Air Concentrations Research Articles

Conductometric H2S Sensors Based on TiO2 Nanoparticles.

High-performance hydrogen sulfide (H2S) sensors are mandatory for many industrial applications. However, the development of H2S sensors still remains a challenge for researchers. In this work, we report the study of a TiO2-based conductometric sensor for H2S monitoring at low concentrations. TiO2 samples were first synthesized using the sol-gel route, annealed at different temperatures (400 and 600 °C), and thoroughly characterized to evaluate their morphological and microstructural properties. Scanning electronic microscopy, Raman scattering, X-ray diffraction, and FTIR spectroscopy have demonstrated the formation of clusters of pure anatase in the TiO2 phase. Increasing the calcination temperature to 600 °C enhanced TiO2 crystallinity and particle size (from 11 nm to 51 nm), accompanied by the transition to the rutile phase and a slight decrease in band gap (3.31 eV for 400 °C to 3.26 eV for 600 °C). Sensing tests demonstrate that TiO2 annealed at 400 °C displays good performances (sensor response Ra/Rg of ~3.3 at 2.5 ppm and fast response/recovery of 8 and 23 s, respectively) for the detection of H2S at low concentrations in air.

Frailty Was Associated With Atmospheric NO2 Levels: A Geospatial Approach.

Recent evidence has linked air pollution with frailty, yet little is known about the role of NO2 in this association. Our aim was to assess the association between frailty and NO2 air concentrations in Mexican older adults. We used georeferenced data from the population-based Nutrition and Health Survey in Mexico (NHNS) 2021, representative of national and subnational regions, to measure a frailty index based on 31 health deficits in adults aged 50 and older. Air pollution due to NO2 concentrations was estimated from satellite images validated with data from surface-level stations. Maps were produced using Jensen's Natural break method. The association of frailty and NO2 concentrations was measured using the frailty index (multivariate fractional response logit regression) and a frailty binary variable (frailty index [FI] ≥0.36, multivariate logit regression). There was a positive and significant association of the frailty index with the NO2 concentrations, adjusting for age, sex, urban and rural area, years of education, socioeconomic status, living arrangement, particulate matter smaller than 2.5 microns, and indoor pollution. For each standard deviation increase in NO2 concentrations measured 10 years before the survey, the odds of being frail were 15% higher, and the frailty index was 14.5% higher. The fraction of frailty attributable to NO2 exposure ranged from 1.8% to 23.5% according to different scenarios. Frailty was positively associated with exposure to NO2 concentrations. Mapping frailty and its associated factors like NO2 air concentrations can contribute to the design of targeted pro-healthy aging policies.

Estimation of Formaldehyde Levels in Indoor Air of Gross Anatomy Laboratory

Introduction: Medical students spend majority of their times in Anatomy lab during their first year MBBS. Formalin has attracted attention as a health hazard for students and instructors as formalin concentrations in air of gross anatomy laboratories are often higher than permissible limits. Despite the known toxicity of formaldehyde and its potential health effects, laboratory workers and others have little enthusiasm for reducing or replacing the formaldehyde working solution Materials and Methods: The FA concentration (in ppm) of indoor air in Anatomy laboratory was measured using a SMILEDRIVE Portable air quality pollution meter. The mean FA concentration was measured after 1 hour after the cadavers were shifted to dissection table at three different levels a. At the level of floor b. At the level of roof c. 2 feets above the table (Breathing Zone of medical students) Three air samples from the breathing zones were tested and mean concentration of FA was taken with exhaust fan on at the level of roof and recorded as a. S1R- First immediately before the dissection (Zero hour), b. S2R- Second sample was collected after one hour after first sample was taken (First hour) and c. S3R- Third sample after two hours after first sample was taken (Second hour). Three air samples from the breathing zones were tested and mean concentration of FA was taken with exhaust fan on at the level of floor and recorded as a. S1F- First immediately before the dissection (Zero hour), b. S2F- Second sample was collected after one hour after first sample was taken (First hour) and c. S3F- Third sample after two hours after first sample was taken (Second hour). Results: The vertical distribution of FA was measured by taking the mean air samples at the level of floor, at roof level and about 2 feet above dissection table immediately after the cadavers were shifted to tables. It was found to be about 0.54ppm at the level of floor, 0.52 at the breathing zone and 0.51 ppm at roof level. The FA concentration was highest at the level of floor and least at the level of roof. On comparing S2F and S2R the p value was 1.335. Thus, it was not statistically significant. On comparing S3F and S3R the p value was 0.411. Thus, it was not statistically significant. Conclusion: The mean FA at the level of floor was 0.54 ppm. At the breathing zone the mean FA concentration was 0.51 ppm before the dissection was started. Exhaust fans at the level of roof were switched on and the second sample was taken after 1 hour. The FA concentration was 0.23 ppm. Third sample was taken at 2nd hour and FA concentration was 0.11 ppm. The exhaust fans at the level of floor were switched on. The air samples were measured at 0, 1st and 2nd hour at breathing zones. It was 0.51, 0.31 and 0,15 ppm respectively.

