Introduction

Human exposure occurs when a person comes into contact with a pollutant of a certain concentration during a certain period of time (Ott et al. 2007). This means that exposure requires both the pollutant and the person to be present. People can be exposed to contaminants by inhalation, ingestion and dermal contact. In the past, scientists have paid much attention to the study of exposure to outdoor air contaminants, because they have realised the seriousness of outdoor air pollution problems. However, each indoor micro-environment has unique characteristics, determined by the local outdoor air, specific building characteristics and indoor activities. Consequently, each individual’s personal exposure will be determined by the different indoor micro-environments to which the person is exposed, and the time spent in each (Stranger et al. 2007).

Many studies are being conducted on indoor air pollution, because most people spend a lot of their time indoors, living, working, and studying (Lee et al. 2001a, 2002a, b; Li et al. 2001). Reports about buildings with air-related problems have received increasing attention since the 1970s (Hodgson 1992; Spangler and Sexton 1983). Sick building syndrome (SBS) is a commonly used term for symptoms resulting from problems with indoor air quality (IAQ). Complaints common to SBS include allergic rhinitis, headaches, flu-like symptoms, watering of eyes and difficulty in breathing (Mishra et al. 1992). The first official study about SBS that examined more than one structure was published in 1984 (Finnigan et al. 1984).

IAQ problems in schools may be even more serious than in other categories of buildings, due to higher occupant density and insufficient outside air supply, aggravated by frequent poor construction and/or maintenance of school buildings. Therefore, odour and comfort complaints have been related to IAQ problems in schools, as well as increased incidence of allergic, asthma and infectious diseases. Poor IAQ can also affect scholarly performance and attendance, since children are more vulnerable than adults to health risks from exposure to environmental hazards (Daisey et al. 2003; Godoi et al. 2009). The significance of IAQ in schools is underscored by the large number of studies worldwide (Blondeau et al. 2005; Chew et al. 2005; Godoi et al. 2009; Godwin and Batterman 2007; Griffiths and Eftekhari 2008; Hodgson et al. 2004; Kim et al. 2007; Klinmalee et al. 2009; Lee and Chang 2000; Meklin et al. 2002; Mukerjee et al. 2009; Shendell et al. 2004; Sohn et al. 2009; Stranger et al. 2008; Zhang et al. 2006). However, most of these studies concentrate on a specific group of pollutants or on thermal conditions. Multidisciplinary indoor field campaigns, measuring a wide range of health-relevant chemical and physical properties, are still lacking. In Lisbon, the fraction of children with asthma and rhinitis is about 15% and 40%, respectively (Plácido 2004), and the school work environment has not received much attention. Therefore, IAQ in Portuguese schools is almost unknown. The main aims of this work are: (a) to measure indoor comfort parameters (temperature, relative humidity, CO, CO2 and total VOCs) and bacterial and fungal contamination in three representative schools, (b) to evaluate VOCs, carbonyls and NO2 gaseous pollutants, by passive sampling, in indoor and outdoor air at 14 schools, and (c) to identify possible sources, activities or other conditions contributing to the measured levels.

Materials and methods

Description of schools

Indoor and outdoor air samples were collected at 14 schools with wide geographical coverage representing the Lisbon urban area, in May and June 2009. Two classrooms from each of the 14 schools were selected for this study, all depending only on natural ventilation through doors and windows. Details of each sampling site are listed in Table 1.

Table 1 Characteristics of each school
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Comfort parameters and airborne microorganisms

For measurement of comfort parameters and airborne microorganisms, 3 of the 14 schools were selected: schools A, B and C. These schools were previously considered representative of all the elementary-level educational institutions (Khan et al. 2007a, b). Continuous measurements of temperature, relative humidity (RH), CO2 and total VOCs were performed with an automatic portable indoor air quality probe (IQ-610, GrayWolf® monitor) in one classroom of each school during the 8-h occupancy periods. This IAQ monitor includes a Pt100 probe for measuring temperature, a capacitance probe to sense RH and a CO2 non-dispersive infrared sensor, all of them with an extremely fast response. The monitor also includes a photo-ionisation detector to track total VOCs over time. It displays measurements in real time, allowing logged data to be downloaded to WolfSense® personal computer (PC) software for analysis. The equipment was supplied with a factory calibration certificate, but it is checked prior to next use with appropriate calibration kits. Indoor CO2 levels are an indicator of adequacy of outdoor air ventilation relative to indoor occupant density.

