3.1. Variation in CO2, temperature and RH% conditions and PM2.5 concentrations inside and outside sport facilities
Table 2 provides descriptive statistics, including median, minimum, maximum, quartiles, and percentiles, representing the distribution of measured parameters over the entire 3-day measurement periods. Non-parametric statistical measures (median and percentiles) were used instead of mean and standard deviation due to the non-normal distribution of data among the tested groups and sub-groups of air quality parameters (Shapiro-Wilk test, p < 0.05). The distribution of PM2.5 concentration did not meet normal distribution criteria, primarily due to high-concentration episodes of PM2.5 and CO2 during training sessions in the sports rooms, as well as peaks of high humidity resulting from water vapor exhaust during training and the influx of 'wet' air through opened windows. Figures 4–8 display the daily-averaged concentrations of PM2.5, temperature, and humidity fluctuations indoors and outdoors in 5 sport rooms averaged over 15-minute intervals throughout the 3-day measurement periods.
The 'Nowa' Hall Gym was monitored over three days from April 28 to April 30, 2022 (Fig. 3 and Fig. 4). Gym sessions typically ran from 8:30 a.m. to 3:15 p.m. (Fig. 9) and focused on strength training, utilizing local atlas equipment, electric treadmills, stationary bikes, and rowing ergometers. Daily cleaning occurred from 6:00 a.m. to 7:00 a.m. Figure 3 illustrates variations in CO2 concentration, indicating rapid increases during gym classes followed by subsequent declines. Distinct peaks were observed between 9:00 a.m. to 3:30 p.m., aligning with university class hours (10:15 a.m. to 11:45 a.m., 12:00 p.m. to 1:30 p.m., and 1:45 p.m. to 3:15 p.m.). Despite similar attendance, the magnitude of peaks differed due to varying student activity levels. On April 28, trainees had higher exercise intensity. During unoccupied periods, CO2 concentrations dropped to outdoor levels (around 450 ppm). No matter the location, temperature and humidity patterns correlated with external atmospheric conditions (Fig. 4–8). For instance, humidity increased at 9:25 a.m. at 'Nowa' Hall Gym (Fig. 4), possibly due to athletes taking showers. Particulate matter levels were primarily influenced by external air conditions.
Data collection in the 'Nowa' Hall spanned three days: May 9 to May 11, 2022 (Fig. 3 and Fig. 5). Measurements commenced at approximately 8:00 a.m. each day and concluded around the same time on the following day. Students engaged in volleyball or basketball activities based on their assigned groups. Daily cleaning occurred from 6:00 a.m. to 7:00 a.m. Figure 3 illustrates changes in CO2 concentration, showing patterns similar to those observed in the gym within the same facility ('Nowa' and OSiR facilities). The commencement of training sessions led to a noticeable increase in CO2 concentration, which subsequently decreased after classes. The 'Nowa' Hall had the highest temperature among all monitored areas (Table 2), attributed to elevated outside temperatures during that period (Table 2 and Fig. 5). Relative humidity remained consistently low due to favorable weather conditions and the absence of precipitation. Particulate matter concentration primarily depended on external air conditions (Fig. 5). Increases in outdoor PM concentration corresponded to increases in the hall's particulate matter levels (Fig. 4 and Fig. 5).
Measurements in the OSiR Hall spanned three days: May 25, 26, and 31, 2022 (Fig. 3 and Fig. 6). They commenced at approximately 8:30 a.m. and concluded at a similar time the following day. Depending on their enrolled group, students played either volleyball or basketball. Daily cleaning occurred between 6:00 and 7:00 a.m. In Fig. 3, which depicts variations in carbon dioxide concentration, similar patterns can be observed as in other sports rooms. When the trainees began their training sessions, there was an increase in CO2 concentration, followed by a decrease after the classes concluded. The temperature remained relatively stable on May 25, 2022, and May 26, 2022, throughout the day. On May 31, 2022, the temperature inside the hall notably corresponded with the external temperature (Fig. 7) and remained consistently high on all three days. May 25, 2022, recorded the highest relative humidity due to heavy rainfall, as supported by the average relative humidity in the outdoor air, which reached 90% during that time (Fig. 7). The concentration of particulate matter was primarily influenced by external air conditions.
