Influence of Technological Housing Conditions on the Concentration of Airborne Dust in Dairy Farms in the Summer: A Case Study

Simple Summary Due to modern housing systems and new barn concepts, an indoor environment on dairy farms has become very important. Airborne dust is a significant pollutant in the indoor environment of animal barns. An increased concentration of small airborne dust particles can cause health problems for farm animals and workers. This research shows that cattle barns with straw bedding cause more indoor airborne dust than barns without straw. Increased ventilation airflow has a positive effect on reducing the concentration of airborne dust particles, which was especially evident in the comparison of older, massive brick cowsheds compared to modern, light, uninsulated barns. The installation and operation of axial fans with a horizontal axis of rotation significantly help natural ventilation in terms of airborne dust concentration reduction. The results of the research showed that a large proportion of airborne dust particles in the summer are made up of the smallest dust particles. Abstract This research shows the size composition of airborne dust fractions in selected dairy barns down to the smallest particles, including factors that influence this composition. Measurements with a Dust-Track 8530 laser photometer took place in the summer at external temperatures of 29.5 to 36 °C. In barns with straw bedding, the average total dust concentration TDC was 66.98 ± 28.38 μg·m−3 (PM10 60.11 ± 19.93 μg·m−3, PM4 49.48 ± 13.76 μg·m−3, PM2.5 44.78 ± 10.18 μg·m−3, and PM1 38.43 ± 9.29 μg·m−3). In barns without straw bedding, the average TDC was 55.91 ± 36.6 μg·m−3, PM10 33.71 ± 13.86 μg·m−3, PM4 30.69 ± 15.29 μg·m−3, PM2.5 27.02 ± 13.38 μg·m−3, and PM1 22.93 ± 10.48 μg·m−3. The largest TDC of 108.09 ± 32.93 μg·m−3 (PM10 69.80 ± 18.70 μg·m−3, PM4 68.20 ± 18.41 μg·m−3, PM2.5 53.27 ± 14.73 μg·m−3, and PM1 38.46 ± 5.55 μg·m−3) was measured in an old cowshed with stanchion housing for 113 cows, straw bedding, and ventilation through windows. In a modern cowshed for loose housing of 440 lactating cows without straw bedding, with natural ventilation and 24 axial fans, TDC was 53.62 ± 49.52 μg·m−3, PM10 20.91 ± 5.24 μg·m−3, PM4 17.11 ± 3.23 μg·m−3, PM2.5 13.71 ± 0.92 μg·m−3, and PM1 12.69 ± 2.82 μg·m−3. In all investigated barns, a large proportion of airborne dust particles (54.38 ± 20.82% of TDC) consists of the smallest PM1 dust particles (from 12.69 ± 2.82 μg·m−3 to 48.48 ± 1.18 μg·m−3).


Introduction
Considerable attention has long been paid to stressful situations and conditions for farm animals [1,2]. Animals' welfare can be threatened by many factors; exposure to adverse climatic conditions can also lead to stress conditions [3].
The indoor environment in animal houses is characterized by a significant biological load, which causes a large production of harmful substances. In terms of air cleanliness, in addition to gaseous pollutants, airborne dust is an important pollutant. The concentration of airborne dust is greatly influenced by the animal species, the housing technology, the − Inhalable fraction: occurs in the air and is inhaled through the nose or mouth. If the size of dust particles exceeds 10 µm, then such particles are attached mainly in the upper respiratory tract; − Thoracic fraction: of the total inhaled airborne dust, the fraction that penetrates beyond the larynx after inhalation; − Respirable fraction: entering areas of the respiratory system that do not have cilia-type epithelium. Such particles do not exceed 4 µm; they penetrate into the alveoli and are therefore very dangerous.
To clarify measurement and assessment methods, in addition to the total airborne dust mass concentration (TDC), dust particles are divided according to size into PM 10 , PM 4 , PM 2.5, and PM 1 fractions.
