Characteristics of indoor and outdoor airborne fungi at suburban and urban homes in two seasons

Literature has suggested association between damp environments, microbial exposure, and higher prevalence of respiratory symptoms and diseases. The study began by evaluating the airborne fungal concentrations at urban and suburban areas of a typical metropolitan city in southern Taiwan for the estimation of related health risks. A group of representative homes, based on the housing characteristics questionnaires completed earlier, were selected from two parts of the city; urban and suburban. Burkard sampler (BURKARD, Rickmansworth, England) was used to collect airborne fungi onto agar plates with malt-extract. After incubation and identification, concentrations of airborne fungi were calculated as CFU/m3. The geometric mean (GM) concentration for indoors was 8946 (4372-18,306) CFU/m3 in winter and 4381 (1605-11,956) in summer. For outdoors, it was 11,464 (5767-22,788) CFU/m3 in winter and 4689 (1895-11,603) in summer. In summer, the total fungal concentration, both indoors and outdoors of suburban homes, were significantly higher than those of urban homes. The dominant fungi contributing to such a difference were indoor Cladosporium spp. and outdoor Penicillium spp. (P < 0.01). The indoor/outdoor ratio (I/O) was similar in two areas except for Penicillium spp. in winter and Aspergillus spp. in summer; both higher in the suburban area. Significantly higher levels of airborne fungi were observed in this region than those seen in northern Taiwan or other parts of the world. Future investigations are needed to further examine the effects of these exposures on the related health problems.     

Indoor and outdoor concentrations of Japanese cedar pollens and total suspended particulates: A case study at a kindergarten in Japan

Japanese cedar pollinosis (JCP) caused by allergenic cedar and cypress pollens is one of major economic and health issues in Japan. The present study reported here aimed to provide basic data to understand the status of early life exposures to airborne cedar and cypress pollens in school settings. In particular, the study investigated relationships between indoor and outdoor concentrations of airborne cedar and cypress pollens and total suspended particulates (TSP) in a kindergarten in Japan. Overall, outdoor concentrations of the airborne pollens and TSP were higher than the indoor concentrations, i.e., indoor to outdoor (I/O) ratios of 0.043–0.055 and 0.545 for the airborne pollens and TSP, respectively. The smaller I/O ratios for the pollens were expected because the larger pollen grains (20–30 μm in diameter) were less likely penetrated to indoor environment than for smaller airborne particulates. The present study also found increased TSP concentrations during the pollen season was likely attributed to increased airborne pollen concentrations. By understanding the status of indoor and outdoor concentrations of airborne cedar and cypress pollens in school settings, early life exposures to these allergenic pollens should be effectively minimized to prevent subsequent progression to JCP symptoms.     

The spatial and temporal variations in PM10 mass from six UK homes

People spend the majority of their time indoors mostly in the domestic environment, where their health may be effected by significant airborne particulate pollution. The indoor/outdoor air quality at six homes in Wales and Cornwall was investigated, based on different locations (urban, suburban, rural) and household characteristics (smokers, non-smokers). The spatial and temporal variations in PM10 mass were monitored for a calendar year, including ambient weather conditions. The activities of individuals within a household were also recorded. Monitoring of PM10 took place inside (kitchen, living room, bedroom) homes, along with concomitant collections outdoors. Samples were subjected to gravimetric analysis to determine PM10 concentrations and examined by scanning electron microscopy to identify the types of particles present on the filters. The results of the study show there are greater masses of PM10 indoors, and that the composition of the indoor PM10 is controlled by outdoor sources, and to a lesser extent by indoor anthropogenic activities, except in the presence of tobacco smokers. The indoor and outdoor PM10 collected was characterised as being a heterogeneous mixture of particles (soot, fibres, sea salt, smelter, gypsum, pollen and fungal spores).     

