Indoor Ozone Concentrations Research Articles

Real-time evaluation of terpene emissions and exposures during the use of scented wax products in residential buildings with PTR-TOF-MS

Scented wax products, such as candles and wax warmers/melts, are popular fragranced consumer products that are commonly used in residential buildings. As scented wax products are intentionally fragranced to produce pleasant smellscapes for occupants, they may represent an important source of volatile organic compounds (VOCs) to indoor atmospheres. The aim of this study is to evaluate terpene emission factors (EFs) and inhalation intake fractions (iFs) for scented wax products to better understand their impact on indoor chemistry and chemical exposures. Full-scale emission experiments were conducted in the Purdue zEDGE Test House using a variety of scented candles (n = 5) and wax warmers/melts (n = 14) under different outdoor air exchange rates (AERs). Terpene concentrations were measured in real-time using a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS). PTR-TOF-MS measurements revealed that scented candle and wax warmer/melt products emit a variety of monoterpenes (C10H16) and oxygen-containing monoterpenoids (C10H14O, C10H16O, C10H18O, C10H20O), with peak concentrations in the range of 10−1 to 102 ppb. Monoterpene EFs were much greater for scented wax warmers/melts (C10H16 EFs ∼ 102 mg per g wax consumed) compared to scented candles (C10H16 EFs ∼ 10−1 to 100 mg per g wax consumed). Significant emissions of reactive terpenes from both products, along with nitrogen oxides (NO, NO2) from candles, depleted indoor ozone (O3) concentrations. Terpene iFs were similar between the two products (iFs ∼ 103 ppm) and increased with decreasing outdoor AER. Terpene iFs during concentration decay periods were similar to, or greater than, iFs during active emission periods for outdoor AERs ≤ 3.0 h−1. Overall, scented wax warmers/melts were found to release greater quantities of monoterpenes compared to other fragranced consumer products used in the home, including botanical disinfectants, hair care products, air fresheners, and scented sprays.

Rethinking building envelope design: Machine learning approaches to evaluate its impact on indoor ozone exposures

Ozone is widely recognized as an ambient air contaminant that causes acute and chronic health effects. However, there is a limited number of studies investigating indoor exposures to ozone in occupied houses and linking design variables to the predictive power of indoor ozone levels. This study focuses on typical envelope airflow paths used in residences in the Philadelphia area in the United States. The model development draws from the field data, including indoor and outdoor ozone concentration, environmental parameters, and building characteristics from four building envelopes. Five machine learning algorithms (i.e., support vector machine, lasso regression, random forest, Bayesian bridge regression, and gradient boosting) are employed, with indoor ozone concentration as the dependent variable, as it indicates how the hot and sunny weather that might lead to the possibility of indoor air quality (IAQ) alerts due to ozone. The results showed that gradient boosting model based on all field measurements had the highest R-squared value of 0.974 and low enough root mean square error (RMSE) and mean absolute error (MAE) which are 1.182 and 0.788, respectively. We conclude that indoor ozone forecasting model based on inputting environmental survey (ES) in addition to either design variables or indoor environment characteristics can effectively predict and can therefore be used at the building design phase to improve healthy living environments.

Ozone Loss: A Surrogate for the Indoor Concentration of Ozone-Derived Products.

Ozone concentrations tend to be substantially lower indoors than outdoors, largely because of ozone reactions with indoor surfaces. When there are no indoor sources of ozone, a common condition, the net concentration of gaseous products derived from indoor ozone chemistry scales linearly with the difference between outdoor and indoor ozone concentrations, termed "ozone loss." As such, ozone loss is a metric that might be used by epidemiologists to disentangle the adverse health effects of ozone's oxidation products from those of exposure to ozone itself. The present paper examines the characteristics, potential utility, and limitations of the ozone loss concept. We show that for commonly occurring indoor conditions, the ozone loss concentration is directly proportional to the total rate constant for ozone removal on surfaces (ksum) and inversely proportional to the net removal of ozone by air exchange (λ) plus surface reactions (ksum). It follows that the ratio of indoor ozone to ozone loss is equal to the ratio of λ to ksum. Ozone loss is a promising metric for probing potential adverse health effects resulting from exposures to products of indoor ozone chemistry. Notwithstanding its virtues, practitioners using it should be mindful of the limitations discussed in this paper.