Risk assessment for perfluorooctanoic acid (PFOA) in air, blood serum and water: mortality from liver and kidney disease

BackgroundCancer and non-cancer associations have been observed with PFAS (perfluoroalkyl and polyfluoroalkyl) substances in the general population, in populations from locally contaminated environments and in exposed workers.MethodsA quantitative risk assessment...

Radon Concentration in Air and Evaluation of the Radiation Dose in Villages near Shizhuyuan, Southern Hunan, China

Radon is one of the important natural sources of radiation and pollutants. When radon and its progeny are inhaled by the human body, they can cause radiation damage to the respiratory system and can lead to lung cancer. Indoor and outdoor radon concentrations were measured in five villages near Shizhuyuan W-polymetallic deposit using a RAD7 detector; moreover, the corresponding radiation dose and lifetime risk probability were evaluated. The results show that the average value of indoor radon concentration was 216.6±121.1 Bq m−3, which is above the worldwide average indoor radon level of 40 Bq m−3, and the average outdoor value was 34.6±13.4 Bq m−3, which is higher than the worldwide outdoor average of 10 Bq m−3. A total of 42% of the dwellings investigated in our study had a higher radon level than the Chinese permissible indoor radon level of 200 Bq m−3. The total annual effective dose ranged from 5.21 mSv y−1 to 49.38 mSv y−1, with an average value of 14.63 mSv y−1, which is higher than the ICRP recommended value of 3–10 mSv y−1. This average total dose value corresponds to an average lifetime risk probability of 5.8% for residents in the whole study area.

Mercury from Icelandic geothermal activity: High enrichments in soils, low emissions to the atmosphere

Geothermal activity is a natural source of mercury (Hg) to surface environments, but its contributions as part of the larger geogenic flux to the global Hg budget are poorly understood, in part due to large geographic gaps in emissions data where no measurements have been made. In this study we report the results of a field campaign over 2021 and 2022 on the highly active volcanic island country of Iceland. Six geothermal sites across the country were investigated for soil gaseous elemental mercury (GEM) and total Hg (THg) concentrations through a series of measurements made across the diffuse degassing surface. At 10 cm depth, soil GEM concentrations were often hundreds and in some cases thousands of times higher than ambient surface air concentrations. Geothermal soils were also highly enriched in THg due to the sorption of hydrothermal Hg on the characteristically fine, thermally-altered clays and silts. Soil “hotspots” displayed THg concentrations exceeding 100 µg g−1 comparable to levels in areas heavily contaminated by anthropogenic activity and in Hg-rich mineral soils. Strong correlations were observed between soil GEM, THg and soil temperature, and intensive measurements made at small spatial scales (∼1 m2) demonstrated the representativeness of individual sampling points. By adapting an active sampling gradient method for determining soil–air gas fluxes, we estimate an Icelandic geothermal GEM flux of 1.8 kg a−1 and a total Icelandic GEM flux, including non-geothermal areas, of ∼18 kg a−1. This work shows that Icelandic geothermal activity can generate high GEM and THg concentrations in the local soil environment, but its contribution to global Hg cycling appears to be minor.

