Assessing the influence of indoor exposure to "outdoor ozone" on the relationship between ozone and short-term mortality in U.S. communities

Pedestrian flow-environmental pollutants interactions and health risks to residents in high-occupancy public areas of apartment buildings

The current interaction of pedestrian flow and environmental pollutants in high-occupancy public areas of apartment and the risks of residents being exposed to environmental pollutants are issues that are often overlooked but urgently need to be addressed. In this study, we provide a comprehensive of pedestrian flow-environmental pollutants interactions and health risks to residents in first-floor public areas of apartment with high-occupancy. The main findings indicate that under closed management conditions, there is a significant increase in TVOC and noise levels during the peak periods of nighttime pedestrian flow. In the correlation analysis, the significant impact of time granularity selection in clarifying the correlation between pedestrian flow and environmental pollutants has been highlighted, with larger time granularities generally showing stronger correlations, while finer time granularities may help identify specific risks in areas directly connected to the external environment. There is a significant correlation exists between pedestrian flow and environmental pollutants (TVOC, ozone, and noise), with higher concentrations of these pollutants observed during peak pedestrian flow periods, thereby increasing the risk of residents being exposed to adverse environmental conditions. To mitigate the risks associated with TVOC pollution and noise exposure, it is crucial to maintain proper ventilation, avoid conducting cleaning or maintenance activities during peak hours, and implement noise-reducing measures, such as distancing noise sources from residential areas or installing soundproofing barriers. Additionally, the study identifies total volatile organic compounds originating from property maintenance activities and clarifies their dispersion patterns, emphasizing the importance of developing robust, standardized maintenance protocols for indoor environmental quality assurance. This research can improve the environmental sustainability of apartment buildings and provide a theoretical basis for the development of environmental health strategies for high-occupancy public areas of apartment buildings.

Impacts of residential indoor air quality and environmental risk factors on adult asthma-related health outcomes in Chicago, IL

BACKGROUND

Residential environments are known to contribute to asthma.

OBJECTIVE

To examine the joint impacts of exposures to residential indoor and outdoor air pollutants and housing risk factors on adult asthma-related health outcomes.

METHODS

We analyzed >1-year of data from 53 participants from 41 homes in the pre-intervention period of the Breathe Easy Project prior to ventilation and filtration retrofits. Health outcomes included surveys of asthma control, health-related quality of life, stress, and healthcare utilizations. Environmental assessments included quarterly measurements of indoor and outdoor pollutants (e.g., HCHO, CO, CO2, NO2, O3, and PM), home walk-throughs, and surveys of environmental risk factors. Indoor pollutant concentrations were also matched with surveys of time spent at home to estimate indoor pollutant exposures.

RESULTS

Cross-sectional analyses using mixed-effects models indicated that lower annual average asthma control test (ACT) scores were associated (p < 0.05) with higher indoor NO2 (concentration/exposure: β = -2.42/-1.57), indoor temperature (β = -1.03 to -0.94), and mold/dampness (β = -3.09 to -2.41). In longitudinal analysis, lower ACT scores were also associated (p < 0.05) with higher indoor NO2 concentrations (β = -0.29), PM1 (concentration/exposure: β = -0.12/-0.24), PM2.5 (concentration/exposure: β = -0.12/-0.26), and PM10 (concentration/exposure: β = 10.14/-0.28). Emergency department visits were associated with poorer asthma control [incidence rate ratio (IRR) = 0.84; p < 0.001], physical health (IRR = 0.95; p < 0.05), mental health (IRR = 0.95; p < 0.05), higher I/O NO2 ratios (IRR = 1.30; p < 0.05), and higher indoor temperatures (IRR = 1.41; p < 0.05).

SIGNIFICANCE

Findings suggest that residential risk factors, including indoor air pollution (especially NO2 and particulate matter), higher indoor temperature, and mold/dampness, may contribute to poorer asthma control.

IMPACT

This study highlights the importance of residential indoor air quality and environmental risk factors for asthma control, health-related quality of life, and emergency department visits for asthma. Two timescales of mixed models suggest that exposure to indoor NO2 and particulate matter, higher indoor temperature, and mold/dampness was associated with poorer asthma control. Additionally, emergency department visits were associated with poorer asthma control and health-related quality of life, as well as higher I/O NO2 ratios and indoor temperatures. These findings deepen our understanding of the interrelationships between housing, air quality, and health, and have important implications for programs and policy.

The effect of built-in and portable ionizers on in-cabin ozone concentrations in light-duty vehicles

This paper investigates the effects of ionizers on the ozone concentration within vehicle cabins by using a series of measurements combined with a kinetic box model. Testing consisted of measuring ozone concentration during static tests where the ventilation of the test vehicle was turned on and off depending on the test. This testing was repeated for three different portable ionizers and two vehicles with built-in ionizers. Ionizer A produced ozone at a rate of ∼0.04 ppb s^-1 (∼0.68 mg h^-1), which increased the in-cabin O₃ concentrations of a Mitsubishi Mirage to ∼10 ppb with the fan off and ∼6 ppb in the recirculation mode. In the fresh air mode, in-cabin O₃ concentrations were dominated by outdoor-to-indoor transport. Ionizer B and C produced O₃ at a rate of less than 0.008 ppb s^-1 (<0.14 mg h^-1); however, during retesting, ionizer C was shown to emit large amounts of ozone for short amounts of time while being tested up close. The same testing was completed on vehicles with built-in ionizers; these produced <0.01 ppb s^-1 (<0.32 mg h^-1 in the Buick Enclave and <0.25 mg h^-1 in the Hyundai Genesis), and in-cabin O₃ concentrations were again dominated by outdoor-to-indoor transport with fresh air ventilation. While ionizers are currently regulated, the negative impact they have on in cabin air quality is important to continue monitoring.

Effect of ambient O3 on mortality due to circulatory and respiratory diseases in a high latitude city of northeast China

In recent years, O₃ pollution had been worsening in China and became a major challenge for human health. To evaluate the O₃ effects on circulatory and respiratory mortality in Harbin, a high latitude city of northeast China, we applied a time-series study from 2014 to 2016. After collecting data and adjusting for the effects of confounders, we built the generalized additive model to assess the associations between O₃ and mortality at different lag days. The results showed that an interquartile-range (IQR) increase in O₃ concentration corresponded to excess risk (ER) of 2.00% (95%CI: - 0.25-4.30%) for circulatory mortality at lag 0 and 8.02% (95%CI: 4.18-12.01%) for respiratory mortality at lag 2 days in the single-pollutant model. Stratified analysis showed that O₃ had a greater effect on females than on males. The effect of O₃ exposure on circulatory mortality was stronger during the warm period, while the opposite trend was founded for respiratory mortality. The sensitivity analysis showed that the effects of O₃ were relatively independent and the major results were robust.

Reactions and Products of Squalene and Ozone: A Review

This critical review describes the squalene-ozone (SqOz) reaction, or squalene ozonolysis. Ambient ozone penetrates indoors and drives indoor air chemistry. Squalene, a component of human skin oil, contains six carbon-carbon double bonds and is very reactive with ozone. Bioeffluents from people contribute to indoor air chemistry and affect the indoor air quality, resulting in exposures because people spend the majority of their time indoors. The SqOz reaction proceeds through various formation pathways and produces compounds that include aldehydes, ketones, carboxylic acids, and dicarbonyl species, which have a range of volatilities. In this critical review of SqOz chemistry, information on the mechanism of reaction, reaction probability, rate constants, and reaction kinetics are compiled. Characterizations of SqOz reaction products have been done in laboratory experiments and real-world settings. The effect of multiple environmental parameters (ozone concentration, air exchange rate (AER), temperature, and relative humidity (RH)) in indoor settings are summarized. This critical review concludes by identifying the paucity of available exposure, health, and toxicological data for known reaction products. Key knowledge gaps about SqOz reactions leading to indoor exposures and adverse health outcomes are provided as well as an outlook on where the field is headed.