The respirable fraction is taken in the event of airborne dust with a predominantly fibrogenic effect. The sources of airborne dust in barns are primarily housed animals, feed, and bedding, and therefore airborne dust in barns is primarily organic [4][5][6][7][8][9], which does not pose a risk of fibrogenic effects. Determining other fractions may be justified for research and special tasks.
Occupational exposure limits (OELs) are regulatory values (concentration limits) that indicate levels of exposure that are considered to be safe (health-based) for a hazardous contaminant in the air of a workplace.
According to [35], this type of airborne dust has only irritating effects (poultry feathers, particles of feed, straw, and sawdust). Occupational Exposure Limits important for animal houses are for animal dust: feathers (4 mg·m −3 ), wool, fur, and other animal dust (6 mg·m −3 ), for straw, and cereals (6 mg·m −3 ).
Measured airborne dust inside this type of building is not aggressive; therefore, as a criterion for comparative evaluation of the measured values, it could be interesting to use the limit level of outdoor airborne dust. According to the Air Protection Act No. 201/2012 [37], the PM 10 limit value in 24 h is 50 µg·m −3 , the 1-year limit value is 40 µg·m −3 , and the 1-year limit value for PM 2.5 is 25 µg·m −3 . According to [38], the limit level for PM 10 is 50 µg·m −3 for a 24 h exposure period and 25 µg·m −3 for an annual exposure period; the limit level for PM 2.5 is 25 µg·m −3 for a 24 h exposure period and 8 µg·m −3 for an annual exposure period.
According to [6,38,39], measurement of the PM 1 fraction is important and should also have been considered in monitoring programs and possibly in future regulations because the magnitude of this fraction might not be negligible. Thus, differential particle sampling is encouraged, even going down to the ultra-fine fraction. In summary, research should address particle composition and sources, particle size, PM levels, and the factors influencing these.
The time of day or night and the technological operations and activities that take place in the animals' houses also influence the concentration of airborne dust in the buildings [4,[40][41][42][43]. Dust concentration will increase significantly, e.g., during bedding or feeding [4,8,9,[40][41][42][43][44]. The season of the year and high air humidity also influence airborne dust concentration [4,41,43]. Higher airborne dust concentrations were therefore found inside the buildings for farm animals in the winter, and researchers from northern Europe pay a lot of attention to measuring airborne dust [4,10,27,28,41,43].
Light airborne dust particles also spread to the surroundings of farms. Research on airborne dust on cattle farms is therefore conducted not only inside the barns but also in the paddock during the summer [45].
The experiments with dairy cows were conducted in an air-conditioned cowshed. The effect of the regulated ionic microclimate on the emission of PM 10 dust particles was positive, and airborne dust concentration was slightly reduced [46].
The aim of this research is to demonstrate that the size composition of airborne dust fractions in dairy cattle barns is important to examine in more detail, down to the smallest particles, including the factors that influence this composition.

Description of Buildings Used for Research
This research was carried out on several farms located in the Czech Republic. The Czech Republic lies in a mild climate zone that is characterized by the alternation of four seasons. Due to its location in the central part of the European mainland, the influence of the ocean and the westerly direction of airflow prevail here [47]. In the territory of the Czech Republic, the long-term monthly average air temperature has a simple annual pattern with a minimum mainly in January and a maximum mainly in July and August. The average air temperature in the Czech Republic from 1961 to 1970 in July was 16.7 • C and in August 15.8 • C, and from 2012 to 2021 in July it was 19.9 • C and in August 18.3 • C [48]. Relative air humidity ranges from 60-80% on an annual average. It is significantly influenced by daily temperatures and the amount of precipitation. The lowest is usually between April and August.
Airborne dust concentration was measured during the summer when no technological operations such as milking, feeding, cleaning, or bedding with straw were taking place in the barns. For this research, all barns investigated are in the same climatic region, typical for agricultural conditions. The buildings for dairy cattle housing were selected in such a way that the causes of possible differences in the airborne dust concentrations inside the investigated buildings could be identified and shown. Barns thus represent the most common types of agricultural buildings for housing dairy cows and other categories of cattle in the Czech Republic; however, the building structure, building materials, and technological equipment for housing differ. The numbers of housed animals are also different, which, however, also corresponds to their use in the operation of dairy cattle farms.
