Dynamic behavior of indoor ultrafine particles (2.3‐64 nm) due to burning candles in a residence

A major source of human exposure to ultrafine particles is candle use. Candles produce ultrafine particles in the size range under 10 nm, with perhaps half of the particles less than 5 nm. For these small particles at typically high concentrations, coagulation and deposition are two dominant mechanisms in aerosol size dynamics. We present an updated coagulation model capable of characterizing the relative contributions of coagulation, deposition, and air exchange rates. Size‐resolved coagulation and decay rates are estimated for three types of candles. Number, area, and mass distributions are provided for 93 particle sizes from 2.33 to 64 nm. Total particle production was in the range of 10¹³ min^?1. Peak number, area, and mass concentrations occurred at particle sizes of <3, 20, and 40 nm, respectively. Both the number and area concentrations greatly exceeded background concentrations in the residence studied. Contributions of coagulation, deposition, and air exchange rates to particle losses were 65%, 34%, and 0.3% at high concentrations (10⁶ cm^?3), while they are 17%, 81%, and 1.7% at lower concentrations (3 × 10⁴ cm^?3), respectively. The increased particle production for the very smallest particles (2.33‐2.50 nm) suggests that even smaller particles may be important to study.     

Emission rates and the personal cloud effect associated with particle release from the perihuman environment

Inhalation exposure to elevated particulate matter levels is correlated with deleterious health and well‐being outcomes. Despite growing evidence that identifies humans as sources of coarse airborne particles, the extent to which personal exposures are influenced by particle releases near occupants is unknown. In a controlled chamber, we monitored airborne total particle levels with high temporal and particle‐size resolution for a range of simulated occupant activities. We also sampled directly from the subject's breathing zone to characterize exposures. A material‐balance model showed that a sitting occupant released 8 million particles/h in the diameter range 1‐10 μm. Elevated emissions were associated with increased intensity of upper body movements and with walking. Emissions were correlated with exposure, but not linearly. The personal PM₁₀ exposure increment above the room‐average levels was 1.6‐13 μg/m³ during sitting, owing to spatial heterogeneity of particulate matter concentrations, a feature that was absent during walking. The personal cloud was more discernible among larger particles, as would be expected for shedding from skin and clothing. Manipulating papers and clothing fabric was a strong source of airborne particles. An increase in personal exposure was observed owing to particle mass exchange associated with a second room occupant.     

Particle number emission rates of aerosol sources in 40 German households and their contributions to ultrafine and fine particle exposure

More representative data on source-specific particle number emission rates and associated exposure in European households are needed. In this study, indoor and outdoor particle number size distributions (10–800 nm) were measured in 40 German households under real-use conditions in over 500 days. Particle number emission rates were derived for around 800 reported indoor source events. The highest emission rate was caused by burning candles (5.3 × 10¹³ h⁻¹). Data were analyzed by the single-parameter approach (SPA) and the indoor aerosol dynamics model approach (IAM). Due to the consideration of particle deposition, coagulation, and time-dependent ventilation rates, the emission rates of the IAM approach were about twice as high as those of the SPA. Correction factors are proposed to convert the emission rates obtained from the SPA approach into more realistic values. Overall, indoor sources contributed ~ 56% of the daily-integrated particle number exposure in households under study. Burning candles and opening the window leads to seasonal differences in the contributions of indoor sources to residential exposure (70% and 40% in the cold and warm season, respectively). Application of the IAM approach allowed to attribute the contributions of outdoor particles to the penetration through building shell and entry through open windows (26% and 15%, respectively).     

