoor emission factors of toluene and limonene were found to be highest with the average values of 80.9 and 18.9 μg m⁻² h⁻¹, respectively. Principal component analysis was applied to the emission factors of 13 VOCs, producing three components based on source similarities. Furthermore, a questionnaire survey investigation and field measurements of building air exchange pointed to indoor air complaints related to inadequate ventilation.     

Mathematical modelling of hydrogen sulphide emission and removal in aerobic biofilters comprising chemical oxidation

Four different empirical expressions have been compared for estimating the removal of hydrogen sulphide (H₂S) from wastewater by chemical oxidation during its treatment in an aerated biofilter. The relative importance of this removal process is considered in a mass balance proposed by an emission model. Two of the four models investigated were able to predict the mean H₂S removed fraction within a confidence interval of 95% and they demonstrated good agreement with experimental data. Biodegradation and oxidation were the two main removal mechanisms in the biofilter whereas stripping and volatilization made only minor contributions. However they can be of significance when the emission rates are calculated.     

Influencing factors of carbonyl compounds and other VOCs in commercial airliner cabins: On-board investigation of 56 flights

Volatile organic compounds (VOCs) as a non-negligible aircraft cabin air quality (CAQ) factor influence the health and comfort of passengers and crew members. On-board measurements of carbonyls (short-chain (C₁-C₆)) and other volatile organic compounds (VOCs, long-chain (C₆-C₁₆)) with a total of 350 samples were conducted in 56 commercial airliner cabins covering 8 aircraft models in this study. The mean concentration for each individual carbonyl compound was between 0.3 and 8.3 μg/m³ (except for acrolein & acetone, average = 20.7 μg/m³) similar to the mean concentrations of other highly detected VOCs (long-chain (C₆-C₁₆), 97% of which ranged in 0–10 μg/m³) in aircraft cabins. Formaldehyde concentrations in flights were significantly lower than in residential buildings, where construction materials are known formaldehyde sources. Acetone is a VOC emitted by humans, and its concentration in flights was similar to that in other high-occupant density transportation vehicles. The variation of VOC concentrations in different flight phases of long-haul flights was the same as that of CO₂ concentration except for the meal phase, which indicates the importance of cabin ventilation in diluting the gaseous contaminants, while the sustained and slow growth of the VOC concentrations during the cruising phase in short-haul flights indicated that the ventilation could not adequately dilute the emission of VOCs. For the different categories of VOCs, the mean concentration during the cruising phase of benzene series, aldehydes, alkanes, other VOCs (detection rate > 50%), and carbonyls in long-haul flights was 44.2 µg/m³, 17.9 µg/m³, 18.6 µg/m³, 31.5 µg/m³, and 20.4 µg/m³ lower than those in short-haul flights, respectively. Carbonyls and d-limonene showed a significant correlation with meal service (p < 0.05). Unlike the newly decorated rooms or new vehicles, the inner materials were not the major emission sources in aircraft cabins. Practical Implications.

• The on-board measurements of 56 flights enrich the VOC database of cabin environment, especially for carbonyls. The literature review of carbonyls in the past 20 years contributes to the understanding the current status of cabin air quality (CAQ).
• The analysis of VOC concentration variation for different flight phases, flight duration, and aircraft age lays a foundation for exploring effective control methods, including ventilation and purification for cabin VOC pollution.
• The enriched VOC data is helpful to explore the key VOCs of aircraft cabin environment and to evaluate the acute/chronic health exposure risk of pollutants for passengers and crew members.

     

Evaluation of impact factors on VOC emissions and concentrations from wooden flooring based on chamber tests

In this study, the impact factors of temperature, relative humidity (RH), air exchange rate, and volatile organic compound (VOC) properties on the VOC (toluene, n-butyl acetate, ethylbenzene, and m,p-xylene) specific emission rates (SERs) and concentrations from wooden flooring were investigated by chamber test for 8 days. The tested wood in this study is not common solid wood, but composite wood made of combined wood fibers. The experiments were conducted in a stainless-steel environmental test chamber coated with Teflon. The experimental results within 8 days of testing showed that, when the temperature increased from 15 to 30 °C, the VOC SERs and concentrations increased 1.5–129 times. When the RH increased from 50% to 80%, the VOC concentrations and SERs increased 1–32 times. When the air change rate increased from 1 to 2 h⁻¹, the VOC concentrations decreased 9–40%, while the VOC SERs increased 6–98%. The relations between the boiling points of the VOCs and each of the normalized VOC SERs and concentrations were linear with negative slopes. The relations between the vapor pressures of the VOCs and each of the normalized VOC SERs and concentrations were linear with positive slopes. At 15 °C, RH50%, the relations between the diffusivities of VOCs and each of the normalized VOC equilibrium SERs and concentrations were linear with a positive slope.     

