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Polycyclic aromatic compounds (PACs) are major airborne pollutants. However, their assessment has mostly been restricted to 16 priority polycyclic aromatic hydrocarbons (PAHs). In this work, 76 PACs including PAHs, oxy-PAHs, nitro-PAHs, azaarenes, and thiaarenes were monitored in an urban residential environment. A short-term campaign was conducted at three dwellings in Strasbourg, France, with low-volume PM10 samplers operated simultaneously outdoors and indoors. Household dust was also sampled in these dwellings. The PACs of interest were extracted by pressurized liquid extraction in toluene and acetonitrile, and quantified by GC-MS/MS. The total concentration of PACs in PM10 was between 67 and 179 ng·m−3 outdoors and between 62 and 401 ng·m−3 indoors. Total PAC levels in settled dust varied from 3.5 to 31 μg·g−1, and from 0.44 to 3.88 μg·m−2. Due to the high influence of surfaces dust load, the interpretation of PAC concentrations in settled dust was different if mass concentrations or surface concentrations were studied. This sampling campaign concurrent with a winter pollution event led to exceptionally high concentrations of PACs. The samples of this work set maximum values for PAHs and oxy-PAHs in airborne particles among recent European studies, and an absolute maximum value for azaarenes. However, the acute short-term exposure of Strasbourg inhabitants to PACs during this pollution event is balanced by the normal concentrations of PACs in household dust, which characterizes better the long-term exposure. Source apportionment was performed thanks to PAH diagnostic ratios. It indicated a prevalence of road traffic and a possibility of PAH photochemical aging in dust. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants formed during incomplete combustion or pyrolysis of organic material. The reliable quantification of PAH in airborne samples is still difficult, costly, and time-consuming due to the use of offline techniques, including long sampling on filters/adsorbents, laboratory extraction, purification, and concentration steps before analysis. To tackle these drawbacks, this work focused on the development of a fully automatic gas chromatograph (GC) equipped with a flame ionization detector (FID) and a sample preconcentration unit (PC) for gas sampling. This instrument was validated under laboratory-controlled conditions in the range 0–10 ng for 18 PAH. The chromatographic separation was rather satisfactory except for two PAH pairs, which were quantified together. For all compounds, the peak areas increased perfectly with the gaseous PAH concentration (R2 > 0.98), without any significant memory effect between two consecutive analyses. Considering a gaseous sample volume of 1 L, the extrapolated limits of detections (LOD) were in the range 19.9–62.6 ng/m3, depending on the PAH. Its analytical performances were then compared to those of the offline reference UHPLC-fluorescence method, widely used for airborne PAH monitoring. This was also compared with the very few portable or continuously operating instruments. [ABSTRACT FROM AUTHOR]

An intensive field campaign was conducted to monitor indoor air formaldehyde in two French elementary schools for 5 weeks, where the experimental conditions were modified every week. Formaldehyde concentration was monitored using two portable laboratory prototypes with a detection limit of 1 μg m−3 and a temporal resolution of 2 s. Carbon dioxide concentration, temperature (T), and relative humidity (RH) were also recorded over the whole field campaign. To take advantage of continuous measurement of formaldehyde for post-data analysis, these 2-s raw formaldehyde concentrations were then used to recalculate the average values for several time steps, i.e., 1 min, 10 min, 1 h, and 1 day. This paper highlights that a time resolution of 10 min is sufficient and well adapted to monitor most of the variations of formaldehyde concentrations observed in these two classrooms. The weekly mean formaldehyde concentrations calculated were in the ranges of 25.6–33.8 μg m−3 and 14.7–26.8 μg m−3 for schools 1 (S1) and 2 (S2), respectively, once excluded an unwanted painting event in S1. The results obtained were in excellent agreement with those determined by using the reference method based on DNPH derivatization. The results also revealed that building materials and furniture were two significant formaldehyde emission sources. Unlike most of the studies found in the literature in which formaldehyde is monitored using passive sampling, continuous measurements allowed us to estimate real children's exposure. When considering only the children's occupation time, a significant decrease in average formaldehyde concentration ranging between 20 and 34 % was observed for weeks 4 and 5 when the occupants followed specific strategies for natural ventilation. Opening the windows as soon as the CO2 exceeds the thresholds appears to be the most efficient way to limit exposure to formaldehyde in the two investigated schools. The findings of this paper demonstrate the importance of continuous and accurate formaldehyde measurements with at least 10-min time resolution which could serve as a roadmap for future developments of formaldehyde low-cost sensors. [ABSTRACT FROM AUTHOR]