Chamber bioaerosol study: human emissions of size‐resolved fluorescent biological aerosol particles

Humans are a prominent source of airborne biological particles in occupied indoor spaces, but few studies have quantified human bioaerosol emissions. The chamber investigation reported here employs a fluorescence‐based technique to evaluate bioaerosols with high temporal and particle size resolution. In a 75‐m³ chamber, occupant emission rates of coarse (2.5–10 μm) fluorescent biological aerosol particles (FBAPs) under seated, simulated office‐work conditions averaged 0.9 ± 0.3 million particles per person‐h. Walking was associated with a 5–6× increase in the emission rate. During both walking and sitting, 60–70% or more of emissions originated from the floor. The increase in emissions during walking (vs. while sitting) was mainly attributable to release of particles from the floor; the associated increased vigor of upper body movements also contributed. Clothing, or its frictional interaction with human skin, was demonstrated to be a source of coarse particles, and especially of the highly fluorescent fraction. Emission rates of FBAPs previously reported for lecture classes were well bounded by the experimental results obtained in this chamber study. In both settings, the size distribution of occupant FBAP emissions had a dominant mode in the 3–5 μm diameter range.     

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 K_OA 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 K_OA of the SVOCs: a change of K_OA from 10⁹ to 10¹³ results in a change of only 2–30%. Sensitivity analysis identifies the deposition rate of PM_2.5 as a primary factor influencing the relationship between ventilation and exposure for SVOCs with log K_OA = 13. The relationship between ventilation rate and air speed near surfaces needs to be further substantiated.     

Size‐resolved fluorescent biological aerosol particle concentrations and occupant emissions in a university classroom

This study is among the first to apply laser‐induced fluorescence to characterize bioaerosols at high time and size resolution in an occupied, common‐use indoor environment. Using an ultraviolet aerodynamic particle sizer, we characterized total and fluorescent biological aerosol particle (FBAP) levels (1–15 μm diameter) in a classroom, sampling with 5‐min resolution continuously during eighteen occupied and eight unoccupied days distributed throughout a one‐year period. A material‐balance model was applied to quantify per‐person FBAP emission rates as a function of particle size. Day‐to‐day and seasonal changes in FBAP number concentration (N_F) values in the classroom were small compared to the variability within a day that was attributable to variable levels of occupancy, occupant activities, and the operational state of the ventilation system. Occupancy conditions characteristic of lecture classes were associated with mean N_F source strengths of 2 × 10⁶ particles/h/person, and 9 × 10⁴ particles per metabolic g CO₂. During transitions between lectures, occupant activity was more vigorous, and estimated mean, per‐person N_F emissions were 0.8 × 10⁶ particles per transition. The observed classroom peak in FBAP size at 3–4 μm is similar to the peak in fluorescent and biological aerosols reported from several studies outdoors.     

Size and mineral composition of airborne particles generated by an ultrasonic humidifier

This study describes the size distribution and concentration of particles expelled by a portable, 3‐L ultrasonic humidifier. The ultrasonic humidifier was filled with waters of varying mineral content and hardness. Aerosol size distributions were measured during 8 hours of humidifier operation in a typical bedroom. Humidifiers produced approximately 1.22 × 10¹⁰‐2.50 × 10¹⁰ airborne particles per milliliter of water consumed, resulting in airborne particle concentrations of 3.01‐5.91 × 10⁴ #/cm³, with modes ranging between 109 and 322 nm in diameter. The emission rate of particles varied by water type from 1.02 × 10⁹ to 2.27 × 10⁹ #/s. Lower mineral waters produced fewer, smaller particles when compared to higher mineral waters. Chemical analyses of particles collected with a cascade impactor indicated that the minerals in emitted particles had the same relative mineral concentrations as the fill water. Our results demonstrate that ultrasonic humidifiers should be considered a source of inhalation exposure to minerals dissolved in water, and that the magnitude of exposure to inhalable particles will vary with water quality.     

