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Variations in Particle Concentrations and Indoor Air Parameters in Classrooms in the Heating and Summer Seasons

Variations in Particle Concentrations and Indoor Air Parameters in Classrooms in the Heating and... Simultaneous measurements of the indoor and outdoor particle mass (PM) and particle number () concentrations as well as the air temperature, relative humidity (), and CO2 concentrations have been conducted in 6 occupied (L) and unoccupied (V) classrooms in 3 secondary schools in Lublin, Poland, in the heating (H) and summer (S) seasons. The schools were located in residential areas where the majority of private houses are heated by means of coal-burning stoves. The ratios of the average particle concentrations in occupied and unoccupied classrooms (L/V) were higher during the heating season measurements. The ratios of the average particle concentrations during the measurements in the heating and summer seasons (H/S) were higher in occupied classrooms. In both seasons the average PM and concentrations amounted to 239 g/m3 and 7.4×103/cm3 in the occupied classrooms, and to 76 g/m3 and 5.4×103/cm3 in the unoccupied classrooms, respectively. The particle exposures experienced by students were higher in the monitored classrooms than outdoors and were on average about 50% higher in the heating than in the summer season. A positive correlation between mass concentrations of coarse particles and indoor air temperature, and CO2 concentrations in both seasons was observed. The concentrations of fine particles were negatively correlated with the indoor air parameters in the heating season, and positively correlated in the summer season. INTRODUCTION The quality of the indoor air significantly affects people's health and their well-being. Apart from such contaminants as volatile organic compounds also the aerosol particles present in the air have an impact on the quality of the indoor air in apartments, offices, schools and other educational premises as well as in means of transport [8, 9, 27]. School facilities are among the premises in which indoor particle concentrations can considerably exceed ambient particle concentrations [5, 10, 12]. Despite the fact that certain characteristic particle emission sources do not or seldom exist, e.g. smoking and cooking, particles generated in classrooms may be as toxic as particles in the ambient air [11]. Such particles can also pose a biological threat to students' health [7]. School-aged children spend a significant portion of their time indoors in classrooms. They are also more susceptible than adults to the harmful effects of indoor particles [3, 30]. Particles which are suspended in the classroom air are to a large extent responsible for increased allergies, respiratory infections, asthma exacerbations and deteriorating lung function parameters among students [34]. In turn, such health problems are related to reduced students' attendance and performance [18, 29]. Indoor particle concentration levels in typical classrooms are mainly dependent on the presence of the students and their physical activity [1, 10, 33]. They are also influenced by the outdoor air particle concentration changes and ventilation intensity [13]. In general, the higher the air exchange rate, the lower the indoor particle concentrations [12]. The outdoor and indoor microclimatic parameters can also be of significance [6, 26]. Despite intensive research, it is still not entirely clear how the concentrations of indoor particles in classrooms are associated with the occupation, outdoor particle emissions and with the indoor and outdoor air parameters related to a given season. The factors which influence the particle concentrations in classrooms and the relations between them can be important when student exposures and associated health risks are determined. The present study constitutes a part of a broader study the preliminary results of which have been reported elsewhere [7, 25]. Its aim was to assess the indoor air quality in typical school classrooms in Lublin, Poland and to characterize the key factors that have an impact on this quality. The purpose of this study was to investigate the particle mass (PM) and particle number () concentrations in classrooms. Special emphasis was placed on the influence of students' presence, the outdoor particle emissions from coal-burning stoves in residential houses located near the school, the season and the indoor and outdoor air thermal parameters. MATERIAL AND METHODS The measurements were conducted in 6 classrooms in 3 secondary schools in Lublin, Poland. The population of the city and its close surroundings is about 590,000 inhabitants. The population density is 2407/km2 [32]. Lublin is mostly surrounded by rural areas. The schools were located in different parts of the city in densely populated residential areas, where a significant number of private residential houses are heated by means of coal stoves. One of the schools was built in 1930, the other two were built in 1970. Table 1 summarizes the characteristics of the monitored classrooms and provides the measurement dates. In each school (numbers in parentheses), two classrooms were chosen for monitoring. These classrooms were used for teaching either computer science (C1) or biology (C2) and they were located on the first, second and third floor of the school buildings. The classrooms had various floor areas (from 29 to 71 m2) and volumes (from 96 to 250 m3). The maximum occupancy depended on the size of the classroom and ranged between 18­34 students. All the classrooms had ceramic tile floors and were equipped with standard school furniture. Traditional blackboards for chalk were used in the biology classrooms and whiteboards for color-board markers were used in the computer science classrooms. None of the monitored classrooms had air conditioning systems which is a standard for school facilities in Poland. Natural ventilation was obtained through large double-glazed PCV windows. Table 1. Characteristics of the monitored classrooms and the measurement dates School 1 Classroom attributes Floor number Volume Floor area Number of seats Measurements Heating season (H) Summer season (S) L V L V 03.09.10 03.13.10 06.10.10 06.12.10 03.10.10 03.14.10 06.11.10 06.13.10 [m ] School 2 3 205 57 18 03.30.10 04.03.10 05.20.10 05.22.10 C2(2) 2 250 69 34 03.31.10 04.04.10 05.21.10 05.23.10 1 3 School 3 C1(3) 221 71 22 03.16.10 03.20.10 06.15.10 06.19.10 1 183 59 32 03.17.10 03.21.10 06.16.10 06.20.10 C1(1) 2 96 29 18 130 46 32 [m ] L ­ occupied classroom, V ­ unoccupied classroom Continuous measurements of indoor and outdoor air particulate matter concentration levels, thermal parameters and CO2 concentrations were performed both in the heating season (H), and then again in the summer season (S). Two-day measurements were performed in classrooms during teaching hours (L) and in unoccupied classrooms (V) and lasted for a few hours per day. The sampling devices for the indoor measurements were placed on empty desks in the middle of the classrooms at the height of 110 cm. The sampling devices for the parallel outdoor measurements were located outside the windows of the monitored classrooms. Laser photometers Dust Trak DRX model 8533 (TSI Inc., Shoreview, MN, USA) were used for continuous determination of the concentrations of particle size-segregated mass fractions , PM2.5, Respirable, 0, and (Total Suspended Particle). Fractions and PM2.5 characterize mass concentration of fine particles with an aerodynamic diameter less than or equal to 1 m and 2.5 m cut point, respectively. Mass concentrations of coarse particles (greater than 2.5 m cut point) are characterized by 0 and fractions. Because the data obtained for PM2.5 and Respirable fraction did not differ significantly, the latter was not considered in this paper. Number concentrations of particles with the size range from 0.02 to greater than 1 m were determined using the P-Trak model 8525 (TSI