Indoor Ozone Research Articles

Reviewing MnOx-based catalysts for decomposition of indoor ozone

Ozone is a highly reactive gas and one of important air pollutants for both indoor and outdoor environments. The Occupational Safety and Health Administration (OSHA) guideline for the ozone level limit at workplaces is 100 ppb for 8-hour exposure and the Health Canada guideline for the residential buildings is 20 ppb for 8 hour exposure. Therefore, applying an ozone removal technology in indoor environments is crucial when outdoor ozone concentration is high and/or where strong ozone emission sources exist. Activated carbon-based filters, thermal oxidation, catalytic oxidation, and photocatalytic oxidation are air treatment technologies that have been applied for ozone removal. Among these technologies, the catalytic oxidation approach showed better results, particularly manganese oxide (MnOx) based catalysts, which can decompose ozone to oxygen at room temperature. The low cost as well as high catalytic activity are among the advantages of MnOx-based catalysts. High specific surface area, high density of oxygen vacancy, high reducibility, low average oxidation state, and low relative humidity are beneficial for ozone decomposition over the catalyst. This review presents the importance of ozone removal from the indoor environments, its exposure issues, and the recent studies on MnOx-based catalyst for ozone decomposition.

Indoor Photochemistry Involving Ozone in Rural Location of Kannur−A Tropical Site in India

This study reports the indoor ozone (O3) pollution in the rural location of Kannur, a tropical site in India, during March 2018 and the influence of their most important determinants. Measurements of indoor O3, NO, NO2 and NOx were carried out in a residential building for a period of one week. Measurements were taken from the kitchen, as it had been identified as the most polluted spot. The background concentrations of O3, NO, NO2 and NOx were also monitored. Indoor O3 originates mainly from the outdoor environment and is also produced from indoor sources. The results show that there is a higher level of indoor O3 during cooking hours. The study indicated that cooking activities in the kitchen had a strong impact on the indoor O3 level. Ozone is an important gaseous pollutant which may lead to severe health problems such as decreased lung function and respiratory symptoms.

Cardiorespiratory responses to low-level ozone exposure: The inDoor Ozone Study in childrEn (DOSE)

BackgroundIndoor air pollution has emerged as a significant environmental and public health concern in recent years. However, evidence regarding the cardiorespiratory effects of indoor ozone is limited, and the underlying biological mechanisms are unclear, especially in children. Our study aimed to assess the cardiorespiratory responses to indoor ozone exposure in children. MethodsA repeated-measure study was conducted in 46 middle-school children in Beijing, China. Real-time concentrations of ozone, along with co-pollutants including particulate matter (PM) and black carbon (BC), were monitored in classrooms from Monday to Friday. Three repeated health measurements of cardiorespiratory functions, including ambulatory electrocardiogram (ECG), blood pressure, fractional exhaled nitric oxide (FeNO) and lung function, were performed on each participant. Mixed-effect models were used to evaluate the effects of indoor ozone exposure. ResultsThe mean (SD) indoor ozone concentration was 8.7 (6.6) ppb during the study period, which was largely below the current guideline and standards. However, even this low-level ozone exposure was associated with reduced cardiac autonomic function and increased heart rate (HR) in children. For instance, per interquartile range (IQR) increase in ozone at 2-hour moving average was associated with −7.8% (95% CI: −9.9%, −5.6%) reduction in standard deviation of all normal-to-normal intervals (SDNN), and 2.6% (95% CI: 1.6%, 3.6%) increment in HR. In addition, the associations were stronger at high BC levels (BC ≥ 3.7 μg/m3). No significant associations were found for airway inflammation and pulmonary function. ConclusionsExposure to low-level indoor ozone that is not associated with respiratory effects was significantly related to disturbed cardiac autonomic function and increased HR in children, which suggested a possible mechanism through which ozone may affect cardiovascular health in children, and indicated more protective measures should be taken to alleviate the acute adverse effects of indoor ozone in this susceptible population.

Contributions of Indoor and Outdoor Sources to Ozone in Residential Buildings in Nanjing.