Ambient Particulate Air Pollution and Daily Hospital Admissions in 31 Cities in Poland

A strong and consistent association has been observed between morbidity or mortality rates and PM concentration, and is well documented in many countries. In Poland, despite poor air quality, studies concerning the evaluation of acute health effects of ambient air pollution on morbidity from respiratory or cardiovascular diseases are rare. We examined the short-term impact of PMx concentration on hospital admission in 31 Polish cities based on the daily PM10, PM2.5 concentration, meteorological variables, and hospital data. The generalized additive model (GAM) and a random-effects meta-analysis were used to assess the impact of air pollution on morbidity within the exposed population. Almost 1.6 million cardiovascular admissions and 600 thousand respiratory disorders were analyzed. The RR values for PM10-related cardiovascular and respiratory hospital admissions in Poland are equal to 1.0077 (95% confidence interval, 1.0062 to 1.0092) and 1.0218 (95% confidence interval, 1.0182 to 1.0253), respectively, while for PM2.5 1.0088 (95% confidence interval, 1.0072 to 1.0103) and 1.0289 (95% confidence interval, 1.0244 to 1.0335), respectively. Moreover, a moderate heterogeneity of RR estimates was observed between the analyzed cities (I2 values from 27% to 45%). The presented analysis confirms the significant association between hospital admission and PMx concentration, especially during heating seasons.

Indoor air quality impacts of residential mechanical ventilation system retrofits in existing homes in Chicago, IL

Mechanical ventilation systems are used in residences to introduce ventilation air and dilute indoor-generated pollutants. A variety of ventilation system types can be used in home retrofits, influencing indoor air quality (IAQ) in different ways. Here we describe the Breathe Easy Project, a >2-year longitudinal, pseudo-randomized, crossover study designed to assess IAQ and adult asthma outcomes before and after installing residential mechanical ventilation systems in 40 existing homes in Chicago, IL. Each home received one of three types of ventilation systems: continuous exhaust-only, intermittent powered central-fan-integrated-supply (CFIS), or continuous balanced system with an energy recovery ventilator (ERV). Homes with central heating and/or cooling systems also received MERV 10 filter replacements. Approximately weeklong field measurements were conducted at each home on a quarterly basis throughout the study to monitor environmental conditions, ventilation operation, and indoor and outdoor pollutants, including size-resolved particles (0.3-10 μm), ozone (O₃), nitrogen dioxide (NO₂), carbon dioxide (CO₂), carbon monoxide (CO), and indoor formaldehyde (HCHO). Mean reductions in indoor/outdoor (I/O) ratios across all systems after the intervention were approximately 12% (p = 0.001), 10% (p = 0.008), 42% (p < 0.001), 39% (p = 0.002), and 33% (p = 0.007), for CO₂, NO₂, and estimated PM₁, PM_2.5, and PM₁₀, respectively. There was a reduction in I/O ratios for all measured constituents with each type of system, on average, but with varying magnitude and levels of statistical significance. The magnitudes of mean differences in I/O pollutant concentrations ratios were generally largest for most pollutants in the homes that received continuous balanced with ERV and smallest in the homes that received intermittent CFIS systems, with apparent benefits to providing ventilation continuously rather than intermittently. All ventilation system types maintained similar indoor temperatures during pre- and post-intervention periods.

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 4-6 ppb 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.

Prediction of Air Pollutant Concentration Based on One-Dimensional Multi-Scale CNN-LSTM Considering Spatial-Temporal Characteristics: A Case Study of Xi’an, China

Air pollution has become a serious problem threatening human health. Effective prediction models can help reduce the adverse effects of air pollutants. Accurate predictions of air pollutant concentration can provide a scientific basis for air pollution prevention and control. However, the previous air pollution-related prediction models mainly processed air quality prediction, or the prediction of a single or two air pollutants. Meanwhile, the temporal and spatial characteristics and multiple factors of pollutants were not fully considered. Herein, we establish a deep learning model for an atmospheric pollutant memory network (LSTM) by both applying the one-dimensional multi-scale convolution kernel (ODMSCNN) and a long-short-term memory network (LSTM) on the basis of temporal and spatial characteristics. The temporal and spatial characteristics combine the respective advantages of CNN and LSTM networks. First, ODMSCNN is utilized to extract the temporal and spatial characteristics of air pollutant-related data to form a feature vector, and then the feature vector is input into the LSTM network to predict the concentration of air pollutants. The data set comes from the daily concentration data and hourly concentration data of six atmospheric pollutants (PM2.5, PM10, NO2, CO, O3, SO2) and 17 types of meteorological data in Xi’an. Daily concentration data prediction, hourly concentration data prediction, group data prediction and multi-factor prediction were used to verify the effectiveness of the model. In general, the air pollutant concentration prediction model based on ODMSCNN-LSTM shows a better prediction effect compared with multi-layer perceptron (MLP), CNN, and LSTM models.

The Influence of Outdoor Particulate Matter PM2.5 on Indoor Air Quality: The Implementation of a New Assessment Method

Epidemiological research has shown that there is a positive correlation between the incidence of disease and mortality in humans and the mass concentration of particulate matter. An average 1 g of suspended dust emitted in a room results in the same exposure as 1 kg emitted to the outside air. In this study, the authors described the state of knowledge on dust pollution inside and outside buildings (I/O ratios), and methods of testing the PM infiltration process parameters. According to the law of indoor–outdoor particle mass balance and the physical basis of aerosol penetration theory, a relatively simple but new method for estimating the penetration factor P was tested. On the basis of the curve of dynamic changes of internal dust concentration in the process of particle concentration decay and next of the followed curve of dynamic rebound of particle concentration, authors measured penetration factor of ambient PM2.5 through building envelope. Authors modification of the method is to be used for determining the value of the particle deposition rate k not from the course of the characteristics in the transient state (the so-called particle concentration decay curves) but from the concentration rebound course, stimulated by natural particle infiltration process. Recognition measurements of the mass concentration of suspended PM2.5 and PM10 particles inside the rooms were carried out. In this study, the choice of the prediction particle penetration factor P calculation method was supported by the exemplary calculation of the p value for a room polluted by PM2.5. The preliminary results of the penetration factors determined by this method P = 0.61 are consistent with the P factor values from the literature obtained so far for this dimensional group of dusts.

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.

Estimating the Potential Health Benefits of Air Quality Warnings

National, state, and local air quality authorities issue warnings urging residents to stay indoors or to take other precautions when pollutant levels are expected to exceed defined thresholds. Previous work explores the impact of warnings on specific activities but not the health improvements that might result if individuals fully responded to the recommendations. We estimate these potential health impacts using recent pollution data in three U.S. locations: Denver, Colorado; Los Angeles, California; and Pittsburgh, Pennsylvania. We focus on mortality risks among the elderly, who are particularly vulnerable. Under the strong assumptions of no infiltration and no offsetting indoor sources, we estimate that the benefits associated with avoiding ambient ozone and fine particle exposure are generally less than $14 per person for one additional hour spent indoors on days when air quality thresholds are exceeded. These estimates are sensitive to assumptions regarding the relationship between decreased exposure and mortality risks. Individuals' decisions to stay indoors likely depend on the value of the health benefits compared with the value of forgone work and leisure activities. While the national warning system provides flexibility and allows individuals to tailor their responses to personal circumstances, our analysis suggests that its benefits under typical conditions are small. The benefits of warnings under wildfire or other extreme conditions may be much greater.

