Ppb Ozone Research Articles

Modeling impacts of indoor environmental variables on secondary organic aerosol formation

There are numerous air pollutants indoors including chemicals emitted from building environments as well as outdoor-origin species due to human activities. Despite the significance of indoor air quality, the atmospheric process indoors is not well studied. In this study, the secondary organic aerosol (SOA) formation from the oxidation of α-pinene blended with toluene was simulated under varying indoor environments (lamps, NO2, ozone, and inorganic seed) using the UNIfied Partitioning Aerosol Reaction (UNIPAR) model. Explicitly predicted lumping species produced during the atmospheric oxidation of precursors are used in the model and they process multiphase partitioning and aerosol phase reactions. The performance of the model was demonstrated using indoor chamber experiments in both dark conditions (ozonolysis) and light conditions with commercialized fluorescent or LED lamps. α-Pinene SOA was dominated by ozonolysis even in the presence of indoor light. Toluene, which is known to be photochemically processed, was oxidized in the dark condition with OH radicals that were derived from ozonolysis products of α-pinene. At given dark simulation conditions (10 ppb α-pinene, 30 ppb ozone, and 50 ppb of toluene), toluene contributed 15 % of SOA mass. α-Pinene SOA was insensitive to hygroscopicity of inorganic seed, but toluene blended with α-pinene increased the sensitivity to seed conditions due to the formation of oligomeric matter via aqueous reactions of reactive toluene products. In the presence of NO2. α-pinene SOA formation significantly increased with increasing NO2 owing to the reaction of α-pinene with nitrate radicals to form low volatile products. This study concludes that ozone and NO2, intruded from outdoors to indoors, effectively oxidize terpenes and furthermore aromatic hydrocarbons with OH radicals originating from ozonolysis of terpenes. The reaction paths with ozone and nitrate radicals are more effective at forming SOA than that with OH radical under the indoor light condition with commercialized lamps.

Optimizing air quality and health Co-benefits of mitigation technologies in China: An integrated assessment

Carbon mitigation technologies lead to air quality improvement and health co-benefits, while the practical effects of the technologies are dependent on the energy composition, technological advancements, and economic development. In China, mitigation technologies such as end-of-pipe treatment, renewable energy adoption, carbon capture and storage (CCS), and sector electrification demonstrate significant promise in meeting carbon reduction targets. However, the optimization of these technologies for maximum co-benefits remains unclear. Here, we employ an integrated assessment model (AIM/enduse, CAM-chem, IMED|HEL) to analyze air quality shifts and their corresponding health and economic impacts at the provincial level in China within the two-degree target. Our findings reveal that a combination of end-of-pipe technology, renewable energy utilization, and electrification yields the most promising results in air quality improvement, with a reduction of fine particulate matter (PM2.5) by −34.6 μg m−3 and ozone by −18.3 ppb in 2050 compared to the reference scenario. In contrast, CCS technology demonstrates comparatively modest improvements in air quality (−9.4 μg m−3 for PM2.5 and −2.4 ppb for ozone) and cumulative premature deaths reduction (−3.4 million from 2010 to 2050) compared to the end-of-pipe scenario. Notably, densely populated regions such as Henan, Hebei, Shandong, and Sichuan experience the most health and economic benefits. This study aims to project effective future mitigation technologies and climate policies on air quality improvement and carbon mitigation. Furthermore, it seeks to delineate detailed provincial-level air pollution control strategies, offering valuable guidance for policymakers and stakeholders in pursuing sustainable and health-conscious environmental management.

Facile Synthesis of Amorphous MnOx Catalysts for Efficient Ozone Elimination in Domestic Refrigerators