Inc., Shoreview, MN, USA) condensation particle counters. The indoor and outdoor air temperature and relative humidity () were measured by Onset Hobo U12 External Data Logger sensors with the temperature measurement range from ­20 to 70°C and the from 5 to 95%. The GMD/W20 sensors manufactured by VAISALA with a measurement range from 0 to 5000 ppm were used to measure the CO2 concentration. The chosen sampling interval for all the measuring instruments was 60 s. Before the measurements, all instruments were calibrated by their producers. The distribution of the measurement results allowed to use the Spearmen correlation coefficients as indicators of the mutual relations between the indoor and outdoor PM and concentrations, air parameters, occupation and characteristic attributes of the classrooms. RESULTS AND DISCUSSION PM and concentration changes Different coexisting factors affecting particle concentration levels in the monitored classrooms are evident on the indoor PM and concentration time series. Figures 1 and 2 illustrate the exemplary PM and concentration changes in an occupied and empty classroom C1(1), in a determined time period, during one-day measurements performed respectively in the heating and summer seasons. The time series data for PM and concentrations in the outdoor air and also for the indoor and outdoor air temperature (Temp), relative humidity () and CO2 concentrations are also shown. In both seasons the presence and physical activity of students in the classrooms seem to be the most important factors which change the particulate matter concentration levels and the measured indoor air parameters. The observable fluctuations are clearly connected with the changes in the classroom occupancy status. Their rough quantity evaluation for particle concentrations could be accomplished by taking into account the maximum and average PM and concentration levels. For example, in the heating season measurements, the maximum concentrations of the fraction which periodically occur in the variably occupied classroom C1(1) were up to 14 times higher than the average level (~50 g/m3) in the unoccupied classroom. In the summer season measurements this proportion was lower ( maximum concentrations were up to 4 times higher than the average level), however, the average concentration level in the empty classroom was slightly higher (~80 g/m3). The maximum concentrations during the measurements in both seasons reached the average concentration levels in the outdoor air. The biggest increases of the PM and concentration levels were observed at the beginning of the classes and during breaks between classes. This can be explained by the increased physical activity of the students during that time which in consequence results in the intensified air movement in the classrooms. This, in turn, increases the resuspension of dust particles deposited on indoor surfaces and thus the particle concentration in the indoor air [22, 23]. Resuspension mainly affects supermicrometer particles but in the case of the considered classrooms it could be of significance for smaller (about 1 m) particles as well. The considerable amounts of such particles originate from emissions from coal-burning stoves in the residential houses located near the schools. The main mass concentration of coal combustion particles ranges between 0.8­10 m with predominance of 1­2 m particles [21]. These particles enter the classrooms and are deposited on indoor surfaces and could be accumulated due to insufficient cleaning. During the students' physical activity they undergo resuspension processes and they have a major impact on the measured PM concentrations. They could also affect the measured concentrations due to particle detection range of the applied instruments. During the breaks between classes, especially in the summer season, the classrooms were frequently ventilated by opening the windows and doors. This manner of ventilation caused additional intensive indoor air movement and substantial changes in the indoor particle concentrations. It is also important to note that the average outdoor particle concentration levels were higher than the corresponding indoor levels in the vacant classrooms [16, 19]. According to the number of studies, in naturally ventilated spaces, such as the monitored classrooms, the input of the outdoor particles is a very important factor which has an impact on the indoor particle concentration levels [12, 20]. Moreover, I O 60 30 11:02 11:31 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 90 60 30 11:02 11:31 12:00 12:28 O I 12:57 13:26 13:55 14:24 14:52 15:21 15:50 50 11:02 11:31 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 I O Number of students I O 11:31 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 15:50 [ 103/cm 3] 18 12 6 11:02 11:31 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 80 I O 15:50 16:19 10:48 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 0 20 60 40 11:02 11:31 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 1200 800 400 11:02 11:31 12:00 12:28 I O 12:57 13:26 13:55 14:24 14:52 15:21 15:50 Fig. 1. Indoor (I) and outdoor (O) particle mass (PM) and particle number () concentration, air temperature (Temp), relative humidity () and CO2 concentration time series in the occupied (L) and unoccupied (V) classroom C1(1) during one school day in the heating (H) season measurements particles generated by other unidentified sources inside the schools, e.g. cleaning or renovation activity could also have entered the classrooms. During the classes, when the students were already seated and their physical activity was relatively low, a decrease of the indoor particle concentrations was observed. It was especially visible for concentrations of coarse particles characterized by 0 and fractions. These particles undergo effective gravitational sedimentation hence they were relatively quickly removed from the indoor air and deposited on indoor surfaces as dust [2, 24]. The concentrations of fine particles ( and PM2.5 fractions) decreased to I O [ 103/cm 3] O I O I O I O I O I 60 30 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 15:50 90 I O 10 5 16:19 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:12 0 15 10 5 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:12 16:19 0 15 10 5 16:19 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:12 0 15 10 O I 60 30 12:00 12:28 12:57 13:26 I O 14:52 15:21 15:50 O I 50 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 15:50 I O O I Number of students 150 50 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 15:50 I O 5 16:19 0 15 10 5 16:19 O I 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:12 [ 103/cm 3] O I 12:28 12:57 13:26 13:55 14:24 14:52 15:21 15:50 O I 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:12 18 12 6 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 15:50 80 10 5 16:19 11:02 11:16 11:31 11:45 60 40 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 15:50 I O 5 16:19 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:12 0 15 10 5 I O 1200 800 400 12:00 12:28 12:57 13:26 14:52 15:21 15:50 Fig. 2. Indoor (I) and outdoor (O) particle mass (PM) and particle number () concentration, air temperature (Temp), relative humidity () and CO2 concentration time series in the occupied (L) and unoccupied (V) classroom C1(1) during one school day in the summer season (S) measurements a lesser extent. This, in turn, results from the greater stability of these particles to remain suspended in the indoor air [14, 15]. Occupation and season The presence of the students in all the monitored classrooms, regardless of the season, resulted in a significant increase in the concentrations of the measured particles. For example, for the measurements in both seasons, the average concentrations of the and in the occupied classrooms amounted to 61 and 239 g/m3, and in the I O I O I O [ 103/cm 3] 0 [g/m 3] PM2 .5 [g/m ] classrooms could be the effect of the already mentioned, instable ventilation