Tritium Behavior from Vine to Wine

The hydrogen radioactive isotope, tritium, not only reflects seasonal variation in precipitation but also variations on a local level. To use this radioisotope in authentication and geographical indication procedures, the tritium levels in vines, grapes, and wine were measured in two forms: (1) tissue-free water tritium (TFWT), measured in the free water of the plant or the aqueous phase of the wine; (2) organically bound tritium (OBT), measured in the organic part of the plant or wine (as ethanol). This paper presents the tritium behavior in vines from May to October and in the wine produced from harvested grapes for both tritium forms (TFWT and OBT) in connection with environmental tritium concentrations in air and precipitations during the 2019–2023 vegetation periods near the Râmnicu Vâlcea city. If the tritium of tissue-free water was influenced by precipitation and air humidity during the harvest period, the organically bound tritium recorded a maximum level with a delay of 1–2 months compared with tritium’s seasonal variation in precipitation and air. The tritium values of early mean in precipitation and ethanol from wine were approximately an average value of 11 TU for all 5 years of observations.

Effects of legacy mining on mercury concentrations in conifer needles and mushrooms in northern Palatinate, Germany

Due to integrated pollution prevention and control measures and the reduced burning of coal, air concentrations of mercury (Hg0) are currently levelling off. In the future, however, evasion from land surfaces will probably reverse this trend. Reasons are the rising temperatures and the loss of forest cover caused by calamities, droughts, storms and wildfires. Plant leaves constitute an important matrix for the accumulation of gaseous mercury and uptake and re-volatilisation by plants depends on the species, the vitality and the age and morphology of leaf organs. It has been shown that older conifer needles show higher concentrations than young needles and Hg accumulation is increasing throughout the season.In present study, we collected branches from Norway Spruce (Picea abies) in a former cinnabar mining region in Northern Palatinate, where artisanal and small-scale mining left innumerable waste dumps. While mining, smelting and processing of the ores were terminated during WWII, high total mercury concentrations remained in the top soils locally, with presumably only small fractions being plant available. In the lab, up to seven needle age classes were analysed. 1000 needle weights increased with age and as expected, also the Hg concentrations were elevated in the older needles. Needle concentrations were higher than those reported from other national biomonitoring programs confirming the regional imprint from legacy mercury. To complement our biomonitoring study, we collected edible mushrooms in former mining areas. Hg concentrations in most samples exceeded the EU maximum residue levels (MRL), while only a few broke the existing cadmium and lead limits. Tolerable weekly intake (TWI) for inorganic mercury would be surpassed with the consumption of a small portion of mushrooms. Further studies should be performed on the outgassing of Hg from mine wastes and the incorporation of Hg in the local food web, including its methylation and biomagnification.