Residential air-change rates: A critical review

Air-change rate is an important parameter influencing residential air quality. This article critically assesses the state of knowledge regarding residential air-change rates, emphasizing periods of normal occupancy. Cumulatively, about 40 prior studies have measured air-change rates in approximately 10,000 homes using tracer gases, including metabolic CO₂ . The central tendency of the air-change rates determined in these studies is reasonably described as lognormal with a geometric mean of 0.5 h^-1 and a geometric standard deviation of 2.0. However, the geometric means of individual studies vary, mainly within the range 0.2-1 h^-1 . Air-change rates also vary with time in residences. Factors influencing the air-change rate include weather (indoor-outdoor temperature difference and wind speed), the leakiness of the building envelope, and, when present, operation of mechanical ventilation systems. Occupancy-associated factors are also important, including window opening, induced exhaust from flued combustion, and use of heating and cooling systems. Empirical and methodological challenges remain to be effectively addressed. These include clarifying the time variation of air-change rates in residences during occupancy and understanding the influence of time-varying air-change rates on tracer-gas measurement techniques. Important opportunities are available to improve understanding of air-change rates and interzonal flows as factors affecting the source-to-exposure relationships for indoor air pollutants.

Personal exposure to ambient PM2.5, PM10, O3, NO2, and SO2 for different populations in 31 Chinese provinces

Most epidemiological studies usually employ ambient air pollutant concentrations as a proxy of personal exposure to air pollutants originating outdoors, which could lead to a biased estimation of health effects. Herein, we modeled infiltration and exposure factors as the modifications of personal exposure to ambient PM_2.5, PM₁₀, O₃, NO₂, and SO₂ for all seasons, genders, and ages in 31 Chinese provinces. The annual average exposure factors of PM₁₀, PM_2.5, O₃, NO₂, and SO₂ were 0.42 ± 0.13 (arithmetic mean ± standard deviation), 0.68 ± 0.14, 0.34 ± 0.12, 0.50 ± 0.14, and 0.40 ± 0.13, respectively. We observed significant age, gender, seasonal, and geographical differences in infiltration and exposure factors for all studied ambient air pollutants. These factors were higher in southern China than in the north, and they were the highest in summer and the lowest in winter. The exposure factor of minors (age < 18 years) was significantly lower than that of adults (age ≥ 18 years, P < 0.01). Adult males had higher exposure factors than females (P < 0.01). Epidemiological studies utilizing outdoor concentrations of air pollutants could overestimate personal exposure to these pollutants. The present study could help in reducing the bias in the estimation of the health effects of air pollutants.

Ozone Deposition on Free-Running Indoor Materials and the Corresponding Volatile Organic Compound Emissions: Implications for Ventilation Requirements

Recently, tropospheric ozone has become a public health concern worldwide, along with the continuous battle against ambient fine particulate matter in countries like China. In this study, we investigate the impact of indoor ozone pollution using seven materials categorized as either wood-based panels or synthetic fibers, which were freely-stored in an office/lab environment. Most materials were considered as used and aged more than 1–2 years. An experimental apparatus was used to study ozone deposition and detect volatile organic compound (VOC) emissions from the specimens when exposed to ozone at three concentration levels: <10, 100, and 300 ppb. A simplified model is proposed to discuss ventilation requirements based on a standard room. We found that the mean ozone deposition velocities from the seven materials ranged from 0.005 to 0.062 cm·s−1. Both the engineering wood and some of the synthetic fibers were, moreover, prone to ozone deposition. Second, 15 VOCs were found in the sampling air from a 24-VOC target list after ozone exposure. The emission rates of the VOCs from all seven materials were then determined. Third, when the ozone concentration in the outdoor air is not severely high, it is possible to use ventilation to maintain acceptable indoor air quality.

Breathing-rate adjusted population exposure to ozone and its oxidation products in 333 cities in China

While PM_2.5 (particles with aerodynamic diameter less than 2.5 µm) concentrations in China are beginning to decline because of pollution abatement measures, ozone (O₃) concentrations continue to rise. In this study, we have used a Monte Carlo approach to estimate breathing-rate adjusted (BRA) population exposure to ozone and its oxidation products based on hourly O₃ measurements collected in 2017 from monitoring stations in 333 Chinese cities. The median measured outdoor O₃ concentration in these cities was 31 ppb, while the median calculated indoor concentrations of ozone and ozone-derived oxidation products were 7.5 ppb and 21 ppb, respectively. The median BRA O₃ exposure concentration was 12 ppb, ranging from 2.2 ppb to 18 ppb among the cities. Eastern and central cities had higher exposure concentrations, while northeastern and western cities had lower. On average, the residents of these cities spent 88% of their time indoors. Consequently, even with breathing rate adjustments, indoor O₃ exposure averaged 50% of the total O₃ exposure nationwide. The median BRA exposure concentration for ozone-derived products was 18 ppb, ranging from 4.5 ppb to 32 ppb among the cities. On average, BRA exposure concentrations were 1.6 times larger for oxidation products than for ozone, while seasonal variations of exposure concentrations were smaller for oxidation products than for ozone. As many of the products of indoor ozone chemistry are toxic, the health consequences of exposure to such products should be further investigated.

Tuning the fill percentage in the hydrothermal synthesis process to increase catalyst performance for ozone decomposition

The performance of Ce-OMS-2 catalysts was improved by tuning the fill percentage in the hydrothermal synthesis process to increase the oxygen vacancy density. The Ce-OMS-2 samples were prepared with different fill percentages by means of a hydrothermal approach (i.e. 80%, 70%, 50% and 30%). Ce-OMS-2 with 80% fill percentage (Ce-OMS-2-80%) showed ozone conversion of 97%, and a lifetime experiment carried out for more than 20 days showed that the activity of the catalyst still remained satisfactorily high (91%). For Ce-OMS-2-80%, Mn ions in the framework as well as K ions in the tunnel sites were replaced by Ce⁴⁺, while for the others only Mn ions were replaced. O₂-TPD and H₂-TPR measurements proved that the Ce-OMS-2-80% catalyst possessed the greatest number of mobile surface oxygen species. XPS and XAFS showed that increasing the fill percentage can reduce the AOS of Mn and augment the amount of oxygen vacancies. The active sites, which accelerate the elimination of O₃, can be enriched by increasing the oxygen vacancies. These findings indicate that increasing ozone removal can be achieved by tuning the fill percentage in the hydrothermal synthesis process.

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

BACKGROUND

Indoor 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.

METHODS

A 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.

RESULTS

The 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.

CONCLUSIONS

Exposure 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.