Use of temporal/seasonal- and size-dependent bioaerosol data to characterize the contribution of outdoor fungi to residential exposures

With the use of published temporal/seasonal and particle size distribution of outdoor bioaerosol data and meteorological information in the subtropical climate, we characterized the airborne fungal concentration indoor/outdoor/personal exposure relationships in a wind-induced naturally ventilated residence. We applied a size-dependent indoor/outdoor ratio model coupled with a compartmental lung model based on a hygroscopic growth factor as a function of relative humidity on aerodynamic diameter and concentration of fungal spores. The higher indoor airborne fungal concentrations occurred in early morning and late afternoon in which median values were 699.29 and 626.20 CFU m(-3) in summer as well as 138.71 and 99.01 CFU m(-3) in winter, respectively, at 2 am and 8 pm. In the absence of indoor sources, summer has higher mean indoor/outdoor ratios of airborne fungal concentration (0.29-0.58) than that in winter (0.12-0.16). Lung region of extrathoracic (ET) has higher fungal concentration lung/indoor ratios (0.7-0.8) than that in bronchial (BB; 0.41-0.60), bronchiolar (bb; 0.12-0.40), and alveolar-interstitial (AI); 0.01-0.24) regions. The highest airborne fungal deposition dose (95th-percentile is 4600 CFU) occurred in 11 pm-5 am in region AI in that the 95th-percentile fungal deposition rate was 0.22 CFU s(-1).     

Changes in profiles of airborne fungi in flooded homes in southern Taiwan after Typhoon Morakot

In August 2009, the historic Typhoon Morakot brought extreme rainfall and resulted in flooding which spread throughout southern Taiwan. This study compared the difference between fungal concentrations before and after the disaster in selected homes of the Tainan metropolitan area, which were hit hardest by the catastrophe. A group of 83 households available from a prior cohort established with random sampling out of a regional population in southern Taiwan was contacted successfully by telephone. Twenty-five of these reported to have suffered from floods of various degrees at this time. Around 2 weeks after the event, at which time most of the remedial process had been completed by self-efforts and public health endeavours, 14 of these 25 (56%) agreed to participate in measurements of the airborne microbial concentrations. The averages (standard deviation) of the total culturable fungal concentrations in children's bedrooms and flooded rooms were 18,181 (25,854) colony-forming units per cubic metre (CFU/m³) and 13,440 (11,033) CFU/m³, respectively. The airborne fungal spore levels in the 2 above-mentioned indoor sites were 221,536 (169,640) spores/m³ and 201,582 (137,091) spores/m³, respectively. The average indoor/outdoor ratios in the children's bedrooms were 4.2 for culturable fungi and 1.4 for fungal spores. These values were higher than the respective values measured in the same homes during the previous year: 1.1 and 0.6. In terms of the specific fungal profile, the percentages of Aspergillus spp. increased significantly in both the indoor and outdoor environments after the event. To this date, this study is among the limited research that has been conducted to quantitatively demonstrate that fungal manifestation is likely to persist in flooded homes even after seemingly robust remedial measures have been put into place. Studies to examine the potential health implications and effectiveness of better remedial technology remain much needed.     

Ozone in Residential Air: Concentrations,I/O Ratios,Indoor Chemistry,and Exposures

Ozone concentrations were measured in indoor and outdoor residential air during the summer of 1992. Six homes located in a New Jersey suburban area were chosen for analysis, and each home was monitored for 6 days under different ventilation and indoor combustion conditions. The 5-hour average ozone concentration outdoors over the monitoring period was 95 ± 36 ppbv. One third of the days exceeded the National Ambient Air Quality Standard (NAAQS), one-hour maximum concentration of 120 ppb. The mean indoor to outdoor (I/O) ratios of ozone concentration ranged from 0.22 ± 0.09 to 0.62 ± 0.11, depending upon ventilation rate and indoor gas combustion. The presence of indoor gas combustion can significantly decrease the I/O ratio. Because of the great amount of time that people spend indoors, the indoor residential exposures were estimated to account for 57% of the total residential exposures. One type of the possible gas-phase reactions for indoor ozone, the reaction of ozone with a volatile organic compound containing unsaturated carbon-carbon bonds, is discussed with some supporting evidence provided in the study.     

上海地区冬季住宅室内外颗粒物浓度的相关性

对上海市某住宅建筑室内外PM10、PM2.5、PM1的浓度进行了测量,研究了最小通风量(外门窗关闭)条件下3种天气时颗粒浓度随时间变化的规律以及相关性,分析了颗粒物浓度与环境温湿度参数之间的关系。研究结果显示,测试期间,室内外空气中细颗粒(PM 2.5)占可吸入颗粒(PM 10)浓度比例分别达65%和87%以上;无明显室内源时,I/O比值小于1且随粒径减小而减小;室内外颗粒浓度相关性与粒径大小有关系,PM1、PM2.5的浓度相关性大于PM10。研究还表明,颗粒物浓度的关联性与天气状况有关系,多云、雨天和阴天时浓度关联性有显著差别;颗粒物的浓度受到室内外温湿度的影响,且受天气状况影响而呈现复杂性。     

