Factors affecting variability in gaseous and particle microenvironmental air pollutant concentrations in Hong Kong primary and secondary schools

School-age children are particularly susceptible to exposure to air pollutants. To quantify factors affecting children's exposure at school, indoor and outdoor microenvironmental air pollutant concentrations were measured at 32 selected primary and secondary schools in Hong Kong. Real-time PM₁₀, PM_2.5, NO_2, and O₃ concentrations were measured in 76 classrooms and 23 non-classrooms. Potential explanatory factors related to building characteristics, ventilation practice, and occupant activities were measured or recorded. Their relationship with indoor measured concentrations was examined using mixed linear regression models. Ten factors were significantly associated with indoor microenvironmental concentrations, together accounting for 74%, 61%, 46%, and 38% of variations observed for PM_2.5, PM₁₀, O_3, and NO₂ microenvironmental concentrations, respectively. Outdoor concentration is the single largest predictor for indoor concentrations. Infiltrated outdoor air pollution contributes to 90%, 70%, 75%, and 50% of PM_2.5, PM₁₀, O_3, and NO₂ microenvironmental concentrations, respectively, in classrooms during school hours. Interventions to reduce indoor microenvironmental concentrations can be prioritized in reducing ambient air pollution and infiltration of outdoor pollution. Infiltration factors derived from linear regression models provide useful information on outdoor infiltration and help address the gap in generalizable parameter values that can be used to predict school microenvironmental concentrations.     

Indoor and outdoor PM2.5 and PM10 concentrations in the air during a dust storm

Asian dust storms (ADS) originating from the arid deserts of Mongolia and China are a well-known springtime meteorological phenomenon throughout East Asia. The ventilation systems in office utilize air from outside and therefore it is necessary to understand how these dust storms affect the concentrations of PM_2.5 and PM₁₀ in both the indoor and outdoor air. We measured dust storm pollution particles in an office building using a direct-reading instrument (PC-2 Quartz Crystal Microbalance, QCM) that measured particle size and concentration every 10 min for 1 h, three times a day. A three-fold increase in the concentrations of PM_2.5 and PM₁₀ in the indoor and outdoor air was recorded during the dust storms. After adjusting for other covariates, autoregression models indicated that PM_2.5 and PM₁₀ in the indoor air increased significantly (21.7 μg/m³ and 23.0 μg/m³ respectively) during dust storms. The ventilation systems in high-rise buildings utilize air from outside and therefore the indoor concentrations of fine and coarse particles in the air inside the buildings are significantly affected by outside air pollutants, especially during dust storms.     

Outdoor sources of indoor air pollution

Conservation measures that seal a building, such as storm window installation, can significantly reduce its energy requirements. These measures also protect its occupants from air pollutants having outdoor sources but amplify any harmful effects of those generated indoors. Which effect is greater?Since it is inadequate to consider pollution levels constant, we assume that they follow daily cycles and can thus be well represented by Fourier series. We conclude that the indoor concentration of any pollutant generated solely outdoors also follows a daily cycle but its maximum lags behind and is lower than the outdoor maximum to an extent depending in an inverse manner on v, the air exchange (ventilation + infiltration) rate. A simple measure of the daily variation of pollutant concentrations and indoor production rates can be derived from their Fourier series and used to test whether these quantities can be assumed constant.Although average daily indoor and outdoor pollutant concentrations of any pollutant are the same if there are no indoor sinks, lowering v will still protect a building's occupant if: (1) the outdoor peak or variation above its average is much greater than its average, and (2) the peak is short-lived.Lowering v probably raises indoor average and peak pollutant concentrations from all indoor sources by at least as much as it lowers only peaks from just one outdoor source, rush hour traffic, thus increasing indoor pollutant levels.     