Emerging investigator series: primary emissions, ozone reactivity, and byproduct emissions from building insulation materials

Building insulation materials can affect indoor air by (i) releasing primary volatile organic compounds (VOCs) from building enclosure cavities to the interior space, (ii) mitigating exposure to outdoor pollutants through reactive deposition (of oxidants, e.g., ozone) or filtration (of particles) in infiltration air, and (iii) generating secondary VOCs and other gas-phase byproducts resulting from oxidant reactions. This study reports primary VOC emission fluxes, ozone (O3) reaction probabilities (γ), and O3 reaction byproduct yields for eight common, commercially available insulation materials. Fluxes of primary VOCs from the materials, measured in a continuous flow reactor using proton transfer reaction-time of flight-mass spectrometry, ranged from 3 (polystyrene with thermal backing) to 61 (cellulose) μmol m-2 h-1 (with total VOC mass emission rates estimated to be between ∼0.3 and ∼3.3 mg m-2 h-1). Major primary VOC fluxes from cellulose were tentatively identified as compounds likely associated with cellulose chemical and thermal decomposition products. Ozone-material γ ranged from ∼1 × 10-6 to ∼30 × 10-6. Polystyrene with thermal backing and polyisocyanurate had the lowest γ, while cellulose and fiberglass had the highest. In the presence of O3, total observed volatile byproduct yields ranged from 0.25 (polystyrene) to 0.85 (recycled denim) moles of VOCs produced per mole of O3 consumed, or equivalent to secondary fluxes that range from 0.71 (polystyrene) to 10 (recycled denim) μmol m-2 h-1. Major emitted products in the presence of O3 were generally different from primary emissions and were characterized by yields of aldehydes and acetone. This work provides new data that can be used to evaluate and eventually model the impact of "hidden" materials (i.e., those present inside wall cavities) on indoor air quality. The data may also guide building enclosure material selection, especially for buildings in areas of high outdoor O3.

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.

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 ≥25 years 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: 35 900-137 700) premature all-cause mortalities in urban China. If the current Chinese indoor ozone standards (80 ppbv (160 µg/m³ ); 56 ppbv (112 µg/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.

The impact of air exchange rate on ambient air pollution exposure and inequalities across all residential parcels in Massachusetts

Individual housing characteristics can modify outdoor ambient air pollution infiltration through air exchange rate (AER). Time and labor-intensive methods needed to measure AER has hindered characterization of AER distributions across large geographic areas. Using publicly-available data and regression models associating AER with housing characteristics, we estimated AER for all Massachusetts residential parcels. We conducted an exposure disparities analysis, considering ambient PM_2.5 concentrations and residential AERs. Median AERs (h^-1) with closed windows for winter and summer were 0.74 (IQR: 0.47-1.09) and 0.36 (IQR: 0.23-0.57), respectively, with lower AERs for single family homes. Across residential parcels, variability of indoor PM_2.5 concentrations of ambient origin was twice that of ambient PM_2.5 concentrations. Housing parcels above the 90th percentile of both AER and ambient PM_2.5 (i.e., the leakiest homes in areas of highest ambient PM_2.5)-vs. below the 10 percentile-were located in neighborhoods with higher proportions of Hispanics (20.0% vs. 2.0%), households with an annual income of less than $20,000 (26.0% vs. 7.5%), and individuals with less than a high school degree (23.2% vs. 5.8%). Our approach can be applied in epidemiological studies to estimate exposure modifiers or to characterize exposure disparities that are not solely based on ambient concentrations.

Redistribution of PM2.5 -associated nitrate and ammonium during outdoor-to-indoor transport

Nitrate and ammonium ions are major constituents of outdoor PM_2.5 . Human exposure to these ions occurs primarily indoors. To assess the adverse outcomes from exposure to them, it is necessary to quantify the relationships between outdoor and indoor PM_2.5 nitrate and ammonium. The relationships for the two semi-volatile ions are more complex than those of non-volatile PM_2.5 constituents (eg, sulfate, elemental carbon). This study presents a mechanistic description of their outdoor-indoor relationships that incorporates a dynamic gas-particle partitioning and key parameters such as the pH and water content of PM_2.5 . Compared to measurements of nitrate and ammonium, the model has normalized mean biases of -9% and -42% and correlation coefficients of 0.95 and 0.68 for nitrate and ammonium, respectively. This suggests satisfactory agreement for nitrate, but less strong for ammonium. Sensitivity analysis on key parameters indicates that the model generally works well across a range of values typical of indoor settings. The model's performance is sensitive to pH and water content in PM_2.5 , which control the gas-particle partitioning process. Indoor PM_2.5 tends to be more acidic than outdoor PM_2.5 , raising potential health concern. The model provides insights in exposure assessment, source apportionment, and health-composition attribution of indoor PM_2.5 .

Urban heat and air pollution: A framework for integrating population vulnerability and indoor exposure in health risk analyses

Urban growth and climate change will exacerbate extreme heat events and air pollution, posing considerable health challenges to urban populations. Although epidemiological studies have shown associations between health outcomes and exposures to ambient air pollution and extreme heat, the degree to which indoor exposures and social and behavioral factors may confound or modify these observed effects remains underexplored. To address this knowledge gap, we explore the linkages between vulnerability science and epidemiological conceptualizations of risk to propose a conceptual and analytical framework for characterizing current and future health risks to air pollution and extreme heat, indoors and outdoors. Our framework offers guidance for research on climatic variability, population vulnerability, the built environment, and health effects by illustrating how health data, spatially resolved ambient data, estimates of indoor conditions, and household-level vulnerability data can be integrated into an epidemiological model. We also describe an approach for characterizing population adaptive capacity and indoor exposure for use in population-based epidemiological models. Our framework and methods represent novel resources for the evaluation of health risks from extreme heat and air pollution, both indoors and outdoors.

Modeling transient particle transport by fast fluid dynamics with the Markov chain method

Fast simulation tools for the prediction of transient particle transport are critical in designing the air distribution indoors to reduce the exposure to indoor particles and associated health risks. This investigation proposed a combined fast fluid dynamics (FFD) and Markov chain model for fast predicting transient particle transport indoors. The solver for FFD-Markov-chain model was programmed in OpenFOAM, an open-source CFD toolbox. This study used two cases from the literature to validate the developed model and found well agreement between the transient particle concentrations predicted by the FFD-Markov-chain model and the experimental data. This investigation further compared the FFD-Markov-chain model with the CFD-Eulerian model and CFD-Lagrangian model in terms of accuracy and efficiency. The accuracy of the FFD-Markov-chain model was similar to that of the other two models. For the two studied cases, the FFD-Markovchain model was 4.7 and 6.8 times faster, respectively, than the CFD-Eulerian model, and it was 137.4 and 53.3 times faster than the CFD-Lagrangian model in predicting the steady-state airflow and transient particle transport. Therefore, the FFD-Markov-chain model is able to greatly reduce the computing cost for predicting transient particle transport in indoor environments.

Ozone and cardiac arrest: The role of previous hospitalizations

BACKGROUND

Several studies have reported associations between exposure to particulate matter and incidence of out-of-hospital cardiac arrest (OHCA) and some have observed associations with ozone (O₃). There are no studies investigating susceptibility based on previous disease history to short-term O₃ exposure and the risk of OHCA.

AIM

To investigate the role of previous cardiovascular-related hospitalizations in modifying the associations between the risk of OHCA and short-term increase in O₃ concentrations.

METHODS

A time-stratified case-crossover analysis of 11,923 OHCA registered in the Swedish Register for Cardiopulmonary Resuscitation from 2006 to 2014 was performed. Using personal identification numbers, OHCA were linked to all previous hospitalizations in Sweden since 1987 to create susceptible groups based on the principal diagnosis code at discharge. Susceptibility was based on hospitalization for i) acute myocardial infarction; ii) heart failure; iii) arrhythmias; iv) diabetes; v) hypertension; and vi) stroke. Moving 2 and 24-h averages for O₃, PM_2.5, PM₁₀, and NO₂ were constructed from hourly averages.

RESULTS

A 10 μg/m³ higher 2-h average O₃ concentration was associated with a 2% higher risk of OHCA (95% CI, 0% 3%). Associations were similar for 24-h average O₃ and in individuals with or without hospitalizations for AMI, heart failure, diabetes, hypertension or stroke. Individuals with previous hospitalizations for arrhythmias had a lower risk of OHCA with higher O₃. No associations were observed for other pollutants.

