Carbon dioxide guidelines for indoor air quality: a review.

BACKGROUND: The importance of building ventilation to protect health has been more widely recognized since the COVID-19 pandemic. Outdoor air ventilation in buildings dilutes indoor-generated air pollutants (including bioaerosols) and reduces resulting occupant exposures. Many countries and organizations have advisory guidelines or mandatory standards for minimum ventilation rates (VRs) to maintain indoor air quality (IAQ). Because directly measuring VRs is often difficult, many IAQ guidelines instead specify indoor concentration limits for carbon dioxide (CO2), using CO2 exhaled by building occupants as an indicator of VR. Although indoor CO2 guidelines are common, the evidence basis for the various CO2 limits has not been clear. OBJECTIVE: To review current indoor CO2 guidelines worldwide and the supportive evidence provided. METHODS: We identified worldwide CO2-based guidelines for IAQ or ventilation, along with any supportive evidence provided. We excluded occupational guidelines for CO2 levels ≥5000 ppm. RESULTS: Among 43 guidelines identified, 35 set single CO2 concentration limits and eight set multi-tiered limits; 16 mentioned no specific human effect to be controlled, 19 specified only odor dissatisfaction, five specified non-infectious health effects, and three specified airborne infectious disease transmission. The most common indoor CO2 limit was 1000 ppm. Thirteen guidelines specified maximum CO2 limits as extended time-weighted averages, none with evidence linking averaged limits to occupant effects. Of only 18 guidelines citing evidence to support limits set, we found this evidence persuasive for eight. Among these eight guidelines, seven set limits to control odor perception. One provided 17 scientifically-based CO2 limits, for specific example space uses and occupancies, to control long-range COVID-19 transmission indoors. IMPACT: Many current indoor carbon dioxide (CO2) guidelines for indoor air quality specified no adverse effects intended for control. Odor dissatisfaction was the effect mentioned most frequently, few mentioned health, and three mentioned control of infectious disease. Only one CO2 guideline was developed from scientific models to control airborne transmission of COVID-19. Most guidelines provided no supportive evidence for specified limits; few provided persuasive evidence. No scientific basis is apparent for setting one CO2 limit for IAQ across all buildings, setting a CO2 limit for IAQ as an extended time-weighted average, or using a one-time CO2 measurement to verify a desired VR.

Chemical Composition of Electronic Vaping Products from School Grounds in California.

INTRODUCTION: The use of electronic vaping products (EVPs) containing nicotine, marijuana, and/or other substances remains prominent among youth; with EVPs containing nicotine being the most commonly used tobacco product among youth since 2014. However, a detailed understanding of the chemical composition of these products is limited. METHODS: During February 25th-March 15th, 2019, a total of 576 EVPs, including 233 e-cigarette devices (with 43 disposable vape pens) and 343 e-liquid cartridges/pods/bottled e-liquids, were found or confiscated from a convenience sample of 16 public high schools in California. Liquids inside 251 vape pens and cartridges/pods/bottled e-liquids were analyzed using a gas chromatography/mass spectrometry (GC/MS). For comparison, new JUUL pods, the most commonly used e-cigarette among youth during 2018-2019, with different flavorings and nicotine content were purchased and analyzed. RESULTS: For e-cigarette cartridges/pods/bottled e-liquids, nicotine was detected in 204 of 208 (98.1%) samples. Propylene glycol (PG) and vegetable glycerin (VG) were dominant solvents in nicotine-containing EVPs. Among 43 disposable vape pen devices, cannabinoids such as tetrahydrocannabinol (THC) or cannabidiol (CBD) were identified in 39 of 43 (90.1%) samples, of which 3 contained both nicotine and THC. Differences in chemical compositions were observed between confiscated or collected JUULs and purchased JUULs. Measured nicotine was inconsistent with labels on some confiscated or collected bottled e-liquids. CONCLUSIONS: EVPs from 16 participating schools were found to widely contain substances with known adverse health effects among youth, including nicotine and cannabinoids. There was inconsistency between labeled and measured nicotine on the products from schools. IMPLICATIONS: This study measured the main chemical compositions of EVPs found at 16 California public high schools. Continued efforts are warranted, including at the school-level, to educate, prevent and reduce youth use of EVPs.