conditions during the measurements or the coexistence of other affecting factors e.g. particle sources inside the schools or particle concentration changes in the outdoor air [4, 17, 21, 22]. It was also observed that for the measurements in both seasons the ranges of particle concentration changes were greater in occupied classrooms. For example, the ranges of the and the fraction concentration changes in the occupied classrooms were on average about 5 and 18 times greater than in the empty classrooms respectively. In the case of concentrations, such ratio amounted to about 7. The average coefficient of variation (CV) values for and concentrations in the occupied classrooms amounted to 19.0 and 42.5%, and in the empty classrooms to 6.4 and 9.7%, respectively. The corresponding average CV values for the concentrations were 20.5 and 5.2%. The maximum standard error of the evaluated CVs was 1.2%. The ratios of the average particle concentrations in the occupied and empty classrooms (L/V) in the heating and summer season measurements are presented in Table 2. Table 2. Occupied-to-unoccupied ratios (L/V) of the average particle mass (PM) and particle number () concentrations in the monitored classrooms during the heating (H) and summer season (S) measurements. N is a time-weighted average number of students present during the measurement periods which include the breaks between the classes when the students were not present in the room empty classrooms to 49 and 76 g/m3, respectively. The average concentration in the occupied classrooms amounted to 7.4×103/cm3 and to 5.4×103/cm3 in the empty classrooms. Occurring cases of higher and concentrations in the empty Classroom H C1(1) S H S H S H C2(2) C1(3) S H S H S H S 2.14 1.74 1.90 1.50 0.75 1.24 1.61 0.76 1.07 0.52 1.78 1.21 1.56 1.16 PM2.5 2.09 1.76 1.92 1.50 0.75 1.27 1.64 0.78 1.07 0.53 1.80 1.22 1.55 1.18 0 2.69 1.63 2.65 1.68 1.36 1.96 2.04 1.22 1.80 1.14 2.39 1.94 2.16 1.60 5.03 1.52 4.27 2.34 3.49 3.59 3.30 2.45 4.19 2.49 3.94 3.72 4.04 2.69 0.72 0.94 3.20 0.99 2.40 1.60 2.68 1.37 1.26 0.81 3.32 1.31 2.26 1.17 N 13.2 ± 6.9 (16­18) 11.6 ± 5.6 (15­16) 9.2 ± 4.6 (10­13) 6.5 ± 7.5 (7­17) 11.2 ± 5.9 (12­17) 11.2 ± 5.3 (12­16) 18.4 ± 10.2 (22­29) 19.2 ± 9.7 (25­26) 12.3 ± 6.5 (14/19) 10.7 ± 8.8 (12­24) 13.9 ± 7.5 (16/22) 10.5 ± 10.9 (14­28) 13.0 ± 3.6 (15­20) 11.6 ± 3.4 (15­22) Average N ­ mean ± sdev. (median-maximal) number of students. In all the monitored classrooms the L/V ratios were higher in the heating season and their biggest values were for the concentrations of coarse particles. It may indicate that more particles, especially coarse ones, were generated by students in the classrooms in that season. However, it has to be pointed out that the number of students in the monitored classrooms was, on average, slightly higher during the heating season measurements (Table 2). In the heating season, the concentrations of the considered particles in the occupied classrooms were higher than in the summer season. It is connected with the increased outdoor particle emissions from coal combustion in that season and the increased particle deposition and resuspension in the classrooms. Table 3 presents the ratios of the average PM and concentrations in the heating and summer seasons (H/S) for the occupied and empty classrooms. The values of H/S ratios in the occupied classrooms are, on average, higher for the coarse particles. For example, the average H/S ratio amounted to 1.26 for the fraction and 1.43 for the fraction. In case of vacant classrooms these ratios for all considered particles were smaller than 1. The exposures experienced by students in the monitored classrooms were higher in the occupied classrooms than those estimated outside. In the heating season they were on average about 50% higher. It has to be noted that a substantial portion of the PM exposures (~50%) and the exposures (~30%) were attributed to particles generated inside the classrooms. Indoor air parameters The indoor air parameters in the monitored classrooms are affected by heating (in winter), by the outdoor air parameters, intensity of the ventilation as well as the presence of students Table 3. Heating to summer season ratios (H/S) of the average particle mass (PM) and particle number () concentrations for the occupied (L) and unoccupied (V) classrooms Classroom L C1(1) C2(2) C1(3) Average V L V L V L V L V L V L V 0.80 0.65 1.51 1.17 0.86 1.44 1.69 0.80 1.36 0.66 1.37 0.93 1.26 0.94 PM2.5 0.80 0.68 1.53 1.19 0.87 1.46 1.67 0.80 1.35 0.67 1.37 0.93 1.27 0.96 0 1.35 0.81 1.84 1.16 0.64 0.92 1.32 0.79 1.25 0.80 1.23 1.00 1.27 0.91 2.25 0.68 1.89 1.04 0.90 0.93 0.98 0.73 1.51 0.89 1.05 0.99 1.43 0.88 1.25 1.63 1.61 0.50 2.14 1.44 1.63 0.83 1.19 0.76 0.99 0.39 1.47 0.93 (Figs. 1, 2). The fluctuations of the indoor air temperature, and CO2 concentration were most distinct during the time when classes were held in the heating season. During the breaks between classes when students were not present in the classrooms and ventilation conditions were not significantly changed (windows were not opened and doors were only opened occasionally) systematic changes of the measured indoor air parameters were observed. For example, an almost exponential decrease of the CO2 concentrations occurs in the classrooms. The impact of the changing ventilation conditions was more visible during the lessons and breaks in the summer season measurements when less regular fluctuations of the indoor air parameters were observed. In empty classrooms, the measured indoor air parameters were also not stable. In this case other factors, e.g. related to the previous classroom occupation or the presence of the persons setting up the measurement devices could be significant. During the classes the indoor CO2 concentrations frequently exceeded the level of 1000 ppm, which according to the ASHRAE Standards 62-1989 is the threshold concentration for satisfactory comfort. The CO2 concentration did not meet the ASHRAE Standards in 56% of the teaching hours in the heating season and in 41% of the teaching hours in the summer season measurements. CO2 concentration readings over 1500 ppm were found in about 25% and 7% of the teaching hours in the heating and summer season measurements, respectively. Several strong relations between the indoor air parameters and particle concentrations were observed in the monitored classrooms. The average tendencies of these relations for the heating and summer season measurements were determined on the basis of the mean correlation coefficients. This way a positive correlation between the mass concentration of coarse particles and indoor air parameters in occupied classrooms for the measurement periods in both seasons was obtained. A negative correlation between the mass and number concentration of fine particles and the measured indoor air parameters was determined for the heating season, whereas a positive correlation was found for the summer season measurements. The exemplary relations between the , and , and the indoor air temperature, and CO2 concentration in the heating and summer seasons, which best represent the above mentioned tendencies are shown in Figure 3. All the presented correlations are statistically significant, p < 0.01. Comparison with previous research The simultaneous measurements of PM and concentrations in occupied and empty classrooms as well as outdoors in both the heating and summer seasons are seldom reported. If they were performed, they were not confronted with the indoor and outdoor air parameters. Most of the individual results presented in this paper are comparable with those in previous studies. Based on the 6-week (October­November) measurements performed in two classrooms in one primary school in Munich, Fromme et al. [11] reported the median PM2.5 concentration of 37.4 g/m3 and 0 of 118.2 g/m3 indoors, while the corresponding results for the outdoor air were 17.0 g/m3 and 24.2 g/m3. Heudorf et al. [13] measured the indoor air quality in two primary