Relationship between outdoor and indoor air quality in eight French schools

In the frame of the French national research program PRIMEQUAL (inter-ministry program for better air quality in urban environments), measurements of outdoor and indoor pollution have been carried out in eight schools in La Rochelle (France) and its suburbs. The buildings were naturally ventilated by opening the windows, or mechanically ventilated, and showed various air permeabilities. Ozone, nitrogen oxides (NO and NO(2)), and airborne particle (particle counts within 15 size intervals ranging from 0.3 to 15 mum) concentrations were continuously monitored indoors and outdoors for two 2-week periods. The indoor humidity, temperature, CO(2) concentration (an indicator of occupancy), window openings and building permeability were also measured. The temporal profiles of indoor and outdoor concentrations show ozone and nitrogen oxides behave differently: NO and NO(2) indoor/outdoor concentration ratios (I/O) were found to vary in a range from 0.5 to 1, and from 0.88 to 1, respectively, but no correlation with building permeability was observed. On the contrary, I/O ratios of ozone vary in a range from 0 to 0.45 and seem to be strongly influenced by the building air-tightness: the more airtight the building envelope, the lower the ratio. Occupancy, through re-suspension of previously deposited particles and possible particle generation, strongly influences the indoor concentration level of airborne particles. However, this influence decreases with particle size, reflecting the way deposition velocities vary as a function of size. The influence of particle size on deposition and penetration across the building envelope is also discussed by analyzing the I/O ratios measured when the buildings were unoccupied, by comparing the indoor concentrations measured when the buildings were occupied and when they were not (O/U ratios), and by referring to previously published studies focussing on this topic. Except one case, I/O were found to vary in the range from 0.03 to 1.79. All O/U are greater than one and increase up to 100 with particle size. PRACTICAL IMPLICATIONS: Assessing children's total exposure requires the knowledge of outdoor and indoor air contaminant concentrations. The study presented here provides data on compared outdoor and indoor concentration levels in school buildings, as well as information on the parameters influencing the relationship between outdoor and indoor air quality. It may be used as a basis for estimating indoor concentrations from outdoor concentrations data, or as a first step in designing buildings sheltering children against atmospheric pollution.     

Assessment of airborne bacteria and fungi in food courts

A study was undertaken to determine the effect of variations in temperature, relative humidity, occupancy density and location (indoor/outdoor) on the concentrations of viable airborne bacterial and fungal spores at an air-conditioned and a non air-conditioned food stall in Singapore. Typically, bioaerosols consisted of 50.5% bacteria and 49.5% fungi in the indoor environment. In contrast, for the outdoor environment, bacteria on an average only accounted for 20.6% of culturable airborne microorganisms whereas fungal concentrations were 79.4%. Results on bioaerosol size distributions revealed that 67% of indoor bacteria and 68% of outdoor bacteria, 85% of indoor fungi and 68% of outdoor fungi were associated with fine mode particulates (<3.3 μm). Occupant density was the key factor that affected indoor airborne bacteria concentrations while concentrations of outdoor airborne bacteria depended strongly on ambient temperature. Indoor fungal concentration was positively correlated to relative humidity whereas outdoor fungal concentration was positively correlated to relative humidity and negatively correlated to temperature. The study also compared the biological air quality between a non air-conditioned food stall (Stall A) and an air-conditioned food stall (Stall B). The dining area of the former had lower bacterial concentrations as compared to the latter, while fungal spore’s concentrations showed a reverse trend. The dominant airborne bacteria genera were Staphylococcus, Pseudomonas, Alcaligens, and Corynebacterium whereas Penicillium, Aspergillus and Cladosporium were the most common fungal genera and groups in both food stalls.     

建筑室内外空气真菌浓度相关性案例测试分析

选取某高校学生办公室进行室内外空气真菌浓度相关性和粒径的研究.结果表明:室内空气真菌浓度变化范围为1 698～4 429 cfu/m3,最大值出现在12:00;室外浓度范围为3 569?29 452 cfu/m3,最大值也出现在12:00.室内外空气真菌浓度比值均小于1,Spearman相关性分析显示室内外空气真菌呈显...     