Comparative Mask Protection against Inhaling Wildfire Smoke, Allergenic Bioaerosols, and Infectious Particles.

This work compares relative mask inhalation protection against a range of airborne particle sizes that the general public may encounter, including infectious particles, wildfire smoke and ash, and allergenic fungal and plant particles. Several mask types available to the public were modeled with respirable fraction deposition. Best-case collection efficiencies for cloth, surgical, and respirator masks were predicted to be lowest (0.3, 0.6, and 0.8, respectively) for particle types with dominant sub-micrometer modes (wildfire smoke and human-emitted bronchial particles). Conversely, all mask types were predicted to achieve good collection efficiency (up to ~1.0) for the largest-sized particle types, including pollen grains, some fungal spores, and wildfire ash. Polydisperse infectious particles were predicted to be captured by masks with efficiencies of 0.3-1.0 depending on the pathogen size distribution and the type of mask used. Viruses aerosolized orally are predicted to be captured efficiently by all mask types, while those aerosolized from bronchiolar or laryngeal-tracheal sites are captured with much lower efficiency by surgical and cloth masks. The predicted efficiencies changed very little when extrathoracic deposition was included (inhalable rather than respirable fraction) or when very large (100 µm) particles were neglected. Actual mask fit and usage will determine protection levels in practice, but the relative comparisons in this work can inform mask guidance for different inhalation hazards, including particles generated by yard work, wildfires, and infections.

Secondary indoor air pollution and passive smoking associated with cannabis smoking using electric cigarette device-demonstrative in silico study.

With electronic (e)-liquids containing cannabis components easily available, many anecdotal examples of cannabis vaping using electronic cigarette devices have been reported. For electronic cigarette cannabis vaping, there are potential risks of secondary indoor air pollution from vapers. However, quantitative and accurate prediction of the inhalation and dermal exposure of a passive smoker in the same room is difficult to achieve due to the ethical constraints on subject experiments. The numerical method, i.e., in silico method, is a powerful tool to complement these experiments with real humans. In this study, we adopted a computer-simulated person that has been validated from multiple perspectives for prediction accuracy. We then conducted an in silico study to elucidate secondary indoor air pollution and passive smoking associated with cannabis vaping using an electronic cigarette device in an indoor environment. The aerosols exhaled by a cannabis vaper were confirmed to be a secondary emission source in an indoor environment; non-smokers were exposed to these aerosols via respiratory and dermal pathways. Tetrahydrocannabinol was used as a model chemical compound for the exposure study. Its uptake by the non-smoker through inhalation and dermal exposure under a worst-case scenario was estimated to be 5.9% and 2.6% of the exhaled quantity from an e-cigarette cannabis user, respectively.

Chemical Composition of JUUL Pods Collected From Students in California High Schools.

PURPOSE: To examine the chemical composition of JUUL pods collected from a convenience sample of 16 high schools in California to identify possible consumer modification or counterfeit use. METHODS: Using Gas Chromatography-Mass Spectrometry, we quantitatively analyzed the nicotine, propylene glycol (PG), and vegetable glycerin (VG) in JUUL pods (n = 26) collected from California high schools and compared results to commercial 3% (n = 15) and 5% (n = 24) JUUL pods purchased online. RESULTS: Most of the collected JUUL pods (24/26 pods) had a nicotine concentration (43.3 mg/ml, 95% PI: 21.5-65.1) outside the prediction intervals (PI) of the 3% (33.5 mg/ml, 95% PI: 31.8-35.2) and 5% (55.0 mg/ml, 95% PI: 51.5-58.3) commercial JUUL pods. Most (73%) collected JUUL pods had VG concentrations (583.5 mg/ml, PI: 428.9-738.1) lower than the 3% (722.2 mg/ml, PI: 643.0-801.4) and 5% (710.5 mg/ml, PI: 653.1-767.8) commercial JUUL pods. CONCLUSIONS: Used JUUL products collected from high school students or found on school grounds were not chemically consistent with the manufacturer's stated formulations.

A numerical investigation of the potential effects of e-cigarette smoking on local tissue dosimetry and the deterioration of indoor air quality.