Widespread occurrence of pesticides in low-income housing

BackgroundLow socioeconomic status (SES) residents living in social housing, which is subsidized by government or government-funded agencies, may have higher exposures to pesticides used in indoor residences since pesticides are applied due to structural deficiencies, poor maintenance, etc.ObjectiveTo estimate exposure of residents in low-SES social housing built in the 1970s to legacy and current-use pesticides and to investigate factors related to exposures.MethodsTwenty-eight particle-phase pesticides were measured in the indoor air of 46 units in seven low-income social housing, multi-unit residential buildings (MURBs) in Toronto, Canada using portable air cleaners deployed for 1 week in 2017. Pesticides analyzed were legacy and current use in the classes: organochlorines, organophosphates, pyrethroids, and strobilurins.ResultsAt least one pesticide was detected in 89% of the units with detection frequencies (DF) for individual pesticides of up to 50%, including legacy organochlorines and current-use pesticides. Current-use pyrethroids had the highest DF and concentrations, with the highest particle-phase concentration for pyrethrin I at 32,000 pg/m3. Heptachlor, restricted for use in Canada in 1985, had the highest estimated maximum total air (particle plus gas phase) concentration of 443,000 pg/m3. Heptachlor, lindane, endosulfan I, chlorothalonil, allethrin, and permethrin (except in one study) had higher concentrations than those measured in low-income residences reported elsewhere. In addition to the intentional use of pesticides to control pests and their use in building materials and paints, tobacco smoking was significantly correlated with the concentrations of five pesticides used on tobacco crops. The distribution of pesticides with high DF in individual buildings suggested that pest eradication programs by the building management and/or pesticide use by residents were the major sources of measured pesticides.ImpactLow-income social housing fills a much-needed demand, but the residences are prone to pest infestation and hence pesticide use. We found exposure to at least 1 of 28 particle-phase pesticides in 89% of all 46 units tested, with the highest DF and concentrations for current-use pyrethroids and long-banned organochlorines (e.g., DDT, heptachlor) due to very high persistence indoors. Also measured were several pesticides not registered for use indoors, e.g., strobilurins used to treat building materials and pesticides used on tobacco crops. These results, which are the first Canadian data for most pesticides indoors, show widespread exposure to numerous pesticides.

Removal efficiency of restroom ventilation revisited for short-term evaluation

Ventilation efficiency or contaminant removal efficiency is often evaluated using the ratio between the concentrations in the exhaust air and the room air. This ratio does not truly represent the expectation of ventilation in restrooms, where dynamic airflow fields and sources are more typical. This study focuses on a short-term (10 min) pollutant removal percentage in a residential restroom featuring a dynamic airflow field, particularly with the onset of window-induced stack ventilation during toilet uses. Thirteen ventilation scenarios of a residential restroom were studied using the numerical method that was validated by a mock-up experiment. The scenarios differed in the operation of the exhaust fan and window. Results show that the 10-min pollutant removal percentage of a typical exhaust ventilation system at 10 h-1 air change rate (ACH) is only 68.5%. Under exhaust ventilation, opening the window can introduce both adverse short circuit and favorable stack ventilation depending on the difference between the indoor and outdoor temperatures. As the temperature difference increases from 0 to 12.5 °C, the removal percentage increases from below 50%, a drop due to short circuit, to above 98% thanks to a tripled ventilation rate. The human thermal plume has notable effect on the removal percentage, but its effect can be neglected with the presence of stack ventilation. The hybrid ventilation strategy has impact on perceived air quality and thermal comfort. When the outdoor air is colder, opening the window under exhaust ventilation may increase the current sitting user’s exposure to the self-produced pollutants but can reduce the exposure of the next immediate standing user. In addition, opening the window in cold days will make the toilet user thermally uncomfortable with reduced local temperatures and increased airflow velocities. The study highlights the importance of using the short-term removal percentage to evaluate the performance of restroom ventilation.

A Multidisciplinary Approach to the Evaluation of Air Quality and Thermo-Hygrometric Conditions for the Conservation of Heritage Manuscripts and Printed Materials in Historic Buildings: A Case Study of the Sala del Dottorato of the University of Perugia as a Model for Heritage Preservation and Occupants’ Comfort

The Sala del Dottorato (Hall of Graduates) is a magnificent library in the University of Perugia which plays the double role of providing optimal conservation of valuable books and manuscripts while also hosting important events. This double role is closely connected to contrasting indoor microclimatic conditions. This paper presents the results of a multidisciplinary study, begun in 2019, which investigates optimal conditions for the conservation of volumes by monitoring thermo-hygrometric and air quality parameters. The study describes the current conditions of the Hall (in terms of air temperature, relative humidity and concentration of CO2), highlighting critical aspects, defining strategies for their mitigation and control, and outlining future developments. Improvement measures relate to the installation of a permanent monitoring system with alarm settings and data storage, technical interventions on the windows, and the restoration of several volumes. The paper shows the importance of monitoring as an instrument of control in real time and provides guidelines for management to be implemented according to indoor microclimatic conditions.