A study of a control strategy utilizing outdoor air to reduce the wintertime carbon dioxide levels in a typical Taiwanese bedroom

A CO₂ concentration of more than 1000 ppm has been monitored in Taiwanese bedrooms during sleeping hours in the wintertime. The high indoor CO₂ levels were caused by poor ventilation due to insufficient ventilation rates. This study sought to reduce the wintertime CO₂ concentration level in a typical Taiwanese bedroom with less outdoor air to maintain thermal comfort. CO₂ was used as an indicator to assess whether an adequate ventilation rate has been obtained to dilute or remove harmful pollutants. With the help of the thermal buoyancy effect, the CO₂ generated in the bedroom was effectively removed by means of less outdoor air. Through computational fluid dynamics simulations, the appropriate window and transom locations with the corresponding outdoor air supply volume, as well as the lowest possible outdoor air temperature were identified.     

An experimental study of air quality inside large athletic halls

Air quality in two large athletic halls with different ventilation (natural and mechanical) was investigated in relation to outdoor pollution and meteorological conditions. Simultaneous measurements of O₃, NO, NO₂ and SO₂ were performed in the halls at two heights (at the arena and spectators’ seats) and outdoors. BTX concentrations at the spectators’ seats and outdoor NMHCs, CH₄, PM₁₀ and CO concentrations were also measured. Analysis of diurnal variations of the pollutants’ concentrations, cross correlation analysis of the concentration time-series and principal component analysis were applied to the collected data. Results revealed that outdoor pollution significantly affected indoor air quality of both halls. However, this effect was different for the two buildings, depending on the ventilation types, the wind direction prevailing at the areas and the kind of indoor activity recorded. It was found that the latter parameters controlled the pollutants concentration levels in the halls and their response to the changes of the outdoor pollution levels. Temperature and pollution stratification enhancing during athletic events were also evident in both halls but with different characteristics observed, such as the spatial distribution of the indoor pollutants. The airflow patterns prevailing in each hall, imposed by the ventilation operation schemes were important factors.     

Improvement of natural ventilation in a large factory building using a louver ventilator

When heat generated from facilities inside a large factory building is not discharged outside the building due to a stagnant ventilation flow, the working environment of workers becomes worse, and the cooling of high-temperature products is delayed. In this study, wind tunnel tests were conducted to investigate the natural ventilation of entrained air inside a large factory building. The scale-down factory-building models were embedded in a simulated atmospheric boundary layer (ABL), and the mean and fluctuating velocity fields were measured using a two-frame particle image velocimetry (PIV) technique. For the original factory model, some of the outdoor air came in the factory building through the one-third open windward wall, while the stagnant flow region existed in the rear part of the target area. In order to improve the indoor ventilation environment of the present factory building, three different types of the louver ventilator were attached at the upper one-third open windward wall of the factory model. Among the three louver ventilators tested in this study, the ventilator model ?3 with the outer louver (θ_o=90°) and the inner louver (θ_i=−70°) was found to improve the natural ventilation inside the target factory-building model. It increased the flow rate of the entrained air by aligning the outer louver blades with the oncoming wind and guiding the entrained air down to the ground surface with the elongated inner louver blades.     

Real-time measurements of PM2.5 and ozone to assess the effectiveness of residential indoor air filtration in Shanghai homes

Portable air cleaners are increasingly used in polluted areas in an attempt to reduce human exposure; however, there has been limited work characterizing their effectiveness at reducing exposure. With this in mind, we recruited forty-three children with asthma from suburban Shanghai and deployed air cleaners (with HEPA and activated carbon filters) in their bedrooms. During both 2-week filtration and non-filtration periods, low-cost PM_2.5 and O₃ air monitors were used to measure pollutants indoors, outdoors, and for personal exposure. Indoor PM_2.5 concentrations were reduced substantially with the use of air cleaners, from 34 ± 17 to 10 ± 8 µg/m³, with roughly 80% of indoor PM_2.5 estimated to come from outdoor sources. Personal exposure to PM_2.5 was reduced from 40 ± 17 to 25 ± 14 µg/m³. The more modest reductions in personal exposure and high contribution of outdoor PM_2.5 to indoor concentrations highlight the need to reduce outdoor PM_2.5 and/or to clean indoor air in multiple locations. Indoor O₃ concentrations were generally low (mean = 8±4 ppb), and no significant difference was seen by filtration status. The concentrations of pollutants and the air cleaner effectiveness were highly variable over time and across homes, highlighting the usefulness of real-time air monitors for understanding individual exposure reduction strategies.     