The research included the measurement and evaluation of indoor airborne dust in buildings: dairy production cowsheds for lactating cows LC (number of housed animals inside the building): LC 100, LC 113, LC 116, LC 210, LC 440, barn for dry cows DC 23, cowshed for maternity cows MC 27, calf hutch CaH 1, barn for calves CaB 36, and for comparison, also in one barn with beef cows and calves BC 38.
Summary information about the researched barns and selected construction and operational parameters is processed in Table 1. Dairy production cowsheds for lactating cows (LC 100) are used for housing 100 Jersey cows in cubicles with straw bedding. The roof with a central ridge slot is covered by plastic plates, partly completed by translucent fiberglass; gable walls are partly made from wood and partly from PVC mesh; side walls are made from PVC mesh, which can be covered by the vertically movable PVC tarpaulin.
Old cowshed LC 113, with 113 Holstein dairy cows, has stanchion housing with straw bedding. Ventilation is through slightly open windows and doors. In addition to dairy cows, calves are also housed in the barn in the first period after giving birth for approximately 2 weeks, near the lactating dairy cow-their mother.
Old cowshed for lactating cows LC 116 with a capacity of 116 dairy cows is constructed from massive stone and brick walls. It is used for housing 80 Jersey cows in individual cubicles with straw bedding. The natural ventilation of the building is through partially open windows and doors.
Modern cowshed LC 210 with loose housing technology for 210 Holstein lactating cows has comfort cubicles covered by separated dried manure solids as bedding. Longitudinal walls are made of woven fabric mesh and variable side curtains, which, together with a ventilation roof ridge slot, enable natural ventilation. Eight fans improve the ventilation of the building in the summer.
Dairy production cowshed LC 440 for Holstein lactating cows is a new modern cowshed for loose housing of lactating cows. It is a semi-closed building with comfort cubicles covered by separated dried manure solids as bedding. The walls are made of woven fabric mesh with variable side curtains and a roof ridge slot for natural ventilation. If the air temperature is over 24 • C, the installed 24 axial fans switch automatically to improve ventilation.
The cowshed DC 23 for dry Holstein cows is a massive brick structure. It has an outdoor feeding passage and a rest area with loose housing on deep litter. The central slot of the roof ridge and the open windows allow ventilation. In summer, ventilation is improved by four axial fans.
Cowshed for maternity Holstein cows (MC 27) are used for housing 27 dairy cows before and at the time of calving. The maternity cowshed has free housing with straw bedding in nine maternity pens. Natural ventilation is provided by the ridge roof and mesh side walls.
Individual outdoor hutches, CaH 1, are used for Holstein calves in the first breeding period (2 months). It is made of white polyethylene. CaH has a length of 150 cm, a width of 112 cm, and a height of 135 cm. The floor is covered daily with straw bedding.
Barn for calves CaB 36 is a modern, spacious wooden building for housing 36 Jersey calves during the milk feeding period. Calves are in individual pens with straw bedding. The barn has sufficient natural ventilation thanks to the large open areas of the side walls, which are open in the summer and covered only with mesh.
Barn for Angus beef cattle BC 38 is a reconstructed brick cowshed (originally for dairy cows) used for beef cows with calves and beef cattle fattening (during the measurement of 38 animals) in group pens with littered lying areas. The natural ventilation of the barn is provided by partly open windows in the walls and a ridge roof slot.

Data Acquisition and Processing
Temperatures and relative humidity of the air were measured by instruments and sensors from the Ahlborn company (Ahlborn Mess-und Regelungstechnik GmbH, Eichenfeldstraße 1, 83607 Holzkirchen, Germany) outside and inside the buildings with registration at intervals of 1 min.