Bubble linking anterior growth strategy to prepare hydrogel tubes with different range, branch and voyager function

Hydrogel tubes (HTs) represent a significant facet of hydrogel morphology. Nevertheless, the continuous, rapid, and facile fabrication of hydrogel tubes remains a formidable challenge. In this study, we introduce a novel technique named as Anterior Growth (AG) for the continuous preparation of HTs. This innovative approach employs air bubbles as guidance to direct the growth of polyvinyl alcohol (PVA) HTs crosslinked by copper ions in alkaline solution. Various factors that affect the sizes of HTs from micrometers to millimeters have been explored, including gauge of needles, air bubble volumes, injection rates, and concentrations of NaOH, copper nitrate and PVA. Single HT with various sizes can be easily fabricated by simply adjusting injection rates. The reversibility of PVA-Cu2+ crosslinking makes it possible to produce HTs with multiple branches in a convenient way by generating an orifice out of the HT wall and then repeating the growing process. Inspired by plant thigmotropism, HTs can be guided to grow along designed shapes such as different angles and patterns by combination of air bubble and silicone rubble substrates. Remarkably, this method allows HTs to serve as voyagers navigating intricate flow channels with a projected trajectory, indicating the capabilities of patterning and traversing complex channels. To further application, AG allows other materials to prepare HTs such as sodium alginate or more, showcasing excellent practical value.

Effect of oxy-fuel combustion with different O2/CO2 fractions on the pulverized coal combustion mechanism and heat transfer characteristics in rotary kilns: A numerical simulation study

Oxy-fuel combustion combined with carbon capture and storage is the most effective and direct technology to achieve carbon neutrality in cement industry. In this work, numerical simulation was employed to investigate the effects of air combustion and oxy-fuel combustion with different O2/CO2 fractions on the airflow field, temperature field, pulverized coal combustion mechanism, heat transfer characteristics and NOx distribution in rotary kiln. The results show that the airflow field under different conditions has no significant change. When transitioning from the air condition to the oxy-fuel condition, the ignition point of pulverized coal extends backward by approximately 0.2 m. The maximum temperature decreases from 2306 K to 2052 K, and the temperature becomes more uniform. As the oxygen concentration in the primary air increases, both the maximum and average temperatures gradually rise, and the flame length shortens from 25.4 m to 24.16 m. In the rotary kiln, the locations of char oxidation and gasification reactions differ, but these reaction locations remain consistent under different conditions. Under oxy-fuel conditions, the oxidation rate and oxidation proportion of char decrease, while the gasification rate and gasification proportion of char increase, resulting in a shortening of the burnout distance of coal from 34.5 m to 31.3 m. With increasing oxygen concentration in the primary air, the rates of char oxidation and gasification gradually rise, further shortening the burnout distance. The decrease in temperature at the front end of the rotary kiln under oxy-fuel conditions reduces the total heat transfer in the burning zone by 15 %. When the oxygen content of the primary air is 70 %, it ensures stable calcination of clinker. Additionally, under oxy-fuel conditions, the NOx generation is significantly reduced. With the increase of oxygen concentration in the primary air, the NOx concentration at the outlet decreases slightly from 451 ppm to 406 ppm, due to the increase in kiln temperature that favors the reduction of fuel NOx.

Biomarkers of occupational benzene exposure: A Systematic Review to estimate the exposure levels and individual susceptibility at low doses.