Electronic (e)-cigarette smoking is considered to be less harmful than traditional tobacco smoking because of the lack of a combustion process. However, e-cigarettes have the potential to release harmful chemicals depending on the constituents of the vapor. To date, there has been significant evidence on the adverse health effects of e-cigarette usage. However, what is less known are the impacts of the chemicals contained in exhaled air from an e-cigarette smoker on indoor air quality, the second-hand passive smoking of residents, and the toxicity of the exhaled air. In this study, we develop a comprehensive numerical model and computer-simulated person to investigate the potential effects of e-cigarette smoking on local tissue dosimetry and the deterioration of indoor air quality. We also conducted demonstrative numerical analyses for first-hand and second-hand e-cigarette smoking in an indoor environment. To investigate local tissue dosimetry, we used newly developed physiologically based pharmacokinetic/toxicokinetic models that reproduce inhalation exposure by way of the respiratory tract and dermal exposure through the human skin surface. These models were integrated into the computer-simulated person. Our numerical simulation results quantitatively demonstrated the potential impacts of e-cigarette smoking in enclosed spaces on indoor air quality.

An improved mechanism-based model for predicting the long-term formaldehyde emissions from composite wood products with exposed edges and seams.

Emissions of formaldehyde from building materials and furniture can cause adverse health effects. Traditional models generally only consider emissions as a physical process that can be characterized by three key parameters: the initial emittable concentration, the diffusion coefficient and the partition coefficient. However, the physical-based model causes discrepancy in predicting long-term formaldehyde emissions for the cases where chemical reaction (i.e., hydrolysis) occurs over time. In this study, an improved mechanism-based model was developed by combining the chemical reaction process with a physical mass transfer process to more accurately predict the long-term emission behaviors. The chamber testing data of formaldehyde emissions from exposed edges and seams of a laminate flooring product made with composite wood core for about 1.5 year was used to validate the model. Results indicate that the mechanism-based model characterizes well the long-term formaldehyde emissions from the tested material. Predictions of different models further demonstrate the advantages of this improved model compared with the physical model or with empirical models. This study is the first attempt to check the feasibility of including the chemical reaction term in emission modeling and to quantitatively explore the importance of its contribution to long-term formaldehyde emissions, which includes most of the indoor emissions from materials and furniture.

Measurement of heating coil temperature for e-cigarettes with a "top-coil" clearomizer.

OBJECTIVES: To determine the effect of applied power settings, coil wetness conditions, and e-liquid compositions on the coil heating temperature for e-cigarettes with a "top-coil" clearomizer, and to make associations of coil conditions with emission of toxic carbonyl compounds by combining results herein with the literature. METHODS: The coil temperature of a second generation e-cigarette was measured at various applied power levels, coil conditions, and e-liquid compositions, including (1) measurements by thermocouple at three e-liquid fill levels (dry, wet-through-wick, and full-wet), three coil resistances (low, standard, and high), and four voltage settings (3-6 V) for multiple coils using propylene glycol (PG) as a test liquid; (2) measurements by thermocouple at additional degrees of coil wetness for a high resistance coil using PG; and (3) measurements by both thermocouple and infrared (IR) camera for high resistance coils using PG alone and a 1:1 (wt/wt) mixture of PG and glycerol (PG/GL). RESULTS: For single point thermocouple measurements with PG, coil temperatures ranged from 322 ‒ 1008°C, 145 ‒ 334°C, and 110 ‒ 185°C under dry, wet-through-wick, and full-wet conditions, respectively, for the total of 13 replaceable coil heads. For conditions measured with both a thermocouple and an IR camera, all thermocouple measurements were between the minimum and maximum across-coil IR camera measurements and equal to 74% ‒ 115% of the across-coil mean, depending on test conditions. The IR camera showed details of the non-uniform temperature distribution across heating coils. The large temperature variations under wet-through-wick conditions may explain the large variations in formaldehyde formation rate reported in the literature for such "top-coil" clearomizers. CONCLUSIONS: This study established a simple and straight-forward protocol to systematically measure e-cigarette coil heating temperature under dry, wet-through-wick, and full-wet conditions. In addition to applied power, the composition of e-liquid, and the devices' ability to efficiently deliver e-liquid to the heating coil are important product design factors effecting coil operating temperature. Precautionary temperature checks on e-cigarettes under manufacturer-recommended normal use conditions may help to reduce the health risks from exposure to toxic carbonyl emissions associated with coil overheating.

A Device-Independent Evaluation of Carbonyl Emissions from Heated Electronic Cigarette Solvents.