Ozone has become one of the most serious air pollutants in China in recent years. Since people spend most of their time indoors, the ozone in the indoor environment could be a major factor affecting the occupants’ health. The indoor ozone in residential buildings mainly comes from two sources: outdoor atmosphere and indoor ozone produced by electrical devices. In this study, a typical residence in Nanjing was taken as an example to calculate and compare the contributions of indoor and outdoor sources to ozone in the building. A questionnaire survey about the type, the placement, and the frequency of use of the ozone emission devices was performed to provide the basis for the settings of indoor ozone sources. The multi-zone software CONTAM was used hourly to simulate the ozone concentration in summer and in winter with inner doors either closed or open, and it was noted whether there were ozone emission devices indoors or not. Source contribution was quantified and compared by three methods in this paper: (1) the average indoor/outdoor (I/O) ratio, (2) the I/O ratio frequency, and (3) the ratio of indoor ozone concentration without ozone sources to that with ozone sources. The results showed that the contribution of outdoor sources was much greater than that of indoor sources in summer, but in winter, the frequency of I/O > 1 could reach 55.8% of the total seasonal time, and the ratio of indoor ozone concentration without sources to that with sources could reach as high as 74.3%. This meant that the indoor concentration had the potential to exceed the outdoor. Furthermore, human respiratory exposure in different ages and genders was calculated. It was found that teenagers aged 10–18 years old and female adults had a higher respiratory exposure level.

Indoor ozone estimation from outdoor ozone and LBNL relocatable classroom study data

Lawrence Berkeley National Laboratory (LBNL) conducted a nested, case-crossover-design public school-based study in two different climate regions of California in 2000–2003. This included exploring operating profiles of two mechanical ventilation (HVAC) systems (alternated over a period of approximately nine weeks during 2001 Fall school semester) in pairs of classrooms sited adjacent to one another, equipped with either standard or alternate (low-emissivity) interior finish materials. Our retrospective analysis included inferring estimated indoor ozone concentrations. Because ozone can react with certain indoor pollutants to generate secondary organic aerosols, a mass-balanced based indoor/outdoor ratio expression was used to model indoor ozone to subsequently model indoor particles from possible ozone-initiated chemistry. When Indirect-Direct Evaporative Cooling (IDEC) HVAC was running, surface (especially ceiling) reactions dominated ozone loss processes. When standard Bard heat-pump air-conditioning (HPAC) HVAC system was running, damper setting (air excluded from building envelope), ventilation and/or gas phase reactions accounted for most indoor-outdoor ozone differences. Future research should explore outdoor air and surface chemistry contributions to indoor air pollution.

Ozone in urban China: Impact on mortalities and approaches for establishing indoor guideline concentrations.

Reducing indoor ozone levels may be an effective strategy to reduce total exposure and associated mortality. Here we estimate (a) premature mortalities attributable to ozone for China's urban population ≥25years of age; (b) the fraction of total exposure occurring indoors; and (c) mortalities that can be potentially avoided through meeting current and more stringent indoor ozone standards/guidelines based on 1-hour daily maxima. To estimate ozone-attributable premature mortalities, we used hourly outdoor ozone concentrations measured at 1497 monitoring stations located in 339 Chinese cities and a published concentration-response model. We proceeded to estimate province-specific infiltration factors and co-occurring hourly indoor ozone concentrations. For the year 2015, we estimated that indoor exposures accounted for 59% (95% confidence interval (CI): 26%-79%) of the total ozone exposure that resulted in 70800 (95% CI: 35900-137700) premature all-cause mortalities in urban China. If the current Chinese indoor ozone standards (80ppbv (160µg/m3 ); 56ppbv (112µg/m3 )) were met, the mean estimates of reduction in mortalities would be indistinguishable from zero. With stricter 1-hour indoor ozone guidelines, the expected mortality reductions increase exponentially per unit decrease in indoor ozone. The analysis in this paper should help facilitate formulating present and future indoor ozone guidelines.