Indoor ozone/human chemistry and ventilation strategies

This study aimed to better understand and quantify the influence of ventilation strategies on occupant‐related indoor air chemistry. The oxidation of human skin oil constituents was studied in a continuously ventilated climate chamber at two air exchange rates (1 h^?1 and 3 h^?1) and two initial ozone mixing ratios (30 and 60 ppb). Additional measurements were performed to investigate the effect of intermittent ventilation (“off” followed by “on”). Soiled t‐shirts were used to simulate the presence of occupants. A time‐of‐flight‐chemical ionization mass spectrometer (ToF‐CIMS) in positive mode using protonated water clusters was used to measure the oxygenated reaction products geranyl acetone, 6‐methyl‐5‐hepten‐2‐one (6‐MHO) and 4‐oxopentanal (4‐OPA). The measurement data were used in a series of mass balance models accounting for formation and removal processes. Reactions of ozone with squalene occurring on the surface of the t‐shirts are mass transport limited; ventilation rate has only a small effect on this surface chemistry. Ozone‐squalene reactions on the t‐shirts produced gas‐phase geranyl acetone, which was subsequently removed almost equally by ventilation and further reaction with ozone. About 70% of gas‐phase 6‐MHO was produced in surface reactions on the t‐shirts, the remainder in secondary gas‐phase reactions of ozone with geranyl acetone. 6‐MHO was primarily removed by ventilation, while further reaction with ozone was responsible for about a third of its removal. 4‐OPA was formed primarily on the surfaces of the shirts (~60%); gas‐phase reactions of ozone with geranyl acetone and 6‐MHO accounted for ~30% and ~10%, respectively. 4‐OPA was removed entirely by ventilation. The results from the intermittent ventilation scenarios showed delayed formation of the reaction products and lower product concentrations compared to continuous ventilation.     

Ultrafine particles generated from coloring with scented markers in the presence of ozone

High concentrations of ultrafine particles (UFPs) have been previously reported during school art activities. This is possibly due to secondary organic aerosols (SOAs) formed from reactions between ozone and volatile organic compounds emitted from art products. Four brands of markers, three scented and one unscented, were tested inside a stainless steel chamber at eight different ozone concentrations between 0 and 300 ppb. Out of the 32 tested markers, only the lemon‐ and orange‐scented markers from one brand reacted with ozone to form UFPs. Limonene, pinene, and several other terpenes were identified as ingredients of ink in SOA‐forming markers. Coloring with one lemon‐scented marker for 1 min without ozone generated on average approximately 26 ± 4 ppb of limonene inside the chamber. At 150 ppb ozone, using one lemon marker for 1 min formed on average 7.7 × 10¹⁰ particles. The particle size distribution indicated an initial mode of 15 nm which grew to 40 nm. At 50 ppb ozone and below, no significant SOA formation occurred. The number of particles formed is moderately correlated with the mass of ink used (R² = 0.68). Based on these data, scented markers are not likely a strong source of SOA under normal indoor ozone levels.     

Characterizing particle resuspension from mattresses: chamber study

People spend approximately one‐third of their lives sleeping, where they can be exposed to a myriad of particle‐bound biological agents and chemical pollutants that originate within mattresses and bedding, including allergens, fungal spores, bacteria, and particle‐phase semi‐volatile organic compounds. Full‐scale particle resuspension experiments were conducted in an environmental chamber, where volunteers performed a prescribed movement routine on an artificially seeded mattress. Human movements in bed, such as rolling from the prone to supine position, were found to resuspend settled particles, leading to elevations in airborne particle concentrations. Resuspension rates were estimated for the size fractions of 1–2 μm, 2–3 μm, 3–5 μm, 5–10 μm, and 10–20 μm, and were in the range of 10^?3 to 10¹ h^?1. Particle size had the most significant impact on the resuspension rate, whereas dust loading, volunteer body mass, and ventilation rate had a much smaller impact. Resuspension increased with the intensity of a movement, as characterized by surface vibrations, and decreased with repeated movement routines. Inhalation exposure was characterized with the intake fraction metric. Intake fractions increased as the particle size and ventilation rate decreased and ranged from 10² to 10⁴ inhaled particles per million resuspended, demonstrating that a significant fraction of released particles can be inhaled by sleeping occupants.     