Bacterial and fungal colony-forming units per cubic metre of air (CFU/m3) were monitored by liquid impinger sampling (May and Harper 1957) in the two classrooms and playgrounds during 1 day in each one of the three main schools. The flow rate was set at 2.5 L/min. At each sampling location (classrooms and playgrounds), 1-h samples were taken. To obtain representative results, five replicates were obtained per site.

Sampling and analysis of VOCs, carbonyls and NO2

VOCs and carbonyls were sampled in parallel using Radiello® (Fondazione Salvatore Maugeri, Padova, Italy) diffusive passive tubes (cartridge codes 130 and 165, respectively) for 14 consecutive days. At each sampling location, for each one of these two groups of compounds, two replicate samples were collected. Indoor samples were collected at height of about 1.5 m above the floor. The diffusive samplers were positioned at a distance exceeding 1 m from any window or door. Outdoor passive samples were collected at height of about 2 m above the ground. The VOC adsorbing cartridges consist of 60-mm-long stainless-steel net cylinders, with 100 mesh grid opening and 5.8 mm diameter, packed with 530 ± 30 mg activated charcoal with particle size of 35–50 mesh (Cocheo et al. 1996).

VOCs were extracted from the exposed samplers with 2 mL carbon disulphide (CS2 from Aldrich) containing 2-fluorotoluene (from Aldrich) as internal standard. The glass vials were shaken for approximately 30 min. The analyses of the extracts were performed by gas chromatography (Chrompack CP 9001) coupled to a flame ionisation detector (GC/FID), using nitrogen carrier gas at constant pressure of 20 psi. A 100% dimethylpolysiloxane column (0.2 mm, 50 m, film thickness 0.5 μm) was used. The temperature program was as follows: 50°C for 5 min, 5°C/min up to 80°C, 15°C/min up to 135°C, 20°C/min up to 220°C, final isotherm for 20 min. Injector and detector temperatures were 240°C and 300°C, respectively. The equipment was calibrated before and during the analyses of samples by injecting standard solutions of all compounds identified in CS2, specifically: pentane, n-hexane, cyclohexane, n-heptane, n-butyl acetate, styrene, α-pinene, sabinene, β-pinene, n-decane, (+)-3-carene, limonene (all from Fluka), methyl acetate, ethyl acetate, isooctane, m+p-xylene, o-xylene (all from Merck), benzene (AnalytiCals), toluene (Lab-Scan) and γ-terpinene (Aldrich). Four standard solutions, each one containing five compounds in CS2, were prepared. The analytes in these four standard solutions were present at concentrations of 40, 20, 10 and 5 ng/μL. The limit of detection was calculated for ethyl acetate, cyclohexane, isooctane, n-heptane, toluene, n-decane and limonene. Depending on the analyte, the limit of detection [LOD = 3.3(s/S), where s is the STDEV of areas and S is the slope] ranged from 0.34 to 2.52 ng/μL (Pegas et al. 2010), corresponding to environmental concentrations between 0.27 and 2.97 μg/m3.