OBJECTIVES: To investigate how the two main electronic (e-) cigarette solvents-propylene glycol (PG) and glycerol (GL)-modulate the formation of toxic volatile carbonyl compounds under precisely controlled temperatures in the absence of nicotine and flavor additives. METHODS: PG, GL, PG:GL = 1:1 (wt/wt) mixture, and two commercial e-cigarette liquids were vaporized in a stainless steel, tubular reactor in flowing air ranging up to 318°C to simulate e-cigarette vaping. Aerosols were collected and analyzed to quantify the amount of volatile carbonyls produced with each of the five e-liquids. RESULTS: Significant amounts of formaldehyde and acetaldehyde were detected at reactor temperatures ≥215°C for both PG and GL. Acrolein was observed only in e-liquids containing GL when reactor temperatures exceeded 270°C. At 318°C, 2.03±0.80 µg of formaldehyde, 2.35±0.87 µg of acetaldehyde, and a trace amount of acetone were generated per milligram of PG; at the same temperature, 21.1±3.80 µg of formaldehyde, 2.40±0.99 µg of acetaldehyde, and 0.80±0.50 µg of acrolein were detected per milligram of GL. CONCLUSIONS: We developed a device-independent test method to investigate carbonyl emissions from different e-cigarette liquids under precisely controlled temperatures. PG and GL were identified to be the main sources of toxic carbonyl compounds from e-cigarette use. GL produced much more formaldehyde than PG. Besides formaldehyde and acetaldehyde, measurable amounts of acrolein were also detected at ≥270°C but only when GL was present in the e-liquid. At 215°C, the estimated daily exposure to formaldehyde from e-cigarettes, exceeded United States Environmental Protection Agency (USEPA) and California Office of Environmental Health Hazard Assessment (OEHHA) acceptable limits, which emphasized the need to further examine the potential cancer and non-cancer health risks associated with e-cigarette use.

In-situ Real-Time Monitoring of Volatile Organic Compound Exposure and Heart Rate Variability for Patients with Multiple Chemical Sensitivity.

In-situ real-time monitoring of volatile organic compound (VOC) exposure and heart rate variability (HRV) were conducted for eight multiple chemical sensitivity (MCS) patients using a VOC monitor, a Holter monitor, and a time-activity questionnaire for 24 h to identify the relationship between VOC exposure, biological effects, and subjective symptoms in actual life. The results revealed no significantly different parameters for averaged values such as VOC concentration, HF (high frequency), and LF (low frequency) to HF ratio compared with previous data from healthy subjects (Int. J. Environ. Res. Public Health 2010, 7, 4127-4138). Significant negative correlations for four subjects were observed between HF and amounts of VOC change. These results suggest that some patients show inhibition of parasympathetic activities along with VOC exposure as observed in healthy subjects. Comparing the parameters during subjective symptoms and normal condition, VOC concentration and/or VOC change were high except for one subject. HF values were low for five subjects during subjective symptoms. Examining the time-series data for VOC exposure and HF of each subject showed that the subjective symptoms, VOC exposure, and HF seemed well related in some symptoms. Based on these characteristics, prevention measures of symptoms for each subject may be proposed.

Formaldehyde emissions from ventilation filters under different relative humidity conditions.

Formaldehyde emissions from fiberglass and polyester filters used in building heating, ventilation, and air conditioning (HVAC) systems were measured in bench-scale tests using 10 and 17 cm(2) coupons over 24 to 720 h periods. Experiments were performed at room temperature and four different relative humidity settings (20, 50, 65, and 80% RH). Two different air flow velocities across the filters were explored: 0.013 and 0.5 m/s. Fiberglass filters emitted between 20 and 1000 times more formaldehyde than polyester filters under similar RH and airflow conditions. Emissions increased markedly with increasing humidity, up to 10 mg/h-m(2) at 80% RH. Formaldehyde emissions from fiberglass filters coated with tackifiers (impaction oils) were lower than those from uncoated fiberglass media, suggesting that hydrolysis of other polymeric constituents of the filter matrix, such as adhesives or binders was likely the main formaldehyde source. These laboratory results were further validated by performing a small field study in an unoccupied office. At 80% RH, indoor formaldehyde concentrations increased by 48-64%, from 9-12 µg/m(3) to 12-20 µg/m(3), when synthetic filters were replaced with fiberglass filtration media in the HVAC units. Better understanding of the reaction mechanisms and assessing their overall contributions to indoor formaldehyde levels will allow for efficient control of this pollution source.