Phosphates in high concentrations are harmful pollutants for the environment, and new and cheap solutions are currently needed for phosphate removal from polluted liquid media. Iron oxide nanoparticles show a promising capacity for removing phosphates from polluted media and can be easily separated from polluted media under an external magnetic field. However, they have to display a high surface area allowing high removal pollutant capacity while preserving their magnetic properties. In that context, the reproducible synthesis of magnetic iron oxide raspberry-shaped nanostructures (RSNs) by a modified polyol solvothermal method has been optimized, and the conditions to dope the latter with cobalt, zinc, and aluminum to improve the phosphate adsorption have been determined. These RSNs consist of oriented aggregates of iron oxide nanocrystals, providing a very high saturation magnetization and a superparamagnetic behavior that favor colloidal stability. Finally, the adsorption of phosphates as a function of pH, time, and phosphate concentration has been studied. The undoped and especially aluminum-doped RSNs were demonstrated to be very effective phosphate adsorbents, and they can be extracted from the media by applying a magnet. [ABSTRACT FROM AUTHOR]

Accurate and continuous monitoring of indoor air quality is crucial to understand and prevent airborne diseases, since humans spend most of their routine time indoors. Aldehydes are of particular interest as they are irritants and usually present in indoor air at concentrations from 2 to 10 times higher than in outdoor air. Formaldehyde, the most abundant one, is classified as carcinogenic category 1B under European Regulation (EC) No 1272/2008. In indoor air, aldehydes mainly originate from construction materials such as plywood, insulating materials and paints. Some aldehydes have a pungent and fruity odour at high concentrations but may be undetected at low concentration. To be able to implement preventive measures, there is a need for continuous, fast, accurate and robust techniques for quantification of aldehydes in indoor air. In this work, two different systems which have been developed for monitoring of formaldehyde and other aldehydes are presented: a portable microdevice based on the derivatization of formaldehyde for continuous fluorometric detection, and an Automatic Gas 2D-chromatograph equipped with a thermodesorption unit and flame ionization detector (auto-TD-GC-FID). These techniques were compared under laboratory-controlled measurements. The portable microdevice specifically quantifies formaldehyde down to ppb levels. It is compact and uses a specific aqueous reagent to convert formaldehyde into a fluorescent product, 100 mL enabling a continuous monitoring for 4 days. The auto-TD-GC-FID is an automatic gas chromatograph permitting formaldehyde and acetaldehyde quantification from ppb to ppm levels. It runs continuously with successive 15-min cycles. This instrument only requires a power supply and gas generators or gas cylinders of hydrogen, air, and nitrogen. Our experimental results demonstrate that both analytical devices quantify formaldehyde accurately. [ABSTRACT FROM AUTHOR]

The presence of polycyclic aromatic hydrocarbons (PAHs) and particulate matter (PM) in air is known to provoke deleterious effects on human health. This work focused on the monitoring of PM and PAHs in the air over four weeks in a peri-urban site in Strasbourg (France), using a three-stage cascade impactor and a particle analyser allowing PM1, PM2.5 and PM10 discrimination. Meteorological conditions were monitored to study their influence on the pollutant levels. The average PM10 concentration of the cascade impactor and particle analyser varied from 11.8 to 80.2 µg/m3 and 10.6 to 220.2 µg/m3, respectively. The PAH total concentration ranged in 1.1–7.6 ng/m3 and a predominance of 5- and 6-ring PAHs was observed. PAHs were also more abundant in finer particles (PM1). Specifically, identified PAHs are traffic tracers suggesting that vehicular emission was one of its main sources. Two pollution episodes, associated with either a Saharan dust wind episode or traffic pollution, were observed, and led to PM10 and PM2.5 surpassing the daily limit values established by the European Union despite the traffic limitations according to the COVID restrictions. The total PAH concentrations were the highest during these periods suggesting PAHs might be bound to and transported via dust particles. [ABSTRACT FROM AUTHOR]