ABSTRACT Amorphous manganese oxide catalysts, aimed at efficient ozone removal in refrigerators, were synthesized using a simple redox method. Factors like crystallinity of structure, textural properties, and Fe doping significantly affect the catalyst’s performance. The Fe-doped KMF-250 showcased outstanding ozone decomposition capabilities, efficiently eliminating 10,000 ppb of ozone at an average rate of ca. 13.3 , under conditions of 6 °C and 36% relative humidity in a refrigerator chamber (144 L). Moreover, this catalyst exhibits extraordinary stability, outperforming existing commercial catalysts in terms of both durability and efficiency. The incorporation of even a minimal amount of Fe (0.84 wt%) considerably raised the amount of low-valence Mn, resulting in more crystal defects and oxygen vacancies. The existence of Fe in MnOx was also found playing an important role in promoting the desorption of the oxygen species and enhancing the oxygen mobility to generate oxygen vacancies, both of which contribute to the quick recovery of the catalyst. The catalyst’s large specific surface area, combined with optimal Fe doping, are crucial for its superior catalytic performance. This research delivers a potent MnOx catalyst suitable for ozone removal in refrigerators and viable for mass production.

Influence of Ventilation on Formation and Growth of 1-20 nm Particles via Ozone-Human Chemistry.

Ozone reaction with human surfaces is an important source of ultrafine particles indoors. However, 1-20 nm particles generated from ozone-human chemistry, which mark the first step of particle formation and growth, remain understudied. Ventilation and indoor air movement could have important implications for these processes. Therefore, in a controlled-climate chamber, we measured ultrafine particles initiated from ozone-human chemistry and their dependence on the air change rate (ACR, 0.5, 1.5, and 3 h-1) and operation of mixing fans (on and off). Concurrently, we measured volatile organic compounds (VOCs) and explored the correlation between particles and gas-phase products. At 25-30 ppb ozone levels, humans generated 0.2-7.7 × 1012 of 1-3 nm, 0-7.2 × 1012 of 3-10 nm, and 0-1.3 × 1012 of 10-20 nm particles per person per hour depending on the ACR and mixing fan operation. Size-dependent particle growth and formation rates increased with higher ACR. The operation of mixing fans suppressed the particle formation and growth, owing to enhanced surface deposition of the newly formed particles and their precursors. Correlation analyses revealed complex interactions between the particles and VOCs initiated by ozone-human chemistry. The results imply that ventilation and indoor air movement may have a more significant influence on particle dynamics and fate relative to indoor chemistry.

Highly responsive and selective ozone sensor based on Ga doped ZnS-ZnO composite sprayed films.

Ozone detection is currently the subject of wide scientific and technological research, motivated by its harmful impact on human safety, environment and health. With the aim of searching for new highly sensitive materials for ozone detection, Ga-doped ZnS and ZnS-ZnO films were deposited by a spray pyrolysis technique. The obtained films were annealed at 400 °C for two hours. The ozone sensing properties were investigated by measuring the sensor resistance for several ozone concentrations ranging from 30 to 120 ppb. The sensor response reveals a dependence on the gallium concentration. The best response was obtained with 4% doping gallium. The sensitivity is 4.5 ppb-1 at 260 °C and the response to 30 ppb ozone is 150. Moreover, the sensor shows high performance such as good selectivity and fast rapidity.

Reduced graphene oxide-cuprous oxide composites for low concentration ozone detection

In this research, cuprous oxide (pristine Cu2O) and rGO (reduced graphene oxide)-doped Cu2O were prepared using a simple synthetic route and adopted as sensitive materials for ozone detection. The microstructural, morphological and compositional properties of as-prepared samples have been analyzed by several characterization techniques including X-ray diffraction (XRD), High resolution transmission electron microscopy (HRTEM), Energy dispersive spectrometer (EDS), UV-Visible spectrophotometer (UV–vis), Multi-functional field emission scanning electron microscope (FESEM), X-ray Photoelectron Spectroscopy (XPS) and Brunauer-Emmett-Teller (BET). Meanwhile, the sensing features of as-prepared samples have been investigated carefully and the as-prepared 0.5 wt% rGO-Cu2O exhibited best ozone sensing properties, such as high stability, sensitivity and selectivity. It can be found that the response value of 0.5 wt% rGO-Cu2O-based sensor towards 20 ppb ozone and 1 ppm ozone were 9.2/1734, respectively, and the corresponding response and recovery times were 11/64 s and 11/411 s, respectively. More importantly, the detection limit of the 0.5 wt% rGO-Cu2O sensor was as low as 0.1 ppb. Furthermore, the possible mechanism for the enhanced sensing performance of the as-prepared rGO-Cu2O has been discussed.