The Almemo 2690 with temperature and humidity sensors of the FHA 646 for outside measurement, together with the FY A600 sensor for CO 2 measurement, was kept in a special weather station box.
The Almemo 2590-9 with sensors FHA 646 and FY A600 were used inside the barns near the animals. Temperature and humidity sensors of the FHA 646 type have a range of use from −20 to 80 • C and from 5 to 98% relative humidity. The measuring range of the capacitive sensor of relative humidity ranges from 0 to 100%, with an accuracy of ±2% in the range <90% relative humidity. The concentration of CO 2 was measured by the Ahlborn sensors FY A600, with an operative range of 0 to 0.5% and an accuracy of ±0.01%.
The total dust mass concentration was measured by the special exact laser-photometer instrument Dust-Track™ II Aerosol Monitor 8530 produced by TSI in the USA, 500 Cardigan Road, Shoreview, MN 55126, with an operating range of 0.001 to 150 mg·m −3 and a resolution of ±0.1% of the reading of 0.001 mg·m −3 , whichever is greater. Zero calibration was used before every use.
Size-selective impactors can be attached to the inlet of the Dust-Track™ II Aerosol Monitor 8530. Size-selective impactors are used to pre-condition the size range of the particles entering the instrument. PM 1 , PM 2.5 , PM 4, and PM 10 impactors were used to measure segregated mass fractions of airborne dust.
For the purpose of this measurement, 90 airborne dust concentration data points were collected for the total airborne dust concentration as well as for each PM size fraction of dust in each measured building. The measurement frequency was 2 s. Measurements were taken sequentially for each barn during warm summer days. The Dust-Track™ II device was always placed in a representative location of the investigated building at a height of 0.6 m above the floor.
The acquired datasets were processed using MS Excel, and some of the results (assessing whether differences between evaluated datasets are significant or not) were verified by the statistical software TIBCO SW Data Science Workbench Statistica Version 6 (ANOVA and Tukey's HSD (Honestly Significant Difference) test). Data processed in the form of charts was processed in MS Excel.

Results
The average temperatures and relative humidity of the outdoor air at the time of airborne dust measurement are summarized in Table 2. The average temperatures of the outdoor air ranged from 29.5 ± 0.2 • C to 36.0 ± 0.1 • C, and the average relative humidity ranged from 16.5 ± 0.2% to 40.3 ± 0.1%. Table 2. Basic parameters of the outside air and inside the barns at the time of airborne dust measurement. Table 2 also shows the corresponding temperatures, relative humidity, and CO 2 concentration of the indoor air in the buildings at the time of airborne dust measurement. Average indoor air temperatures ranged from 27.2 ± 0.2 • C to 43.3 ± 0.1 • C, and average relative humidity ranged from 15.4 ± 0.1% to 50.3 ± 2.9%.
The CO 2i concentration inside the barns at the time of measurement in half of the buildings corresponded to the outdoor CO 2e concentration, which was 400 ppm. In four buildings, the concentration of CO 2i was slightly increased, ranging from 410 ± 0 ppm to 583 ± 171 ppm; in one barn, it was 939 ± 132 ppm.
The airborne dust measurement results are summarized in Table 3. In addition to the total dust mass concentration (TDC), the concentrations of individual fractions PM 10 , PM 4 , PM 2.5, and PM 1 are also shown in Table 3 for individual buildings. The measured results of total dust mass concentration show significant differences between some buildings. Total dust mass concentration was the highest in cowshed LC 113 (108.09 ± 32.93 µg·m −3 ), an old cowshed with stanchion housing and straw bedding.
The use of plenty of bedded straw and limited ventilation was also manifested in the older brick barns DC 23 (86.81 ± 33.59 µg·m −3 ) and BC 38 (76.33 ± 17.72 µg·m −3 ). The difference in total dust mass concentration between them was not statistically significant.
Between  ), there was no statistically significant difference in total dust mass concentration. However, there are barns with and without straw bedding and significant differences in housing technology, as well as in terms of the concentration of housed animals inside buildings.