Continuous measurement of reactive oxygen species inside and outside of a residential house during summer

Reactive oxygen species (ROS) are an important contributor to adverse health effects associated with ambient air pollution. Despite infiltration of ROS from outdoors, and possible indoor sources (eg, combustion), there are limited data available on indoor ROS. In this study, part of the second phase of Air Composition and Reactivity from Outdoor aNd Indoor Mixing campaign (ACRONIM-2), we constructed and deployed an online, continuous, system to measure extracellular gas- and particle-phase ROS during summer in an unoccupied residence in St. Louis, MO, USA. Over a period of one week, we observed that the non-denuded outdoor ROS (representing particle-phase ROS and some gas-phase ROS) concentration ranged from 1 to 4 nmol/m³ (as H₂O₂). Outdoor concentrations were highest in the afternoon, coincident with peak photochemistry periods. The indoor concentrations of particle-phase ROS were nearly equal to outdoor concentrations, regardless of window-opening status or air exchange rates. The indoor/outdoor ratio of non-denuded ROS (I/O_ROS) was significantly less than 1 with windows open and even lower with windows closed. Combined, these observations suggest that gas-phase ROS are efficiently removed by interior building surfaces and that there may be an indoor source of particle-phase ROS.     

室内空气甲醛和氨与室外气象条件相关性研究

为了解寒冷地区哈尔滨市室内空气污染物随气候变化的特性,通过对哈尔滨市某一新建楼房办公室进行一年的室内空气甲醛和氨实验检测,确定了室内外环境温度与室内空气甲醛和氨浓度的关系。实验结果表明,气象状况（季节、风力、雨雪等）变化和哈尔滨生活环境特点使室内外温差改变较大,从而导致室内空气甲醛和氨浓度呈现规律性变化。本研究结果具有地区代表性,为完善室内空气污染物检测和评价体系提供依据。     

Studying the indoor air quality in three non-residential environments of different use: A museum,a printery industry and an office

The aim of the present study was to identify the main sources contributing to the air pollution of three indoor environments of different use: a museum, a printery industry and an office. For that purpose, particulate matter (TSP, PM₁₀, PM_2.5), inorganic pollutants (NO_x, SO₂, O₃) and organic compounds (BTX, formaldehyde) were monitored. Factors such as the kind of the activities occurred indoors, the emissions from the existing equipment, the number of occupants, the ventilation pattern and the outdoor background substantially varied among the three sites.     

Air infiltration in Catalan dwellings and sealed rooms: An experimental study

In this study, we performed a series of trials to measure the infiltration air exchange rate (ACH) of several single-family dwellings throughout Catalonia, as well as the ACH of sealed rooms that could be used as indoor shelters. A shelter is an indoor room where people can take protection in case of a toxic gas release, while the toxic cloud passes through the dwelling. Experimental measurements were made using the tracer gas decay technique with CO₂ as the tracer gas in 2 periods—summer and winter—with the aim of characterizing air infiltration in Catalan dwellings. The geometric means obtained for the ACH of shelters and dwellings were 0.16 and 0.23 h⁻¹, respectively, that is, lower than those reported for North American (0.56 h⁻¹) and Greek (0.76 h⁻¹) dwellings. In general, the ACH was lower for shelters than for dwellings, and the average reduction obtained in shelters with respect to dwellings was 35%. The largest reductions were obtained in old dwellings with small floor areas and few stories. As for meteorological conditions, we found that the ACH of dwellings was more closely linked to wind speed than indoor–outdoor temperature difference, while the ACH of shelters was more affected by indoor–outdoor temperature and temperature differences inside the dwelling, particularly in dwellings with 3 or more stories.     