Operational aspects of the desulfurization process of energy gases mimics in biotrickling filters

Biological removal of reduced sulfur compounds in energy-rich gases is an increasingly adopted alternative to conventional physicochemical processes, because of economical and environmental benefits. A lab-scale biotrickling filter reactor for the treatment of high-H₂S-loaded gases was developed and previously proven to effectively treat H₂S concentrations up to 12,000 ppm_v at gas contact times between 167 and 180 s. In the present work, a detailed study on selected operational aspects affecting this system was carried out with the objective to optimize performance. The start-up phase was studied at an inlet H₂S concentration of 1000 ppm_v (loading of 28 g H₂S m⁻³ h⁻¹) and inoculation with sludge from a municipal wastewater treatment plant. After reactor startup, the inlet H₂S concentration was doubled and the influence of different key process parameters was tested. Results showed that there was a significant reduction of the removal efficiency at gas contact times below 120 s. Also, mass transfer was found to be the main factor limiting H₂S elimination, whereas performance was not influenced by the bacterial colonization of the packed column after the initial startup. The effect of gas supply shutdowns for up to 5 days was shown to be irrelevant on process performance if the trickling liquid recirculation was kept on. Also, the trickling liquid velocity was investigated and found to influence sulfate production through a better use of the supplied dissolved oxygen. Finally, short-term pH changes revealed that the system was quite insensitive to a pH drop, but was markedly affected by a pH increase, affecting both the biological activity and the removal of H₂S. Altogether, the results presented and discussed herein provide new insight and operational data on H₂S removal from energy gases in biotrickling filters.     

Factors controlling volatile organic compounds in dwellings in Melbourne,Australia

This study characterized indoor volatile organic compounds (VOCs) and investigated the effects of the dwelling characteristics, building materials, occupant activities, and environmental conditions on indoor VOC concentrations in 40 dwellings located in Melbourne, Australia, in 2008 and 2009. A total of 97 VOCs were identified. Nine VOCs, n‐butane, 2‐methylbutane, toluene, formaldehyde, acetaldehyde, d‐limonene, ethanol, 2‐propanol, and acetic acid, accounted for 68% of the sum of all VOCs. The median indoor concentrations of all VOCs were greater than those measured outdoors. The occupant density was positively associated with indoor VOC concentrations via occupant activities, including respiration and combustion. Terpenes were associated with the use of household cleaning and laundry products. A petroleum‐like indoor VOC signature of alkanes and aromatics was associated with the proximity of major roads. The indoor VOC concentrations were negatively correlated (P < 0.05) with ventilation. Levels of VOCs in these Australian dwellings were lower than those from previous studies in North America and Europe, probably due to a combination of an ongoing temporal decrease in indoor VOC concentrations and the leakier nature of Australian dwellings.     

Emission behavior of formaldehyde and TVOC from engineered flooring in under heating and air circulation systems

Formaldehyde and volatile organic compounds (VOCs) from the adhesive, flooring, and flooring with adhesive were measured using a desiccator, a 20-L chamber and a field and laboratory emission cell (FLEC). Flooring with an adhesive is similar to that used in construction was applied to a floor heating system and an air circulation system, and the surface temperature of the flooring was set to 20 °C, 26 °C and 32 °C. The rate of formaldehyde emission from the flooring was the highest at 32 °C using a desiccator and decreased with time. The formaldehyde and aldehyde emissions from the samples using a 20-L chamber and FLEC showed a similar tendency. The VOCs emission trends with the 20-L chamber and FLEC were similar. The rate of formaldehyde and TVOC emission determined using FLEC was higher than that determined using the 20-L chamber method. The flooring emitted primarily benzene, toluene, ethylbenzene, styrene, xylene, as well as some unknown VOCs. There was a strong correlation between formaldehyde and TVOC emission for the 20-L chamber and FLEC. Samples using a floor heating system showed higher formaldehyde emission than those using an air circulation system. The level of TVOC emission was higher from the samples using an air circulation system than those using the floor heating system.     