The projected increase of civil aviation activity, the degradation of air quality and the location of Beirut Airport embedded in a very urbanized area, in addition to the special geography and topography surrounding the airport which plays a significant role in drawing emissions to larger distances, demanded an assessment of the spatial impact of the airport activities on the air quality of Beirut and its suburbs. This is the first study in the Middle East region that model pollutant concentrations resulting from an international airport's activities using an advanced atmospheric dispersion modelling system in a country with no data. This followed validation campaigns showing very strong correlations (r = 0.85) at validation sites as close as possible to emission sources. The modelling results showed extremely high NO2 concentrations within the airport vicinity, i.e., up to 110 μg∙m-3 (which is greater than the World Health Organization annual guidelines) posing a health hazard to the workers in the ramp. The major contribution of Beirut–Rafic Hariri International Airport to the degradation of air quality was in the airport vicinity; however, it extended to Beirut and its suburbs in addition to affecting the seashore area due to emissions along the aircraft trajectory; this is an aspect rarely considered in previous studies. On the other hand, elevated volatile organic compound levels were observed near the fuel tanks and at the aerodrome center. This study provides (ⅰ) a methodology to assess pollutant concentrations resulting from airport emissions through the use of an advanced dispersion model in a country with no data; and (ⅱ) a tool for policy makers to better understand the contribution of the airport's operations to national pollutant emissions, which is vital for mitigation strategies and health impact assessments. [ABSTRACT FROM AUTHOR]

This work aims at developing and validating under laboratory-controlled conditions a gas mixture generation device designed for easy on-site or laboratory calibration of analytical instruments dedicated to air monitoring, such as analysers or sensors. This portable device, which has been validated for formaldehyde, is compact and is based on the diffusion of liquid formaldehyde through a short microporous interface with an air stream to reach non-Henry equilibrium gas–liquid dynamics. The geometry of the temperature-controlled assembly has been optimised to allow easy change of the aqueous solution, keeping the microporous tube straight. The formaldehyde generator has been coupled to an on-line formaldehyde analyser to monitor the gas concentration generated as a function of the liquid formaldehyde concentration, the temperature, the air gas flow rate, and the microporous tube length. Our experimental results show that the generated gaseous formaldehyde concentration increase linearly between 10 and 1740 µg m−3 with that of the aqueous solution ranging between 0 and 200 mg L−1 for all the gas flow rates studied, namely 25, 50 and 100 mL min−1. The generated gas phase concentration also increases with increasing temperature according to Henry's law and with increasing the gas–liquid contact time either by reducing the gas flow rate from 100 to 25 mL min−1 or increasing the microporous tube length from 3.5 to 14 cm. Finally, the performances of this modular formaldehyde generator are compared and discussed with those reported in the scientific literature or commercialised by manufacturers. The technique developed here is the only one allowing to operate with a low flow rate such as 25 to 100 mL min−1 while generating a wide range of concentrations (10–1000 µg m−3) with very good accuracy. [ABSTRACT FROM AUTHOR]

The present field campaign was conducted in two French primary schools for 5 weeks, where the experimental conditions were modified every week. During the first week, the classrooms were empty and not occupied, whereas the furniture was added the second week. For the three last weeks, the classrooms were normally occupied by students and various scenarios of ventilation were applied. BTEX concentrations were monitored by using novel portable pre-industrial prototypes with low gas and energy consumption, which worked continuously and operated in near real time with a time resolution of 10 min. The BTEX concentrations were compared to CO2 measurements since the latter is commonly considered as a confinement indicator. In both schools, BTEX were not detected during the absence of students indicating that neither building materials nor furniture emit such compounds. Once the schools occupied by students, BTEX have been detected from time to time, and their concentrations ranged as follows: 0-12 ppb (benzene); 0-29 ppb (toluene), 0-4 ppb (ethylbenzene), 0-11 ppb (m/p-xylenes), and 0-10 ppb (o-xylene) excluding huge values due to paint emissions in one of the schools. Toluene was found to be strongly correlated to high levels of CO2, showing that it was emitted by internal students activities scheduled at the end of mornings. On the contrary, benzene peak was not correlated to high values of CO2, suggesting that it comes from external sources. [ABSTRACT FROM AUTHOR]