Vanadium-doped MnO2 for efficient room-temperature catalytic decomposition of ozone in air

Outdoor or indoor ozone pollution recently regains the attentions due to new findings on its risk even at very low level. The room-temperature catalytic material is key to abate indoor ozone pollution. Here we prepared a series of vanadium-doped MnO2 (V-MnO2) via a one-step hydrothermal redox reaction between MnO4− and Mn2+ with addition of vanadate. The vanadium-doped MnO2 exhibited weaker crystallinity with exposure of high-index facets such as (301), much larger specific surface area, enhanced surface acidity and had lower oxidation state of Mn. Accordingly, the amount of oxygen vacancies was greatly increased, which is not only revealed by H2-TPR and O2-TPD but also confirmed by stronger peroxide signals in electron paramagnetic resonance. V-MnO2(0.15) with the largest specific surface area of 309.8 m2/g not only exhibited stable activity for high concentration of ozone under humid condition, it also showed high ozone removal efficiency when it was coated on the low pressure-drop nonwoven fabric under the real filtration velocity. Thus, vanadium-doping is a facile method to improve the room-temperature activity of MnO2 for indoor ozone decomposition under the humid condition.

Wood stove use and other determinants of personal and indoor exposures to particulate air pollution and ozone among elderly persons in a Northern Suburb.

A six‐month winter‐spring study was conducted in a suburb of the northern European city of Kuopio, Finland, to identify and quantify factors determining daily personal exposure and home indoor levels of fine particulate matter (PM2.5, diameter <2.5 µm) and its light absorption coefficient (PM2.5abs), a proxy for combustion‐derived black carbon. Moreover, determinants of home indoor ozone (O3) concentration were examined. Local central site outdoor, home indoor, and personal daily levels of pollutants were monitored in this suburb among 37 elderly residents. Outdoor concentrations of the pollutants were significant determinants of their levels in home indoor air and personal exposures. Natural ventilation in the detached and row houses increased personal exposure to PM2.5, but not to PM2.5abs, when compared with mechanical ventilation. Only cooking out of the recorded household activities increased indoor PM2.5. The use of a wood stove room heater or wood‐fired sauna stove was associated with elevated concentrations of personal PM2.5 and PM2.5abs, and indoor PM2.5abs. Candle burning increased daily indoor and personal PM2.5abs, and it was also a determinant of indoor ozone level. In conclusion, relatively short‐lasting wood and candle burning of a few hours increased residents’ daily exposure to potentially hazardous, combustion‐derived carbonaceous particulate matter.

How do breath and skin emissions impact indoor air chemistry?

People are an important source of pollution indoors, through activities such as cleaning, and also from "natural" emissions from breath and skin. This paper investigates natural emissions in high-occupancy environments. Model simulations are performed for a school classroom during a typical summer in a polluted urban area. The results show that classroom occupants have a significant impact on indoor ozone, which increases from ~9 to ~20ppb when the pupils leave for lunch and decreases to ~14ppb when they return. The concentrations of 4-OPA, formic acid, and acetic acid formed as oxidation products following skin emissions attained maximum concentrations of 0.8, 0.5, and 0.1ppb, respectively, when pupils were present, increasing from near-zero concentrations in their absence. For acetone, methanol, and ethanol from breath emissions, maximum concentrations were ~22.3, 6.6, and 21.5ppb, respectively, compared to 7.4, 2.1, and 16.9ppb in their absence. A rate of production analysis showed that occupancy reduced oxidant concentrations, while enhancing formation of nitrated organic compounds, owing to the chemistry that follows from increased aldehyde production. Occupancy also changes the peroxy radical composition, with those formed through isoprene oxidation becoming relatively more important, which also has consequences for subsequent oxidant concentrations.

Role of location, season, occupant activity, and chemistry in indoor ozone and nitrogen oxide mixing ratios.

Understanding the oxidizing environment indoors is important for predicting indoor air quality and its impact on human health. We made continuous time-resolved measurements (30 s) of several oxidants and oxidant precursors (collectively referred to as oxidant*): ozone (O3), nitric oxide (NO), and NO2* - the sum of nitrogen dioxide (NO2) and nitrous acid (HONO). These species were measured in three indoor environments - an occupied residence, a chemistry laboratory, and an academic office - in Syracuse, New York, during two seasons in 2017 and 2018. Oxidant* levels differed greatly between the residence, the lab and the office. Indoor-to-outdoor ratios (I/O) of O3 were 0.03 and 0.67 in the residence and office; I/ONO (I/ONO2*) were 11.70 (1.26) in the residence and 0.13 (1.70) in the office. Little seasonal variability was observed in the lab and office, but O3 and NO2* levels in the residence were greater in spring than in winter, while NO levels were lower. Human activities such as cooking and opening patio doors resulted in large changes in oxidant* mixing ratios in the residence. In situ chamber experiments demonstrated that the increase in O3 and NO2* levels during door-open periods was due to a combination of physical mixing between indoor and outdoor air, gas-phase production of NO2 from O3-NO chemistry, and heterogeneous formation of HONO on indoor surfaces. Our results also highlight the importance of chemistry (with NO, alkenes, and surfaces) in O3 mixing ratios in the residence, especially during door-open periods.