Measurements of children's exposures to particles and nitrogen dioxide in Santiago, Chile

An exposure study of children (aged 10-12 years) living in Santiago, Chile, was conducted. Personal, indoor and outdoor fine and inhalable particulate matter (< 2.5 .m in diameter, PM2.5 and < 10 microm in diameter, PM10, respectively), and nitrogen dioxide (NO2) were measured during pilot (N = 8) and main (N = 20) studies, which were conducted during the winters of 1998 and 1999, respectively. For the main study, personal, indoor and outdoor 24-h samples were collected for five consecutive days. Similar mean personal, indoor and outdoor PM2.5 concentrations (69.5, 68.5 and 68.1 microg/m3, respectively) were found. However, for coarse particles (calculated as the difference between measured PM10 and PM2.5, PM2.5-10), indoor and outdoor levels (35.4 and 47.4 microg/m3) were lower than their corresponding personal exposures (76.3 microg/m3). Indoor and outdoor NO2 concentrations were comparable (35.8 and 36.9 ppb) and higher than personal exposures (25.9 ppb). Very low ambient indoor and personal O3 levels were found, which were mostly below the method's limit of detection (LOD). Outdoor particles contributed significantly to indoor concentrations, with effective penetration efficiencies of 0.61 and 0.30 for PM2.5 and PM2.5-10, respectively. Personal exposures were strongly associated with indoor and outdoor concentrations for PM2.5, but weakly associated for PM2.5-10. For NO2, weak associations were obtained for indoor-outdoor and personal-outdoor relationships. This is probably a result of the presence of gas cooking stoves in all the homes. Median I/O, P/I and P/O ratios for PM2.5 were close to unity, and for NO2 they ranged between 0.64 and 0.95. These ratios were probably due to high ambient PM2.5 and NO2 levels in Santiago, which diminished the relative contribution of indoor sources and subjects' activities to indoor and personal PM2.5 and NO2 levels.     

Characterizing airborne fungal and bacterial concentrations and emission rates in six occupied children's classrooms

Baseline information on size‐resolved bacterial, fungal, and particulate matter (PM) indoor air concentrations and emission rates is presented for six school classrooms sampled in four countries. Human occupancy resulted in significantly elevated airborne bacterial (81 times on average), fungal (15 times), and PM mass (nine times) concentrations as compared to vacant conditions. Occupied indoor/outdoor (I/O) ratios consistently exceeded vacant I/O ratios. Regarding size distributions, average room‐occupied bacterial, fungal, and PM geometric mean particle sizes were similar to one another while geometric means estimated for bacteria, fungi, and PM mass during vacant sampling were consistently lower than when occupied. Occupancy also resulted in elevated indoor bacterial‐to‐PM mass‐based and number‐based ratios above corresponding outdoor levels. Mean emission rates due to human occupancy were 14 million cells/person/h for bacteria, 14 million spore equivalents/person/h for fungi, and 22 mg/person/h for PM mass. Across all locations, indoor emissions contributed 83 ± 27% (bacteria), 66 ± 19% (fungi), and 83 ± 24% (PM mass) of the average indoor air concentrations during occupied times.     

Real‐time transformation of outdoor aerosol components upon transport indoors measured with aerosol mass spectrometry

Outdoor aerosols are transported indoors, where their component concentrations depend on aerosol size, physiochemical properties, indoor sources and losses, and cross‐environment gradients of temperature and relative humidity. We explored these dependencies by measuring real‐time outdoor and indoor non‐refractory, submicron (PM₁) aerosol component mass concentrations in a mixed‐use laboratory space with an Aerodyne mini‐aerosol mass spectrometer (AMS) and black carbon (BC) with an aethalometer. The median indoor/outdoor (I/O) ratios were 0.60 for sulfate, 0.25 for nitrate, 0.52 for ammonium, 0.73 for organics, and 0.61 for BC. Positive matrix factorization (PMF) on organic aerosol data identified hydrocarbon‐like (HOA), cooking (COA), and oxygenated (OOA) factors. By assuming sulfate was nonvolatile, lost only by mechanical processes, and without indoor sources, the transformations of other components i due to partitioning changes or indoor sources were parameterized by normalizing their I/O ratios by sulfate's I/O ratio, that is, (I/O)_i/SO4. Component‐specific behavior was quantified by regressions of (I/O)_i/SO4 to outdoor‐to‐indoor temperature differences. Nitrate and HOA strongly and OOA weakly showed losses with increasing temperatures indoors vs. outdoors, and HOA likely had an indoor source. To our knowledge, this is the first reported deployment of an AMS to analyze real‐time indoor aerosol composition and outdoor‐to‐indoor transformation.     