The measurements in the OSiR Hall Gym spanned three days: June 1 to June 3, 2022 (Fig. 3 and Fig. 8). Data collection commenced at approximately 9:00 a.m. each day and concluded at a similar time the following day. Students primarily engaged in strength training activities, utilizing local atlas equipment, barbells, and dumbbells, and performed exercises on electric treadmills, stationary bikes, and rowing ergometers. Daily cleaning of the gymnasium took place between 6:00 a.m. and 7:00 a.m. Figure 3 presents changes in carbon dioxide concentration, showing an increase when the trainees commenced their classes and a subsequent decrease upon completion. Notably, between 19:00 and 20:00 on June 1, 2022, and June 2, 2022, the highest recorded indications of CO2 exceeded 1859 ppm (calculated based on 10-minute averages), while according to 1-minute averages, this CO2 was 4,248 ppm (Fig. 3). This elevation can be attributed to the intensive training carried out in close proximity to the monitoring meters. The air temperature generally remained consistent, except for a notable increase between 18:00 and 20:00 on June 1, 2022, and June 2, 2022 (Fig. 8). During this time, the facility was utilized by external groups who engaged in more rigorous and committed training sessions. Relative humidity remained relatively stable throughout all days, except for the 19:00 and 20:00 time period (Fig. 8). Furthermore, the concentration of particulate matter primarily depended on external air conditions.
Throughout the entire sampling campaign (April 28 to June 6, 2002), the median of daily outdoor temperature (averaged over 24 hours) fluctuated between 3.0°C around 'Nowa' Hall Gym and 26.6°C close to 'Nowa' Hall, while indoor air temperature ranged from 17.1°C (OSiR Hall) to 27.2°C ('Nowa' Hall). The average daily temperature inside sport facilities during the entire measurement period was 22.7°C (Table 2).
Outdoor temperature had only a slight effect on indoor temperature, as depicted in Fig. 4–8. Despite the study being conducted during the spring period when outdoor temperatures tend to vary greatly, the results indicate that the indoor environment of sports facilities can be effectively regulated to maintain a stable temperature for users. Decreases in outside temperature, especially at night and in the morning, did not lead to significant deviations in indoor temperature values. There was a slight increase in indoor temperatures observed in OSiR Gym during the afternoon hours when several people were training (Table 2, Fig. 8). Physical activity generates heat, which is transferred to the surrounding air and can cause the temperature in the immediate vicinity to rise. As evidenced by measurements conducted at OSiR Hall, the temperature inside sports facilities during the day showed minimal deviation, with a maximum difference of 1.6°C (Table 2). Outdoor humidity levels varied across different days and locations, with daily averaged outdoor humidity ranging from 37% (measured on May 16th at Konarskiego Hall) to 89.9% (measured on May 25th at OSiR Hall) (Table 2).
In general, air humidity levels during April and the first days of May were lower compared to the middle of May and June (Table 2). The average air humidity during the entire measurement period was 57.1% relative humidity (RH), with a variation of 13.9% RH. Indoor air humidity closely fluctuated with outdoor humidity levels, especially on hot days when windows were opened. However, it is evident that the indoor air humidity levels at New Hall Gym, New Hall, and Konarskiego Hall were significantly lower than the recommended optimal conditions for indoor sports facilities. During April 28–30, the mean air humidity in the New Hall Gym was only 20% RH (Table 2), well below the recommended range for indoor sports facilities. In comparison, the mean air humidity in the New Hall building was slightly higher, around 25% RH during the same period. In contrast, higher humidity values of 50.8% (from May 25–31) and 51.7% (from June 1–6) were recorded in OSiR Hall and OSiR Gym, respectively. The difference in indoor humidity levels was also reflected in the indoor temperatures of the facilities, with the New Hall building showing noticeably higher temperatures. The daily temperature range in the New Hall building was recorded to be between 23.7°C and 26.5°C (Table 2), exceeding the typical recommended range for indoor sports facilities.