Assessment of chemical and microbiological parameters of indoor swimming pool atmosphere using multiple comparisons

The aim of this study was to evaluate the air quality of an indoor swimming pool, analyzing diurnal and seasonal variations in microbiological counts and chemical parameters. The results indicated that yeast and bacteria counts, as well as carbon dioxide (CO₂), nitrogen oxides (NO_x) and O₃ concentrations, showed significant diurnal difference. On the other hand, temperature, relative humidity (R.H.), yeast counts and concentrations of CO₂, particles, O₃, toluene, and benzene showed seasonal differences. In addition, the relationship between indoor and outdoor air and the degree of correlation between the different parameters have been calculated, suggesting that CO₂, fine particles and NO_x would have indoor origin due to the human activity and secondary reactions favored by the chemical and environmental conditions of the swimming pool; while O₃, benzene and toluene, would come from outside, mainly. The overall results indicated that indoor air quality (IAQ) in the swimming pool building was deficient by the high levels of CO₂ and microorganisms, low temperatures, and high R.H., because frequently the limits established by the legislation were exceeded. This fact could be due to the poor ventilation and the inadequate operation of heating, ventilation, and air‐conditioning systems.     

Particle‐associated polycyclic aromatic hydrocarbons in a representative urban location (indoor‐outdoor) from South Europe: Assessment of potential sources and cancer risk to humans

PM₁₀‐bound polycyclic aromatic hydrocarbons (PAHs) levels were monitored at urban locations (outdoor/indoor) within the city of Madrid between May 2017 and April 2018. Fourteen PAH congeners were measured, potential emission sources were identified as were potential carcinogenic risks. The ΣPAHs averaged 0.577 and 0.186 ng/m³ in outdoor and indoor air, with a high linear correlation per individual mean PAH and month. The largest contributors to the ΣPAHs were the high‐molecular‐weight PAHs. Principal component analysis‐multiple linear regression results showed that emissions from diesel and vehicular processes explained 27% and 23% of the total variance of outdoor and indoor air, while combustion processes accounted for 30% and 25% in ambient and indoor air, respectively. During the cold season, biomass burning plus coal and wood combustion were additional sources of outdoor emissions. The heavy‐, medium‐ and light‐molecular‐weight PAH originating from outdoor sources accounted for 72%, 80%, and ~60% of the indoor levels of the three respective PAH groups. Average BaP concentration was 0.029 and 0.016 ng/m³ in outdoor and indoor air, respectively. Estimated BaPeq concentration averaged 0.072, 0.035, and 0.027 ng/m³ for outdoor, indoor, and indoor‐generated individual PAH concentrations, respectively. The estimated carcinogenic risk falls within the range of acceptable risk targeted by the US‐EPA.     

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

A six‐month winter‐spring study was conducted in a suburb of the northern European city of Kuopio, Finland, to identify and quantify factors determining daily personal exposure and home indoor levels of fine particulate matter (PM_2.5, diameter <2.5 µm) and its light absorption coefficient (PM_2.5abs), a proxy for combustion‐derived black carbon. Moreover, determinants of home indoor ozone (O₃) concentration were examined. Local central site outdoor, home indoor, and personal daily levels of pollutants were monitored in this suburb among 37 elderly residents. Outdoor concentrations of the pollutants were significant determinants of their levels in home indoor air and personal exposures. Natural ventilation in the detached and row houses increased personal exposure to PM_2.5, but not to PM_2.5abs, when compared with mechanical ventilation. Only cooking out of the recorded household activities increased indoor PM_2.5. The use of a wood stove room heater or wood‐fired sauna stove was associated with elevated concentrations of personal PM_2.5 and PM_2.5abs, and indoor PM_2.5abs. Candle burning increased daily indoor and personal PM_2.5abs, and it was also a determinant of indoor ozone level. In conclusion, relatively short‐lasting wood and candle burning of a few hours increased residents’ daily exposure to potentially hazardous, combustion‐derived carbonaceous particulate matter.     