Investigation of meteorological conditions and BrO during ozone depletion events in Ny-Ålesund between 2010 and 2021

Abstract. During polar spring, ozone depletion events (ODEs) are often observed in combination with bromine explosion events (BEEs) in Ny-Ålesund. In this study, two long-term ozone data sets (2010–2021) from ozonesonde launches and in situ ozone measurements have been evaluated between March and May of each year to study ODEs in Ny-Ålesund. Ozone concentrations below 15 ppb were marked as ODEs. We applied a composite analysis to evaluate tropospheric BrO retrieved from satellite data and the prevailing meteorological conditions during these events. During ODEs, both data sets show a blocking situation with a low-pressure anomaly over the Barents Sea and anomalously high pressure in the Icelandic Low area, leading to transport of cold polar air from the north to Ny-Ålesund with negative temperature and positive BrO anomalies found around Svalbard. In addition, a higher wind speed and a higher, less stable boundary layer are noticed, supporting the assumption that ODEs often occur in combination with polar cyclones. Applying a 20 ppb ozone threshold value to tag ODEs resulted in only a slight attenuation of the BrO and meteorological anomalies compared to the 15 ppb threshold. Monthly analysis showed that BrO and meteorological anomalies are weakening from March to May. Therefore, ODEs associated with low-pressure systems, high wind speeds, and blowing snow more likely occur in early spring, while ODEs associated with low wind speed and stable boundary layer meteorological conditions seem to occur more often in late spring. Annual evaluations showed similar weather patterns for several years, matching the overall result of the composite analysis. However, some years show different meteorological patterns deviating from the results of the mean analysis. Finally, an ODE case study from the beginning of April 2020 in Ny-Ålesund is presented, where ozone was depleted for 2 consecutive days in combination with increased BrO values. The meteorological conditions are representative of the results of the composite analysis. A low-pressure system arrived from the northeast to Svalbard, resulting in high wind speeds with blowing snow and transport of cold polar air from the north.

Chemical Fate of Oils on Indoor Surfaces: Ozonolysis and Peroxidation.

Unsaturated triglycerides found in food and skin oils are reactive in ambient air. However, the chemical fate of such compounds has not been well characterized in genuine indoor environments. Here, we monitored the aging of oil coatings on glass surfaces over a range of environmental conditions, using mass spectrometry, nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR) techniques. Upon room air exposure (up to 17 ppb ozone), the characteristic ozonolysis products, secondary ozonides, were observed on surfaces near the cooking area of a commercial kitchen, along with condensed-phase aldehydes. In an office setting, ozonolysis is also the dominant degradation pathway for oil films exposed to air. However, for indoor enclosed spaces such as drawers, the depleted air flow makes lipid autoxidation more favorable after an induction period of a few days. Forming hydroperoxides as the major primary products, this radical-mediated peroxidation behavior is accelerated by indoor direct sunlight, but the initiation step in dark settings is still unclear. These results are in accord with radical measurements, indicating that indoor photooxidation facilitates radical formation on surfaces. Overall, many intermediate and end products observed are reactive oxygen species (ROS) that may induce oxidative stress in human bodies. Given that these species can be widely found on both food and household surfaces, their toxicological properties are worth further attention.

Year-long ground-based observations of bromine oxide over Bharati Station, Antarctica

Bromine chemistry plays an important role in tropospheric ozone depletion events in polar regions. Autocatalytic reactions lead to bromine explosion events, causing ozone depletion to near-zero levels in the polar troposphere. Bromine chemistry over Antarctica is not fully understood, and ground-based observations are scarce. This work presents year-long observations of bromine oxide (BrO) over the Bharati station (69.41°S, 76.19°E) using Multi-axis Differential Optical Absorption Spectroscopy (MAX-DOAS) from December 2018 to February 2020. The results show that elevated BrO mixing ratios were found during spring (September), with a maximum value of 10.21 ± 4.38 pptv for clear sky conditions and 33.15 ± 2.23 pptv for cloudy conditions. BrO was not observed above the detection limit (∼3 × 1013 molecule cm−2) outside spring on clear days. In general, lower mixing ratios were observed on clear days over Bharati compared to stations in West Antarctica. This indicates a different source strength over East Antarctica compared to West Antarctica. BrO vertical column densities were high during spring, with a maximum value of 1.34 ± 0.35 × 1014 molecule cm−2. The vertical profiles of the BrO mixing ratios show a peak at the surface during spring (average of 6.5 ± 1.91 pptv), decreasing sharply with altitude. Back trajectories show that air masses passing over the first year ice showed higher BrO, although factors such as meteorology play an important role in determining the absolute levels. Using a box model, we show that bromine chemistry can deplete as much as 2.15 ppb of ozone in a day at the Bharati Station on clear days, which shows that it does not lead to complete ozone depletion events over Bharati.