school classrooms in Frankfurt/M for 3 weeks (February­March). Their findings showed that the average level of 0 was 69 g/m3 and that the measured concentrations were determined by the occupancy, student activity and the frequency of cleaning the classrooms. Lower PM concentrations in a lecturing room in Prague were observed by Branis et al. [6] during the measurements in the fall season 0,14 0,10 22,5 23,0 Tempera tura 0,14 0,10 0,06 r = 0 .71 2 y = - 0.3 55 + 0.021x 20,0 Tempera tura [ ] °C r = - 0.636 y = 0.767 - 0.028x 0,06 22,0 23,5 [°C] 24,0 24,5 19,0 0,5 0,3 0,1 19,0 18 19,5 20,5 21,0 0,5 0,3 0,1 r = 0.442 y = -1 .87 3 + 0.096x r = 0.717 y = -4 .90 9 + 0.25 8x 22,5 23,0 23,5 [° C] 24,0 24,5 19,5 20,0 [° C] 20,5 21,0 6 22,0 r = -0.826 y = 162.437 - 6.437x 22,5 23,0 23,5 [°C] Temperatura 24,0 24,5 22,0 18 r = 0.331 Temperatura y = -53.027 + 3.216x 19,5 20,0 20,5 [°C] 21,0 6 19,0 Temp 0,14 0,10 Temp 0,14 0,10 0,06 0,02 37 0,5 0,3 0,1 37 39 41 43 0,02 24 26 28 30 [% ] r = - 0.7 84 0,06 y = 0 .31 9 - 0 .00 6x r = 0.5 76 y = - 0.213 + 0.006x [% ] 0,5 r = 0.427 0,3 0,1 24 y = - 0.17 9 + 0.017 x r = 0.5 45 y = - 1.46 2 + 0 .042x [103 /cm3 ] r = -0.876 y = 52.610 - 1.280x 26 28 30 32 r = 0.890 y = -7.568 + 0.261x 0,12 0,08 0,04 500 1000 0,7 r = 0.521 0,5 0,3 0,1 500 1000 1500 [mg/m 3 ] 0,12 0,08 0,04 r = - 0.7 15 y = 0 .170 - 0 .000 03x [p p m] r = 0.812 y = - 0.006 + 0 .000 06x [p p m] y = 0.17 6 + 0.0001 x 500 0,7 r = 0.81 7 0,5 0,3 0,1 y = - 0.3 35 + 0.0007x 2000 [ppm] 2500 3000 CO2 r = -0.872 y = 23.973 - 0.006x r = 0.818 y = 2.729 + 0.002x CO2 [ppm] 2000 [ppm] [ppm] Fig. 3. The relation between the particle mass ( and ), particle number () concentrations and indoor air temperature (Temp), relative humidity () and CO2 concentration in the occupied classrooms in the heating (H) and summer (S)seasons (October­November). The average indoor PM2.5 concentration amounted to 21.9 g/m3 and 42,3 g/m3 for 0. However, as they pointed out the PM concentrations were measured by the gravimetrical method whose readings are lower than from photometers (e.g. TSI Dust Trak). Relatively smaller concentrations of 0 were also found in 40 classrooms in Korea [28]. The average level was 46.7 g/m3 in the summer and 39.1 g/m3 in the winter. Fromme et al. [10] reported the median daily values of PM concentrations measured in 58 classrooms in Munich and a neighboring district in the winter between 2.7 and 80.8 g/m3 (average: 23 g/m3) for PM2.5 and between 16.3 and 313 g/m3 (average 105 g/m3) for 0,. In the summer the concentrations of PM2.5 ranged between 4.6 and 34.8 g/m3 (average 13.5 g/m3) and the concentrations of 0 between 18.3 and 178 g/m3 (average 71.7 g/m3). Zwodziak et al. [34] measured the indoor and outdoor particle concentrations in a secondary school in Wroclaw in the winter/spring and summer/autumn seasons. The average 0 particle concentration was 115.2 g/m3 indoors and 53.8 g/m3 outdoors. The concentrations of and PM2.5 were slightly higher inside the school than outdoors and their average values amounted to 23.2 g/m3 and 46.4 g/m3, respectively. It has been also indicated that there is a significant correlation between the PM2.5 concentration and students' lung function parameters. When it comes to the concentrations, Guo et al. [12] reported the results of a 2 week measurement period in September in a village primary school classroom in Australia. The average concentration (particles 0.014­0.800 m) amounted to 2.11×103/cm3 indoors and 2.93×103/cm3 outdoors. Fromme et al. [10] found that the median concentrations (particles 0.010­0.487 m) measured in 36 classrooms in Munich in the summer, ranged between 2.62 and 12.14×103/cm3 (average: 6.5×103/cm3). Weichenthal et al. [31] performed measurements in Canada in 37 classrooms. Their study showed the average indoor level (particles 0.020­0.100 m) of 5.0×103/cm3, and the average outdoor level of 9.0×103/cm3. Mullen et al. [23] measured the concentration of particles 0.006­0.100 m in 6 classrooms in northern California in the summer and winter. In the presence of the students the mean indoor levels ranged between 5.2­16.5×103/cm3 (average: 10.8×103/cm3). The corresponding outdoor concentrations were 9.0­26.0×103/cm3 (average: 18.1×103/cm3). The CO2 concentrations in the monitored classrooms are also largely consistent with those in other published studies. Fromme et al. [10] reported the CO2 median levels in 85 classrooms in 64 schools in Munich and a neighboring district which ranged between 589 and 4172 ppm (average: 1759 ppm) in the winter, and between 480 and 1875 ppm (average: 890 ppm) in the summer. The corresponding outdoor CO2 concentrations varied from 386 to 472 ppm in the winter, and from 341 to 485 ppm in the summer. In the studies carried out by Heudorf et al. [13], the mean CO2 levels in classrooms in 2 schools in Frankfurt/M were from 1051 to 1459 ppm. The relationships between the particle concentration and the indoor air temperature, and CO2 concentration in the monitored classrooms are also, to a large extent, consistent with those in the previous studies. Branis et al. [6] demonstrated a high positive correlation between the concentration and the of indoor and ambient air (the respective correlation coefficients amounted to 0.605 and 0.789). Fromme et al. [10] indicated a significant PM2.5 concentration decrease by 6.4 g/m3 in the winter and an increase by 1.7 g/m3 in the summer per each 10% increase. Polednik and Dudzinska [27] demonstrated that coarse aerosol and bioaerosol particle and the CO2 concentrations in an air-conditioned auditorium could be an indicator of the perceived air quality due to correlative and mutual relations with the indoor air parameters. The estimated student exposures to particles in the monitored classrooms are also comparable with the student exposures reported in previous studies. The daily-integrated exposure to ultra fine particles by students in 6 elementary school classrooms in northern California estimated by Mullen et al. [23] was 52×103/cm3 h/day. In turn, the exposure experienced by these students in their homes was approximately 6 times higher and amounted to 320×103/cm3 h/day. The measurements in the monitored classrooms were carried out in real field conditions with varied student activity, classroom ventilation, and outdoor air parameters. Most probably this was the reason why the significant correlations between the particle concentration and the number of students present or classroom location in school buildings, classroom volume, floor area, furnishing materials and blackboard or whiteboard usage in the classrooms reported in some previous studies were hard to find. CONCLUSIONS The results of the measurements performed in classrooms in selected schools in Lublin are consistent with the results reported in previous research in terms of the obtained trends. The PM and concentrations mainly depend on the presence of students and are manifold higher in occupied than in unoccupied classrooms. The significant differences in the levels of PM and concentrations are observed in the measurements performed during the heating and the summer seasons. This is considerably influenced by coal combustion in the residential houses located in the vicinity of the schools. Such particle emissions substantially contribute to students' exposure and may cause adverse health effects. The mass concentrations of coarse particles in the occupied classrooms were positively correlated with the indoor air temperature, and CO2 concentration. The mass and number concentration of fine particles were negatively correlated with indoor air parameters in the heating season, and positively correlated in the summer season. ACKNOWLEDGEMENTS This research was carried out within the Projects 4955/T02/2008/34, financed by the Polish Ministry of Science and Higher Education. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Environmental Protection de Gruyter

Variations in Particle Concentrations and Indoor Air Parameters in Classrooms in the Heating and Summer Seasons