Polycyclic aromatic hydrocarbons: levels and phase distributions in preschool microenvironment

This work aims to characterize levels and phase distribution of polycyclic aromatic hydrocarbons (PAHs) in indoor air of preschool environment and to assess the impact of outdoor PAH emissions to indoor environment. Gaseous and particulate (PM₁ and PM_2.5) PAHs (16 USEPA priority pollutants, plus dibenzo[a,l]pyrene, and benzo[j]fluoranthene) were concurrently sampled indoors and outdoors in one urban preschool located in north of Portugal for 35 days. The total concentration of 18 PAHs (ΣPAHs) in indoor air ranged from 19.5 to 82.0 ng/m³; gaseous compounds (range of 14.1–66.1 ng/m³) accounted for 85% ΣPAHs. Particulate PAHs (range 0.7–15.9 ng/m³) were predominantly associated with PM₁ (76% particulate ΣPAHs) with 5‐ring PAHs being the most abundant. Mean indoor/outdoor ratios (I/O) of individual PAHs indicated that outdoor emissions significantly contributed to PAH indoors; emissions from motor vehicles and fuel burning were the major sources.     

Variation in indoor particle number and PM2.5 concentrations in a radio station surrounded by busy roads before and after an upgrade of the HVAC system

Indoor particle number and PM_2.5 concentrations were investigated in a radio station surrounded by busy roads. Two extensive field measurement campaigns were conducted to determine the critical parameters affecting indoor air quality. The results indicated that indoor particle number and PM_2.5 concentrations were governed by outdoor air, and were significantly affected by the location of air intake and design of HVAC system. Prior to the upgrade of the HVAC system and relocation of the air intake, the indoor median particle number concentration was 7.4×10³ particles/cm³ and the median PM_2.5 concentration was 7 μg/m³. After the relocation of air intake and the redesign of the HVAC system, the indoor particle number concentration was between 2.3×10³ and 3.4×10³ particles/cm³, with a median value of 2.7×10³ particles/cm³, and the indoor PM_2.5 concentration was in the range of 3–5 μg/m³, with a median value of 4 μg/m³. By relocating the air intake of the HVAC, the outdoor particle number and PM_2.5 concentrations near the air intake were reduced by 35% and 55%, respectively. In addition, with the relocation of air intake and the redesign of the HVAC system, the particle number penetration rate was reduced from 42% to 14%, and the overall filtration efficiency of the HVAC system (relocation of air intake, pre-filter, AHU and particle losses in the air duct) increased from 58% to 86%. For PM_2.5, the penetration rate after the upgrade was approximately 18% and the overall filtration efficiency was 82%. This study demonstrates that by using a comprehensive approach, including the assessment of outdoor conditions and characterisation of ventilation and filtration parameters, satisfactory indoor air quality can be achieved, even for those indoor environments facing challenging outdoor air conditions.     

Indoor NH3 variation and its relationship with outdoor NH3 in urban Beijing

Online measurements of indoor and outdoor ammonia (NH₃) were conducted at a university building in Haidian District, Beijing, to investigate their variation characteristics, indoor-outdoor differences, influencing factors, and possible contribution of indoor NH₃ to atmospheric NH₃. Indoor NH3 mixing ratios varied greatly among the rooms of the same building. Indoor NH₃ mixing ratio peaked at 1.43 ppm in a toilet. Both indoor and outdoor NH₃ mixing ratios exhibited higher values during summer and lower values during winter and correlated significantly with relative humidity and temperature. Moreover, their daily mean mixing ratios were significantly correlated with each other. But indoor and outdoor NH₃ in cold months exhibited quite different diurnal variations. During the measurement period, indoor NH₃ mixing ratios were substantially higher than those outdoors, by an average factor of 3.1 (1.0–6.6). This indicates that indoor NH₃ could be a source of outdoor atmospheric NH₃. The contribution of indoor NH₃ to atmospheric NH₃ was estimated at 0.7 ± 0.5 Gg NH₃-N·a⁻¹, accounting for approximately 1.0 ± 0.7% of total emissions in Beijing and being comparable to industry, biomass combustion, and soil emissions, but lower than transportation emissions. The influence of COVID-19 control measures caused indoor and outdoor NH₃ mixing ratios to decrease by 22.8% and 19.3%, respectively—attributable to decreased human activity and traffic flow.     