A novel methodology to evaluate health impacts caused by VOC exposures using real-time VOC and Holter monitors.

While various volatile organic compounds (VOCs) are known to show neurotoxic effects, the detailed mechanisms of the action of VOCs on the autonomic nervous system are not fully understood, partially because objective and quantitative measures to indicate neural abnormalities are still under development. Nevertheless, heart rate variability (HRV) has been recently proposed as an indicative measure of the autonomic effects. In this study, we used HRV as an indicative measure of the autonomic effects to relate their values to the personal concentrations of VOCs measured by a real-time VOC monitor. The measurements were conducted for 24 hours on seven healthy subjects under usual daily life conditions. The results showed HF powers were significantly decreased for six subjects when the changes of total volatile organic compound (TVOC) concentrations were large, indicating a suppression of parasympathetic nervous activity induced by the exposure to VOCs. The present study indicated these real-time monitoring was useful to characterize the trends of VOC exposures and their effects on autonomic nervous system.

Air pollution and young children's inhalation exposure to organophosphorus pesticide in an agricultural community in Japan.

Assessment of airborne organophosphorus pesticides in houses of young children (1-6 years old) and childcare facilities was conducted following pesticide applications in an agricultural community in Japan. Trichlorfon and fenitrothion, applied in two separate periods, were frequently detected from outdoor and indoor air. Dichlorvos, the primary degradation product of trichlorfon, was also detected after the application of trichlorfon. Both the outdoors and indoor concentration of applied pesticide were shown to increase with decreasing distance from the pesticide-applied farm. Indoor concentration of these pesticides significantly correlated with outdoor concentration (p=0.001 for trichlorfon and p=0.001 for fenitrothion), indicating infiltration of applied pesticide inside. Ratio of indoor to outdoor concentration (I/O ratio) of fenitrothion was higher for houses with windows open during the application than those with closed windows (median value: 0.74 vs. 0.16, p=0.003). However, a similar trend was not observed for trichlorfon as well as dichlorvos in the first period. Dichlorvos was found to have a higher I/O ratio than trichlorfon during the period, and clear correlation between indoor concentrations of dichlorvos and those of trichlorfon suggested increased decomposition of trichlorfon in the indoor environment. Daily inhalation exposure estimated by using the fixed measurement data and time-activity questionnaire ranged from 0 to 35 ng/kg/day for trichlorfon, from 0 to 26 ng/kg/day for dichlorvos, and from 0 to 44 ng/kg/day for fenitrothion. Median inhalation exposure from indoor air accounted for 74%, 86.3%, and 45% of the daily inhalation exposure, respectively. For kindergarteners or nursery school children, inhalation exposure at childcare facilities was comparable with or more than that at home, indicating that pollution level at childcare facilities had potential of high impact on children's exposure. Estimated daily inhalation exposures were inversely correlated to the proximity of their activity location to the pesticide-applied farm.

Field validation of an active sampling cartridge as a passive sampler for long-term carbonyl monitoring.

A carbonyl sampler originally designed for the active sampling method (Sep-Pak XPoSure) was used for long-term passive sampling, and its applicability as a passive sampler was examined through field experiments. The uptake rates of passive sampling were determined experimentally from collocated passive and active samplings for various sampling periods. The obtained uptake rates of formaldehyde, acetaldehyde, and acetone were 1.48, 1.23, and 1.08 mL/min, respectively. These uptake rates were consistent for a wide range of the sampling term (12 hr-2 weeks). Uptake rates of each carbonyl were proportional to the diffusion coefficients of each. Therefore, the ratios of diffusion coefficients were used to calculate the uptake rates of carbonyls for which the rates were not determined experimentally. Lower limits of determination were 2.16-17.5 microg/m3 for 2-week sampling. It was confirmed that 2-week monitoring of carbonyl concentrations up to 118-229 microg/m3 was possible. Relative standard deviations of the passive method generated from the repeatability test were 2-12.3% error for five samplings, and the recovery efficiencies were larger than 90%. Thus, the passive sampler was found to be highly suitable for long-term monitoring of carbonyl compounds.