Carbonyls collected in cartridges filled with 2,4-dinitrophenylhydrazine reacted to give the corresponding 2,4-dinitrophenylhydrazones. These were extracted with 2 mL acetonitrile (Fisher Scientific). The glass vials were shaken for approximately 30 min, and the extract filtered through 0.45-μm disc membrane filters (filtration kit RAD 174) and injected into the high-performance liquid chromatography (HPLC) system. The analytical system consisted of a Jasco PU-980 pump, a Rheodyne manual injection valve (sample loop of 20 μL), a Supelcosil LC-18 column (250 × 4.6 mm, 5 μm; Supelco) and a Jasco MD-1510 diode array detector, all connected in series. Isocratic elution at room temperature was performed using acetonitrile/water solution (60/40, v/v) as the mobile phase at flow rate of 1.5 mL/min. The carbonyl concentrations were quantified using external calibration curves constructed from standard solutions of TO11/IP6A carbonyl—DNPH Mix (Supelco). The limit of detection (LOD) ranged from 1.29 to 2.09 μg/mL, depending on the analyte.

NO2 concentrations were also passively monitored for 14 days. The diffusive tubes (with steel grids impregnated with triethanolamine) chemiadsorb NO2, as nitrite, which was quantified by visible spectrophotometry (Bhugwant and Hoareau 2003).

Results and discussion

Comfort parameters and airborne microorganisms

The daily variation of comfort parameters throughout the 2-week monitoring period was recorded. To illustrate contrasting conditions, two specific days were chosen to exemplify the daily profiles. The mean daily temperature and RH values during the monitoring period, taken at the three main schools, ranged from 21.9 ± 1.09°C to 25.9 ± 1.56°C and from 34.6 ± 3.49% to 56.2 ± 3.28%, respectively (Fig. 1). In general, the temperature varied between 18.6°C and 28.2°C, whereas RH was in the 25.1–66.8% interval. Thermal comfort requirements differ for each individual due to factors such as clothing, activity level, age and physiology. ANSI/ASHRAE standard 55–2004 (2004) describes the temperature and humidity ranges that are comfortable for 80% of people engaged in chiefly sedentary activities. These values were conceived for adults in office environments and presume “normal indoor clothing”. The effects of moderate heat stress on performance of office work in subjects aged 18–29 years were evaluated through questionnaires by Witterseh et al. (2004). Raised temperature increased eye, nose and throat irritation (P < 0.05), headache intensity (P < 0.05) and difficulty in thinking clearly (P < 0.01) and concentrating (P < 0.01), and decreased self-estimated performance. Usually, the recommended indoor temperature ranges for comfort are 20–23°C in winter and 23–26°C in the summer. The suggested indoor RH values for comfort are in the range 30–60%. Control of RH also helps limit growth of microorganisms. Maintaining RH below 50% inhibits mould growth, dust mite infestation and bacteria. If RH levels fall below 25%, building occupants can experience respiratory irritation and possibly dry, itchy eyes and skin. Generally, in every school studied, the temperature and RH values were within the recommended ranges.

Fig. 1
figure 1

Indoor daily mean temperature (°C) and relative humidity (RH, %). Bars indicate standard deviations (STDEV)

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The National System for Energy and Indoor Air Quality Certification of Buildings (Regulamento dos Sistemas Energéticos de Climatização de Edifícios, RSECE) establishes an acceptable maximum value (AMV) of CO2 of 1,800 mg/m3 for buildings in Portugal (RSECE 2006). CO2 levels ranged widely (705–6,821 mg/m3) and exceeded 1,800 mg/m3 in all three main schools. Carbon dioxide concentrations are often used as a surrogate for the rate of outside air supply per occupant. Indoor CO2 levels above about 1,000 ppm are normally considered as indicative of ventilation rates that are unacceptable with respect to body odours. Concentrations of CO2 below 1,000 ppm do not always guarantee that the ventilation rate is adequate for removal of air pollutants from indoor sources (Daisey et al. 2003). The indoor concentrations of CO2 showed inadequate classroom air exchange rates. Figure 2 depicts the variation of indoor CO2 concentrations in a typical working day in the three main schools. Strong correlation of CO2 levels with occupancy was observed. CO2 spikes were even more pronounced when students started physical activities inside the classrooms, such as art classes or entrance from and exit to the playground. Seppanen et al. (1999) reviewed available literature for the association between both ventilation rates and CO2 concentrations and health. The authors were not able to determine a clear threshold value for CO2 below which further reductions in concentration were not associated with further decreases in SBS symptoms. However, 7 of the 16 studies reviewed suggested that the risk of SBS symptoms continued to decrease with decreasing CO2 concentrations below 800 ppm. Above all, CO2 measurements in schools indicate that most classrooms probably do not meet ANSI/ASHRAE standard 62–1999 (1999) for minimum ventilation rate of 2.5 L/s per person. Concentrations of a variety of pollutants emitted by occupants and building materials and furnishings will be higher under these conditions than if the ASHRAE ventilation standard were met. The potential for increased risks of contracting certain communicable respiratory illnesses, such as influenza and common colds, in classrooms with low ventilation rates is higher than in adequately ventilated places (Fisk 2001).