Fungal aerosol composition in moldy basements

Experimental aerosolization studies revealed that fungal fragments including small fragments in the submicrometer size are released from fungal cultures and have been suggested to represent an important fraction of overall fungal aerosols in indoor environments. However, their prevalence indoors and outdoors remains poorly characterized. Moldy basements were investigated for airborne fungal particles including spores, submicron fragments, and larger fragments. Particles were collected onto poly‐L‐lysine‐coated polycarbonate filters and qualitatively and quantitatively analyzed using immunogold labeling combined with field emission scanning electron microscopy. We found that the total fungal aerosol levels including spores, submicrometer, and larger fragments in the moldy basements (median: 80 × 10³ m^?3) were not different from that estimated in control basements (63 × 10³ m^?3) and outdoor (90 × 10³ m^?3). However, mixed effect modeling of the fungal aerosol composition revealed that the fraction of fragments increased significantly in moldy basements, versus the spore fraction that increased significantly in outdoor air. These findings provide new insight on the compositional variation of mixed fungal aerosols in indoor as compared to outdoor air. Our results also suggest that further studies, aiming to investigate the role of fungal aerosols in the fungal exposure‐disease relationships, should consider the mixed composition of various types of fungal particles.     

Assessment of the aerosolization potential for fungal spores in moldy homes

The airborne fungal concentration measured with air samplers during specific time intervals may not adequately represent the indoor air quality because of the sporadic nature of spore release from sources. The conventional source evaluation (e.g. swab and tape sampling) characterizes the mold source but does not relate to the fraction of spores that can be aerosolized from a contaminated material. As an alternative to these methods, we have recently developed and laboratory-tested a novel Fungal Spore Source Strength Tester (FSSST). It allows assessing the potential of aerosolization of fungal spores from contaminated surfaces under the most favorable release conditions. In this study, the FSSST was used to characterize the release of spores from four building materials in mold-problem homes. The spores of different species were efficiently aerosolized by the FSSST, exhibiting a total spore release rate ranging approximately from 10(2) to 10(3) cm2/min. For all tested materials, <2% of the spores on the contaminated surface were released during the tests. The airborne spore concentration estimated from the release rate data was found in most cases to be significantly greater than the concentration actually measured in these environments with simultaneous air sampling. The results suggest that the FSSST can be used for the assessment of maximum potential exposure to airborne spores released from identified sources in homes. PRACTICAL IMPLICATIONS: A recently developed FSSST was found to be suitable to measure the aerosolization potential of indoor fungal sources at the most favorable release conditions. The FSSST generates the data that allows assessing the strength of mold sources in homes with respect to their maximum ability to contaminate indoor air with fungi. The novel approach bridges two conventional methods, the air sampling and the direct source evaluation (e.g. swab sampling), thus providing a better representation of the airborne fungal exposure than these methods individually. The device prototype can be used for evaluating the effectiveness of environmental interventions by taking samples before and after the intervention. As a broader application, the FSSST can be utilized for assessing the release of various hazardous biological and non-biological particles from contaminated surfaces.     

Indoor birch pollen concentrations differ with ventilation scheme,room location,and meteorological factors

Indoor pollen concentrations are an underestimated human health issue. In this study, we measured hourly indoor birch pollen concentrations on 8 days in April 2015 with portable pollen traps in five rooms of a university building at Freising, Germany. These data were compared to the respective outdoor values right in front of the rooms and to background pollen data. The rooms were characterized by different aspects and window ventilation schemes. Meteorological data were equally measured directly in front of the windows. Outdoor concentration could be partly explained with phenological data of 56 birches in the surrounding showing concurrent high numbers of trees attaining flowering stages. Indoor pollen concentrations were lower than outdoor concentrations: mean indoor/outdoor (I/O) ratio was highest in a room with fully opened window and additional mechanical ventilation (.75), followed by rooms with fully opened windows (.35, .12) and lowest in neighboring rooms with tilted window (.19) or windows only opened for short ventilation (.07). Hourly I/O ratios depended on meteorology and increased with outside temperature and wind speed oriented perpendicular to the window opening. Indoor concentrations additionally depended on the previously measured concentrations, indicating accumulation of pollen inside the rooms even after the full flowering period.     