Volatile organic compounds in 169 energy-efficient dwellings in Switzerland

Exposure to elevated levels of certain volatile organic compounds (VOCs) in households has been linked to deleterious health effects. This study presents the first large-scale investigation of VOC levels in 169 energy-efficient dwellings in Switzerland. Through a combination of physical measurements and questionnaire surveys, we investigated the influence of diverse building characteristics on indoor VOCs. Among 74 detected compounds, carbonyls, alkanes, and alkenes were the most abundant. Median concentration levels of formaldehyde (14 μg/m³), TVOC (212 μg/m³), benzene (<0.1 μg/m³), and toluene (22 μg/m³) were below the upper exposure limits. Nonetheless, 90% and 50% of dwellings exceeded the chronic exposure limits for formaldehyde (9 μg/m³) and TVOC (200 μg/m³), respectively. There was a strong positive correlation among VOCs that likely originated from common sources. Dwellings built between 1950s and 1990s, and especially, those with attached garages had higher TVOC concentrations. Interior thermal retrofit of dwellings and absence of mechanical ventilation system were associated with elevated levels of formaldehyde, aromatics, and alkanes. Overall, energy-renovated homes had higher levels of certain VOCs compared with newly built homes. The results suggest that energy efficiency measures in dwellings should be accompanied by actions to mitigate VOC exposures as to avoid adverse health outcomes.     

An experimental study of relative humidity effect on VOCs’ effective diffusion coefficient and partition coefficient in a porous medium

Most building materials are porous media. As a critical environmental factor, the influence of relative humidity on VOCs diffusion is still not well understood. In this study, VOC transport and sorption in a porous medium in the building materials (calcium silicate) were measured under three levels of relative humidity (25%, 50% and 80%) by using a dynamic dual chamber method. Tests were conducted for water-soluble compound (formaldehyde) and non-soluble compound (toluene). In addition, the transport of acetaldehyde, hexanal, benzaldehyde, butanol and decane through the calcium silicate were also tested at 50%RH to study the relationship between the effective diffusion coefficient (D_e), partition coefficient (K_ma) and the VOCs’ physical properties (molecular weight, vapor pressure and Henry’s law constant). Experimental results showed that: relative humidity in the 80%RH led to a higher partition coefficient for formaldehyde compared to 50%RH. However, between 25% and 50%RH, there was no significant difference in partition coefficient. Partition coefficient of toluene decreased with the increase of humidity due to competition of water molecules for pore surface area and the non-solubility nature of toluene. Relative humidity had no significant influence on the effective diffusion coefficient on both formaldehyde and toluene for the range of moisture conditions tested. The solubility of VOCs was found to correlate with the partition coefficient of VOCs. The partition coefficient of VOCs was not simply inversely proportional to the vapor pressure of the compound, but also increased with the increase of Henry’s law constant.     

Preserving Shipboard AFFF Fire Protection System Performance While Preventing Hydrogen Sulfide Formation

There is a very serious problem aboard US Navy ships from generation of toxic hydrogen sulfide (H₂S) in Aqueous Film-Forming Foam (AFFF) solutions used for shipboard fire protection. This is the result of the action of sulfate reducing bacteria (SRB) in mixtures of seawater and AFFF, which remain stagnant for significant time periods in shipboard fire protection system piping. Similar to microbial generation of H₂S in sewage, over time microbes present in seawater consume organic materials in the AFFF mixture and can deplete the dissolved oxygen. If the reduction-oxidation potential falls low enough, anaerobic action of the SRB on the sulfate present in seawater can then result in H₂S generation, reaching dangerous levels. The recommended ceiling for exposure to H₂S is only 10 ppm. If the microbes causing oxygen depletion and/or the SRB can be eliminated (or sufficiently minimized), the dangerous generation of H₂S would not occur. The Navy Technology Center for Safety and Survivability is participating in a research project for the Naval Sea Systems Command (NAVSEA) to evaluate several treatment modalities for their ability to inhibit H₂S formation in AFFF/seawater mixtures and for possible deleterious effects on AFFF performance. Various approaches have been considered employing laboratory evaluations (dynamic surface tension and Ross-Miles foamability), and 28 ft² (2.6 m²) pool fire extinguishment and burnback protection field tests (Military Standard MIL-F-24385F). The protocol selected for NAVSEA shipboard H₂S generation mitigation testing is a combination of a commercial broad-spectrum biocide with a molybdenum compound which is a specific inhibitor of SRB.     