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de Gruyter
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2083-4772
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10.2478/aep-2013-0037
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Abstract

Simultaneous measurements of the indoor and outdoor particle mass (PM) and particle number () concentrations as well as the air temperature, relative humidity (), and CO2 concentrations have been conducted in 6 occupied (L) and unoccupied (V) classrooms in 3 secondary schools in Lublin, Poland, in the heating (H) and summer (S) seasons. The schools were located in residential areas where the majority of private houses are heated by means of coal-burning stoves. The ratios of the average particle concentrations in occupied and unoccupied classrooms (L/V) were higher during the heating season measurements. The ratios of the average particle concentrations during the measurements in the heating and summer seasons (H/S) were higher in occupied classrooms. In both seasons the average PM and concentrations amounted to 239 g/m3 and 7.4×103/cm3 in the occupied classrooms, and to 76 g/m3 and 5.4×103/cm3 in the unoccupied classrooms, respectively. The particle exposures experienced by students were higher in the monitored classrooms than outdoors and were on average about 50% higher in the heating than in the summer season. A positive correlation between mass concentrations of coarse particles and indoor air temperature, and CO2 concentrations in both seasons was observed. The concentrations of fine particles were negatively correlated with the indoor air parameters in the heating season, and positively correlated in the summer season. INTRODUCTION The quality of the indoor air significantly affects people's health and their well-being. Apart from such contaminants as volatile organic compounds also the aerosol particles present in the air have an impact on the quality of the indoor air in apartments, offices, schools and other educational premises as well as in means of transport [8, 9, 27]. School facilities are among the premises in which indoor particle concentrations can considerably exceed ambient particle concentrations [5, 10, 12]. Despite the fact that certain characteristic particle emission sources do not or seldom exist, e.g. smoking and cooking, particles generated in classrooms may be as toxic as particles in the ambient air [11]. Such particles can also pose a biological threat to students' health [7]. School-aged children spend a significant portion of their time indoors in classrooms. They are also more susceptible than adults to the harmful effects of indoor particles [3, 30]. Particles which are suspended in the classroom air are to a large extent responsible for increased allergies, respiratory infections, asthma exacerbations and deteriorating lung function parameters among students [34]. In turn, such health problems are related to reduced students' attendance and performance [18, 29]. Indoor particle concentration levels in typical classrooms are mainly dependent on the presence of the students and their physical activity [1, 10, 33]. They are also influenced by the outdoor air particle concentration changes and ventilation intensity [13]. In general, the higher the air exchange rate, the lower the indoor particle concentrations [12]. The outdoor and indoor microclimatic parameters can also be of significance [6, 26]. Despite intensive research, it is still not entirely clear how the concentrations of indoor particles in classrooms are associated with the occupation, outdoor particle emissions and with the indoor and outdoor air parameters related to a given season. The factors which influence the particle concentrations in classrooms and the relations between them can be important when student exposures and associated health risks are determined. The present study constitutes a part of a broader study the preliminary results of which have been reported elsewhere [7, 25]. Its aim was to assess the indoor air quality in typical school classrooms in Lublin, Poland and to characterize the key factors that have an impact on this quality. The purpose of this study was to investigate the particle mass (PM) and particle number () concentrations in classrooms. Special emphasis was placed on the influence of students' presence, the outdoor particle emissions from coal-burning stoves in residential houses located near the school, the season and the indoor and outdoor air thermal parameters. MATERIAL AND METHODS The measurements were conducted in 6 classrooms in 3 secondary schools in Lublin, Poland. The population of the city and its close surroundings is about 590,000 inhabitants. The population density is 2407/km2 [32]. Lublin is mostly surrounded by rural areas. The schools were located in different parts of the city in densely populated residential areas, where a significant number of private residential houses are heated by means of coal stoves. One of the schools was built in 1930, the other two were built in 1970. Table 1 summarizes the characteristics of the monitored classrooms and provides the measurement dates. In each school (numbers in parentheses), two classrooms were chosen for monitoring. These classrooms were used for teaching either computer science (C1) or biology (C2) and they were located on the first, second and third floor of the school buildings. The classrooms had various floor areas (from 29 to 71 m2) and volumes (from 96 to 250 m3). The maximum occupancy depended on the size of the classroom and ranged between 18­34 students. All the classrooms had ceramic tile floors and were equipped with standard school furniture. Traditional blackboards for chalk were used in the biology classrooms and whiteboards for color-board markers were used in the computer science classrooms. None of the monitored classrooms had air conditioning systems which is a standard for school facilities in Poland. Natural ventilation was obtained through large double-glazed PCV windows. Table 1. Characteristics of the monitored classrooms and the measurement dates School 1 Classroom attributes Floor number Volume Floor area Number of seats Measurements Heating season (H) Summer season (S) L V L V 03.09.10 03.13.10 06.10.10 06.12.10 03.10.10 03.14.10 06.11.10 06.13.10 [m ] School 2 3 205 57 18 03.30.10 04.03.10 05.20.10 05.22.10 C2(2) 2 250 69 34 03.31.10 04.04.10 05.21.10 05.23.10 1 3 School 3 C1(3) 221 71 22 03.16.10 03.20.10 06.15.10 06.19.10 1 183 59 32 03.17.10 03.21.10 06.16.10 06.20.10 C1(1) 2 96 29 18 130 46 32 [m ] L ­ occupied classroom, V ­ unoccupied classroom Continuous measurements of indoor and outdoor air particulate matter concentration levels, thermal parameters and CO2 concentrations were performed both in the heating season (H), and then again in the summer season (S). Two-day measurements were performed in classrooms during teaching hours (L) and in unoccupied classrooms (V) and lasted for a few hours per day. The sampling devices for the indoor measurements were placed on empty desks in the middle of the classrooms at the height of 110 cm. The sampling devices for the parallel outdoor measurements were located outside the windows of the monitored classrooms. Laser photometers Dust Trak DRX model 8533 (TSI Inc., Shoreview, MN, USA) were used for continuous determination of the concentrations of particle size-segregated mass fractions , PM2.5, Respirable, 0, and (Total Suspended Particle). Fractions and PM2.5 characterize mass concentration of fine particles with an aerodynamic diameter less than or equal to 1 m and 2.5 m cut point, respectively. Mass concentrations of coarse particles (greater than 2.5 m cut point) are characterized by 0 and fractions. Because the data obtained for PM2.5 and Respirable fraction did not differ significantly, the latter was not considered in this paper. Number concentrations of particles with the size range from 0.02 to greater than 1 m were determined