Indoor ozone levels, houseplants and peak expiratory flow rates among healthy adults in Taipei, Taiwan

The association between houseplants and indoor air quality improvement has been reported in previous studies. However, the effect of houseplant-emitted isoprene on the association between ozone (O3) formation and respiratory health remains unclear. We recruited 60 adult subjects from 60 houses with or without houseplants (1:1) in Taipei; twelve house visits were conducted in each home throughout 2014. The indoor air pollutants that were measured consisted of particulate matter less than or equal to 2.5 μm in diameter (PM2.5), O3 and isoprene. Peak expiratory flow rate (PEFR) was measured in each study subject during each house visit. Household information was collected by a questionnaire. Mixed-effects models were used to explore the association between indoor air pollution levels and PEFR. We found that the concentrations of O3 and isoprene in houses with houseplants were higher than those in houses without houseplants. In contrast, PM2.5 levels and % predicted PEFR were higher in houses without houseplants than in those with houseplants. Moreover, increased levels of O3 and PM2.5 in houses with houseplants were associated with a decreased % predicted PEFR, especially in the summer. We concluded that increased levels of indoor O3 and PM2.5 were associated with decreased PEFR. The presence of houseplants was associated with indoor O3, isoprene and PEFR variations in the summer.

Assessment of environmental and ergonomic hazard associated to printing and photocopying: a review.

"Knowledge is power" and distribution of knowledge is fueled by printing and photocopying industry. Even as printing and photocopying industry have revolutionized the availability of documents and perceptible image quickly at extremely inexpensive and affordable cost, the boon of its revolution has turned into a bane by irresponsible, uncontrolled and extensive use, causing irreversible degradation to not only ecosystem by continuous release of ozone and other volatile organic compounds (VOCs) but also the health of workers occupationally exposed to it. Indoor ozone level due to emission from different photocopying equipment's increases drastically and the condition of other air quality parameters are not different. This situation is particularly sedate in extremely sensitive educational and research industry where sharing of knowledge is extremely important to meet the demands. This work is an attempt to catalogue all the environmental as well as health impacts of printing or photocopying. It has been observed that printing/photocopying operation is a significant factor contributing to indoor air quality degradation, which includes increase in concentration of ozone, VOCs, semi-volatile organic compounds (SVOCs) and heavy metals such as cadmium, selenium, arsenic, zinc, nickel, and other pollutants from photocopy machines. The outcome of this study will empower the manufactures with information regarding ozone and other significant emission, so that their impact can be reduced.

Effects of tightening standards for indoor ozone levels on associated mortalities in urban China: a population-based modelling study

BackgroundPrevious studies have shown that exposure to ozone is associated with mortality. Reducing indoor ozone of outdoor origin may be an effective short-term method to reduce overall ozone exposure and the associated premature mortality. Here, we estimated (1) premature mortalities attributable to ozone for individuals aged 25 years and over in urban China, (2) the proportion of this mortality associated with time indoors, and (3) the mortality that might be achieved by meeting the current Chinese Indoor Air Quality Standard (IAQS) or Assessment Standard for Healthy Buildings (ASHB), as well as more stringent guidelines. MethodsOutdoor ozone concentrations were measured hourly at all 1497 government monitoring stations (as at 2015) located in 339 cities dispersed across China, and these data were used to estimate premature mortality in 2015 from circulatory and respiratory causes based on a concentration–response model derived from an extended analysis of the American Cancer Society Cancer Prevention Study II. We used estimated air exchange rates, ozone penetration factors, and ozone surface removal rates to estimate the corresponding indoor ozone concentrations for the hourly outdoor ozone measurements. Finally, we estimated mortality reductions that might be achieved in urban China by meeting different 1-h indoor ozone standards or guidelines. FindingsWe estimated that there were 61 000 premature deaths from respiratory and cardiovascular disease attributable to ozone among individuals aged 25 years or over in urban China in 2015. Indoor exposures accounted for 87% (53 000) of this total. If the current indoor ozone standards (IAQS 80 ppb; ASHB 56 ppb) were met, the reduction in total mortality would be indistinguishable from zero. To be meaningful, an indoor standard should be no higher than 30 ppb. InterpretationRegardless of whether a person is outdoors or indoors, the mortality risks associated with long-term ozone exposure are derived using data from outdoor ozone monitoring stations. Outdoor concentrations of ozone are substantially higher than the time-matched estimates of indoor ozone concentrations, reflecting the reactive chemistry of ozone indoors. Globally, guidelines for indoor ozone concentrations should be substantially lower than guidelines for outdoor ozone concentrations to account for both ozone and its indoor reaction products. FundingNatural Science Foundation of China (numbers 51420105010 and 51521005) and the National Key Research and Development Program of China (number 2017YFC0702700).