A field measurement study of the effects of outdoor pollutants and room volumes on indoor fine particle and ozone concentrations

Air pollution, represented by ozone (O3) and fine particulate matter (PM2.5), threatens the health of urban residents. This study examined 24 residential buildings in Nanjing to investigate the factors that affect indoor ozone and PM2.5 concentrations. Windows closed/open state, room geometry, ventilation rate, and pollutant removal and emission rates are taken as influencing factors. The correlation between influence factors and indoor air quality was analyzed to help residents in Nanjing understand which factors significantly affect indoor air quality. Fitted methods were employed to assess the removal and emission rates of pollutants. It was found that for the bedroom of 10–20 m2 (i.e., 30–60 m3), the air change rate (ACR, h−1) of infiltration is relatively more correlated with the room volume than other room volumes. The increase in indoor ozone concentration due to windows opening is below the indoor air quality standard in China (160 μg/m3) and the USA (70 μg/m3) under the test period in these measured cases. Therefore, when natural ventilation is adopted for residential buildings in Nanjing, outdoor fine particle concentrations should be a priority concern.

The By-Product of Ozone from Electrostatic Air Cleaners

Indoor Air Quality (IAQ) contributes to the health and comfort of people living and working indoors. Poor IAQ can be linked to indoor and outdoor sources of contaminants. One recent solution for improving IAQ is the use of Electrostatic (ES) Air Cleaning technology. An ES air cleaner can be installed in an heating, ventilation, and air conditioning system where it pre-filters large dust particles and shocks smaller particles into a collection tray. However, ES air cleaners have been known to give off ozone as a by-product, which is, itself, an air contaminant. Ozone is found outdoors as product of sunlight combining nitrogen oxides and volatile organic compounds generated from man-made pollution. Indoor ozone concentration will depend on the introduction of outdoor ozone indoors through natural ventilation, mechanical ventilation, and infiltration through the building’s envelope (in order of importance). Two different ES air cleaners, A and B, were installed in the air conditioning system of research House #2 of the TRANE Residential Heating and Cooling Research Lab at the University of Texas at Tyler. A series of ozone experiments were conducted, which included measuring the baseline ozone levels at the research houses with different levels of insulation, observing the increase in ozone due to the powering on of mechanical ventilation, and observing the increase in ozone due to the powering on of the installed ES air cleaners. The baseline ozone levels observed in research house #2, whose envelope is more tightly insulated, was found to be lower than in research house #1 whose envelope is less tightly insulated. With regards to mechanical ventilation, an increase in ozone levels were seen in addition to an even higher increase in ozone levels when the ES air cleaners were powered on in tandem. In terms of the single contribution of the ES air cleaners in raising indoor ozone levels, the data shows that although the ES air cleaners increased the ozone concentration in the house, the levels are not of concern as they were less than the FDA limit on indoor ozone generation. KEYWORDS: Indoor Air Quality; Ozone; Electrostatic Air Cleaner; Infiltration; Mechanical Ventilation; HVAC; Pollutant; Indoor Contaminant

Health Impacts of Surface Ozone in Outdoor and Indoor Environments of Hattar Industrial Units, KPK, Pakistan