New efficient approaches to the characterization of fly ash and particulate matter (PM) have to be developed in order to better understand their impacts on environment and health. Polycyclic aromatic hydrocarbons (PAH) contained in PM from biomass burning have been identified as genotoxic and cytotoxic, and some tools already exist to quantify their contribution to PM. Optical fluorescence microscopy is proposed as a rapid and relatively economical method to allow the quantification of PAH in different particles emitted from biomass combustion. In this study samples were collected in the flue gas of biomass-combustion facilities with nominal output ranging from 40 kW to 17.3 MW. The fly ash samples were collected with various flue gas treatment devices (multicyclone, baghouse filter, electrostatic precipitator); PM samples were fractionated from the flue gas with a DEKATI® DGI impactor. A method using fluorescence observations (at 470 nm), white-light observations and image processing has been developed with the aim of quantifying fluorescence per sample. Organic components of PM and fly ash, such as PAH, humic-like substances (HULIS) and water-soluble organic carbon (WSOC) were also quantified. Fluorescence microscopy analysis method assessment was first realized with fly ash that was artificially coated with PAH and HULIS. Total amounts of PAH in the three size fractions of actual PM from biomass burning strongly correlated with the intensities of fluorescence. These encouraging results contribute to the development of a faster and cheaper method of quantifying particle-bound PAH. Copyright 2015 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

In this work, a novel generator of gas mixtures previously numerically investigated and based on axial gas pulses coupled to a micromixer has been conceived, manufactured, and validated. Standard gaseous pollutant mixtures and pure nitrogen or pure air were introduced in a microdevice designed to generate alternating axial gas pulses which were downstream homogenized by means of a multi-stage modular micromixer. The dilution, and therefore the final pollutant concentration, was controlled by two parameters: the ratio between the times of each of the two gas pulses and the partial pressure of the pollutant(s) mixture added to the device. The gas mixture generator was coupled to an analyzer to monitor the concentration of aromatic pollutants. The response time was optimized to be lower than 2 min in accordance with the analytical instrument. The quantity of pollutants measured at the micromixer's outlet increased linearly with the expected gas concentration of 3.7–100 ppb generated by this novel microfluidic generator and fitted perfectly with those obtained by a reference gas dilution bench. At 5 ppb, the precision on the concentration generated is close to that obtained with the conventional gas mixing bench, i.e., around 10%. [ABSTRACT FROM AUTHOR]

Deep-UV absorption spectrometry for detection of toxic airborne gases, for instance, Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX) has drawn considerable attention owing to its high sensitivity and reliability. However, the development of a deep-UV absorbance detector having good sensitivity, portability, and a low-volume gas cell with applicability for a micro Gas Chromatography (μGC) is challenging. Herein we present a novel, self-referenced, and portable deep-UV absorbance detector with a microliter (275 μL) gas cell having minimal dead volume. It has excellent compatibility with μGC for detection of individual BTEX components in a mixed sample at a sub-ppm level. The design consists of the latest, portable, and cost-effective optical and electronic components, i.e., deep-UV LED, hollow-core waveguide, and photodiodes. The detector directly measures the absorbance values in volts using an integrated circuit with a log-ratio amplifier. The prototype was tested with direct injection of toluene-N2 (1.5 ppm to 50 ppm) and good linearity (R2 = 0.99) with a limit of detection of 196 ppb was obtained. The absorbance detector with μGC setup was tested with a BTEX mixture in N2 at different GC column temperatures. All the BTEX species were sequentially separated and detected with an individual peak for a concentration range of 2.5 ppm to 10 ppm. [ABSTRACT FROM AUTHOR]