Fig. 2
figure 2

Indoor carbon dioxide and carbon monoxide levels in the three main schools

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CO levels ranged from values below LOD to 1.0 mg/m3 (Fig. 2) and did not exceed 12.5 mg/m3, the recommended exposure limit (RSECE 2006). To prevent carboxyhaemoglobin levels in the blood from exceeding 2.5%, the World Health Organization (WHO) has set specific air quality guidelines for distinct averaging periods: 100 mg/m3 (15 min), 60 mg/m3 (30 min), 30 mg/m3 (1 h) and 10 mg/m3 (8 h) (Chaloulakou et al. 2003). CO is one of the most characteristic traffic pollutants usually observed in urban areas. However, in this study, concomitant increases of CO2 and CO concentrations were observed. This suggests a linear correlation between CO and CO2 (r = 0.787) and a direct relationship between increasing concentration and classroom occupancy. CO is produced as a by-product of incomplete combustion of organic materials. In the human body, CO is produced endogenously by the class of enzymes known collectively as heme oxygenase (Mines 1997). CO is detectable in small quantities in the exhaled air of healthy people (Zayasu et al. 1997). Exhaled CO is increased in patients with inflammatory pulmonary diseases such as bronchial asthma, bronchiectasis, upper respiratory tract infections and seasonal allergic rhinitis (Zayasu et al. 1997). This is supported by the fact that inhaled corticosteroids inhibit the increase in exhaled CO in asthmatic patients (Zayasu et al. 1997). According to Jones and Lam (2006), human exposure to microenvironments with high CO levels can increase exhaled CO concentrations. Thus, exhaled CO levels can potentially act as a functional indicator of air pollutant levels. In the city of Lisbon the most common source of total CO emissions is vehicle exhausts (Borrego et al. 2000). Taking into account the CO levels recorded by the three monitoring stations close to the three main schools, mean I/O ratios close to zero were obtained. The highest CO levels were registered in the school located near one of the busiest streets of Lisbon (Avenida da Liberdade). The average daily concentrations measured by the air quality monitoring station in this street were in the range 0.36–0.52 mg/m3. Based on a comprehensive literature review, the INDEX project (Kotzias et al. 2005) concluded that current CO sources in European Union (EU) residences contribute essentially to short-term, rather than long-term, exposure.

Very few measurements of total VOCs in a typical school day are reported in the scientific literature (e.g. Pegas et al. 2009, 2010). Total VOC concentrations could give information about the influence of aerosol sprays, solvents, cleaning agents, pesticides, paints and repellents. The measurements ranged from the LOD (<0.005 mg/m3) to 2.1 mg/m3 and did not surpass the recommended value of 0.6 mg/m3 (RSECE 2006) (Fig. 3). Peak concentrations of VOCs were observed around 10 a.m. at school A, on the first day, decreasing progressively thereafter. This may be explained by the fact that, on this particular day, classrooms were cleaned with VOC-release products in the morning, before classes started. Normally, the cleaning staff tidy up the rooms at the end of the day. An increase in concentrations was also observed at school B during a period coincident with an art class where glue and paints were in use. This shows that collage and painting materials can significantly enhance VOC levels in indoor air. Zhang et al. (2006) also identified a visual art classroom with a relatively high level of VOCs.