This research was carried out to analyze variations in indoor and outdoor ozone concentrations and their health impact on local communities of megacities in Pakistan. For indoor ozone measurements, industrial units of an economic zone, Hattar Industrial Estate, Haripur, KPK, Pakistan, were selected. For outdoor ozone measurements, maximum and minimum peaks from different selected stations of three megacities (Islamabad, Abbottabad, and Haripur Hattar) in Pakistan were analyzed for paired comparisons. The tropospheric ozone levels were measured with the help of a portable SKY 2000-WH-O3 meter from December 2018 to November 2019. According to the findings of this investigation, the indoor ozone concentrations at Hattar Industrial Estate exceeded the permissible limit devised by the WHO. The highest concentration (0.37 ppm) was recorded in the month of May in the food industry, while the lowest concentration (0.00 ppm) was recorded in the cooling area of the steel industry in the month of December. For outdoor ozone concentrations, the maximum concentration (0.23 ppm) was detected in Islamabad in the month of March 2019, whereas the rest of year showed comparatively lower concentrations. In Haripur, the maximum concentration (0.22 ppm) was detected in the month of February 2019 and a minimum concentration (0.11 ppm) was found in the month of November 2019. In Abbottabad, the maximum concentration (0.21 ppm) was detected in the month of March 2019 and the minimum concentration was 0.082 ppm. Increasing tropospheric ozone levels might be harmful for local communities and industrial laborers in the winter season because of the foggy weather. In the Abbottabad and Hattar regions, since COVID infection is indirectly related to low temperature and high emission of gases may compromise the respiratory systems of humans. The results of the present study were shared with industrialists to set precautions for ambient air quality and support the adoption of low emission techniques in industries for the safety of labour and nearby residents.

Effects of an Ozone-Based Domestic Clothes Washer/Dryer on Indoor Air Quality: A Probabilistic Risk Assessment Study

New technologies are facing the market to overcome high energy costs and efficiency regulations. Among these, the use of ozone in domestic appliances has been recently proposed for a cold-water sanitizing system for clothes or even a no-water cycle to refresh clothes. Ozone is a contaminant in indoor environments and its toxicity is mainly due to the strong oxidizing action on cellular components that can reduce lung function and increase respiratory symptoms. This study illustrates a risk assessment for ozone emissions released from new domestic clothes washer/dryer during normal operation and in the case of a failure. Indoor ozone concentrations were measured, and a mass-balance model was applied, considering ozone released from the appliance during the no-water cycle and the outdoor ozone contribution. Monte Carlo analysis was used to derive the probability of exceeding the air quality standards established by the main international organizations for the protection of human health. This study indicated the most suitable ozone generator and the best refresh cycle to minimize health risks. This method can be generally used to assess the potential health risk for the indoor environment, due to the release of harmful emissions from household appliances.

Impacts of building envelope design on indoor ozone exposures and health risks in urban environments

Much of human exposure to ozone takes place indoors. However, few studies have focused on human ozone exposures in normally occupied residential houses in the U.S. urban environments. Only rare studies have explored the implication of building envelope design variables on outdoor ozone penetration. Our study reveals the extent to which outdoor ozone penetrates and persists in the occupied houses in one of the most ozone-polluted cities, as influenced by building characteristics, building geometry, envelope design variables, window conditions and urban meteorology conditions. Through a set of analysis and variable regressions, we found that (1) the ratios of indoor to outdoor ozone concentration (I/O) were higher with windows open (0.700 ± 0.13) than with the windows closed (0.53 ± 0.22); (2) the indoor ozone concentration is typically elevated when the outdoor ozone concentration is high; and (3) design variables such as exterior envelope finishes, wall surface area and window-to-wall ratio are reasonably effective predictors. Our results of health risk evaluation suggest that the observed levels of indoor ozone exposure could pose a considerable risk to human health. Further work is needed to discover how building envelopes can be designed, constructed and maintained to support occupant health.

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.