In Beirut–Rafic Hariri International Airport (RHIA), airport employees stay at least 12 h inside the airport's buildings and suffer from respiratory symptoms. Additionally, direct openings exist between the apron and the arrivals hall providing a pathway for contaminated air to enter the buildings. Hence, we study the impact of Beirut–RHIA's activities on the indoor air of the arrivals hall (impact on employees and passengers) during June, November, and October 2014. Due to their impacts on air quality and human health, assessing of the concentrations of nitrogen dioxide (NO2) and Volatile Organic Compounds (VOCs) was the target of our study by using gas chromatographic techniques (GC-MS and GC-FID) for VOCs and calorimetric methods for NO2 concentrations. NO2 levels indicated a probable hazard to the health of passengers and employees, while measured VOC levels did not present any risks except for acrolein. This is the first study to assess the speciation of a large number of VOCs (46 VOCs) for airport indoor air while revealing a very interesting correlation between aircraft number and the concentrations of VOC groups (namely heavy alkanes, aldehydes and ketones, and monoaromatics). Moreover, this is the first study in Lebanon to assess the speciation of a large number of VOCs in indoor air. [ABSTRACT FROM AUTHOR]

The emergence of new super-insulated buildings to reduce energy consumption can lead to a degradation of the indoor air quality. While some studies were carried out to assess the air quality in these super-insulated buildings, they were usually focused on the measurement of gas phase pollutants such as carbon dioxide and volatile organic compounds. This work reports the first measurements of Polycyclic Aromatic Hydrocarbons (PAHs) associated with particles as a function of time and particle size in a low-energy building. The airborne particles were collected indoors and outdoors over three to four days of sampling using two three-stage cascade impactors allowing to sample simultaneously particles with aerodynamic diameter Dae > 10 µm, 2.5 µm < Dae < 10 µm, 1 µm < Dae < 2.5 µm, and Dae < 1 µm. The 16 US-EPA priority PAHs were then extracted and quantified by high-performance liquid chromatography (HPLC) coupled to fluorescence detection. The resulting total particle concentrations were low, in the ranges 3.73 to 9.66 and 0.60 to 8.83 µg m-3 for indoors and outdoors, respectively. Thirteen PAHs were always detected in all the samples. The total PAH concentrations varied between 290 and 415 pg m−3 depending on the particle size, the environment (indoors or outdoors) and the sampling period considered. More interestingly, the temporal variations of individual PAHs highlighted that high molecular weight PAHs were mainly associated to the finest particles and some of them exhibited similar temporal behaviors, suggesting a common emission source. The indoor-to-outdoor concentration ratios of individual PAH were usually found close to or less than 1, except during the event combining rainy conditions and limited indoor ventilation rate. [ABSTRACT FROM AUTHOR]

This paper describes a compact microfluidic analytical device in a closed-circuit developed for the detection of low airborne formaldehyde levels. The detection is based on the passive trapping of gaseous formaldehyde through a microporous tube into the acetylacetone solution, the derivative reaction of formaldehyde with acetylacetone to form 3,5-Diacetyl-1,4-dihydrolutidine (DDL) and the detection of DDL by fluorescence. The recirculation mode of the analytical device means that the concentration measurement is carried out by quantification of the signal increase in the liquid mixture over time, the instantaneous signal increase rate being proportional to the surrounding gaseous formaldehyde concentration. The response of this novel microdevice is found to be linear in the range 0–278 µg m−3. The reagent volume needed is flexible and depends on the desired analytical resolution time and the concentration of gaseous formaldehyde in the environment. Indeed, if either the gaseous concentration of formaldehyde is high or the reagent volume is low, the fluorescence signal of this recirculating liquid solution will increase very rapidly. Consequently, the sensitivity simultaneously depends on both the reagent volume and the temporal resolution. Considering a reagent volume of 6 mL, the hourly and daily detection limits are 2 and 0.08 µg m−3, respectively, while the reagent autonomy is more than 4 days the airborne formaldehyde concentration does not exceed 50 µg m−3 as it is usually the case in domestic or public indoor environments. [ABSTRACT FROM AUTHOR]