Fig. 3
figure 3

Diurnal variation of total VOCs (non-methane hydrocarbons) in the three main schools

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Table 2 presents indoor and outdoor average levels of total bacterial and total fungal CFU/m3. In all schools, the total fungal and total bacterial colony-forming units in both indoor and outdoor air were above the AMV of 500 CFU/m3 defined by Portuguese legislation (decree-law 79/2006; RSECE 2006). The main factors affecting atmospheric dispersion and survival of microorganisms are relative humidity, temperature, oxygen, wind and air turbulence, air pollutants and water and nutrient availability. Very high levels of microorganisms were obtained in all five replicates performed for every sampling site. Repetition of the whole experiment 1 week apart (again with five replicates) was carried out to confirm the huge microbial counts. It was necessary to count some quadrants of the Micropore filters (0.45 μm) to extrapolate for all quadrants of each filter and estimate the minimum CFU number per sample. The high amounts of bacteria in both indoor and outdoor environments may derive from several factors, including high seasonal level of bioaerosols in outdoor air (spring), and human activities, such as breathing, sweating and movement causing particle resuspension.

Table 2 Measurement results for microorganisms
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High bacteria counts were probably due to high occupancy loading, poor hygienic condition of occupants, inadequate ventilation rates, movement of textiles, food products etc. (Lee et al. 2002; Mentese et al. 2009). Scheff et al. (2000) reported that, in a middle school of Springfield, the indoor fungal and bacterial counts were significantly higher than the outdoor concentrations. Similarly, Jo and Seo (2005) reported, for both total bacteria and total fungi, higher indoor concentrations compared with the outdoor environment at 11 elementary schools in Korea. Mentese et al. (2009) studied different indoor and outdoor environments in terms of bioaerosol contamination. The highest total bacteria counts were measured in kindergartens, elementary schools, restaurants, high schools and homes, while the highest mould levels were observed in kitchens, bathrooms and offices. Gonçalves et al. (2010) studied indoor and outdoor atmospheric fungal spores in the São Paulo metropolitan area (Brazil), and obtained levels above 36,000 CFU.

VOCs, carbonyls and NO2

The aromatic compounds benzene, toluene, ethylbenzene and the xylenes, followed by ethers, alcohols and terpenes, were usually the most abundant classes of VOCs. Generally, indoor total VOC concentrations were markedly higher than those observed outdoors (Fig. 4, Table 3). The sum of the individual VOC concentrations in indoor air varied from 37 to 317 μg/m3. Outdoor concentrations ranged between 6 and 80 μg/m3. In general, all the different classes of VOCs presented higher concentrations indoors than outdoors. Ethanol, dichloromethane, 1,2-dichloropropane, propyl acetate methylcyclohexanol, 2,2-dimethylbutane and 4-methyl-2-pentanone were only found in the indoor air. Those compounds only detected in indoor air probably have an indoor source. Pollutants identified in both indoor and outdoor samples, but with higher concentrations in the indoor environments, may indicate additional indoor sources or inadequate ventilation ratios; for example, terpenes are well known as substances emitted from cleaning products and room fresheners (Singer et al. 2006). Additionally, α-pinene is an intrinsic component of wood and furniture (Yrieix et al. 2010). Other VOC sources in indoor air include cooking fuels, aerosol propellants, refrigerants, paints, varnishes, cosmetics, adhesives, biocides, disinfectants, printed paper etc. (Srivastava et al. 2004). The indoor levels observed in school C may reflect inefficient ventilation conditions (windows and doors were always closed), and cooking activities in the same building as the classrooms. School E presented the highest levels of both aliphatic hydrocarbons and esters in comparison with other schools, probably due to the fact that the building had recently been painted. The highest aromatic hydrocarbon concentrations were observed at school K, likely due to its location in a street canyon with intense traffic.