Characteristics of indoor ozone pollution in residential buildings based on outdoor air pollution

Ozone pollution can not only cause serious effects on human respiratory tract, lung, cardiovascular and immune system, but also lead to secondary pollution of indoor air environment by reacting with human surface sebum, building materials surface and other indoor compounds. As people stay indoors for more than 90% of their time, indoor ozone exposure is far more harmful than outdoor ozone exposure. Indoor ozone mainly comes from the outdoor environment. Therefore, it is an important prerequisite for controlling indoor ozone pollution to master the characteristics of indoor ozone pollution concentration under the influence of outdoor air pollution. The outdoor ozone concentration of 20 representative cities in the five climatic areas of China were investigated in this study. Meanwhile, indoor ozone concentration was predicted based on I/O ratio (indoor-outdoor concentration ratio). Furthermore, the indoor ozone pollution level affected by window opening time, air change rate and ozone deposition velocity was analyzed. The results show that the increase of air change rate and window opening time leads to the rise of indoor ozone pollution level. Moreover, the growing up of ozone deposition velocity may cause more ozone to be removed by the indoor surface, then the indoor ozone concentration decreases. In addition, indoor ozone pollution is the most serious in cold zone and the least serious in mild zone.

Influence of Mechanical Ventilation Systems and Human Occupancy on Time-Resolved Source Rates of Volatile Skin Oil Ozonolysis Products in a LEED-Certified Office Building.

Building mechanical ventilation systems are a major driver of indoor air chemistry as their design and operation influences indoor ozone (O3) concentrations, the dilution and transport of indoor-generated volatile organic compounds (VOCs), and indoor environmental conditions. Real-time VOC and O3 measurements were integrated with a building sensing platform to evaluate the influence of mechanical ventilation modes and human occupancy on the dynamics of skin oil ozonolysis products (SOOPs) in an office in a LEED-certified building during the winter. The ventilation system operated under variable recirculation ratios (RRs) from RR = 0 (100% outdoor air) to RR = 1 (100% recirculation air). Time-resolved source rates for 6-methyl-5-hepten-2-one (6-MHO), 4-oxopentanal (4-OPA), and decanal were highly dynamic and changed throughout the day with RR and occupancy. Total SOOP source rates during high-occupancy periods (10:00-18:00) varied from 2500-3000 μg h-1 when RR = 0.1 to 6300-6700 μg h-1 when RR = 1. Source rates for gas-phase reactions, outdoor air, and occupant-associated emissions generally decreased with increasing RR. The recirculation air source rate increased with RR and typically became the dominant source for RR > 0.5. SOOP emissions from surface reservoirs were also a prominent source, contributing 10-50% to total source rates. Elevated per person SOOP emission factors were observed, potentially due to multiple layers of soiled clothing worn during winter.

Indoor ozone: Concentrations and influencing factors.

Because people spend most of their time indoors, much of their exposure to ozone occurs in buildings, which are partially protective against outdoor ozone. Measurements in approximately 2000 indoor environments (residences, schools, and offices) show a central tendency for average indoor ozone concentration of 4-6ppb and an indoor to outdoor concentration ratio of about 25%. Considerable variability in this ratio exists among buildings, as influenced by seven building-associated factors: ozone removal in mechanical ventilation systems, ozone penetration through the building envelope, air-change rates, ozone loss rate on fixed indoor surfaces, ozone loss rate on human occupants, ozone loss by homogeneous reaction with nitrogen oxides, and ozone loss by reaction with gas-phase organics. Among these, the most important are air-change rates, ozone loss rate on fixed indoor surfaces, and, in densely occupied spaces, ozone loss rate on human occupants. Although most indoor ozone originates outdoors and enters with ventilation air, indoor emission sources can materially increase indoor ozone concentrations. Mitigation technologies to reduce indoor ozone concentrations are available or are being investigated. The most mature of these technologies, activated carbon filtration of mechanical ventilation supply air, shows a high modeled health-benefit to cost ratio when applied in densely occupied spaces.

Effect of Ozone, Clothing, Temperature, and Humidity on the Total OH Reactivity Emitted from Humans.