Measurement of NO3 and N2O5 in a Residential Kitchen

We present direct indoor measurements of the nitrate radical (NO3) and dinitrogen pentoxide (N2O5) produced from combustion cooking emissions in a residential kitchen. When the indoor ozone (O3) concentration was low (∼4 ppbv), nitric oxide (NO) emitted from gas stove combustion suppressed NO3 formation. However, at moderate O3 levels (∼40 ppbv), measured NO3 concentrations reached 3–4 pptv, and the indoor NO3 reactivity loss rate coefficient reached 0.8 s–1. A box model of known chemistry agrees with the reactivity estimate and shows that moderate O3 levels led to a nitrate radical production rate of 7 ppbv h–1. These indoor NO3 production rates and reactivities are much higher than those typically found outdoors. We conclude that at low O3 levels indoor combustion suppresses nitrate radical chemistry, but when sufficient O3 enters residences from outdoors or is emitted directly from indoor sources, gas stove combustion emissions promote indoor NO3 chemistry.

Ventilation and Air Quality in Student Dormitories in China: A Case Study during Summer in Nanjing.

The Air quality in student dormitories can have a major impact on the health of millions of students in China. This study aims to investigate the ventilation and air quality in student dormitories. Questionnaire survey was conducted in eight dormitory buildings and field measurements were conducted in one dormitory during the summer in Nanjing. The survey result reveals that most students thought the indoor and outdoor air quality was neutral and the correlation between indoor and outdoor perceived air quality is statistically significant. There are few indoor PM2.5 and ozone sources in dormitories and natural ventilation is the most common form of ventilation. However, there is no statistically significant correlation between window opening behaviors and the perceptions of indoor and outdoor air quality. The field measurement result shows the measured I/O ratios of PM2.5 and ozone over 37 days are in the range of 0.42–0.79 and 0.21–1.00, respectively. The I/O ratios for PM2.5 and ozone are 0.49 ± 0.05 and 0.26 ± 0.05 in the case of the window being closed, and the I/O ratios for PM2.5 and ozone are 0.65 ± 0.08 and 0.50 ± 0.15 in the case of the window being open. The outdoor and indoor ozone concentrations show pronounced diurnal periodic variations, while the PM2.5 concentrations do not. Finally, recommended open/close window strategies are discussed to reduce indoor pollutant levels. Understanding the indoor/outdoor PM2.5 and ozone concentrations in different window patterns can be a guidance to preventing high indoor PM2.5 and ozone exposure in student dormitories.

Impact of School Air Quality on Children's Respiratory Health.