Methanogenic community development in anaerobic granular bioreactors treating trichloroethylene (TCE)-contaminated wastewater at 37 °C and 15 °C

Four expanded granular sludge bed (EGSB) bioreactors were seeded with a mesophilically-grown granular sludge and operated in duplicate for mesophilic (37 °C; R1 & R2) and low- (15°; R3 & R4) temperature treatment of a synthetic volatile fatty acid (VFA) based wastewater (3 kg COD m⁻³ d⁻¹) with one of each pair (R1 & R3) supplemented with increasing concentrations of trichloroethylene (TCE; 10, 20, 40, 60 mg l⁻¹) and one acting as a control. Bioreactor performance was evaluated by % COD removal efficiency and % biogas methane (CH₄) content. Quantitative Polymerase Chain Reaction (qPCR) was used to investigate the methanogenic community composition and dynamics in the bioreactors during the trial, while specific methanogenic activity (SMA) and toxicity assays were utilized to investigate the activity and TCE/dichloroethylene (DCE) toxicity thresholds of key trophic groups, respectively. At both 37 °C and 15 °C, TCE levels of 60 mg l⁻¹ resulted in the decline of % COD removal efficiencies to 29% (Day 235) and 37% (Day 238), respectively, and in % biogas CH₄ to 54% (Day 235) and 5% (Day 238), respectively. Despite the inhibitory effect of TCE on the anaerobic digestion process, the main drivers influencing methanogenic community development, as determined by qPCR and Non-metric multidimensional scaling analysis, were (i) wastewater composition and (ii) operating temperature. At the apical TCE concentration both SMA and qPCR of methanogenic archaea suggested that acetoclastic methanogens were somewhat inhibited by the presence of TCE and/or its degradation derivatives, while competition by dechlorinating organisms may have limited the availability of H₂ for hydrogenotrophic methanogenesis. In addition, there appeared to be an inverse correlation between SMA levels and TCE tolerance, a finding that was supported by the analysis of the inhibitory effect of TCE on two additional biomass sources. The results indicate that low-temperature anaerobic digestion is a feasible approach for the treatment of TCE-containing wastewater.     

Enrichment of acetogenic bacteria in high rate anaerobic reactors under mesophilic and thermophilic conditions

The objective of the current study was to expand the knowledge of the role of acetogenic Bacteria in high rate anaerobic digesters. To this end, acetogens were enriched by supplying a variety of acetogenic growth supportive substrates to two laboratory scale high rate upflow anaerobic sludge bed (UASB) reactors operated at 37 °C (R1) and 55 °C (R2). The reactors were initially fed a glucose/acetate influent. Having achieved high operational performance and granular sludge development and activity, both reactors were changed to homoacetogenic bacterial substrates on day 373 of the trial. The reactors were initially fed with sodium vanillate as a sole substrate. Although % COD removal indicated that the 55 °C reactor out performed the 37 °C reactor, effluent acetate levels from R2 were generally higher than from R1, reaching values as high as 5023 mg l⁻¹. Homoacetogenic activity in both reactors was confirmed on day 419 by specific acetogenic activity (SAA) measurement, with higher values obtained for R2 than R1.Sodium formate was introduced as sole substrate to both reactors on day 464. It was found that formate supported acetogenic activity at both temperatures. By the end of the trial, no specific methanogenic activity (SMA) was observed against acetate and propionate indicating that the methane produced was solely by hydrogenotrophic Archaea. Higher SMA and SAA values against H₂/CO₂ suggested development of a formate utilising acetogenic population growing in syntrophy with hydrogenotrophic methanogens. Throughout the formate trial, the mesophilic reactor performed better overall than the thermophilic reactor.     