Successful development of a micro-total-analysis system (µTAS, lab-on-a-chip) is strictly related to the degree of miniaturization, integration, autonomy, sensitivity, selectivity, and repeatability of its detector. Fluorescence sensing is an optical detection method used for a large variety of biological and chemical assays, and its full integration within lab-on-a-chip devices remains a challenge. Important achievements were reported during the last few years, including improvements of previously reported methodologies, as well as new integration strategies. However, a universal paradigm remains elusive. This review considers achievements in the field of fluorescence sensing miniaturization, starting from off-chip approaches, representing miniaturized versions of their lab counter-parts, continuing gradually with strategies that aim to fully integrate fluorescence detection on-chip, and reporting the results around integration strategies based on optical-fiber-based designs, optical layer integrated designs, CMOS-based fluorescence sensing, and organic electronics. Further successful development in this field would enable the implementation of sensing networks in specific environments that, when coupled to Internet-of-Things (IoT) and artificial intelligence (AI), could provide real-time data collection and, therefore, revolutionize fields like health, environmental, and industrial sensing. [ABSTRACT FROM AUTHOR]

Formaldehyde (HCHO), a chemical compound used in the fabrication process of a broad range of household products, is present indoors as an airborne pollutant due to its high volatility caused by its low boiling point ( T = − 19 °C). Miniaturization of analytical systems towards palm-held devices has the potential to provide more efficient and more sensitive tools for real-time monitoring of this hazardous air pollutant. This work presents the initial steps and results of the prototyping process towards on-chip integration of HCHO sensing, based on the Hantzsch reaction coupled to the fluorescence optical sensing methodology. This challenge was divided into two individually addressed problems: (1) efficient airborne HCHO trapping into a microfluidic context and (2) 3,5–diacetyl-1,4-dihydrolutidine (DDL) molecular sensing in low interrogation volumes. Part (2) was addressed in this paper by proposing, fabricating, and testing a fluorescence detection system based on an ultra-low light Complementary metal-oxide-semiconductor (CMOS) image sensor. Two three-layer fluidic cell configurations (quartz–SU-8–quartz and silicon–SU-8–quartz) were tested, with both possessing a 3.5 µL interrogation volume. Finally, the CMOS-based fluorescence system proved the capability to detect an initial 10 µg/L formaldehyde concentration fully derivatized into DDL for both the quartz and silicon fluidic cells, but with a higher signal-to-noise ratio (SNR) for the silicon fluidic cell ( S N R s i l i c o n = 6.1 ) when compared to the quartz fluidic cell ( S N R q u a r t z = 4.9 ). The signal intensity enhancement in the silicon fluidic cell was mainly due to the silicon absorption coefficient at the excitation wavelength,   a (λ a b s = 420   nm) = 5 × 10 4   cm − 1 , which is approximately five times higher than the absorption coefficient at the fluorescence emission wavelength, a (λ e m = 515   nm) = 9.25 × 10 3   cm − 1 . [ABSTRACT FROM AUTHOR]

Formaldehyde (HCHO), a chemical compound used in the fabrication process of a broad range of household products, is present indoors as an airborne pollutant due to its high volatility caused by its low boiling point ( T = − 19 °C). Miniaturization of analytical systems towards palm-held devices has the potential to provide more efficient and more sensitive tools for real-time monitoring of this hazardous air pollutant. This work presents the initial steps and results of the prototyping process towards on-chip integration of HCHO sensing, based on the Hantzsch reaction coupled to the fluorescence optical sensing methodology. This challenge was divided into two individually addressed problems: (1) efficient airborne HCHO trapping into a microfluidic context and (2) 3,5–diacetyl-1,4-dihydrolutidine (DDL) molecular sensing in low interrogation volumes. Part (2) was addressed in this paper by proposing, fabricating, and testing a fluorescence detection system based on an ultra-low light Complementary metal-oxide-semiconductor (CMOS) image sensor. Two three-layer fluidic cell configurations (quartz–SU-8–quartz and silicon–SU-8–quartz) were tested, with both possessing a 3.5 µL interrogation volume. Finally, the CMOS-based fluorescence system proved the capability to detect an initial 10 µg/L formaldehyde concentration fully derivatized into DDL for both the quartz and silicon fluidic cells, but with a higher signal-to-noise ratio (SNR) for the silicon fluidic cell ( S N R s i l i c o n = 6.1 ) when compared to the quartz fluidic cell ( S N R q u a r t z = 4.9 ). The signal intensity enhancement in the silicon fluidic cell was mainly due to the silicon absorption coefficient at the excitation wavelength,   a (λ a b s = 420   nm) = 5 × 10 4   cm − 1 , which is approximately five times higher than the absorption coefficient at the fluorescence emission wavelength, a (λ e m = 515   nm) = 9.25 × 10 3   cm − 1 . [ABSTRACT FROM AUTHOR]