Benzene is associated with diverse occupational and public health hazards. It exhibits an ability to rapidlypermeate the skin and contaminate water and food sources, leading to dermal and ingestion exposures. Despite numerous studies examining the associations between benzene and various indicators of harm, the findings have yielded inconsistent results. Furthermore, relying solely on air concentration as a measure of benzene exposure is limited, as it fails to account for internal exposure dose and individual susceptibility. This study aimed to conduct a comprehensive review in order to present current knowledge on benzene biomarkers and their significance in evaluating exposure levels and associated health hazards. The search methodology adhered to the PRISMA guidelines and involved the application of specific inclusion and exclusion criteria across multiple databases including PubMed, Embase, and Web of Science. Two researchers independently extracted and evaluated the relevant data based on predetermined criteria. Following the screening process, a total of 80 articles were considered eligible out of the initially retrieved 1053 articles after undergoing screening and assessment for inclusion. As the level of exposure decreased, specific biomarkers demonstrated a gradual increase in limitations, including heightened background concentrations and vulnerability to confounding factors. The advancement of sampling and analysis techniques will yield new biomarkers. Additionally, when conducting practical work, it is crucial to employ a comprehensive utilization of diverse biomarkers while excluding individual metabolic variations and combined exposure factors.

Fate and transport of viable Bacillus anthracis simulant spores in ambient air during a large outdoor decontamination field exercise

ABSTRACT The Wide Area Demonstration (WAD) was a field exercise conducted under the U.S. EPA’s Analysis of Coastal Operational Resiliency program, in conjunction with the U.S. Department of Homeland Security and the U.S. Coast Guard. The purpose of the WAD was to operationalize at field scale aspects of remediation activities that would occur following an outdoor release of Bacillus anthracis spores, including sampling and analysis, decontamination, data management, and waste management. The WAD was conducted in May 2022 at Fort Walker (formerly known as Fort A.P. Hill) and utilized Bacillus atrophaeus as a benign simulant for B. anthracis. B. atrophaeus spores were inoculated onto the study area at the beginning of the study, and air samples were collected daily during each of the different phases of the WAD using Dry Filter Units (DFUs). Ten DFU air samplers were placed at the perimeter of the study area to collect bioaerosols onto two parallel 47-mm diameter polyester felt filters, which were then subsequently analyzed in a microbiological laboratory for the quantification of B. atrophaeus. The study demonstrated the use of DFUs as a rugged and robust bioaerosol collection device. The results indicated that the highest B. atrophaeus spore air concentrations (up to ~ 5 colony forming units/m3) occurred at the beginning of the demonstration (e.g. during inoculation and characterization sampling phases) and generally downwind from the test site, suggesting transport of the spores was occurring from the study area. Very few B. atrophaeus spores were detected in the air after several weeks and following decontamination of exterior surfaces, thus providing an indication of the site decontamination procedures’ effectiveness. No B. atrophaeus spores were detected in any of the blank or background samples. Implications: Following an incident involving a release of Bacillus anthracis spores or other biological threat agent into the outdoor environment, understanding the factors that may affect the bioagent’s fate and transport can help predict viable contaminant spread via the ambient air. This paper provides scientific data for the first time on ambient air concentrations of bacterial spores over time and location during different phases of a field test in which Bacillus atrophaeus (surrogate for B. anthracis) spores were released outdoors as part of a full-scale study on sampling and decontamination in an urban environment. This study advances the knowledge related to the fate and transport of bacterial spores (such as those causing anthrax disease) as an aerosol in the outdoor environment over the course of three weeks in a mock urban environment and has exposure and health risk implications. The highest spore air concentrations occurred at the beginning of the study (e.g. during inoculation of surfaces and characterization sampling), and in the downwind direction, but diminished over time; few B. atrophaeus spores were detected in the air after several weeks and following decontamination. Therefore, in an actual incident, potential reaerosolization of the microorganism and subsequent transport in the air during surface sampling and remediation efforts should be considered for determining exclusion zone locations and estimating potential risk to neighboring communities. The data also provide evidence suggesting that the large-scale decontamination of outdoor surfaces may reduce air concentrations of the bioagent, which is important since exposure of B. anthracis via inhalation is a primary concern.