Biodegradation potential of bulking agents used in sludge bio-drying and their contribution to bio-generated heat

Straw and sawdust are commonly used bulking agents in sludge composting or bio-drying. It is important to determine if they contribute to the biodegradable volatile solids pool. A sludge bio-drying process was performed in this study using straw, sawdust and their combination as the bulking agents. The results revealed that straw has substantial biodegradation potential in the aerobic process and sawdust has poor capacity to be degraded. The temperature profile and bio-drying efficiency were highest in the trial that straw was added, as indicated by a moisture removal ratio and VS loss ratio of 62.3 and 31.0%, respectively. In separate aerobic incubation tests, straw obtained the highest oxygen uptake rate (OUR) of 2.14 and 4.75 mg O₂ g⁻¹VS h⁻¹ at 35 °C and 50 °C, respectively, while the highest OUR values of sludge were 12.1 and 5.68 mg O₂ g⁻¹VS h⁻¹ at 35 °C and 50 °C and those of sawdust were 0.286 and 0.332 mg O₂ g⁻¹VS h⁻¹, respectively. The distribution of biochemical fractions revealed that soluble fractions in hot water and hot neutral detergent were the main substrates directly attacked by microorganisms, which accounted for the initial OUR peak. The cellulose-like fraction in straw was transformed to soluble fractions, resulting in an increased duration of aerobic respiration. Based on the potential VS degradation rate, no bio-generated heat was contributed by sawdust, while that contribution by straw was about 41.7% and the ratio of sludge/straw was 5:1 (w/w, wet basis).     

Effects of water vapor on activated carbon load equalization of gas phase toluene

Experimental testing and numerical simulations were conducted to assess the effects of elevated water vapor concentrations on the ability of granular activated carbon (GAC) to achieve load equalization of dynamically varying gas-phase toluene concentrations. Columns packed with Calgon BPL 4 × 6 mesh GAC were subjected to intermittent (8 h/day) toluene loading in air streams containing up to 90% relative humidity. Influent toluene concentrations ranged from 100 to 1000 ppm_v, and GAC column empty bed residence times ranged from 1.5 to 10 s. In comparison to load equalization performance achieved with dry air, high relative humidity improved load attenuation at high influent toluene concentration (e.g., 1000 ppm_v) but decreased the degree of load attenuation at low influent toluene concentration (e.g., 100 ppm_v). Model simulations conducted using a pore and surface diffusion model were in good general agreement with experimental observations. Collectively, results demonstrate that GAC columns can be of practical benefit as passively-operated load equalization devices even in the case of high relative humidity. Such systems may prove useful as a pre-treatment process for biofilters and other air pollution control devices that would otherwise be subjected to wide variation in contaminant loading.     

Indoor air quality in Portuguese schools: levels and sources of pollutants

Indoor air quality (IAQ) parameters in 73 primary classrooms in Porto were examined for the purpose of assessing levels of volatile organic compounds (VOCs), aldehydes, particulate matter, ventilation rates and bioaerosols within and between schools, and potential sources. Levels of VOCs, aldehydes, PM_2.5, PM₁₀, bacteria and fungi, carbon dioxide (CO₂), carbon monoxide, temperature and relative humidity were measured indoors and outdoors and a walkthrough survey was performed concurrently. Ventilation rates were derived from CO₂ and occupancy data. Concentrations of CO₂ exceeding 1000 ppm were often encountered, indicating poor ventilation. Most VOCs had low concentrations (median of individual species <5 μg/m³) and were below the respective WHO guidelines. Concentrations of particulate matter and culturable bacteria were frequently higher than guidelines/reference values. The variability of VOCs, aldehydes, bioaerosol concentrations, and CO₂ levels between schools exceeded the variability within schools. These findings indicate that IAQ problems may persist in classrooms where pollutant sources exist and classrooms are poorly ventilated; source control strategies (related to building location, occupant behavior, maintenance/cleaning activities) are deemed to be the most reliable for the prevention of adverse health consequences in children in schools.