Total dust mass concentration was the lowest in maternity cowshed MC 27 (37.59 ± 13.74 µg·m −3 ) for housing cows before and after calving. A large amount of straw bedding is used in the pens, but the pens for the cows are spacious, and the natural ventilation through the mesh walls, supplemented by fans, has a very good effect on the cleanliness of the inside air.
There are also significant differences in the assessment of the PM 10 dust fraction between some barns. The highest PM 10  In order to compare barns with and without straw bedding and to find out whether the use of straw has a significant effect on total dust mass concentration and how it affects individual fractions PM 10  This comparison of the two sets shown in Table 4 shows what the differences are and where the conditions are better from this point of view. In individual columns, the different superscript letters mean that there is a significant difference between the values in the column.  Table 5 shows the results of a statistical comparison of the average airborne dust levels (total dust mass concentration, PM 10 Table 7 shows the results of a statistical comparison of the average dust levels in cowsheds with separately housed cows (DC 23, LC 100, LC 210, LC 116, and LC 440), with barns only for calves (CaH 1 and CaB 36), and with barns in which cows are housed together with calves (LC 113, BC 38, and MC 27). Figure 1 is a chart showing summary information on the total dust mass concentration of airborne dust. Each column shows 5 subcomponents of individual size groups of airborne dust particles in the range above 10 µm, from 4 µm to 10 µm, from 2.5 µm to 4 µm, from 1 µm to 2.5 µm, and smaller than 1 µm. The order of the columns in the picture corresponds to the order according to the average size of the total dust mass concentration in barns. The measured values of airborne dust particle fractions are given in mass concentration (µg·m −3 ).   The share of individual fractions of airborne dust particles in the air in individual barns is rather variable. The share of the size distribution of airborne dust particle fractions PM ˂ 1 μm, 1 μm ≤ PM ˂ 2.5 μm, 2.5 μm ≤ PM ˂ 4 μm, 4 μm ≤ PM ˂ 10 μm, 10 μm ≤ PM as a percentage of total dust mass concentration in the examined barns is shown in Table 8 and Figure 2.  The share of individual fractions of airborne dust particles in the air in individual barns is rather variable. The share of the size distribution of airborne dust particle fractions PM < 1 µm, 1 µm ≤ PM < 2.5 µm, 2.5 µm ≤ PM < 4 µm, 4 µm ≤ PM < 10 µm, 10 µm ≤ PM as a percentage of total dust mass concentration in the examined barns is shown in Table 8 and Figure 2. Table 8. The share of the size distribution of dust particle fractions PM < 1 µm, 1 µm ≤ PM < 2.5 µm, 2.5 µm ≤ PM < 4 µm, 4 µm ≤ PM < 10 µm, 10 µm ≤ PM in the examined barns as a percentage of total dust mass concentration. SD-standard deviation. Figure 1. The average mass concentrations (μg·m −3 ) of airborne dust particles in the examined buildings are in the range above 10 μm, from 4 μm to 10 μm, from 2.5 μm to 4 μm, from 1 μm to 2.5 μm, and smaller than 1 μm.
The share of individual fractions of airborne dust particles in the air in individual barns is rather variable. The share of the size distribution of airborne dust particle fractions PM ˂ 1 μm, 1 μm ≤ PM ˂ 2.5 μm, 2.5 μm ≤ PM ˂ 4 μm, 4 μm ≤ PM ˂ 10 μm, 10 μm ≤ PM as a percentage of total dust mass concentration in the examined barns is shown in Table 8 and Figure 2.  The share of the size distribution of dust particle fractions inside the buildings in the range above 10 μm, from 4 μm to 10 μm, from 2.5 μm to 4 μm, from 1 μm to 2.5 μm, and smaller than 1 μm is in.