using the P-Trak model 8525 (TSI Inc., Shoreview, MN, USA) condensation particle counters. The indoor and outdoor air temperature and relative humidity () were measured by Onset Hobo U12 External Data Logger sensors with the temperature measurement range from ­20 to 70°C and the from 5 to 95%. The GMD/W20 sensors manufactured by VAISALA with a measurement range from 0 to 5000 ppm were used to measure the CO2 concentration. The chosen sampling interval for all the measuring instruments was 60 s. Before the measurements, all instruments were calibrated by their producers. The distribution of the measurement results allowed to use the Spearmen correlation coefficients as indicators of the mutual relations between the indoor and outdoor PM and concentrations, air parameters, occupation and characteristic attributes of the classrooms. RESULTS AND DISCUSSION PM and concentration changes Different coexisting factors affecting particle concentration levels in the monitored classrooms are evident on the indoor PM and concentration time series. Figures 1 and 2 illustrate the exemplary PM and concentration changes in an occupied and empty classroom C1(1), in a determined time period, during one-day measurements performed respectively in the heating and summer seasons. The time series data for PM and concentrations in the outdoor air and also for the indoor and outdoor air temperature (Temp), relative humidity () and CO2 concentrations are also shown. In both seasons the presence and physical activity of students in the classrooms seem to be the most important factors which change the particulate matter concentration levels and the measured indoor air parameters. The observable fluctuations are clearly connected with the changes in the classroom occupancy status. Their rough quantity evaluation for particle concentrations could be accomplished by taking into account the maximum and average PM and concentration levels. For example, in the heating season measurements, the maximum concentrations of the fraction which periodically occur in the variably occupied classroom C1(1) were up to 14 times higher than the average level (~50 g/m3) in the unoccupied classroom. In the summer season measurements this proportion was lower ( maximum concentrations were up to 4 times higher than the average level), however, the average concentration level in the empty classroom was slightly higher (~80 g/m3). The maximum concentrations during the measurements in both seasons reached the average concentration levels in the outdoor air. The biggest increases of the PM and concentration levels were observed at the beginning of the classes and during breaks between classes. This can be explained by the increased physical activity of the students during that time which in consequence results in the intensified air movement in the classrooms. This, in turn, increases the resuspension of dust particles deposited on indoor surfaces and thus the particle concentration in the indoor air [22, 23]. Resuspension mainly affects supermicrometer particles but in the case of the considered classrooms it could be of significance for smaller (about 1 m) particles as well. The considerable amounts of such particles originate from emissions from coal-burning stoves in the residential houses located near the schools. The main mass concentration of coal combustion particles ranges between 0.8­10 m with predominance of 1­2 m particles [21]. These particles enter the classrooms and are deposited on indoor surfaces and could be accumulated due to insufficient cleaning. During the students' physical activity they undergo resuspension processes and they have a major impact on the measured PM concentrations. They could also affect the measured concentrations due to particle detection range of the applied instruments. During the breaks between classes, especially in the summer season, the classrooms were frequently ventilated by opening the windows and doors. This manner of ventilation caused additional intensive indoor air movement and substantial changes in the indoor particle concentrations. It is also important to note that the average outdoor particle concentration levels were higher than the corresponding indoor levels in the vacant classrooms [16, 19]. According to the number of studies, in naturally ventilated spaces, such as the monitored classrooms, the input of the outdoor particles is a very important factor which has an impact on the indoor particle concentration levels [12, 20]. Moreover, I O 60 30 11:02 11:31 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 90 60 30 11:02 11:31 12:00 12:28 O I 12:57 13:26 13:55 14:24 14:52 15:21 15:50 50 11:02 11:31 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 I O Number of students I O 11:31 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 15:50 [ 103/cm 3] 18 12 6 11:02 11:31 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 80 I O 15:50 16:19 10:48 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 0 20 60 40 11:02 11:31 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 1200 800 400 11:02 11:31 12:00 12:28 I O 12:57 13:26 13:55 14:24 14:52 15:21 15:50 Fig. 1. Indoor (I) and outdoor (O) particle mass (PM) and particle number () concentration, air temperature (Temp), relative humidity () and CO2 concentration time series in the occupied (L) and unoccupied (V) classroom C1(1) during one school day in the heating (H) season measurements particles generated by other unidentified sources inside the schools, e.g. cleaning or renovation activity could also have entered the classrooms. During the classes, when the students were already seated and their physical activity was relatively low, a decrease of the indoor particle concentrations was observed. It was especially visible for concentrations of coarse particles characterized by 0 and fractions. These particles undergo effective gravitational sedimentation hence they were relatively quickly removed from the indoor air and deposited on indoor surfaces as dust [2, 24]. The concentrations of fine particles ( and PM2.5 fractions) decreased to I O [ 103/cm 3] O I O I O I O I O I 60 30 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 15:50 90 I O 10 5 16:19 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:12 0 15 10 5 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:12 16:19 0 15 10 5 16:19 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:12 0 15 10 O I 60 30 12:00 12:28 12:57 13:26 I O 14:52 15:21 15:50 O I 50 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 15:50 I O O I Number of students 150 50 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 15:50 I O 5 16:19 0 15 10 5 16:19 O I 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:12 [ 103/cm 3] O I 12:28 12:57 13:26 13:55 14:24 14:52 15:21 15:50 O I 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:12 18 12 6 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 15:50 80 10 5 16:19 11:02 11:16 11:31 11:45 60 40 12:00 12:28 12:57 13:26 13:55 14:24 14:52 15:21 15:50 I O 5 16:19 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:12 0 15 10 5 I O 1200 800 400 12:00 12:28 12:57 13:26 14:52 15:21 15:50 Fig. 2. Indoor (I) and outdoor (O) particle mass (PM) and particle number () concentration, air temperature (Temp), relative humidity () and CO2 concentration time series in the occupied (L) and unoccupied (V) classroom C1(1) during one school day in the summer season (S) measurements a lesser extent. This, in turn, results from the greater stability of these particles to remain suspended in the indoor air [14, 15]. Occupation and season The presence of the students in all the monitored classrooms, regardless of the season, resulted in a significant increase in the concentrations of the measured particles. For example, for the measurements in both seasons, the average concentrations of the and in the occupied classrooms amounted to 61 and 239 g/m3, and in the I O I O I O [ 103/cm 3] 0 [g/m 3] PM2 .5 [g/m ] classrooms could be the effect of the already