Several gas molecules of environmental and domestic significance exhibit a strong deep-UV absorption. Therefore, a sensitive and a selective gas detector based on this unique molecular property (i.e., absorption at a specific wavelength) can be developed using deep-UV absorption spectrophotometry. UV absorption spectrometry provides a highly sensitive, reliable, self-referenced, and selective approach for gas sensing. This review article addresses the recent progress in the application of deep-UV absorption for gas sensing owing to its inherent features and tremendous potentials. Applications, advancements, and challenges related to UV emission sources, gas cells, and UV photodetectors are assessed and compared. We present the relevant theoretical aspects and challenges associated with the development of portable sensitive spectrophotometer. Finally, the applications of UV absorption spectrometry for ozone, NO2, SO2, and aromatic organic compounds during the last decades are discussed and compared. A portable UV absorption spectrophotometer can be developed by using LEDs, hollow core waveguides (HCW), and UV photodetectors (i.e., photodiodes). LED provides a portable UV emission source with low power input, low-intensity drifts, low cost, and ease of alignment. It is a quasi-chromatic UV source and covers the absorption band of molecules without optical filters for absorbance measurement of a target analyte. HCWs can be applied as a miniature gas cell for guiding UV radiation for measurement of low gas concentrations. Photodiodes, on the other hand, offer a portable UV photodetector with excellent spectral selectivity with visible rejection, minimal dark current, linearity, and resistance against UV-aging. [ABSTRACT FROM AUTHOR]

The emergence of new super-insulated buildings to reduce energy consumption places the quality of indoor air at the center of the debate. Among the indoor air pollutants, aldehydes are often present, and formaldehyde is of major interest regarding its multiple sources and its health impact. Therefore, French regulations expect to reduce formaldehyde concentrations below 10 μg m−3 in public buildings by 2023. Formaldehyde and other aldehydes were measured for two weeks during an intensive field campaign conducted in a school recently built and equipped with programmable dual-flow ventilation. Aldehydes were monitored with the ISO 16000-3 reference method based on sampling with 2,4-dinitrophenylhydrazine (DNPH) tubes while formaldehyde concentration was continuously measured by using a sensitive near real-time formaldehyde microanalyzer with a detection limit of 1 µg m−3. Formaldehyde was the major aldehyde. Its concentrations varied in the range of 2–25 µg m−3 and decreased by half when mechanical ventilation was ON, while the other ones were always below 5 µg m−3. In addition, an excellent agreement was observed between the different analytical techniques deployed to quantify formaldehyde levels. The microanalyzer was able to measure fast variations of formaldehyde concentration in the studied room, according to the building's ventilation periods. [ABSTRACT FROM AUTHOR]

This paper describes a compact microfluidic analytical device developed for the detection of low airborne formaldehyde concentrations. This microdevice was based on a three-step analysis, i.e., the passive gaseous formaldehyde uptake using a microporous membrane into an acetylacetone solution, the derivatization with acetylacetone to form 3,5-diacetyl-1,4-dihydrolutidine, and the quantification of the latter using fluorescence detection. For a rapid and easier implementation, a cylindrical geometry of the microporous element was considered to perform laboratory-controlled experiments with known formaldehyde concentrations and to establish the proof of concept. This work reports the evaluation of the uptake performance according to the microporous tube length, the liquid flow rate inside the tube, the gas flow rate outside the tube, and the gaseous formaldehyde concentration. A 10.0 cm microporous tube combined with a gas flow rate of 250 NmL/min (normal milliliters per minute) and a liquid flow rate of 17 µL/min were found to be the optimized conditions. In these experimental conditions, the fluorescence signal increased linearly with the gaseous formaldehyde concentration in the range 0–118 µg/m3, with the detection limit being estimated as 0.13 µg/m3 when considering a signal-to-noise ratio of 3. [ABSTRACT FROM AUTHOR]