Remediation of Thirdhand Tobacco Smoke with Ozone: Probing Deep Reservoirs in Carpets.

We assessed the efficacy of ozonation as an indoor remediation strategy by evaluating how a carpet serves as a sink and long-term source of thirdhand tobacco smoke (THS) while protecting contaminants absorbed in deep reservoirs by scavenging ozone. Specimens from unused carpet that was exposed to smoke in the lab ("fresh THS") and contaminated carpets retrieved from smokers' homes ("aged THS") were treated with 1000 ppb ozone in bench-scale tests. Nicotine was partially removed from fresh THS specimens by volatilization and oxidation, but it was not significantly eliminated from aged THS samples. By contrast, most of the 24 polycyclic aromatic hydrocarbons detected in both samples were partially removed by ozone. One of the home-aged carpets was installed in an 18 m3 room-sized chamber, where its nicotine emission rate was 950 ng day-1 m-2. In a typical home, such daily emissions could amount to a non-negligible fraction of the nicotine released by smoking one cigarette. The operation of a commercial ozone generator for a total duration of 156 min, reaching concentrations up to 10,000 ppb, did not significantly reduce the carpet nicotine loading (26-122 mg m-2). Ozone reacted primarily with carpet fibers, rather than with THS, leading to short-term emissions of aldehydes and aerosol particles. Hence, by being absorbed deeply into carpet fibers, THS constituents can be partially shielded from ozonation.

Impacts of usage conditions on performance of ozone removal devices in ventilation systems

Ozone removal devices can be exposed to a wide range of environmental and operating conditions in building ventilation systems, which can affect their ozone removal performance. We evaluated activated carbon and metal oxide filters under varying temperature, relative humidity, ozone concentration, and air speed, as well as after no-ozone periods. Results on new activated carbon filters show that decreasing relative humidity from 50% to 30% decreased single-pass efficiency by 6% relatively at 70 ppb ozone and nearly doubled the degradation rate at 500 ppb ozone; increasing relative humidity to 80% had no effect on efficiency; increasing temperature from 25 to 35 °C increased single-pass efficiency at 70 ppb ozone by 11% relatively and decelerated aging by 22% relatively at 500 ppb ozone. The observed dual effect of water indicates that water can facilitate chemical reactions between ozone and activated carbon, but it can block reactive sites on activated carbon at a high relative humidity. The tested activated carbon and manganese dioxide filters were not sensitive to ozone concentration ranging from 35 to 500 ppb. Activated carbon filters recovered 1%–3% efficiency after 16-h ozone breaks probably due to decomposition of surface oxygen complexes. An air speed increase from 0.6 to 2.7 m/s significantly decreased the single-pass efficiency of all tested devices. A plug flow reactor model proved useful in predicting the impact of air speed on single-pass efficiency as well as the non-linear relationship between single-pass efficiency and time.