Discussion
Previous studies have reported higher airborne dust concentrations in poultry and pig barns compared to cattle barns [4][5][6][7][8][9][10]. As a rule, however, more detailed attention was not paid to the differences in the method of housing, the construction, or the ventilation The share of the size distribution of dust particle fractions inside the buildings in the range above 10 µm, from 4 µm to 10 µm, from 2.5 µm to 4 µm, from 1 µm to 2.5 µm, and smaller than 1 µm is in.

Discussion
Previous studies have reported higher airborne dust concentrations in poultry and pig barns compared to cattle barns [4][5][6][7][8][9][10]. As a rule, however, more detailed attention was not paid to the differences in the method of housing, the construction, or the ventilation system of the barn. Under the conditions of this study, it is possible to look in more detail at the differences in the construction of the barns as well as the housing and ventilation solutions.
The results of extensive measurements [42] in animal houses for poultry, pigs, cattle, and mink showed the lowest concentrations of airborne dust in cattle houses. According to the data in [8], in the barns for cattle, the concentration of airborne dust PM 10 was 100 µg·m −3 , and PM 2.5 only 10 µg·m −3 . The results in Table 3 show that in this research, PM 10 was lower than 100 µg·m −3 in all barns, and PM 2.5 was always higher than 10 µg·m −3 .
The measurement method using the laser-photometer Dust-Track™ II Aerosol Monitor 8530 has the advantage of using impactors for detecting PM dust fractions, including the smallest particles, and is very suitable for comparative measurements between different objects [42].
All measurements in this study were made in the same climatic area during the hot summer season (see Table 2). However, certain differences in outdoor temperature and relative humidity are caused by air temperature fluctuations during the summer. It is practically impossible to achieve the same outdoor parameters for all measurements.
The internal temperatures and air humidity are also slightly different, which is also caused by the different massiveness of the structures, different thermal-technical properties of the investigated buildings, different methods of ventilation, different housing technologies, different excrement removal, etc.
The results in Table 3 show significant differences between individual cattle barns in terms of the selected criteria for evaluating dust concentration. The division and evaluation of the researched barns into different groups (categories) according to several aspects (straw bedding vs. without straw bedding; massive structures vs. light uninsulated sheds; natural ventilation only vs. natural ventilation supplemented with fans) will help to reveal the reserves of the currently existing state and find possibilities for possible improvement of the current situation.
A comparison of the dust measurement results in Table 4 shows that in all measured airborne dust parameters, i.e., total dust mass concentration, PM 10 , PM 4 , PM 2.5 , and PM 1 , the average concentration of dust particles in barns with straw bedding was statistically significantly higher than in barns without straw bedding.
The results in Table 5 show that the total dust mass concentration and the concentration of PM 10 , PM 4 , and PM 2.5 dust particles were significantly higher in the massive constructions with window and door ventilation than in the light barns, where natural ventilation is easier thanks to the walls partially covered only by nets. There was an insignificant difference in the concentration of the smallest dust particles in PM 1 .
The results in Table 6 show that the total dust mass concentrations of PM 10 , PM 4 , PM 2.5, and PM 1 are significantly lower in barns equipped with fans for better ventilation in the summer than in barns that only have natural ventilation and are not equipped with fans. The effect of fans is statistically significant for reducing the total concentration of dust and all size fractions of dust.
No statistically significant difference was found in the assessment of airborne dust concentration according to PM 10 between the assessed groups of barns, but PM 10 exceeded the limit of 50 µg·m −3 in all cases.
When evaluating the concentration of the smallest dust particles of PM 1 , there was a statistically significant difference between all evaluated groups of barns. The worst was PM 1 in barns with calves (PM 1 = 44.10 ± 1.98 µg·m −3 ), the lowest was in cowsheds with cows (PM 1 = 34.05 ± 12.88 µg·m −3 ), and the lowest was PM 1 in common barns with dairy cows and calves (PM 1 = 31.63 ± 9.21 µg·m −3 ).
In all measured buildings, a large part (54.38 ± 20.82%) of the smallest PM 1 dust particles were present in the air. This can be attributed to the fact that these smallest and lightest dust particles move freely in the flowing air, and their settling time is very long, so even a low airspeed keeps them in the air. Part of these small dust particles is removed by ventilation, and part is, on the other hand, swirled inside the space and lifted from the surfaces back into the air in the barn.