The OSiR Hall and OSiR Gym exhibited the highest correlation between indoor and outdoor relative humidity (RH%), indicating effective natural ventilation or open windows during the measurement period (Fig. 7 and Fig. 8). In some cases, indoor RH% was even higher than outdoor RH% in certain facilities, such as the New Hall building on May 11th, May 16th, and May 25th. Figures 4–8 illustrate a comparison of PM2.5 particulate matter concentrations inside (blue line) and in the outside air (orange line) for each individual sport facility. A strong correlation between indoor and outdoor PM2.5 concentrations was observed. On average, indoor concentrations were lower than outdoor levels, as summarized in Table 2. The highest outdoor PM2.5 concentrations were observed near OSiR Hall Gym (9.5 µg/m³) and around 'Konarskiego' Hall (9.7 µg/m³). Slightly higher concentrations were noticed close to OSiR Hall (10.1 µg/m³), and the highest levels were around 'Nowa' Hall Gym (13.9 µg/m³). During periods when outdoor air quality worsened, the PM2.5 concentration inside the sports facilities also increased, as evident in Fig. 4. For example, between 06:05 p.m. (April 28) and 11:25 a.m. (April 29), the indoor PM2.5 concentration averaged around 19.7 µg/m³, while between 10:15 p.m. (April 29) and 9:05 a.m. (April 30), the indoor concentration in 'Nowa' Hall Gym rose to approximately 49.9 µg/m³. During the same averaging periods, outdoor concentrations were 14.82 µg/m³ and 40.42 µg/m³, respectively, significantly influencing indoor conditions. Throughout the entire measurement period, the average PM2.5 concentration in 'Nowa' Hall Gym was 23.36 µg/m³ indoors and 17.76 µg/m³ outdoors. A similar relationship was observed in 'Nowa' Hall between 9:25 p.m. (May 10) and 8:25 a.m. (May 11), with the indoor PM2.5 concentration at 26.3 µg/m³, while the outdoor concentration in the same period averaged 27.06 µg/m³ (Fig. 5). Throughout the entire measurement period in this sport facility, the indoor and outdoor PM2.5 concentrations were 15.56 µg/m³ and 13.56 µg/m³, respectively.
Table 2
Description statistics regarding air quality inside and outside sport facilities
Variable | „Nowa” Hall Gym |
| | | | | | | | | | |
| 376 | 23.0 | 8.2 | 73.8 | 15.5 | 31.9 | 11.2 | 55.5 | 60.1 | 1.3 | 1.0 |
| 375 | 470.5 | 403.3 | 1410.2 | 445.0 | 502.7 | 417.3 | 583.3 | 29.6 | 3.2 | 10.9 |
| 376 | 24.2 | 22.0 | 24.8 | 24.0 | 24.5 | 23.6 | 24.6 | 1.9 | -1.5 | 3.3 |
| 376 | 25.0 | 19.7 | 44.1 | 23.1 | 25.7 | 22.3 | 28.1 | 15.5 | 2.5 | 7.4 |
| 376 | 13.9 | 4.4 | 58.5 | 8.5 | 25.6 | 6.8 | 47.0 | 72.8 | 1.2 | 0.3 |
| 376 | 14.0 | 3.0 | 18.0 | 7.7 | 15.7 | 4.8 | 16.5 | 38.2 | -0.5 | -1.2 |
| 376 | 43.0 | 27.2 | 87.4 | 34.9 | 69.4 | 31.9 | 82.9 | 37.7 | 0.6 | -1.2 |
| „Nowa” Hall |
| | | | | | | | | | | |
| 390 | 15.3 | 8.1 | 31.8 | 12.6 | 21.9 | 10.2 | 26.7 | 35.8 | 0.5 | -0.8 |
| 390 | 500.6 | 402.9 | 807.3 | 453.6 | 551.5 | 430.9 | 621.0 | 15.8 | 1.3 | 1.9 |
| 390 | 25.5 | 20.0 | 27.2 | 24.7 | 26.2 | 24.0 | 26.7 | 4.6 | -1.1 | 2.3 |
| 390 | 33.2 | 20.7 | 47.2 | 28.8 | 35.9 | 23.9 | 39.9 | 17.6 | -0.1 | -0.4 |
| 390 | 11.6 | 6.1 | 44.5 | 8.5 | 19.6 | 7.2 | 27.1 | 53.9 | 1.2 | 1.3 |
| 390 | 17.3 | 8.5 | 26.8 | 13.9 | 21.0 | 11.4 | 22.6 | 25.4 | 0.1 | -1.0 |
| 390 | 44.2 | 23.9 | 73.9 | 33.6 | 57.8 | 29.9 | 68.2 | 30.3 | 0.4 | -1.0 |