Improving outdoor air quality based on building morphology: Numerical investigation

Due to rapid urbanization around the world, high concentrations of vehicular pollutants have deteriorated the outdoor air quality, which can affect the physical and psychological well-being of humans. Numerous strategies have been proposed to overcome these harmful impacts by improving the dispersion of air pollutants. Consequently, a question arises regarding the potential effects of building morphology on the dispersion of pollutants. Subsequently, transient three-dimensional Computational Fluid Dynamics (CFD) simulations are performed to examine the effect of building morphology on PM₁₀ dispersion. Eleven cases with various prototypes and morphological methods are compared with a simple building form to identify the patterns of PM₁₀ dispersion within a given time sequence under a prevailing inflow condition. The results indicate that the different designs of building morphology with varying Relative compactness (R_C) indicator highlight the importance of considering morphological factors to improve outdoor air quality. In addition, the proposed prototypes can reduce PM₁₀ concentrations by approximately 30%–90% at specific points in the studied time sequence. In particular, the vertical, horizontal, and grid folded prototypes can be considered more effective as an approximate decrease between 70% and 90% in PM₁₀ concentrations is observed, which reflects the influence of building morphology on improving outdoor air quality.     

Real-time molecular characterization of air pollutants in a Hong Kong residence: Implication of indoor source emissions and heterogeneous chemistry

Due to the high health risks associated with indoor air pollutants and long-term exposure, indoor air quality has received increasing attention. In this study, we put emphasis on the molecular composition, source emissions, and chemical aging of air pollutants in a residence with designed activities mimicking ordinary Hong Kong homes. More than 150 air pollutants were detected at molecular level, 87 of which were quantified at a time resolution of not less than 1 hour. The indoor-to-outdoor ratios were higher than 1 for most of the primary air pollutants, due to emissions of indoor activities and indoor backgrounds (especially for aldehydes). In contrast, many secondary air pollutants exhibited higher concentrations in outdoor air. Painting ranked first in aldehyde emissions, which also caused great enhancement of aromatics. Incense burning had the highest emissions of particle-phase organics, with vanillic acid and syringic acid as markers. The other noteworthy fingerprints enabled by online measurements included linoleic acid, cholesterol, and oleic acid for cooking, 2,5-dimethylfuran, stigmasterol, iso-/anteiso-alkanes, and fructose isomers for smoking, C₂₈-C₃₄ even n-alkanes for candle burning, and monoterpenes for the use of air freshener, cleaning agents, and camphor oil. We showed clear evidence of chemical aging of cooking emissions, giving a hint of indoor heterogeneous chemistry. This study highlights the value of organic molecules measured at high time resolutions in enhancing our knowledge on indoor air quality.     

Infiltration of fine particles in urban daycares

Singapore is a tropical country with a high density of day-care facilities whose indoor environments may be adversely affected by outdoor fine particle (PM_2.5) air pollution. To reduce this problem requires effective, evidence-based exposure-reduction strategies. Little information is available on the penetration of outdoor PM_2.5 into day-care environments. Our study attempted to address the following objectives: to measure indoor infiltration factor (F_inf) of PM_2.5 from outdoor PM_2.5 and to determine the building parameters that modify the indoor PM_2.5. We collected indoor/outdoor 1-min PM_2.5 from 50 day-care classrooms. We noted mean F_inf ± SD of 0.65 ± 0.22 in day-care rooms which are naturally ventilated and lower F_inf ± SD values of 0.47 ± 0.18 for those that are air-conditioned: values which are lower than those reported in Singapore residences. The air exchange rates were higher in naturally ventilated rooms (1.47 vs 0.86 h⁻¹). However, fine particle deposition rates were lower for naturally ventilated rooms (0.67 ± 0.43 h⁻¹) compared with air-conditioned ones (1.03 ± 0.55 h⁻¹) presumably due to composite rates linked to the filters within the split unit air-conditioners, higher recirculation rates, and interior surfaces in the latter. Our findings indicate that children remaining indoor in daycares where air-conditioning is used can reduce their PM_2.5 exposures during outdoor pollution episodes.