mentioned, instable ventilation conditions during the measurements or the coexistence of other affecting factors e.g. particle sources inside the schools or particle concentration changes in the outdoor air [4, 17, 21, 22]. It was also observed that for the measurements in both seasons the ranges of particle concentration changes were greater in occupied classrooms. For example, the ranges of the and the fraction concentration changes in the occupied classrooms were on average about 5 and 18 times greater than in the empty classrooms respectively. In the case of concentrations, such ratio amounted to about 7. The average coefficient of variation (CV) values for and concentrations in the occupied classrooms amounted to 19.0 and 42.5%, and in the empty classrooms to 6.4 and 9.7%, respectively. The corresponding average CV values for the concentrations were 20.5 and 5.2%. The maximum standard error of the evaluated CVs was 1.2%. The ratios of the average particle concentrations in the occupied and empty classrooms (L/V) in the heating and summer season measurements are presented in Table 2. Table 2. Occupied-to-unoccupied ratios (L/V) of the average particle mass (PM) and particle number () concentrations in the monitored classrooms during the heating (H) and summer season (S) measurements. N is a time-weighted average number of students present during the measurement periods which include the breaks between the classes when the students were not present in the room empty classrooms to 49 and 76 g/m3, respectively. The average concentration in the occupied classrooms amounted to 7.4×103/cm3 and to 5.4×103/cm3 in the empty classrooms. Occurring cases of higher and concentrations in the empty Classroom H C1(1) S H S H S H C2(2) C1(3) S H S H S H S 2.14 1.74 1.90 1.50 0.75 1.24 1.61 0.76 1.07 0.52 1.78 1.21 1.56 1.16 PM2.5 2.09 1.76 1.92 1.50 0.75 1.27 1.64 0.78 1.07 0.53 1.80 1.22 1.55 1.18 0 2.69 1.63 2.65 1.68 1.36 1.96 2.04 1.22 1.80 1.14 2.39 1.94 2.16 1.60 5.03 1.52 4.27 2.34 3.49 3.59 3.30 2.45 4.19 2.49 3.94 3.72 4.04 2.69 0.72 0.94 3.20 0.99 2.40 1.60 2.68 1.37 1.26 0.81 3.32 1.31 2.26 1.17 N 13.2 ± 6.9 (16­18) 11.6 ± 5.6 (15­16) 9.2 ± 4.6 (10­13) 6.5 ± 7.5 (7­17) 11.2 ± 5.9 (12­17) 11.2 ± 5.3 (12­16) 18.4 ± 10.2 (22­29) 19.2 ± 9.7 (25­26) 12.3 ± 6.5 (14/19) 10.7 ± 8.8 (12­24) 13.9 ± 7.5 (16/22) 10.5 ± 10.9 (14­28) 13.0 ± 3.6 (15­20) 11.6 ± 3.4 (15­22) Average N ­ mean ± sdev. (median-maximal) number of students. In all the monitored classrooms the L/V ratios were higher in the heating season and their biggest values were for the concentrations of coarse particles. It may indicate that more particles, especially coarse ones, were generated by students in the classrooms in that season. However, it has to be pointed out that the number of students in the monitored classrooms was, on average, slightly higher during the heating season measurements (Table 2). In the heating season, the concentrations of the considered particles in the occupied classrooms were higher than in the summer season. It is connected with the increased outdoor particle emissions from coal combustion in that season and the increased particle deposition and resuspension in the classrooms. Table 3 presents the ratios of the average PM and concentrations in the heating and summer seasons (H/S) for the occupied and empty classrooms. The values of H/S ratios in the occupied classrooms are, on average, higher for the coarse particles. For example, the average H/S ratio amounted to 1.26 for the fraction and 1.43 for the fraction. In case of vacant classrooms these ratios for all considered particles were smaller than 1. The exposures experienced by students in the monitored classrooms were higher in the occupied classrooms than those estimated outside. In the heating season they were on average about 50% higher. It has to be noted that a substantial portion of the PM exposures (~50%) and the exposures (~30%) were attributed to particles generated inside the classrooms. Indoor air parameters The indoor air parameters in the monitored classrooms are affected by heating (in winter), by the outdoor air parameters, intensity of the ventilation as well as the presence of students Table 3. Heating to summer season ratios (H/S) of the average particle mass (PM) and particle number () concentrations for the occupied (L) and unoccupied (V) classrooms Classroom L C1(1) C2(2) C1(3) Average V L V L V L V L V L V L V 0.80 0.65 1.51 1.17 0.86 1.44 1.69 0.80 1.36 0.66 1.37 0.93 1.26 0.94 PM2.5 0.80 0.68 1.53 1.19 0.87 1.46 1.67 0.80 1.35 0.67 1.37 0.93 1.27 0.96 0 1.35 0.81 1.84 1.16 0.64 0.92 1.32 0.79 1.25 0.80 1.23 1.00 1.27 0.91 2.25 0.68 1.89 1.04 0.90 0.93 0.98 0.73 1.51 0.89 1.05 0.99 1.43 0.88 1.25 1.63 1.61 0.50 2.14 1.44 1.63 0.83 1.19 0.76 0.99 0.39 1.47 0.93 (Figs. 1, 2). The fluctuations of the indoor air temperature, and CO2 concentration were most distinct during the time when classes were held in the heating season. During the breaks between classes when students were not present in the classrooms and ventilation conditions were not significantly changed (windows were not opened and doors were only opened occasionally) systematic changes of the measured indoor air parameters were observed. For example, an almost exponential decrease of the CO2 concentrations occurs in the classrooms. The impact of the changing ventilation conditions was more visible during the lessons and breaks in the summer season measurements when less regular fluctuations of the indoor air parameters were observed. In empty classrooms, the measured indoor air parameters were also not stable. In this case other factors, e.g. related to the previous classroom occupation or the presence of the persons setting up the measurement devices could be significant. During the classes the indoor CO2 concentrations frequently exceeded the level of 1000 ppm, which according to the ASHRAE Standards 62-1989 is the threshold concentration for satisfactory comfort. The CO2 concentration did not meet the ASHRAE Standards in 56% of the teaching hours in the heating season and in 41% of the teaching hours in the summer season measurements. CO2 concentration readings over 1500 ppm were found in about 25% and 7% of the teaching hours in the heating and summer season measurements, respectively. Several strong relations between the indoor air parameters and particle concentrations were observed in the monitored classrooms. The average tendencies of these relations for the heating and summer season measurements were determined on the basis of the mean correlation coefficients. This way a positive correlation between the mass concentration of coarse particles and indoor air parameters in occupied classrooms for the measurement periods in both seasons was obtained. A negative correlation between the mass and number concentration of fine particles and the measured indoor air parameters was determined for the heating season, whereas a positive correlation was found for the summer season measurements. The exemplary relations between the , and , and the indoor air temperature, and CO2 concentration in the heating and summer seasons, which best represent the above mentioned tendencies are shown in Figure 3. All the presented correlations are statistically significant, p < 0.01. Comparison with previous research The simultaneous measurements of PM and concentrations in occupied and empty classrooms as well as outdoors in both the heating and summer seasons are seldom reported. If they were performed, they were not confronted with the indoor and outdoor air parameters. Most of the individual results presented in this paper are comparable with those in previous studies. Based on the 6-week (October­November) measurements performed in two classrooms in one primary school in Munich, Fromme et al. [11] reported the median PM2.5 concentration of 37.4 g/m3 and 0 of 118.2 g/m3 indoors, while the corresponding results for the outdoor air were 17.0 g/m3 and 24.2 g/m3. Heudorf et al. [13] measured the