Indoor concentrations of radioactive aerosols from nuclear accidents.

In previous studies, some of the important factors that affect the spread of radioactive aerosols into indoors were considered. The studies were based on a new CFD approach and provided good descriptions for the deposition of aerosol particles inside small spaces and the penetration of aerosols into buildings through wall cracks. In this article, an application of those studies is implemented, where all the graphical relations that are required to estimate the indoor concentrations of radioactive aerosols from nuclear accidents are provided. This includes the deposition velocities, deposition rate, and the penetration factor. Particular interest is in the Fukushima-Daiichi nuclear power plant accident that took place in Japan in 2011. The aerosols carrying the radioiodine iodine-131 and the radiocesium cesium-134 and cesium-137 are studied. Based on the model's assumptions, and assuming steady-state air concentrations, the radioactive aerosols' concentrations in indoor air are about 97% of the concentrations in outdoor air. The applications demonstrate the model to be convenient and practical.

Aminated reduced graphene oxide-carbon nanotube composite gas sensors for ammonia recognition

Composites based on carbon nanomaterials exhibit many advantageous properties for gas sensing, such as high and fast response, room-temperature operation, and tailoring sensitivity by energy level engineering. However, only the first attempts to employ such chemosensors for gas-sensing applications have been made. In this work, an on-chip multisensor array of carboxylated carbon nanotubes (CNT), aminated reduced graphene oxide (rGO-Am), and CNT/rGO-Am nanocomposite was fabricated using a simple and low-cost spray deposition method. The CNT/rGO-Am sensor demonstrated a fast and high response to NH3 in dry air at low (25 ppm) and high (400 ppm) concentrations of 70 and 115 %, respectively. The response to NH3 in humid air increased and reached 160 % at 400 ppm. The chemosensor exhibited high sensitivity and selectivity toward ammonia with a low detection limit estimated to be below 0.2 ppb. Linear discriminant analysis of the sensor responses to different concentrations of NH3, dry and humid air revealed better discrimination when CNT/rGO-Am composites were used in combination with CNT and rGO-Am sensors in an array. This study demonstrates that composite sensors with junctions between carbon nanomaterials have great potential for practical applications in fast and selective gas detection at room temperature and different humidity.

SiNx/SiO2-Based Fabry-Perot Interferometer on Sapphire for Near-UV Optical Gas Sensing of Formaldehyde in Air.

Fabry-Perot interferometers (FPIs), comprising foundry-compatible dielectric thin films on sapphire wafer substrates, were investigated for possible use in chemical sensing. Specifically, structures comprising two vertically stacked distributed Bragg reflectors (DBRs), with the lower DBR between a sapphire substrate and a silicon-oxide (SiO2) resonator layer and the other DBR on top of this resonator layer, were investigated for operation in the near-ultraviolet (near-UV) range. The DBRs are composed of a stack of nitride-rich silicon-nitride (SiNx) layers for the higher index and SiO2 layers for the lower index. An exemplary application would be formaldehyde detection at sub-ppm concentrations in air, using UV absorption spectroscopy in the 300-360 nm band, while providing spectral selectivity against the main interfering gases, notably NO2 and O3. Although SiNx thin films are conventionally used only for visible and near-infrared optical wavelengths (above 450 nm) because of high absorbance at lower wavelengths, this work shows that nitride-rich SiNx is suitable for near-UV wavelengths. The interplay between spectral absorbance, transmittance and reflectance in a FPI is presented in a comparative study between one FPI design using stoichiometric material (Si3N4) and two designs based on N-rich compositions, SiN1.39 and SiN1.49. Spectral measurements confirm that if the design accounts for phase penetration depth, sufficient performance can be achieved with the SiN1.49-based FPI design for gas absorption spectroscopy in near-UV, with peak transmission at 330 nm of 64%, a free spectral range (FSR) of 20 nm and a full-width half-magnitude spectral resolution (FWHM) of 2 nm.