| „Konarskiego” Hall |
| | | | | | | | | | | |
| 390 | 11.3 | 6.0 | 32.0 | 8.3 | 13.2 | 6.6 | 19.7 | 43.2 | 1.6 | 3.1 |
| 390 | 494.2 | 404.0 | 996.7 | 423.6 | 622.6 | 410.1 | 723.7 | 24.6 | 1.1 | 0.5 |
| 390 | 22.8 | 20.6 | 25.8 | 22.5 | 23.3 | 22.0 | 24.1 | 3.5 | 0.7 | 0.6 |
| 390 | 35.4 | 15.8 | 51.3 | 26.9 | 38.5 | 19.1 | 43.9 | 25.6 | -0.4 | -0.8 |
| 390 | 9.7 | 2.8 | 26.9 | 7.0 | 15.2 | 4.8 | 19.2 | 49.9 | 0.7 | -0.2 |
| 390 | 17.0 | 7.0 | 23.9 | 14.1 | 19.1 | 9.7 | 22.1 | 25.6 | -0.4 | -0.5 |
| 390 | 46.8 | 18.6 | 68.6 | 30.0 | 54.7 | 21.5 | 56.9 | 30.4 | -0.5 | -1.1 |
| „OSiR” Hall |
| | | | | | | | | | | |
| 388 | 16.4 | 6.0 | 49.6 | 10.9 | 22.4 | 8.4 | 35.2 | 52.6 | 1.0 | 0.1 |
| 388 | 509.3 | 421.7 | 910.0 | 446.3 | 638.3 | 433.3 | 766.4 | 23.5 | 0.9 | -0.2 |
| 388 | 20.2 | 17.1 | 21.6 | 19.2 | 21.1 | 17.9 | 21.2 | 6.2 | -0.8 | -0.5 |
| 388 | 61.3 | 29.3 | 84.5 | 48.5 | 73.6 | 38.9 | 76.6 | 23.8 | -0.3 | -1.1 |
| 388 | 10.1 | 4.7 | 33.9 | 8.0 | 13.9 | 6.7 | 17.6 | 44.4 | 1.7 | 4.4 |
| 388 | 15.1 | 8.2 | 23.2 | 12.7 | 20.1 | 10.3 | 21.6 | 26.1 | 0.0 | -1.3 |
| 388 | 76.3 | 40.7 | 95.4 | 55.1 | 91.3 | 46.5 | 94.4 | 25.6 | -0.2 | -1.6 |
| „OSiR” Hall Gym |
| | | | | | | | | | | |
| 389 | 16.5 | 9.9 | 69.0 | 14.1 | 24.9 | 11.8 | 35.2 | 52.3 | 1.8 | 3.5 |
| 389 | 500.8 | 400.9 | 1859.7 | 459.3 | 590.6 | 424.1 | 780.8 | 28.9 | 3.1 | 16.4 |
| 389 | 20.8 | 19.4 | 23.3 | 20.2 | 22.1 | 19.9 | 23.0 | 5.4 | 0.6 | -1.0 |
| 389 | 67.0 | 47.1 | 80.4 | 61.1 | 71.3 | 53.2 | 75.2 | 11.9 | -0.6 | -0.5 |
| 389 | 9.5 | 4.2 | 33.2 | 6.9 | 11.9 | 5.9 | 19.5 | 53.4 | 1.6 | 2.4 |
| 389 | 18.7 | 12.8 | 26.0 | 15.4 | 21.5 | 14.1 | 23.4 | 18.9 | 0.2 | -1.2 |
| 389 | 64.7 | 35.9 | 94.4 | 51.6 | 79.8 | 44.4 | 91.2 | 25.4 | 0.1 | -1.2 |
The increase in particulate concentration during late hours was attributed to intensive late-night workout sessions, mainly involving athletes and individuals engaging in strength training as a hobby. In contrast, such peaks were not observed in 'Konarskiego' Hall (Fig. 6), where the facility was primarily occupied by students participating in table tennis practice. Instead, a relatively constant concentration of PM2.5 was observed, with a notable decrease in indoor PM2.5 concentrations on May 18, 2022, due to no training activities on that day. Between 10:25 a.m. and 5:25 p.m. on May 18, there was a significant decrease in air humidity, likely due to the windows being closed and heating being turned on. On May 16 and 17, an increase in indoor PM2.5 concentrations occurred after 6:00 p.m. due to a table tennis tournament that lasted until 8:00 p.m. Overnight between May 16 and 17, the concentration of PM2.5 inside the hall did not decrease significantly, aligning with other studies suggesting that PM2.5 particles can remain suspended in indoor air for several hours, depending on ventilation and other factors. The PM2.5 concentration indoors in the OSiR Hall during the entire measurement period (May 25–26 and May 31) was 14.8 µg/m³, while outdoor particulate pollution was lower at 10.53 µg/m³ (Table 2). Compared to other facilities, this airborne pollution was similar but lower than the outdoor concentrations around 'Nowa' Hall (Table 2). The proximity of the DTŚ to 'Nowa' Hall may have contributed to the higher outdoor PM2.5 concentration there, but the impact of low emissions from