CONCLUSIONS

Short-term exposure to O₃ was associated with an elevated risk of OHCA, however, previous hospitalizations for cardiovascular diseases were not associated with additionally augmented risks.

Residential HVAC runtime from smart thermostats: characterization, comparison, and impacts

In North America, the majority of homes use forced-air systems for heating and cooling. The proportion of time these systems operate, or runtime, has a significant impact on many building performance parameters. The recent adoption of smart thermostats in many North American homes presents a potential data source for runtime. Smart thermostat data collected from over 7000 homes were compared with nine other investigations and a runtime estimation method based on exterior temperature. The smart thermostat runtimes have a median of 18% across all homes, but show considerable variation between homes, even at constant exterior temperature conditions suggesting that factors besides climate (eg, system sizing, user operation) have a significant impact on runtime. Results from other investigations suggest that smart thermostat runtimes are consistent with other measurement approaches. The practical implications of runtime include the impact on central filtration performance. At low to average runtimes, the filter efficiency matters much less for effectiveness because the system does not run enough for a sufficient air volume to pass through the filter and have a substantial impact on particle concentrations. This work illustrates the importance of measuring runtime for a particular home, and the value of data obtained from smart thermostats.

Personal Ozone Exposure and Respiratory Inflammatory Response: The Role of DNA Methylation in the Arginase-Nitric Oxide Synthase Pathway

Little is known regarding the molecular mechanisms behind respiratory inflammatory response induced by ozone. We performed a longitudinal panel study with four repeated measurements among 43 young adults in Shanghai, China from May to October in 2016. We collected buccal samples and measured the fractional exhaled nitric oxide (FeNO) after 3-day personal ozone monitoring. In buccal samples, we measured concentrations of inducible nitric oxide synthase (iNOS) and arginase (ARG), and DNA methylation of NOS2A and ARG2. We used linear mixed-effect models to analyze the effects of ozone on FeNO, two enzymes and their DNA methylation. A 10 ppb increase in ozone (lag 0-8 h) was significantly associated with a 3.89% increase in FeNO, a 36.33% increase in iNOS, and a decrease of 0.36 in the average methylation (%5mC) of NOS2A. Ozone was associated with decreased ARG and elevated ARG2 methylation, but the associations were not significant. These effects were more pronounced among allergic subjects than healthy subjects. The effects were much stronger when using personal exposure monitoring than fixed-site measurements. Our study demonstrated that personal short-term exposure to ozone may result in acute respiratory inflammation, which may be mainly modulated by NOS2A hypomethylation in the arginase-nitric oxide synthase pathway.

Ambient Ozone Pollution and Daily Mortality: A Nationwide Study in 272 Chinese Cities

BACKGROUND

Few large multicity studies have been conducted in developing countries to address the acute health effects of atmospheric ozone pollution.

OBJECTIVE

We explored the associations between ozone and daily cause-specific mortality in China.

METHODS

We performed a nationwide time-series analysis in 272 representative Chinese cities between 2013 and 2015. We used distributed lag models and over-dispersed generalized linear models to estimate the cumulative effects of ozone (lagged over 0-3 d) on mortality in each city, and we used hierarchical Bayesian models to combine the city-specific estimates. Regional, seasonal, and demographic heterogeneity were evaluated by meta-regression.

RESULTS

At the national-average level, a 10-μg/m³ increase in 8-h maximum ozone concentration was associated with 0.24% [95% posterior interval (PI): 0.13%, 0.35%], 0.27% (95% PI: 0.10%, 0.44%), 0.60% (95% PI: 0.08%, 1.11%), 0.24% (95% PI: 0.02%, 0.46%), and 0.29% (95% PI: 0.07%, 0.50%) higher daily mortality from all nonaccidental causes, cardiovascular diseases, hypertension, coronary diseases, and stroke, respectively. Associations between ozone and daily mortality due to respiratory and chronic obstructive pulmonary disease specifically were positive but imprecise and nonsignificant. There were no statistically significant differences in associations between ozone and nonaccidental mortality according to region, season, age, sex, or educational attainment.

CONCLUSIONS

Our findings provide robust evidence of higher nonaccidental and cardiovascular mortality in association with short-term exposure to ambient ozone in China. https://doi.org/10.1289/EHP1849.

Synergism of Short-Term Air Pollution Exposures and Neighborhood Disadvantage on Initial Stroke Severity

BACKGROUND AND PURPOSE

Little is known about the relation between environment and stroke severity. We investigated associations between environmental exposures, including neighborhood socioeconomic disadvantage and short-term exposure to airborne particulate matter <2.5 μm and ozone, and their interactions with initial stroke severity.

METHODS

First-ever ischemic stroke cases were identified from the Brain Attack Surveillance in Corpus Christi project (2000-2012). Associations between pollutants, disadvantage, and National Institutes of Health Stroke Scale were modeled using linear and logistic regression with adjustment for demographics and risk factors. Pollutants and disadvantage were modeled individually, jointly, and with interactions.

RESULTS

Higher disadvantage scores and previous-day ozone concentrations were associated with higher odds of severe stroke. Higher levels of particulate matter <2.5 μm were associated with higher odds of severe stroke among those in higher disadvantage areas (odds ratio, 1.24; 95% confidence interval, 1.00-1.55) but not in lower disadvantage areas (odds ratio, 0.82; 95% confidence interval, 0.56-1.22; P interaction =0.097).

CONCLUSIONS

Air pollution exposures and neighborhood socioeconomic status may be important in understanding stroke severity. Future work should consider the multiple levels of influence on this important stroke outcome.

Exposure to SVOCs from Inhaled Particles: Impact of Desorption

Inhaled semivolatile organic compounds (SVOCs) are simultaneously present in gas and particle phases. Particles desorb a fraction of their SVOCs moving through the human respiratory tract (RT). Quantifying such desorption is challenging but important since gas- and particle-phase SVOCs deposit in different locations in the RT, encountering different cell populations with varying health consequences. This paper presents a mass transfer model to quantify this desorption process in the head, tracheobronchial, and alveolar regions of the RT. The desorption of SVOCs from inhaled particles can be gauged using the ratio of particle residence time to the time required to achieve particle/gas equilibrium. Results indicate that the larger this ratio is, the more likely particles desorb the SVOCs they carry. For particles smaller than 0.5 μm diameter and SVOCs with a particle/gas partition coefficient (unitless) of 10¹⁰, accounting for desorption reduces the estimated particle-phase SVOC concentrations in the alveolar region by more than 35%; the reduction is almost 700% for 0.05 μm diameter particles. In hypothetical scenarios representing common indoor and outdoor situations, neglecting desorption significantly overestimates the concentration of ultrafine particle associated SVOCs in the alveolar region. This model is a preliminary step toward more nuanced estimates of exposure to inhaled SVOCs.

Long-Term Ozone Exposure and Mortality in a Large Prospective Study

RATIONALE

Tropospheric ozone (O3) is potentially associated with cardiovascular disease risk and premature death. Results from long-term epidemiological studies on O3 are scarce and inconclusive.

OBJECTIVES

In this study, we examined associations between chronic ambient O3 exposure and all-cause and cause-specific mortality in a large cohort of U.S. adults.