Modeling of the Atmospheric Process of Cyanobacterial Toxins in Algal Aerosol

The degradation of microcystin-LR (MC-LR) in cyanobacterial aerosol with atmospheric oxidants, such as ozone and OH radicals, was predicted by the Harmful Algal Aerosol Reaction (HAAR) model. The ozonolysis of MC-LR in cyanobacterial aerosol at nighttime and its photooxidation during the daytime was observed in an outdoor chamber. The HAAR model simulates the impact of humidity and aerosol compositions on MC-LR decay. In the model, gas-particle partitioning of atmospheric oxidants onto algal aerosol was kinetically treated using the absorption and desorption processes. In the model simulation, the half-life of MC-LR estimated with its ozonolysis rate constant (3 × 10–11cc/molecules/s) is 4.6 h ± 0.92 at 66 ppb ozone. With the reaction rate constant for MC-LR with OH radicals (6 × 10–7 cc/molecules/s), the estimated half-life of MC-LR during daytime under Florida’s typical summer sunlight is 6 minutes, suggesting that the reaction with OH radicals dominates daytime MC-LR decay. Under moderate sunlight with a typical wind speed (9.2 km/h), the dispersion and HAAR models predict that 25% of aerosolized MC-LR undergoes the atmospheric process within 0.92 km from a bloom source in Florida’s largest lake, suggesting the critical role of the atmospheric oxidation of MC-LR decay.

Design, calibration, and testing of a mobile sensor system for air pollution and built environment data collection: The urban scanner platform

This paper describes a mobile air pollution sampling system, the Urban Scanner, which aims at gathering dense spatiotemporal air quality data to support urban air quality and exposure science. Urban Scanner comprises custom vehicle-mounted sensors for air pollution, meteorology, and built environment data collection (low-cost sensors, wind anemometer, 360 deg camera, LIDAR, GPS) as well as a server to store, process, and map all gathered geo-referenced sensory information. Two levels of sensor calibration were implemented, both in a chamber and in the field, against reference instrumentation. Chamber tests and a set of mathematical tools were developed to correct for sensor noise (wavelet denoising), misalignment (linear and nonlinear), and hysteresis removal. Models based on chamber testing were further refined based on field co-location. While field co-location captures natural changes in air pollution and meteorology, chamber tests allow for simulating fast transitions in these variables, like the transitions experienced by a mobile sensor in an urban environment. The best suite of models achieved an R2 higher than 0.9 between sensor output and reference station observations and an RMSE of 2.88 ppb for nitrogen dioxide and 4.03 ppb for ozone. A mobile sampling campaign was conducted in the city of Toronto, Canada, to further test Urban Scanner. We observe that the platform adequately captures spatial and temporal variability in urban air pollution, leading to the development of land-use regression models with high explanatory power.

A severe weather system accompanied by a stratospheric intrusion during unusual warm winter in 2015 over the South Africa: An initial synoptic analysis

This study aims to highlight the abnormally warm winter experienced in South Africa during 2015. This work also investigates the synoptic and dynamic aspects of the specific severe weather system (late July 2015) which affected the western, southern, and eastern provinces including some parts in the Northern Cape, Western Cape, Lesotho, KwaZulu-Natal, and Eastern Cape. This is followed by an investigation of the stratospheric-tropospheric transport of the high-level ozone associated with a deep cut-off low weather system over the southern and central regions of South Africa which occurred on 24–25 July 2015. The case characteristics of the dynamical analysis of the weather system associated with a stratospheric-tropospheric intrusion was also determined. This research illustrated that this system was accompanied by deep upper and mid-tropospheric troughs which developed over the eastern part of the country. This resulted in tropopause folding controlled by the upper meandered tropospheric jet stream axis in the east of the upper and mid-tropospheric troughs. This caused the strong downward injection of stratospheric ozone-rich air with a maximum ozone value of 320 ppb at a level of 300 hPa observed using MERRA reanalysis data in the north of the North Cape province together with very dry higher tropospheric air at 300 hPa. In the lower troposphere, ozone levels as high as 61 ppb at 850 hPa were found within these intrusions in the northern-central region during the active cut-off low weather system. Using the Aura-Microwave Limb Sounder (MLS) to determine the vertical ozone profile at different pressure levels over South Africa indicated that a maximum value of approximately 270 ppb ozone was recorded on 24 July 2015. The observational measurements from this study show good agreement with the findings from the reanalysis models together with the results taken from the MERRA database for the specific day of peak ozone activity.

Indoor ozone removal and deposition using unactivated solid and liquid coffee.