indoor air quality in two primary school classrooms in Frankfurt/M for 3 weeks (February­March). Their findings showed that the average level of 0 was 69 g/m3 and that the measured concentrations were determined by the occupancy, student activity and the frequency of cleaning the classrooms. Lower PM concentrations in a lecturing room in Prague were observed by Branis et al. [6] during the measurements in the fall season 0,14 0,10 22,5 23,0 Tempera tura 0,14 0,10 0,06 r = 0 .71 2 y = - 0.3 55 + 0.021x 20,0 Tempera tura [ ] °C r = - 0.636 y = 0.767 - 0.028x 0,06 22,0 23,5 [°C] 24,0 24,5 19,0 0,5 0,3 0,1 19,0 18 19,5 20,5 21,0 0,5 0,3 0,1 r = 0.442 y = -1 .87 3 + 0.096x r = 0.717 y = -4 .90 9 + 0.25 8x 22,5 23,0 23,5 [° C] 24,0 24,5 19,5 20,0 [° C] 20,5 21,0 6 22,0 r = -0.826 y = 162.437 - 6.437x 22,5 23,0 23,5 [°C] Temperatura 24,0 24,5 22,0 18 r = 0.331 Temperatura y = -53.027 + 3.216x 19,5 20,0 20,5 [°C] 21,0 6 19,0 Temp 0,14 0,10 Temp 0,14 0,10 0,06 0,02 37 0,5 0,3 0,1 37 39 41 43 0,02 24 26 28 30 [% ] r = - 0.7 84 0,06 y = 0 .31 9 - 0 .00 6x r = 0.5 76 y = - 0.213 + 0.006x [% ] 0,5 r = 0.427 0,3 0,1 24 y = - 0.17 9 + 0.017 x r = 0.5 45 y = - 1.46 2 + 0 .042x [103 /cm3 ] r = -0.876 y = 52.610 - 1.280x 26 28 30 32 r = 0.890 y = -7.568 + 0.261x 0,12 0,08 0,04 500 1000 0,7 r = 0.521 0,5 0,3 0,1 500 1000 1500 [mg/m 3 ] 0,12 0,08 0,04 r = - 0.7 15 y = 0 .170 - 0 .000 03x [p p m] r = 0.812 y = - 0.006 + 0 .000 06x [p p m] y = 0.17 6 + 0.0001 x 500 0,7 r = 0.81 7 0,5 0,3 0,1 y = - 0.3 35 + 0.0007x 2000 [ppm] 2500 3000 CO2 r = -0.872 y = 23.973 - 0.006x r = 0.818 y = 2.729 + 0.002x CO2 [ppm] 2000 [ppm] [ppm] Fig. 3. The relation between the particle mass ( and ), particle number () concentrations and indoor air temperature (Temp), relative humidity () and CO2 concentration in the occupied classrooms in the heating (H) and summer (S)seasons (October­November). The average indoor PM2.5 concentration amounted to 21.9 g/m3 and 42,3 g/m3 for 0. However, as they pointed out the PM concentrations were measured by the gravimetrical method whose readings are lower than from photometers (e.g. TSI Dust Trak). Relatively smaller concentrations of 0 were also found in 40 classrooms in Korea [28]. The average level was 46.7 g/m3 in the summer and 39.1 g/m3 in the winter. Fromme et al. [10] reported the median daily values of PM concentrations measured in 58 classrooms in Munich and a neighboring district in the winter between 2.7 and 80.8 g/m3 (average: 23 g/m3) for PM2.5 and between 16.3 and 313 g/m3 (average 105 g/m3) for 0,. In the summer the concentrations of PM2.5 ranged between 4.6 and 34.8 g/m3 (average 13.5 g/m3) and the concentrations of 0 between 18.3 and 178 g/m3 (average 71.7 g/m3). Zwodziak et al. [34] measured the indoor and outdoor particle concentrations in a secondary school in Wroclaw in the winter/spring and summer/autumn seasons. The average 0 particle concentration was 115.2 g/m3 indoors and 53.8 g/m3 outdoors. The concentrations of and PM2.5 were slightly higher inside the school than outdoors and their average values amounted to 23.2 g/m3 and 46.4 g/m3, respectively. It has been also indicated that there is a significant correlation between the PM2.5 concentration and students' lung function parameters. When it comes to the concentrations, Guo et al. [12] reported the results of a 2 week measurement period in September in a village primary school classroom in Australia. The average concentration (particles 0.014­0.800 m) amounted to 2.11×103/cm3 indoors and 2.93×103/cm3 outdoors. Fromme et al. [10] found that the median concentrations (particles 0.010­0.487 m) measured in 36 classrooms in Munich in the summer, ranged between 2.62 and 12.14×103/cm3 (average: 6.5×103/cm3). Weichenthal et al. [31] performed measurements in Canada in 37 classrooms. Their study showed the average indoor level (particles 0.020­0.100 m) of 5.0×103/cm3, and the average outdoor level of 9.0×103/cm3. Mullen et al. [23] measured the concentration of particles 0.006­0.100 m in 6 classrooms in northern California in the summer and winter. In the presence of the students the mean indoor levels ranged between 5.2­16.5×103/cm3 (average: 10.8×103/cm3). The corresponding outdoor concentrations were 9.0­26.0×103/cm3 (average: 18.1×103/cm3). The CO2 concentrations in the monitored classrooms are also largely consistent with those in other published studies. Fromme et al. [10] reported the CO2 median levels in 85 classrooms in 64 schools in Munich and a neighboring district which ranged between 589 and 4172 ppm (average: 1759 ppm) in the winter, and between 480 and 1875 ppm (average: 890 ppm) in the summer. The corresponding outdoor CO2 concentrations varied from 386 to 472 ppm in the winter, and from 341 to 485 ppm in the summer. In the studies carried out by Heudorf et al. [13], the mean CO2 levels in classrooms in 2 schools in Frankfurt/M were from 1051 to 1459 ppm. The relationships between the particle concentration and the indoor air temperature, and CO2 concentration in the monitored classrooms are also, to a large extent, consistent with those in the previous studies. Branis et al. [6] demonstrated a high positive correlation between the concentration and the of indoor and ambient air (the respective correlation coefficients amounted to 0.605 and 0.789). Fromme et al. [10] indicated a significant PM2.5 concentration decrease by 6.4 g/m3 in the winter and an increase by 1.7 g/m3 in the summer per each 10% increase. Polednik and Dudzinska [27] demonstrated that coarse aerosol and bioaerosol particle and the CO2 concentrations in an air-conditioned auditorium could be an indicator of the perceived air quality due to correlative and mutual relations with the indoor air parameters. The estimated student exposures to particles in the monitored classrooms are also comparable with the student exposures reported in previous studies. The daily-integrated exposure to ultra fine particles by students in 6 elementary school classrooms in northern California estimated by Mullen et al. [23] was 52×103/cm3 h/day. In turn, the exposure experienced by these students in their homes was approximately 6 times higher and amounted to 320×103/cm3 h/day. The measurements in the monitored classrooms were carried out in real field conditions with varied student activity, classroom ventilation, and outdoor air parameters. Most probably this was the reason why the significant correlations between the particle concentration and the number of students present or classroom location in school buildings, classroom volume, floor area, furnishing materials and blackboard or whiteboard usage in the classrooms reported in some previous studies were hard to find. CONCLUSIONS The results of the measurements performed in classrooms in selected schools in Lublin are consistent with the results reported in previous research in terms of the obtained trends. The PM and concentrations mainly depend on the presence of students and are manifold higher in occupied than in unoccupied classrooms. The significant differences in the levels of PM and concentrations are observed in the measurements performed during the heating and the summer seasons. This is considerably influenced by coal combustion in the residential houses located in the vicinity of the schools. Such particle emissions substantially contribute to students' exposure and may cause adverse health effects. The mass concentrations of coarse particles in the occupied classrooms were positively correlated with the indoor air temperature, and CO2 concentration. The mass and number concentration of fine particles were negatively correlated with indoor air parameters in the heating season, and positively correlated in the summer season. ACKNOWLEDGEMENTS This research was carried out within the Projects 4955/T02/2008/34, financed by the Polish Ministry of Science and Higher Education.

Journal

Archives of Environmental Protection – de Gruyter

Published: Dec 1, 2013

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