Background:Asthma is common in children with indoor pollutants influencing the development of the disease. Since children spend most of their time outside their homes within the school environment, school indoor air quality can directly influence their respiratory health.Aims:This study aims to analyze the indoor and outdoor air quality of Maltese schools and if an association exists between indoor pollutants and respiratory health in children.Settings and Design:Five primary schools were selected with 9- to 11-year-old students participating.Materials and Methods:Standardized health questionnaires and lung function tests were utilized. Indoor and outdoor air sampling together with traffic counts were carried out.Statistical Analysis Used:SPSS version 21 was used and the Chi-squared, logistic regression, and Pearson's correlation were used.Results:The mean indoor PM 2.5 level of 17.78 μg/m3 and CO (9.11 ppm) exceeded World Health Organization thresholds. Indoor ozone levels exceeded the mean European school's indoor ozone concentration of 8 μg/m3. High exposure to formaldehyde, NO2, and ozone was associated with atopy in children. Heavy vehicles passing near the schools were associated with current wheezing (P < 0.001) but not nocturnal cough (P = 0.34).Conclusions:School indoor and outdoor environment has a direct impact on children's respiratory health. This study has identified significant associations between high exposures to indoor air pollutants, school characteristics, and upper and lower airway inflammation.

Ozone reaction with human surfaces: Influences of surface reaction probability and indoor air flow condition

It is well-established that indoor surfaces, such as building materials, act as a sink for indoor ozone. However, comparatively little research has been done regarding ozone reactions with human surfaces such as skin and clothing. Reaction characteristics of human surfaces and airflow around the human body may affect ozone removal and reaction byproduct formation. The objective of this study is to investigate effects of the reactivity of human surfaces, modeled for a range of reaction probabilities (γ), on ozone deposition and reaction byproduct formation. Computational fluid dynamics models are verified and validated with previously published studies, and used to analyze ozone reaction dynamics due to human surfaces under varying indoor air flow conditions. The results show that for indoor environments with air exchange rate <5 h−1, ozone deposition velocity is in the range of 8–10 m/h for human skin oil while it is 2–3 m/h for clean clothing. Surface reactivity of the human body has a larger influence on the ozone deposition velocity than do the air exchange rates or indoor airflow patterns. Modeled emission rates of major reaction byproducts from ozone chemistry with human surfaces included acetone (0.3 mg/h/person), decanal (0.2 mg/h/person), nonanal (0.1 mg/h/person) and 6-MHO (0.1 mg/h/person) for a transport-limited scenario with 90 ppb bulk ozone concentration. These results imply that exposures to indoor ozone and reaction byproducts can be meaningfully modulated by an interaction of building airflow and chemistry occurring on and around individuals, and should be considered in models of human exposure.

Photocatalytic decomposition of indoor ozone motivated by the white-light-emitting diode

TiO2 photocatalysis driven by ultraviolet (UV) light has been utilized to remove harmful indoor ozone in many previous studies. However, UV lamp is energy-consuming, and UV radiation has been classified as a carcinogen. For sustainability and health’s sake, we investigated the photocatalytic degradation of ozone driven by the white-light-emitting diode in the present study. Five different materials including nitrogen-doped TiO2 (TiO2-N), TiO2 hydrogenated at 300 and 350 °C (TiO2-H300 and TiO2-H350), P25 and Merck TiO2 were used as photocatalysts in the experiments. We also examined the effects of relative humidity (RH35-80%), ozone concentration (50–250 ppb) and air flow rate (2–8 Lpm) on the ozone removal efficiency. Because H2O could increase electron–hole recombination by inducing surface structural bending, the ozone removal efficiency of all the photocatalysts decreased with the increase in RH. Among the five photocatalysts, the nanotubular structure of TiO2-N created the largest surface area for the adsorption of ozone, and the nitrogen doping enhanced the visible-light absorbance. Therefore, TiO2-N exhibited the highest apparent reaction rate of ozone decomposition. However, the nanotubular structure of TiO2-N also generated a mass transfer barrier that obstructed the removal of ozone. Fortunately, there was no significant mass transfer limitation in the granular photocatalysts (P25 TiO2, TiO2-H300 and TiO2-H350). This study provides practical data for the implication of visible-light-driven photocatalytic degradation of ozone.

機器備品による化学物質汚染と室内濃度予測に関する研究 : 第1報-事務機器のオゾン発生量算定と室内濃度予測法

機器備品による化学物質汚染と室内濃度予測に関する研究 : 第1報-事務機器のオゾン発生量算定と室内濃度予測法

A-22 オゾン発生源による室内空気汚染に関する研究(第1報) : 特別養護老人ホームにおけるオゾン汚染の実態

A-22 オゾン発生源による室内空気汚染に関する研究(第1報) : 特別養護老人ホームにおけるオゾン汚染の実態