Fig. 4
figure 4

Indoor (two classrooms) and outdoor VOC concentrations (sum of all compounds identified)

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Table 3 Indoor and outdoor VOC and carbonyl concentrations (μg/m3) in all schools
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Among all monitored VOCs, benzene, toluene, ethylbenzene and xylenes (BTEX) are of particular interest due to their known carcinogenic effects (Kotzias et al. 2009). Indoor and outdoor BTEX concentrations are summarised in Table 4. Benzene concentrations were higher for all indoor environments, ranging from 0.2 to a maximum of 0.9 μg/m3. All measurements were below the EU limit value of 5 μg/m3 for mean annual exposure to benzene. However, as it is a carcinogenic compound, the WHO has not yet established a guide or safe value (WHO 2000, 2005). Toluene is a ubiquitous indoor pollutant (Bruno et al. 2008). Its indoor concentrations were higher than the corresponding outdoor levels, ranging from 0.9 to 7.3 μg/m3. Concentrations of ethylbenzene comprise values from 0.3 to 14.2 μg/m3, whereas the xylene isomers, m+p-xylene and o-xylene, were in the ranges 0.6–40 and 0.2–13.5 μg/m3, respectively. Results for BTEX in this study correlate well with those of Stranger et al. (2007), except for toluene. The high benzene and toluene concentrations observed in Lisbon are in the same range as those measured in schools of Oporto, Portugal (Madureira et al. 2009). Toluene levels were very similar to those found in schools of Curitiba, Brazil (Godoi 2009). The BTEX levels in schools of Lisbon are far below the weekly average concentrations in non-residential indoor environments, such as libraries, pharmacies, offices, gymnasiums, newspaper stands, copy centres, coffee shops etc. in Bari, Italy (Bruno et al. 2008). BTEX values were much lower than the WHO guidelines from 2000 and 2005 (260 μg/m3 over 1 week for toluene, 4.8 mg/m3 over 24 h for xylenes). However, some studies have correlated exposure to low concentrations of benzene and toluene with increased risks of cancer or eye and airway irritations (Guieysse et al. 2008).

Table 4 Overview of indoor and outdoor BTEX concentrations in 14 schools in Lisbon
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The highest indoor VOC concentrations were found in schools E, F, G and K. A possible indoor source in schools E and K was the vinyl flooring and floor adhesives, which are described as emitter materials, especially of benzene, toluene, xylenes, styrene and ethylbenzene, among others (Mendell 2007). In addition to these indoor sources, the inadequate ventilation (closed windows) likely favours accumulation of pollutants. New furniture and/or the fact of being a new building could also explain the high levels in school E. The VOC loads in school G are possibly related to the proximity to congested motorways surrounding the city. School F is located close to an old cigarette factory, near motorways, in an area without green spaces and with urban planning deficit. These housing conditions may have contributed to the high concentrations of ethers and alcohols. Better ventilation conditions, lower occupancy density and larger classrooms in school A in relation to other institutions may explain the low indoor levels observed at that school.