Government regulations and environmental conditions are pushing the development of improved miniaturized gas analyzers for volatile organic compounds. One of the many detectors used for gas analysis is the photoionization detector (PID). This paper presents the design and characterization of a microfluidic photoionization detector (or µPID) fabricated using micro milling and electrical discharge machining techniques. This device has no glue and facilitates easy replacement of components. Two materials and fabrication techniques are proposed to produce a layer on the electrodes to protect from ultraviolet (UV) light and possible signal noise generation. Three different microchannels are tested experimentally and their results are compared. The channel with highest electrode area (31.17 mm²) and higher volume (6.47 µL) produces the highest raw signal and the corresponding estimated detection limit is 0.6 ppm for toluene without any amplification unit. [ABSTRACT FROM AUTHOR]

A simple deep-ultraviolet (UV) absorption spectrophotometer based on ultraviolet light-emitting diode (UV LED) was developed for the detection of air-borne toluene with a good sensitivity. A fiber-coupled deep UV-LED was employed as a light source, and a spectrometer was used as a detector with a gas cell in between. 3D printed opto-fluidics connectors were designed to integrate the gas flow with UV light. Two types of hollow core waveguides (HCW) were tested as gas cells: a glass capillary tube with aluminum-coated inner walls and an aluminum capillary tube. The setup was tested for different toluene concentrations (10–100 ppm), and a linear relationship was observed with sensitivities of 0.20 mA·U/ppm and 0.32 mA·U/ppm for the glass and aluminum HCWs, respectively. The corresponding limits of detection were found to be 8.1 ppm and 12.4 ppm, respectively. [ABSTRACT FROM AUTHOR]

Following the fast development of microfluidics over the last decade, the need for methods for mixing two gases in flow at an overall flow rate ranging from 1 to 100 NmL·min−1 with programmable mixing ratios has been quickly increasing in many fields of application, especially in the calibration of analytical devices such as air pollution sensors. This work investigates numerically the mixing of pure gas pulses at flow rates in the range 1–100 NmL·min−1 in a newly designed multi-stage and modular micromixer composed of 4 buffer tanks of 300 µL each per stage. Results indicate that, for a 1 s pulse of pure gas (formaldehyde) followed by a 9 s pulse of pure carrier gas (air), that is a pulses ratio of 1/10, an effective mixing up to 94–96% can be readily obtained at the exit of the micromixer. This is achieved in less than 20 s for any flow rate ranging from 1 to 100 NmL·min−1 simply by adjusting the number of stages, 1 to 16 respectively. By using an already diluted gas bottle containing 100 ppm of a given compound in an inert gas same as the carrier gas, concentrations ranging from 10 to 90 ppm should be obtained by adjusting the pulses ratio between 1/10 and 9/10 respectively. [ABSTRACT FROM AUTHOR]

In this work, a compact gas chromatograph prototype for near real-time benzene, toluene, ethylbenzene and xylenes (BTEX) detection at sub-ppb levels has been developed. The system is composed of an aluminium preconcentrator (PC) filled with Basolite C300, a 20 m long Rxi-624 capillary column and a photoionization detector. The performance of the device has been evaluated in terms of adsorption capacity, linearity and sensitivity. Initially, PC breakthrough time for an equimolar 1 ppm BTEX mixture has been determined showing a remarkable capacity of the adsorbent to quantitatively trap BTEX even at high concentrations. Then, a highly linear relationship between sample volume and peak area has been obtained for all compounds by injecting 100-ppb samples with volumes ranging from 5–80 mL. Linear plots were also observed when calibration was conducted in the range 0–100 ppb using a 20 mL sampling volume implying a total analysis time of 19 min. Corresponding detection limits of 0.20, 0.26, 0.49, 0.80 and 1.70 ppb have been determined for benzene, toluene, ethylbenzene, m/p-xylenes and o-xylene, respectively. These experimental results highlight the potential applications of our device to monitor indoor or outdoor air quality. [ABSTRACT FROM AUTHOR]