Fine and ultrafine particle emissions from microwave popcorn

This study characterized fine (PM_2.5) and ultrafine particle (UFP, diameter < 100 nm) emissions from microwave popcorn and analyzed influential factors. Each pre‐packed popcorn bag was cooked in a microwave oven enclosed in a stainless steel chamber for 3 min. The number concentration and size distribution of UFPs and PM_2.5 mass concentration were measured inside the chamber repeatedly for five different flavors under four increasing power settings using either the foil‐lined original package or a brown paper bag. UFPs and PM_2.5 generated by microwaving popcorn were 150–560 and 350–800 times higher than the emissions from microwaving water, respectively. About 90% of the total particles emitted were in the ultrafine size range. The emitted PM concentrations varied significantly with flavor. Replacing the foil‐lined original package with a brown paper bag significantly reduced the peak concentration by 24–87% for total particle number and 36–70% for PM_2.5. A positive relationship was observed between both UFP number and PM_2.5 mass and power setting. The emission rates of microwave popcorn ranged from 1.9 × 10¹⁰ to 8.0 × 10¹⁰ No./min for total particle number and from 134 to 249 μg/min for PM_2.5.     

Formaldehyde and acetaldehyde exposure mitigation in US residences: in‐home measurements of ventilation control and source control

Measurements were taken in new US residences to assess the extent to which ventilation and source control can mitigate formaldehyde exposure. Increasing ventilation consistently lowered indoor formaldehyde concentrations. However, at a reference air exchange rate of 0.35 h^?1, increasing ventilation was up to 60% less effective than would be predicted if the emission rate were constant. This is consistent with formaldehyde emission rates decreasing as air concentrations increase, as observed in chamber studies. In contrast, measurements suggest acetaldehyde emission was independent of ventilation rate. To evaluate the effectiveness of source control, formaldehyde concentrations were measured in Leadership in Energy and Environmental Design (LEED)‐certified/Indoor airPLUS homes constructed with materials certified to have low emission rates of volatile organic compounds (VOC). At a reference air exchange rate of 0.35 h^?1, and adjusting for home age, temperature and relative humidity, formaldehyde concentrations in homes built with low‐VOC materials were 42% lower on average than in reference new homes with conventional building materials. Without adjustment, concentrations were 27% lower in the low‐VOC homes. The mean and standard deviation of formaldehyde concentration was 33 μg/m³ and 22 μg/m³ for low‐VOC homes and 45 μg/m³ and 30 μg/m³ for conventional.     

Safe velocity of on-fire train running in the tunnel

The safety of a running train on fire in a tunnel is a key issue for rescue operations, and the train velocity is mainly related to its safety. In this study, the relationship between the wind velocity and heat release rate (HRR), temperature field around the train, and flame/smoke pervasion rule were investigated under the conditions of variable train velocity, fire location, and fire source location. Beijing Metro was considered as a typical example, in which the safe velocity was estimated to be ∼41.83 km h⁻¹. Assuming the occurrence of fire at the center of the train, the numerical simulations of the flow field using the sliding grid of CFD were performed for a full-scale tunnel under different HRRs. When the fire source reached to the target section, the velocities of all the monitoring points rapidly increased. The velocities increased as the train tail arrived at the target section. The velocities at the measuring points increased with the increase in height, excluding the value of the position with a distance of 0.025 m from the tunnel ceiling. The average temperature and concentration of smoke in the annular space between the train and tunnel ceiling had the minimum values when the running train on fire moved with a speed of 45 km h⁻¹. Thus, the safe velocity of a subway train on fire should be managed between 41.83 km h⁻¹ and 45 km h⁻¹.     