Managing indoor ozone levels is important because ozone is a hazardous pollutant that has adverse effects on human health. Coffee is a popular daily beverage, and thus, coffee beans and spent coffee grounds are common in many places such as offices, homes, aircraft, cafeterias, and such. The most common material used to remove ozone is activated carbon which can be made from coffee beans or spent coffee grounds with proper activation processes. This paper presents a novel idea: to remove ozone at the level of an indoor environment using unactivated coffee products. This paper examines the ozone removal efficiency and the ozone deposition velocity at 130 ppb ozone for two types of coffee: solid coffee (powder) and liquid coffee (beverage). The activated carbon, the deionized water, and the seawater are also included for comparison and validation purposes. The tests show that the fine coffee powder has a removal efficiency of 58.5% and a deposition velocity of 0.62 cm/s. The liquid coffee has a removal efficiency of 34.4% and a deposition velocity of 0.23 cm/s. The chemical inspections indicate that the oxidation reactions with the carbohydrates in solid coffee and the metal/mineral elements in liquid coffee are responsible for ozone removal. These results have confirmed that ozone removal via coffee is effective, controlling indoor air quality by coffee products is thus becoming possible.

Gas Phase and Gas-Solid Interface Ozonolysis of Nitrogen Containing Alkenes: Nitroalkenes, Enamines, and Nitroenamines.

Emerging contaminants are of concern due to their rapidly increasing numbers and potential ecological and human health effects. In this study, the synergistic effects of the presence of multifunctional nitro, amino and carbon–carbon double bond (C=C) groups on the gas phase ozonolysis in O2 or at the air/solid interface were investigated using five simple model compounds. The gas phase ozonolysis rate constants at 296 K were (3.5 ± 0.9) × 10–20 cm3 molecule–1 s–1 for 2-methyl-1-nitroprop-1-ene and (6.8 ± 0.8) × 10–19 cm3 molecule–1 s–1 for 4-methyl-4-nitro-1-pentene, with lifetimes of 134 and 7 days in the presence of 100 ppb ozone in the atmosphere, respectively. The rate constants for gas phase E-N,N-dimethyl-1-propenylamine and N,N-dimethylallylamine reactions with ozone were too fast (>10–18 cm3 molecule–1 s–1) to be measured, implying lifetimes of less than 5 days. A multiphase kinetics model (KM-GAP) was used to probe the gas–solid kinetics of 1-dimethylamino-2-nitroethylene, yielding a rate constant for the surface reaction of 1.8 × 10–9 cm2 molecule–1 s–1 and in the bulk 1× 10–16 cm3 molecule–1 s–1. These results show that a nitro group attached to the C=C lowers the gas phase rate constant by 2–3 orders of magnitude compared to the simple alkenes, while amino groups have the opposite effect. The presence of both groups provides counterbalancing effects. Products with deleterious health effects including dimethylformamide and formaldehyde were identified by FTIR. The identified products differentiate whether the initial site of ozone attack is C=C and/or the amino group. This study provides a basis for predicting the environmental fates of emerging contaminants and shows that both the toxicity of both the parent compounds and the products should be taken into account in assessing their environmental impacts.

Identification of odour compounds emitted by wooden boards with the presence of indoor ozone

Indoor volatile organic compounds (VOCs) produce odours that reduce perceived air quality. Furnitures and indoor decoration are the main sources of indoor VOCs. Considering the increase in outdoor and indoor ozone concentrations, ozone, as a strong oxidant, can have an impact on indoor odour. Herein, medium-density fibreboard (MDF) and flame retarded plywood (FRP) were selected as experimental materials, and gas chromatography-olfactory-mass spectrometry (GC-O-MS) was performed to identify the odour compounds emitted by materials with and without 100 ppb ozone. MDF1, MDF2 and FRP emitted 6, 8 and 14 different odour compounds, respectively. MDF2 emitted moderate grassy and sour odours. FRP emitted moderate grassy, fruity, rubber and pine incense odours. After 8 h of exposure to ozone at a concentration of 100 ppb, MDF1, MDF2 and FRP emitted different odour compounds, respectively. The characteristic odours of MDF were aggravated. Except for pine incense odour, the intensity of other characteristic odours of FRP was weakened. Through cluster heatmap analysis and principal component analysis, the characteristic odour compounds of MDF and FRP were further clarified. Introducing a SOI model, the results showed that ozone exposure increased the SOI of MDF1 and MDF2 from 3.34 to 4.22 and from 4.11 to 4.44, respectively, and that the odour intensity of FRP decreased from 3.78 to 3.41. It can be determined that ozone may have opposite effects on the odour emitted by different materials. The results clarify the target pollutants for odour control research on wooden board emissions.