People influence indoor air chemistry through their chemical emissions via breath and skin. Previous studies showed that direct measurement of total OH reactivity of human emissions matched that calculated from parallel measurements of volatile organic compounds (VOCs) from breath, skin, and the whole body. In this study, we determined, with direct measurements from two independent groups of four adult volunteers, the effect of indoor temperature and humidity, clothing coverage (amount of exposed skin), and indoor ozone concentration on the total OH reactivity of gaseous human emissions. The results show that the measured concentrations of VOCs and ammonia adequately account for the measured total OH reactivity. The total OH reactivity of human emissions was primarily affected by ozone reactions with organic skin-oil constituents and increased with exposed skin surface, higher temperature, and higher humidity. Humans emitted a comparable total mixing ratio of VOCs and ammonia at elevated temperature-low humidity and elevated temperature-high humidity, with relatively low diversity in chemical classes. In contrast, the total OH reactivity increased with higher temperature and higher humidity, with a larger diversity in chemical classes compared to the total mixing ratio. Ozone present, carbonyl compounds were the dominant reactive compounds in all of the reported conditions.

Observing ozone chemistry in an occupied residence

Outdoor ozone transported indoors initiates oxidative chemistry, forming volatile organic products. The influence of ozone chemistry on indoor air composition has not been directly quantified in normally occupied residences. Here, we explore indoor ozone chemistry in a house in California with two adult inhabitants. We utilize space- and time-resolved measurements of ozone and volatile organic compounds (VOCs) acquired over an 8-wk summer campaign. Despite overall low indoor ozone concentrations (mean value of 4.3 ppb) and a relatively low indoor ozone decay constant (1.3 h-1), we identified multiple VOCs exhibiting clear contributions from ozone-initiated chemistry indoors. These chemicals include 6-methyl-5-hepten-2-one (6-MHO), 4-oxopentanal (4-OPA), nonenal, and C8-C12 saturated aldehydes, which are among the commonly reported products from laboratory studies of ozone interactions with indoor surfaces and with human skin lipids. These VOCs together accounted for ≥12% molecular yield with respect to house-wide consumed ozone, with the highest net product yield for nonanal (≥3.5%), followed by 6-MHO (2.7%) and 4-OPA (2.6%). Although 6-MHO and 4-OPA are prominent ozonolysis products of skin lipids (specifically squalene), ozone reaction with the body envelopes of the two occupants in this house are insufficient to explain the observed yields. Relatedly, we observed that ozone-driven chemistry continued to produce 6-MHO and 4-OPA even after the occupants had been away from the house for 5 d. These observations provide evidence that skin lipids transferred to indoor surfaces made substantial contributions to ozone reactivity in the studied house.

Measurement of ozone deposition velocity onto human surfaces of Chinese residents and estimation of corresponding production of oxidation products

China has been experiencing a sharp increase in outdoor ozone concentration. The deposition velocity of ozone onto human surfaces strongly affects the indoor ozone concentration, and the production of oxidation products. In this study, we measured the deposition velocity of ozone onto human surfaces in six Chinese residential rooms, each housing 1–3 occupants. In addition, we estimated the corresponding emission rate of oxidation products. The measured mean value of the deposition velocity is 14.8 (±10.1) m/h, which is close to those reported in earlier studies in western countries. We also find that the ozone deposition velocity onto human surfaces is positively correlated to the weighted duration from the last laundry and bath/facial-cleansing, and it is negatively correlated to the relative humidity of the indoor air. The estimated emission rates of 6-MHO, 4-OPA, acetone, geranyl acetone, 1,4-butanedial decanal, and all gas-phase products are 7.7 × 1016, 6.7 × 1016, 9.4 × 1016, 9.7 × 1015, 1.3 × 1016, 3.4 × 1016, and 4.8 × 1017 molecule per person h−1, respectively, with an indoor ozone concentration of 5 ppb at steady state. The measured deposition velocity of ozone onto human surfaces of Chinese residents, and the emission rates of the corresponding oxidation products may be applied for the estimation of human exposure to ozone and its oxidation products in China.

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.

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.