A mixing‐length‐scale‐based analytical model for predicting velocity profiles of open‐channel flows with submerged rigid vegetation

In open‐channel flows with submerged vegetation, the vertical velocity profile can often be described by two layers: the vegetation layer in the lower region and the surface layer in the upper non‐vegetated region. In this paper, a new mixing‐length scale of eddy is proposed for predicting the vertical velocity profile of flow in an open‐channel with submerged rigid vegetation. The analytical model of velocity profile is based on the momentum equation of flow where the turbulent eddy viscosity is assumed to have a linear relationship with the local velocity. The proposed model was tested against different datasets from the literature. The 22 datasets used cover a range of submergence [flow depth (H)/vegetation height (h) = 1.25 ~ 3.38], different vegetation densities of ah = 0.11 ~ 1.85 (a defined as the frontal area of the vegetation per unit volume) and bed slopes (S_o = 1.8 × 10^?6 ~4.0 × 10^?3). This study showed that the proposed model can predict the velocity profiles well against all datasets, and that the mixing length scale of eddies (λ) is well related with both vegetation height (h) and flow depth of surface layer (i.e. the height of non‐vegetation layer, H–h). Close examination of λ in the proposed model showed that when λ = 0.03, the model predicts vertical velocity profiles well for all datasets used except for very shallow submergence (i.e. H/h < 1.5).     

Air change rates in urban Chinese bedrooms

The ventilation modalities in most Chinese residences are infiltration and opening windows. We measured infiltration rates and air change rates at night, with no attempt to change occupants' behaviors, of urban residences in five climate zones of China during four seasons. Using the CO₂ decay method, we found the median infiltration rate for 294 residences to be 0.34 h^?1. Using occupant‐generated CO₂ as tracer gas, we determined air change rates over the course of 1 year in 46 bedrooms at night from mass balance considerations. In 54% of the measurements, windows were closed, so ventilation was only by infiltration. Windows were mainly closed when the outdoor temperature was below 15°C and above 26°C. The median infiltration rates did not differ appreciably among seasons and climate zones and were always less than 0.45 h^?1.     

Secondary organic aerosol formation initiated by α‐terpineol ozonolysis in indoor air

Secondary organic aerosol (SOA) owing to reactive organic gas (ROG) ozonolysis can be an important indoor particle source. However, SOA formation owing to ozonolysis of α‐terpineol, which is emitted by consumer product usage and reacts strongly with ozone, has not been systematically quantified. Therefore, we conducted 21 experiments to investigate the SOA formation initiated by α‐terpineol ozonolysis for high (0.84 h^?1), moderate (0.61 h^?1), and low (0.36 h^?1) air exchange rates (AER), which is the frequency with which indoor is replaced by outdoor air. α‐Terpineol concentrations of 6.39 to 226 ppb were combined with high ozone (~25 ppm) to ensure rapid and complete ozonolysis. No reactants were replenished, so SOA peaked quickly and then decreased due to AER and surface losses, and peak SOA ranged from 2.03 to 281 μg/m³ at unit density. SOA mass formation was parameterized with the aerosol mass fraction (AMF), a.k.a. the SOA yield, and AMFs ranged from 0.056 to 0.24. The AMFs strongly and positively correlated with reacted α‐terpineol, whereas they weakly and negatively correlated with higher AERs. One‐product, two‐product, and volatility basis set (VBS) models were fit to the AMF data. Predictive modeling demonstrated that α‐terpineol ozonolysis could meaningfully form SOA in indoor air.     

Air quality,mortality, and economic benefits of a smoke – free workplace law for non‐smoking Ontario bar workers