METHODS

Cancer Prevention Study II participants were enrolled in 1982. A total of 669,046 participants were analyzed, among whom 237,201 deaths occurred through 2004. We obtained estimates of O3 concentrations at the participant's residence from a hierarchical Bayesian space-time model. Estimates of fine particulate matter (particulate matter with an aerodynamic diameter of up to 2.5 μm [PM2.5]) and NO2 concentrations were obtained from land use regression. Cox proportional hazards regression models were used to examine mortality associations adjusted for individual- and ecological-level covariates.

MEASUREMENTS AND MAIN RESULTS

In single-pollutant models, we observed significant positive associations between O3, PM2.5, and NO2 concentrations and all-cause and cause-specific mortality. In two-pollutant models adjusted for PM2.5, significant positive associations remained between O3 and all-cause (hazard ratio [HR] per 10 ppb, 1.02; 95% confidence interval [CI], 1.01-1.04), circulatory (HR, 1.03; 95% CI, 1.01-1.05), and respiratory mortality (HR, 1.12; 95% CI, 1.08-1.16) that were unchanged with further adjustment for NO2. We also observed positive mortality associations with both PM2.5 (both near source and regional) and NO2 in multipollutant models.

CONCLUSIONS

Findings derived from this large-scale prospective study suggest that long-term ambient O3 contributes to risk of respiratory and circulatory mortality. Substantial health and environmental benefits may be achieved by implementing further measures aimed at controlling O3 concentrations.

Field-to-laboratory analysis of clay wall coatings as passive removal materials for ozone in buildings

Ozone reacts readily with many indoor materials, as well as with compounds in indoor air. These reactions lead to lower indoor than outdoor ozone concentrations when outdoor air is the major contributor to indoor ozone. However, the products of indoor ozone reactions may be irritating or harmful to building occupants. While active technologies exist to reduce indoor ozone concentrations (i.e, in-duct filtration using activated carbon), they can be cost-prohibitive for some and/or infeasible for dwellings that do not have heating, ventilating, and air-conditioning systems. In this study, the potential for passive reduction of indoor ozone by two different clay-based interior surface coatings was explored. These coatings were exposed to occupied residential indoor environments and tested bimonthly in environmental chambers for quantification of ozone reaction probabilities and reaction product emission rates over a 6-month period. Results indicate that clay-based coatings may be effective as passive removal materials, with relatively low by-product emission rates that decay rapidly within 2 months.

Numerical investigations of flow and passive pollutant exposure in high-rise deep street canyons with various street aspect ratios and viaduct settings

Vehicular pollutant exposure of residents and pedestrians in high-rise deep street canyons with viaducts and noise barriers requires special concerns because the ventilation capacity is weak and the literature reported inconsistent findings on flow patterns as aspect ratios (building height/street width, H/W) are larger than 2. By conducting computational fluid dynamics (CFD) simulations coupled with the intake fraction iF and the daily pollutant exposure E_t, this paper investigates the impact of street aspect ratios, viaducts and noise barriers on the flow and vehicular passive pollutant exposure in full-scale street canyons (H/W=1-6, W=24m). iF represents the fraction of total emissions inhaled by a population (1ppm=10^-6), while E_t means the extent of human beings' contact with pollutants within one day. CFD methodologies of passive pollutant dispersion modeling are successfully validated by wind tunnel data in Meroney et al. (1996). As a novelty, the two-main-vortex pattern start appearing in full-scale street canyons as H/W changes from 4 to 5, however previous studies using wind-tunnel-scale models (H=6cm) reported two to five vortexes as H/W=2-5. This finding is validated by both smoke visualization in scale-model outdoor field experiments (H=1.2m, W=0.6m) and CFD simulations of Reynolds number independence. Cases with two main vortexes (H/W=5-6) experience much larger daily pollutant exposure (~10³-10⁴mg/m³/day) than those with single main vortex as H/W=1-4 (~10¹-10²mg/m³/day). Moreover leeward-side pollutant exposures are much larger than windward-side as H/W=1-4 while oppositely as H/W=5-6. Assuming a general population density, the total iF is 485-803ppm as H/W=1, 2020-12051ppm as H/W=2-4, and 51112-794026ppm as H/W=5-6. With a single elevated pollutant source, cases with viaducts experience significantly smaller pollutant exposures than cases without viaducts. Road barriers slightly increase pollutant exposure in near-road buildings with H/W=1 while reduce a little as H/W=3 and 5. Two-source cases can experience 2.60-5.52 times pollutant exposure as great as single-source cases.

The influence of street layouts and viaduct settings on daily carbon monoxide exposure and intake fraction in idealized urban canyons

Environmental concerns have been raised on the adverse health effects of vehicle emissions in micro-scale traffic-crowded street canyons, especially for pedestrians and residents living in near-road buildings. Viaduct design is sometimes used to improve transportation efficiency but possibly affects urban airflow and the resultant exposure risk, which have been rarely investigated so far. The personal intake fraction (P_IF) is defined as the average fraction of total emissions that is inhaled by each person of a population (1 ppm = 1 × 10^-6), and the daily carbon monoxide (CO) pollutant exposure (E_t) is estimated by multiplying the average concentration of a specific micro-environment within one day. As a novelty, by considering time activity patterns and breathing rates in various micro-environments for three age groups, this paper introduces IF and E_t into computational fluid dynamic (CFD) simulation to quantify the impacts of street layouts (street width/building height W/H = 1, 1.5, 2), source location, viaduct settings and noise barriers on the source-exposure correlation when realistic CO sources are defined. Narrower streets experience larger P_IF (1.51-5.21 ppm) and CO exposure, and leeward-side buildings always attain higher vehicular pollutant exposure than windward-side. Cases with a viaduct experience smaller P_IF (3.25-1.46 ppm) than cases without a viaduct (P_IF = 5.21-2.23 ppm) if the single ground-level CO source is elevated onto the viaduct. With two CO sources (both ground-level and viaduct-level), daily CO exposure rises 2.80-3.33 times but P_IF only change slightly. Noise barriers above a viaduct raise concentration between barriers, but slightly reduce vehicular exposure in near-road buildings. Because people spend most of their time indoors, vehicular pollutant exposure within near-road buildings can be 6-9 times that at pedestrian level. Although further studies are still required to provide practical guidelines, this paper provides effective methodologies to quantify the impacts of street/viaduct configurations on human exposure for urban design purpose.

Ozone pollution in China: A review of concentrations, meteorological influences, chemical precursors, and effects

High concentrations of ozone in urban and industrial regions worldwide have long been a major air quality issue. With the rapid increase in fossil fuel consumption in China over the past three decades, the emission of chemical precursors to ozone-nitrogen oxides and volatile organic compounds-has increased sharply, surpassing that of North America and Europe and raising concerns about worsening ozone pollution in China. Historically, research and control have prioritized acid rain, particulate matter, and more recently fine particulate matter (PM_2.5). In contrast, less is known about ozone pollution, partly due to a lack of monitoring of atmospheric ozone and its precursors until recently. This review summarizes the main findings from published papers on the characteristics and sources and processes of ozone and ozone precursors in the boundary layer of urban and rural areas of China, including concentration levels, seasonal variation, meteorology conducive to photochemistry and pollution transport, key production and loss processes, ozone dependence on nitrogen oxides and volatile organic compounds, and the effects of ozone on crops and human health. Ozone concentrations exceeding the ambient air quality standard by 100-200% have been observed in China's major urban centers such as Jing-Jin-Ji, the Yangtze River delta, and the Pearl River delta, and limited studies suggest harmful effect of ozone on human health and agricultural corps; key chemical precursors and meteorological conditions conductive to ozone pollution have been investigated, and inter-city/region transport of ozone is significant. Several recommendations are given for future research and policy development on ground-level ozone.