At all locations, the indoor concentrations of atmospheric aldehydes (formaldehyde, acetaldehyde, propionaldehyde and benzaldehyde) were higher than those outdoors, particularly for formaldehyde (Fig. 5), which is classified as a human carcinogen by the International Agency for Cancer Research. Formaldehyde concentrations ranged from 1.48 to 42.3 μg/m3. Higher levels in classrooms than outdoors suggest that indoor sources are more important contributors to the indoor levels than outdoor sources such as infiltration of vehicle exhaust (Ongwandee et al. 2009). Formaldehyde could originate from composite wood and other products with urea–formaldehyde resin, some architectural finishes, tobacco smoke and other combustion processes (Mendel 2007). Concentrations of formaldehyde are significantly affected by season and building age (Dingle and Franklin 2002). It was observed that levels are higher in the presence of furniture bought new or restored less than 1 year before measurements (Lovreglio et al. 2009). In spring and summer, outdoor formaldehyde levels increase due to acceleration of photochemical activity (Lee et al. 2001b), while the opposite trend is observed indoors, since the interchange rate between indoor and outdoor air is higher due to open windows or use of air conditioning (Pilidis et al. 2009). The highest level of formaldehyde was observed at school G. The high levels may be related to the fact that this institution is located in the vicinity of major motorways with very intense traffic. It should be also noted that the ceilings were painted during the Shrovetide period and new furniture was purchased just 1 month before the sampling campaign. In addition, the school corridors are wood coated. Pressed wood products use adhesive containing urea formaldehyde that can break down, releasing formaldehyde into the air. Formaldehyde is also found as a preservative in paint. Acute symptoms from formaldehyde exposure have sometimes been found, including eye, nose and throat irritation, as well as lower airway and pulmonary effects (Kotzias et al. 2009). Among the identified aldehydes, formaldehyde was the most abundant. However, other carbonyl compounds were also present at appreciable amounts: acetaldehyde (0.88–7.02 μg/m3), propionaldehyde (0.48–2.28 μg/m3) and benzaldehyde (0.03–0.96 μg/m3).

Fig. 5
figure 5

Formaldehyde concentration in all schools

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Animal and human experimental studies indicate that NO2 at short-term concentrations exceeding 200 μg/m3 is a pollutant with significant health effects (Kraft et al. 2005). Exposure to NO2 at hourly peak levels of the order of ≥80 ppb, compared with background levels of 20 ppb, was associated with a significant increase of sore throats, colds and absences from school (Pilotto et al. 1997). The average NO2 concentrations were higher outdoors than indoors (Table 5), probably as a result of vehicular exhaust emissions from nearby traffic. The I/O NO2 ratios ranged between 0.36 and 0.95. Indoor NO2 levels were within the interval 15–37 μg/m3, not exceeding the current WHO guideline value of 40 μg/m3 (annual mean) to protect public health. School E, which presented an outdoor concentration of 42 μg/m3, registered the lowest level of indoor NO2 (15 μg/m3), possibly because the windows and the doors were always closed. An average NO2 concentration of 39 μg/m3 was registered in classrooms in Taiyuann, China (Zhao et al. 2008). Levels varying from 9.5 to 23 μg/m3 and from 11 to 19 μg/m3 were obtained, respectively, in the indoor air and outside of elementary schools in Curitiba, Brazil (Godoi et al. 2009). Lee and Chang (2000) found indoor and outdoor NO2 levels ranging from 12 to 176 μg/m3 and 19 to 244 μg/m3, respectively, for five classrooms at different schools in Hong Kong.

Table 5 Indoor and outdoor NO2 concentrations (μg/m3)
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Conclusions

Indoor and outdoor concentrations of NO2, VOCs, carbonyls and microbiological components, and comfort parameters [temperature, relative humidity, carbon dioxide (CO2), carbon monoxide (CO) and total VOCs] were measured in 14 elementary schools in Lisbon. The concentration of CO2 and bioaerosols greatly exceeded the AMV of 1,800 mg/m3 and 500 CFU/m3, respectively, perhaps due to overcrowded classrooms and inefficient ventilation. Schools located near streets with busy traffic presented the highest outdoor (45.7 μg/m3) and lowest indoor (29.6 μg/m3) NO2 levels, possibly because the windows and the doors were always closed. Generally, the assessed VOCs occurred at I/O ratios above unity, showing the important influence of indoor sources and building conditions on IAQ. Most of the gaseous pollutants can be blamed on traffic emissions and indoor sources [some architectural finishes, floor adhesives, polyvinylchloride (PVC) flooring, consumer products and cleaning products]. Better ventilation should be provided for these public buildings, and air cleaners should be used to improve children’s health, and their performance. More studies are needed (currently underway) to find additional possible sources of indoor contamination, to calculate air exchange rates on a seasonal basis, to evaluate if there is a causal relationship between pollutant exposure and health symptoms in schools and to assess if school IAQ can adversely affect academic performance or attendance.