We estimated the impact of a smoke‐free workplace bylaw on non‐smoking bar workers' health in Ontario, Canada. We measured bar workers' urine cotinine before (n = 99) and after (n = 91) a 2004 smoke‐free workplace bylaw. Using pharmacokinetic and epidemiological models, we estimated workers' fine‐particle (PM_2.5) air pollution exposure and mortality risks from workplace secondhand smoke (SHS). workers' pre‐law geometric mean cotinine was 10.3 ng/ml; post‐law dose declined 70% to 3.10 ng/ml and reported work hours of exposure by 90%. Pre‐law, 97% of workers' doses exceeded the 90th percentile for Canadians of working age. Pre‐law‐estimated 8‐h average workplace PM_2.5 exposure from SHS was 419 μg/m³ or ‘Very Poor’ air quality, while outdoor PM_2.5 levels averaged 7 μg/m³, ‘Very Good’ air quality by Canadian Air Quality Standards. We estimated that the bar workers' annual mortality rate from workplace SHS exposure was 102 deaths per 100 000 persons. This was 2.4 times the occupational disease fatality rate for all Ontario workers. We estimated that half to two‐thirds of the 10 620 Ontario bar workers were non‐smokers. Accordingly, Ontario's smoke‐free law saved an estimated 5–7 non‐smoking bar workers' lives annually, valued at CA $50 million to $68 million (US $49 million to $66 million).     

Household air pollution and personal exposure risk of polycyclic aromatic hydrocarbons among rural residents in Shanxi,China

Polycyclic aromatic hydrocarbons (PAHs) are a group of pollutants of widespread concerns. Gaseous and size‐segregated particulate‐phase PAHs were collected in indoor and outdoor air in rural households. Personal exposure was measured and compared to the ingestion exposure. The average concentrations of 28 parent PAHs and benzo(a)pyrene (BaP) were 9000 ± 8390 and 131 ± 236 ng/m³ for kitchen, 2590 ± 2270 and 43 ± 95 ng/m³ for living room, and 2800 ± 3890 and 1.6 ± 0.7 ng/m³ for outdoor air, respectively. The mass percent of high molecular weight (HMW) compounds with 5–6 rings contributed 1.3% to total 28 parent PAHs. Relatively higher fractions of HMW PAHs were found in indoor air compared to outdoor air. Majorities of particle‐bound PAHs were found in the finest PM_0.25, and the highest levels of fine PM_0.25‐bound PAHs were in the kitchen using peat and wood as energy sources. The 24‐h personal PAH exposure concentration was 2100 ± 1300 ng/m³. Considering energies, exposures to those using wood were the highest. The PAH inhalation exposure comprised up to about 30% in total PAH exposure through food ingestion and inhalation, and the population attributable fraction (PAF) for lung cancer in the region was 0.85%. The risks for inhaled and ingested intakes of PAHs were 1.0 × 10^?5 and 1.1 × 10^?5, respectively.     

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.     

Assessment of ultrafine particles in Portuguese preschools: levels and exposure doses

The aim of this work was to assess ultrafine particles (UFP) number concentrations in different microenvironments of Portuguese preschools and to estimate the respective exposure doses of UFP for 3–5‐year‐old children (in comparison with adults). UFP were sampled both indoors and outdoors in two urban (US1, US2) and one rural (RS1) preschool located in north of Portugal for 31 days. Total levels of indoor UFP were significantly higher at the urban preschools (mean of 1.82 × 10⁴ and 1.32 × 10⁴ particles/cm³ at US1 an US2, respectively) than at the rural one (1.15 × 10⁴ particles/cm³). Canteens were the indoor microenvironment with the highest UFP (mean of 5.17 × 10⁴, 3.28 × 10⁴, and 4.09 × 10⁴ particles/cm³ at US1, US2, and RS1), whereas the lowest concentrations were observed in classrooms (9.31 × 10³, 11.3 × 10³, and 7.14 × 10³ particles/cm³ at US1, US2, and RS1). Mean indoor/outdoor ratios (I/O) of UFP at three preschools were lower than 1 (0.54–0.93), indicating that outdoor emissions significantly contributed to UFP indoors. Significant correlations were obtained between temperature, wind speed, relative humidity, solar radiation, and ambient UFP number concentrations. The estimated exposure doses were higher in children attending urban preschools; 3–5‐year‐old children were exposed to 4–6 times higher UFP doses than adults with similar daily schedules.