Chemistry and human exposure implications of secondary organic aerosol production from indoor terpene ozonolysis.

Surface cleaning using commercial disinfectants, which has recently increased during the coronavirus disease 2019 pandemic, can generate secondary indoor pollutants both in gas and aerosol phases. It can also affect indoor air quality and health, especially for workers repeatedly exposed to disinfectants. Here, we cleaned the floor of a mechanically ventilated office room using a commercial cleaner while concurrently measuring gas-phase precursors, oxidants, radicals, secondary oxidation products, and aerosols in real-time; these were detected within minutes after cleaner application. During cleaning, indoor monoterpene concentrations exceeded outdoor concentrations by two orders of magnitude, increasing the rate of ozonolysis under low (<10 ppb) ozone levels. High number concentrations of freshly nucleated sub–10-nm particles (≥105 cm−3) resulted in respiratory tract deposited dose rates comparable to or exceeding that of inhalation of vehicle-associated aerosols.

Establishing an air-liquid interface exposure system for exposure of lung cells to gases

Objective Growing interest in non-animal-based models has led to the development of devices to expose cells to airborne substances. Cells/tissues grown at the air-liquid interface (ALI) are more representative of lung cells/tissues in vivo compared to submerged cell cultures. Additionally, airborne exposures should allow for closer modeling of human lung toxicity. However, such exposures present technical challenges, including maintaining optimal cell health, and establishing consistent exposure monitoring and control. We aimed to establish a reliable system and procedures for cell exposures to gases at the ALI. Methods We tested and adapted a horizontal-flow ALI-exposure system to verify and optimize temperature, humidity/condensation, and control of atmosphere delivery. We measured temperature and relative humidity (RH) throughout the system, including at the outlet (surrogate measures) and at the well, and evaluated viability of lung epithelial A549 cells under control conditions. Exposure stability, dosimetry, and toxicity were tested using ozone. Results Temperatures measured directly above wells vs. outflow differed; using above-well temperature enabled determination of near-well RH. Under optimized conditions, the viability of A549 cells exposed to clean air (2 h) in the ALI system was unchanged from incubator-grown cells. In-well ozone levels, determined through reaction with potassium indigotrisulfonate, confirmed dosing. Cells exposed to 200 ppb ozone at the ALI presented reduced viability, while submerged cells did not. Conclusion Our results emphasize the importance of monitoring near-well conditions rather than relying on surrogate measures. Rigorous assessment of ALI exposure conditions led to procedures for reproducible exposure of cells to gases.

Room temperature optical detection of ultra-low ozone concentration using photoluminescent ZnO nanohybrids

The highly sensitive room temperature (RT) photoluminescence (PL) emission of zinc oxide (ZnO) in the presence of ozone (O3) is demonstrated for the first time. The optical materials examined consist of commercially available luminescent ZnO nanoparticles (ZnO NPs), as well as ZnO/polymer nanohybrids, with different polymeric matrices (poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA) and polydimethylsiloxane (PDMS)), which are excited with a UV pulsed laser source (λex= 248 nm, τex= 15 ns).The PL emission of the ZnO NPs and their nanohybrids (ZnO/PPEGMA, ZnO/PDMS) is investigated upon exposure to ozone gas and their sensing characteristics, such as response (%ΔI), reversibility, response/recovery time are determined, as a function of ozone concentration in synthetic air.Sensing tests revealed that all materials allowed the detection of ozone gas in a wide range of concentrations in synthetic air (1600 down to 50 ppb), with the ZnO/PDMS nanohybrid exhibiting the highest response and recovery time of about 50 s (at 750 ppb ozone concentration) and 100 s, respectively. Finally, its remarkable optical response of about 20% at 50 ppb ozone concentration at RT, underlines the great potential of the ZnO/PDMS nanohybrid to serve as a sensitive probe for ozone detection, thereby introducing new developments in optosensing applications.