Modifications of exposure to ambient particulate matter: Tackling bias in using ambient concentration as surrogate with particle infiltration factor and ambient exposure factor

Numerous epidemiological studies explored health risks attributed to outdoor particle pollution. However, a number of these studies routinely utilized ambient concentration as a surrogate for personal exposure to ambient particles. This simplification ignored the difference between indoor and outdoor concentrations of outdoor originated particles and may bias the estimate of particle-health associations. Intending to avoid the bias, particle infiltration factor (F_inf), which describes the penetration of outdoor particles in indoor environment, and ambient exposure factor (α), which represents the fraction of outdoor particles people are truly exposed to, are utilized as modification factors to modify outdoor particle concentration. In this study, the probabilistic distributions of annually-averaged and seasonally-averaged F_inf and α were assessed for residences and residents in Beijing. F_inf of a single residence and α of an individual was estimated based on the mechanisms governing particle outdoor-to-indoor migration and human time-activity pattern. With this as the core deterministic model, probabilistic distributions of F_inf and α were estimated via Monte Carlo Simulation. Annually-averaged F_inf of PM_2.5 and PM₁₀ for residences in Beijing tended to be log-normally distributed as lnN(-0.74,0.14) and lnN(-0.94,0.15) with geometric mean value as 0.47 and 0.39, respectively. Annually-averaged α of PM_2.5 and PM₁₀ for Beijing residents also tended to be log-normally distributed as lnN(-0.59,0.12) and lnN(-0.73,0.13) with geometric mean value as 0.55 and 0.48, respectively. As for seasonally-averaged results, F_inf and α of PM_2.5 and PM₁₀ were largest in summer and smallest in winter. The obvious difference between these modification factors and unity suggested that modifications of ambient particle concentration need to be considered in epidemiological studies to avoid misclassifications of personal exposure to ambient particles. Moreover, considering the inter-individual difference of F_inf and α may lead to a brand new perspective of particle-health associations in further epidemiological study.

Indoor inhalation intake fractions of fine particulate matter: review of influencing factors

Exposure to fine particulate matter (PM_2.5 ) is a major contributor to the global human disease burden. The indoor environment is of particular importance when considering the health effects associated with PM_2.5 exposures because people spend the majority of their time indoors and PM_2.5 exposures per unit mass emitted indoors are two to three orders of magnitude larger than exposures to outdoor emissions. Variability in indoor PM_2.5 intake fraction (iF_in,total ), which is defined as the integrated cumulative intake of PM_2.5 per unit of emission, is driven by a combination of building-specific, human-specific, and pollutant-specific factors. Due to a limited availability of data characterizing these factors, however, indoor emissions and intake of PM_2.5 are not commonly considered when evaluating the environmental performance of product life cycles. With the aim of addressing this barrier, a literature review was conducted and data characterizing factors influencing iF_in,total were compiled. In addition to providing data for the calculation of iF_in,total in various indoor environments and for a range of geographic regions, this paper discusses remaining limitations to the incorporation of PM_2.5 -derived health impacts into life cycle assessments and makes recommendations regarding future research.

Ozone, Electrostatic Precipitators, and Particle Number Concentrations: Correlations Observed in a Real Office during Working Hours

This study investigates the impacts of outdoor and indoor ozone concentrations, ESP operation and occupancy on particle number concentrations within a modern office in Changsha, China. The office's one-pass air handling system contains a mini-bag filter (MERV 12) followed by an electrostatic precipitator (ESP) and high efficiency particulate air (HEPA) filter. Over a five-week period the system was operated either without the ESP (Stage 1, first-third week) or with the ESP (Stage 2, fourth and fifth week). Ozone and particle number concentrations were measured on working days. During both stages, indoor ozone and particle number concentrations tracked the outdoor ozone concentration. When operating, the ESP produced approximately 29 mg h(-1) of ozone, increasing supply air ozone by 15 ppb and steady-state indoor ozone by about 3 ppb. Occupancy tended to decrease indoor ozone and increase particle levels. During occupancy, indoor particle levels were low (∼2600 particle/cm(3)) when the supply air ozone level was less than 18 ppb. Above this threshold, the supply air ozone concentration and indoor particle number concentration were linearly related, and ESP operation increased the average indoor particle level by about 22 000 particles/cm(3). The implications for worker exposure to both ozone and particles are discussed.

A method to measure the ozone penetration factor in residences under infiltration conditions: application in a multifamily apartment unit

Recent experiments have demonstrated that outdoor ozone reacts with materials inside residential building enclosures, potentially reducing indoor exposures to ozone or altering ozone reaction byproducts. However, test methods to measure ozone penetration factors in residences (P) remain limited. We developed a method to measure ozone penetration factors in residences under infiltration conditions and applied it in an unoccupied apartment unit. Twenty-four repeated measurements were made, and results were explored to (i) evaluate the accuracy and repeatability of the new procedure using multiple solution methods, (ii) compare results from 'interference-free' and conventional UV absorbance ozone monitors, and (iii) compare results against those from a previously published test method requiring artificial depressurization. The mean (±s.d.) estimate of P was 0.54 ± 0.10 across a wide range of conditions using the new method with an interference-free monitor; the conventional monitor was unable to yield meaningful results due to relatively high limits of detection. Estimates of P were not clearly influenced by any indoor or outdoor environmental conditions or changes in indoor decay rate constants. This work represents the first known measurements of ozone penetration factors in a residential building operating under natural infiltration conditions and provides a new method for widespread application in buildings.

Benefit-cost analysis of commercially available activated carbon filters for indoor ozone removal in single-family homes

This study involved the development of a model for evaluating the potential costs and benefits of ozone control by activated carbon filtration in single-family homes. The modeling effort included the prediction of indoor ozone with and without activated carbon filtration in the HVAC system. As one application, the model was used to predict benefit-to-cost ratios for single-family homes in 12 American cities in five different climate zones. Health benefits were evaluated using disability-adjusted life-years and included city-specific age demographics for each simulation. Costs of commercially available activated carbon filters included capital cost differences when compared to conventional HVAC filters of similar particle removal efficiency, energy penalties due to additional pressure drop, and regional utility rates. The average indoor ozone removal effectiveness ranged from 4 to 20% across the 12 target cities and was largely limited by HVAC system operation time. For the parameters selected in this study, the mean predicted benefit-to-cost ratios for 1-inch filters were >1.0 in 10 of the 12 cities. The benefits of residential activated carbon filters were greatest in cities with high seasonal ozone and HVAC usage, suggesting the importance of targeting such conditions for activated carbon filter applications.

Long-Term Ozone Exposure and Mortality in a Large Prospective Study

RATIONALE

Tropospheric ozone (O3) is potentially associated with cardiovascular disease risk and premature death. Results from long-term epidemiological studies on O3 are scarce and inconclusive.

OBJECTIVES

In this study, we examined associations between chronic ambient O3 exposure and all-cause and cause-specific mortality in a large cohort of U.S. adults.

METHODS

Cancer Prevention Study II participants were enrolled in 1982. A total of 669,046 participants were analyzed, among whom 237,201 deaths occurred through 2004. We obtained estimates of O3 concentrations at the participant's residence from a hierarchical Bayesian space-time model. Estimates of fine particulate matter (particulate matter with an aerodynamic diameter of up to 2.5 μm [PM2.5]) and NO2 concentrations were obtained from land use regression. Cox proportional hazards regression models were used to examine mortality associations adjusted for individual- and ecological-level covariates.