domestic heating boilers seemed to have a greater effect on the quality of outdoor air than traffic sources. Notably, the PM2.5 concentrations around ‘Konarskiego’ Hall, the closest to the DTŚ route, were smaller compared to those found near 'Nowa' Hall. A Spearman correlation matrix was performed to observe the relationship between indoor and outdoor PM2.5 levels, and the results are presented in Table 3. The correlation indices were significant with p < 0.05. The strongest correlation between indoor and outdoor PM2.5 concentrations was found in New Hall Gym and 'Konarskiego' Hall, as evident in Fig. 4 and Fig. 6, where the orange and blue lines representing the trend of PM2.5 concentrations indoors and outdoors overlap quite well. The weakest correlation (rs = 0.63) was found in OSiR Hall Gym (Table 3), where particle resuspension, especially marked on June 6, likely due to intensive training by sports professionals, significantly influenced indoor PM2.5 levels.
Table 3
Spearman's rank correlation coefficients between PM2.5 indoor and outdoor
Location | Variable | |
New Hall Gym | | 0.75 |
New Hall | 0.63 |
Konarskiego Hall | 0.74 |
OSiR Hall | 0.58 |
OSiR Hall Gym | 0.37 |
Note: indices which were bolded were significant under p = 0.05 |
Hourly changes in indoor RH% revealed increased humidity during physical exercise, particularly between 7:00–8:00 am and 7:00–8:00 pm (Fig. 4 – Fig. 8). This is likely a result of enhanced gas exchange during strength training, influencing indoor air humidity levels. A correlation matrix (Table 4) was employed to summarize the relationship between the number of individuals training and indoor air humidity, as well as other parameters.
Table 4
Spearman's rank correlation coefficients between total no. of occupants indoor and air quality parameters
Number of individuals in each location | PM2.5in | CO2in | Temp.in | RH%in |
New Hall Gym | -0.31 | -0.08 | 0.33 | -0.01 |
New Hall | 0.13 | -0.13 | -0.58 | 0.64 |
Konarskiego Hall | 0.73 | 0.52 | -0.02 | 0.77 |
OSiR Hall | -0.14 | 0.12 | -0.48 | 0.52 |
OSiR Hall Gym | -0.33 | 0.41 | -0.72 | 0.62 |
Note: indices which were bolded were significant under p < 0.05 |
Figure 9 illustrates that sports facilities were frequented by varying numbers of students, depending on their level of involvement in physical education classes, after-school sports programs, and extracurricular sports teams. The busiest facilities were "Nowa" Hall and OSiR Hall. Participation in sports activities at Silesian University of Technology can vary from a few hours to several hours per week, depending on the individual. Student-athletes engaged in varsity sports programs may devote extensive time to training and competitions. While this study did not estimate the time spent by each student on sport activities, data from sport trainers' diaries indicated higher occupancy on the first days of the week, with more students in the morning and evening hours, and sport professionals and hobbyists in the late hours (Fig. 9). Correlations between the number of occupants and air quality parameters revealed that air relative humidity was generally positively correlated with the number of individuals training, likely due to the exhalation of moist air during training. The only exception was New Hall, which showed practically no correlation (rs² = − 0.01%).