Spatial assessment of pollutants concentration in air and soils impacted by industrial wastes in lagos state, Nigeria

The mega city of Lagos, Nigeria is plagued by various environmental issues, chief amongst them being environmental pollution induced by poor and disjointed urban industrial waste management practices. This study aimed to identify and quantify the types of urban industrial waste generated in Lagos State. The State plays host to the largest population base in Nigeria with over twenty million people. The study adopted a quasi-experimental design. Soil, industrial waste generation and pollutant levels were determined with the aid of a thermal mass gas flow meter. Industrial wastes were measured in situ using a weighting scale, while surface soil samples were collected at depths of 0–30 cm. Results show that 20% of the industrial waste generated in the metropolis was ignitable (possibility of spontaneous combustion). The results were thereafter compared with international standards on the permissible limits for various pollutants in air and soil of Lagos State. Ikorodu had the greatest contribution of industrial waste generated in Lagos, followed by Ikeja, Oshodi, Ojo/Alaba and Surulere. The implications of these results and findings is that a lot needs to be done in terms of appropriate legislation, enforcement and tracking of industrial waste generation in Lagos State for effective monitoring and implementation of management strategies.

Atmospheric concentrations and potential sources of dioxin-like contaminants to Acadia National Park

Acadia National Park (ANP) is located on Mt. Desert Island, ME on the U.S. Atlantic coast. ANP is routinely a top-ten most popular National Park with over four million visits in 2022. The overall contribution and negative effects of long-range atmospheric transport and local sources of dioxin-like contaminants endangering natural and wildlife resources is unknown. Dioxin-like (DL) contaminants polychlorinated dibenzo-p-dioxins (∑PCDD) and polychlorinated dibenzofurans (∑PCDF), non-ortho coplanar PCBs (∑CP4), and polychlorinated naphthalenes (∑PCNs) were measured at the McFarland Hill air monitoring station (44.37⁰N, 68.26⁰W). On a mass/volume basis, total PCNs averaged 90.9 % (788 fg/m3) of DL contaminants measured annually, with 92.9 % of the collected total in the vapor-phase. Alternatively, total dioxin/furans (∑PCDD/Fs) represented 71.6 % of the total toxic equivalence (∑TEQ) (1.018 fg-TEQ/m3), with 69.7 % in the particulate-phase. Maximum concentrations measured for individual sampling events for ∑PCDD/F, ∑CP4, and ∑PCN were 159 (winter), 139 (summer), and 2100 (autumn), fg/m3 respectively. Whereas the maximum ∑TEQ concentrations for individual sampling events for ∑PCDD/F, ∑CP4, and ∑PCN were 2.8 (autumn), 0.38 (summer), and 0.71 (autumn), fg-TEQ/m3 respectively. Pearson correlations were calculated for ∑PCDD/Fs and ∑PCN particulate/vapor-phase air concentrations and PM2.5 wood smoke “indicator” species. The most significant correlations were observed in autumn for particulate-phase ∑PCDD/Fs suggesting a relationship between visitation-generated combustion sources (campfires and/or waste burning) or climate-change mediated forest fires. Significant Clausius-Clapeyron (C–C) correlations observed for particulate-phase ∑PCDDs (r2 = 0.567) as ambient temperatures decreased suggests a connection between localized domestic heating sources or visitor-based burning of wood/trash resources. Alternatively, highly significant C–C vapor-phase ∑CP4-PCBs correlations (r2 = 0.815) implies that the majority of ∑CP4-PCB loading to ANP is from long-range atmospheric transport processes. Based on these findings, Acadia National Park should be classified as a remote site with minor depositional impacts from ∑PCDD/Fs, ∑CP4-PCBs, and ∑PCN atmospheric transport or local diffuse sources.