Determination of volatile organic compounds and associated health risk assessment in residential homes and hostels within an academic institute,New Delhi

The purpose of this study was to investigate the concentrations of volatile organic compounds (VOCs) in different indoor microenvironments of residential homes and hostels in an academic institute, in New Delhi, during March–May 2011. Eleven VOCs (aromatic and halogenated) were assessed. Sampling and analytical procedure were based on National Institute for Occupational Safety and Health (NIOSH) standard method. The lifetime cancer and non‐cancer risk were calculated for targeted VOCs using US Environmental Protection Agency guidelines. The mean concentrations of ∑ VOCs (sum of monitored VOCs) and individual VOC were found to be higher indoors as compared to outdoors at both types of premises. Indoor to outdoor (I/O) ratios of the targeted VOCs exceeded 1.0, suggesting the significant presence of indoor sources. Strong correlations between I/O concentrations of VOCs in the current study suggest the presence of common sources. Factor analysis (FA) was used for source evaluation separately at two premise types. The estimated lifetime cancer risks in the current study for all occupants at both premises exceeded 10^?6.     

Particle size distributions and concentrations of airborne endotoxin using novel collection methods in homes during the winter and summer seasons

A comparison study of novel collection methods for airborne bacteria and endotoxin was performed in an environmentally controlled chamber and in pilot-field studies. Airborne particulate matter was collected in swirling liquid impingers, air-monitoring filter cassettes, and with a micro-orifice uniform deposit impactor (MOUDI) to evaluate aerodynamic particle size distributions. Environmentally controlled chamber studies showed that impingers and MOUDI recovered significantly more airborne bacteria than filter cassettes, whereas collection methods for airborne endotoxin were not significantly different. In addition, total airborne bacteria and endotoxin concentrations were measured indoors and outdoors at three homes in Boulder, CO during winter and summer seasons. Indoor concentrations collected with the three different samplers were significantly different for airborne endotoxin, but not for airborne bacteria. Total airborne bacteria indoors and outdoors significantly varied with seasons. Outdoor airborne endotoxin significantly varied with season; no seasonal variation was seen for indoor airborne endotoxin. Indoor and outdoor levels were not significantly different for both airborne bacteria and endotoxin. The largest proportion of endotoxin was associated with airborne particulate matter <1 microm. PRACTICAL IMPLICATIONS: This study compared sampling methods for airborne endotoxin, a potent and nonspecific immune system stimulant which can induce negative health responses. The data from this study showed that swirling liquid impingers and the micro-orifice uniform deposit impactor (MOUDI) recovered significantly more airborne endotoxin than the more widely adapted method of collecting airborne endotoxin on membrane filters, when collection methods were applied in realistic settings (homes). The MOUDI measured the particle size distribution of airborne endotoxin, which can be useful for determining endotoxin respiratory toxicity and its health effects.     

Characterizing ultrafine particles and other air pollutants at five schools in South Texas

This study examined five schools with different ventilation systems in both urban and rural areas in South Texas. Total particle number concentration, ultrafine particle (UFP, diameter < 100 nm) size distribution, PM(2.5) , and CO(2) were measured simultaneously inside and outside of various school microenvironments. Human activities, ventilation settings, and occupancy were recorded. The study found a greater variation of indoor particle number concentration (0.6 × 10(3) -29.3 × 10(3) #/cm(3) ) than of outdoor (1.6 × 10(3) -16.0 × 10(3) #/cm(3) ). The most important factors affecting indoor UFP levels were related to various indoor sources. Gas fan heaters increased the indoor-to-outdoor ratio (I/O ratio) of total particle number concentrations to 30.0. Food-related activities, cleaning, and painting also contributed to the increased indoor particle number concentration with I/O ratios larger than 1.0. Without indoor sources, the I/O ratios for total particles varied from 0.12 to 0.66 for the five ventilation systems studied. The I/O ratio decreased when the outdoor total particle number concentration increased. Particles with diameters <60 nm were less likely to penetrate and stay airborne in indoor environments than larger particles and were measured with smaller I/O ratios. PRACTICAL IMPLICATIONS: From an exposure assessment perspective, schools are important and little-studied microenvironments where students congregate and spend a large proportion of their active time. This study provides information for indoor and outdoor ultrafine particle concentrations at different types of school microenvironments. These data may allow future epidemiological studies to better estimate exposure and assess ultrafine particles health effects among students.