MEASUREMENTS AND MAIN RESULTS

In single-pollutant models, we observed significant positive associations between O3, PM2.5, and NO2 concentrations and all-cause and cause-specific mortality. In two-pollutant models adjusted for PM2.5, significant positive associations remained between O3 and all-cause (hazard ratio [HR] per 10 ppb, 1.02; 95% confidence interval [CI], 1.01-1.04), circulatory (HR, 1.03; 95% CI, 1.01-1.05), and respiratory mortality (HR, 1.12; 95% CI, 1.08-1.16) that were unchanged with further adjustment for NO2. We also observed positive mortality associations with both PM2.5 (both near source and regional) and NO2 in multipollutant models.

CONCLUSIONS

Findings derived from this large-scale prospective study suggest that long-term ambient O3 contributes to risk of respiratory and circulatory mortality. Substantial health and environmental benefits may be achieved by implementing further measures aimed at controlling O3 concentrations.

Comparison of Highly Resolved Model-Based Exposure Metrics for Traffic-Related Air Pollutants to Support Environmental Health Studies

Human exposure to air pollution in many studies is represented by ambient concentrations from space-time kriging of observed values. Space-time kriging techniques based on a limited number of ambient monitors may fail to capture the concentration from local sources. Further, because people spend more time indoors, using ambient concentration to represent exposure may cause error. To quantify the associated exposure error, we computed a series of six different hourly-based exposure metrics at 16,095 Census blocks of three Counties in North Carolina for CO, NO_x, PM_2.5, and elemental carbon (EC) during 2012. These metrics include ambient background concentration from space-time ordinary kriging (STOK), ambient on-road concentration from the Research LINE source dispersion model (R-LINE), a hybrid concentration combining STOK and R-LINE, and their associated indoor concentrations from an indoor infiltration mass balance model. Using a hybrid-based indoor concentration as the standard, the comparison showed that outdoor STOK metrics yielded large error at both population (67% to 93%) and individual level (average bias between −10% to 95%). For pollutants with significant contribution from on-road emission (EC and NO_x), the on-road based indoor metric performs the best at the population level (error less than 52%). At the individual level, however, the STOK-based indoor concentration performs the best (average bias below 30%). For PM_2.5, due to the relatively low contribution from on-road emission (7%), STOK-based indoor metric performs the best at both population (error below 40%) and individual level (error below 25%). The results of the study will help future epidemiology studies to select appropriate exposure metric and reduce potential bias in exposure characterization.

Impact of asthma, exposure period, and filters on human responses during exposures to ozone and its initiated chemistry products

The impact of asthma, exposure period, and filter condition downstream of the mixing box of air-conditioning system on building occupants' perceptual response, work performance, and salivary α-amylase secretion during exposures to ozone and its initiated chemistry products is studied. The experiments were conducted in a field environmental chamber (FEC) (240 m(3)) simulating an office environment. Experiments were conducted during periods when the air-handling system operated with new or used pleated panel filters at constant recirculation (7/h) and ventilation (1/h) rates. Average ozone and secondary organic aerosols (ozone-initiated chemistry products) measured during non-asthmatic and asthmatic subjects' 3-h exposures in the FEC were in the ranges approximately 20-37 ppb and approximately 1.6-3 μg/m(3), respectively. Asthmatic subjects' perceived odor intensity and sensory (eye, nose, and throat) irritation ratings were generally lower than those of non-asthmatic subjects, possibly explaining why asthmatic subjects accept perceived air quality more than non-asthmatic subjects. However, asthmatic subjects' perceived physiological-like symptom ratings (flu, chest tightness, and headache) and concentrations of secreted salivary α-amylase were generally higher than those of non-asthmatic subjects. Asthmatic subjects had significantly lower accuracy than non-asthmatic subjects in a task that required higher concentration although they had higher work speed. Filter condition did not make any significant difference for subjects' responses.

Modeling indoor air pollution of outdoor origin in homes of SAPALDIA subjects in Switzerland

Given the shrinking spatial contrasts in outdoor air pollution in Switzerland and the trends toward tightly insulated buildings, the Swiss Cohort Study on Air Pollution and Lung and Heart Diseases in Adults (SAPALDIA) needs to understand to what extent outdoor air pollution remains a determinant for residential indoor exposure. The objectives of this paper are to identify determining factors for indoor air pollution concentrations of particulate matter (PM), ultrafine particles in the size range from 15 to 300nm, black smoke measured as light absorbance of PM (PMabsorbance) and nitrogen dioxide (NO2) and to develop predictive indoor models for SAPALDIA. Multivariable regression models were developed based on indoor and outdoor measurements among homes of selected SAPALDIA participants in three urban (Basel, Geneva, Lugano) and one rural region (Wald ZH) in Switzerland, various home characteristics and reported indoor sources such as cooking. Outdoor levels of air pollutants were important predictors for indoor air pollutants, except for the coarse particle fraction. The fractions of outdoor concentrations infiltrating indoors were between 30% and 66%, the highest one was observed for PMabsorbance. A modifying effect of open windows was found for NO2 and the ultrafine particle number concentration. Cooking was associated with increased particle and NO2 levels. This study shows that outdoor air pollution remains an important determinant of residential indoor air pollution in Switzerland.

Evaluating the Long-Term Health and Economic Impacts of Central Residential Air Filtration for Reducing Premature Mortality Associated with Indoor Fine Particulate Matter (PM2.5) of Outdoor Origin

Much of human exposure to fine particulate matter (PM2.5) of outdoor origin occurs in residences. High-efficiency particle air filtration in central heating, ventilating, and air-conditioning (HVAC) systems is increasingly being used to reduce concentrations of particulate matter inside homes. However, questions remain about the effectiveness of filtration for reducing exposures to PM2.5 of outdoor origin and adverse health outcomes. Here we integrate epidemiology functions and mass balance modeling to estimate the long-term health and economic impacts of HVAC filtration for reducing premature mortality associated with indoor PM2.5 of outdoor origin in residences. We evaluate 11 classifications of filters (MERV 5 through HEPA) using six case studies of single-family home vintages and ventilation system combinations located in 22 U.S. cities. We estimate that widespread use of higher efficiency filters would reduce premature mortality by 0.002-2.5% and increase life expectancy by 0.02-1.6 months, yielding annual monetary benefits ranging from $1 to $1348 per person in the homes and locations modeled herein. Large differences in the magnitude of health and economic impacts are driven largely by differences in rated filter efficiency and building and ventilation system characteristics that govern particle infiltration and persistence, with smaller influences attributable to geographic location.

The effect of ventilation on indoor exposure to semivolatile organic compounds

A mechanistic model was developed to examine how natural ventilation influences residential indoor exposure to semivolatile organic compounds (SVOCs) via inhalation, dermal sorption, and dust ingestion. The effect of ventilation on indoor particle mass concentration and mass transfer at source/sink surfaces, and the enhancing effect of particles on mass transfer at source/sink surfaces are included. When air exchange rate increases from 0.6/h to 1.8/h, the steady-state SVOC (gas-phase plus particle phase with log KOA varying from 9 to 13) concentration in the idealized model decreases by about 60%. In contrast, for the same change in ventilation, the simulated indoor formaldehyde (representing volatile organic compounds) gas-phase concentration decreases by about 70%. The effect of ventilation on exposure via each pathway has a relatively insignificant association with the KOA of the SVOCs: a change of KOA from 10(9) to 10(13) results in a change of only 2-30%. Sensitivity analysis identifies the deposition rate of PM2.5 as a primary factor influencing the relationship between ventilation and exposure for SVOCs with log KOA = 13. The relationship between ventilation rate and air speed near surfaces needs to be further substantiated.