The percentage of the smallest PM 1 particles is significantly lower in barns equipped with fans than in barns ventilated only by natural ventilation, as can be seen from the statistical evaluation in Table 6.
The smallest share of PM 1 particles (24%) was in the large-capacity cowshed without straw bedding (LC 440). It is also the smallest in terms of absolute values (PM 1 = 12.69 ± 2.82 µg·m −3 ). Conversely, the largest share (61%) of the largest dust particles above 10 µm was found in this cowshed, LC 440. This is mainly due to the higher airflow speed inside this cowshed. In addition to the natural flow through the mesh walls, 24 axial fans with a horizontal axis of rotation, which help to better ventilate the barn in the summer, are the source of higher flow speeds inside the barn. The PM 1 particles are removed by air streams, and the largest particles above 10 µm recirculate inside the barn.
According to the authors [19], organic dust consists mostly of particles with a diameter of less than 1 µm, which is unacceptable for long-term exposure and can be the cause of asthma, asthmatic syndromes, chronic bronchitis, and hypersensitivity pneumonitis (Farmer's lung). According to the results in Tables 3 and 8 and Figures 1 and 2, it is clear that in this aspect our research and conclusions agree.
In the overall evaluation according to Table 8, the largest particles, 10 µm ≤ PM, are the second fraction of dust particles in percentage order (15.94 ± 18.29%).
The third size fraction of dust particles (4 µm ≤ PM < 10 µm) accounted for 13.70 ± 12.78% of the total dust concentrations in the barns.
The fourth group of dust particles consists of the size fraction 1 µm ≤ PM < 2.5 µm, which had a share of 9.07 ± 4.25%.
The smallest part of the total concentration of dust in the investigated stables was made up of particles 2.5 µm ≤ PM < 4 µm, which were 6.91 ± 3.94%.
The authors [9] report that the average PM 10 in dairy cattle farms (cubicle housing without straw bedding) was 40 µg·m −3 , ranging from 14 to 95 µg·m −3 , and the average PM 2.5 was 13.8 µg·m −3 , ranging from 3.9 up to 24.9 µg·m −3 . The results of PM 10 measured in cowsheds without litter (33.71 ± 13.86 µg·m −3 ), see Table 3, correspond approximately to these average values; the results of PM 10 found in barns with straw bedding (60.11 ± 19.93 µg·m −3 ) correspond to the upper half of the range according to [9]. PM 2.5 values found in cowsheds without straw bedding (27.02 ± 13.38 µg·m −3 ) exceed the data according to [9]. They are even more significantly exceeded by the results from barns with straw bedding (44.78 ± 10.18 µg·m −3 ); see Table 4.
The authors of the research [19] on small dairy farms state that the measured values of PM 10 during the distribution of hay and feed flour did not exceed the limit of 5 mg·m −3 for organic dust, but in some individual cases, they exceeded the value of 10 mg·m −3 . The stated values are thus significantly higher than the results found by this research, presented in Table 3 and others.
Research results in Finnish cubicle cow houses [41] indicate mean concentrations of total airborne dust of 0.2-1.9 µg·m −3 , which is significantly more than the results of the measurements of this research in the summer period, presented in Table 3. Measurements [41] were made during winter and early autumn, when the indoor temperatures and relative humidity varied from 7 to 17 • C (mean 12.7 • C) and 55 to 95% (mean 87%), respectively. The outdoor temperature ranged from +2 to −20 • C. The external and internal conditions differ considerably from those of this research (see Table 2). Due to the cold measurement conditions, the CO 2 concentration results were also higher in the Finnish stables than in the investigated barns of this case study in the Czech Republic in the summer.
The low mean air temperatures and high relative air humidity measured in [43] correspond to the colder climatic regions of Estonia; however, this comparison is interesting for the mutual comparison of airborne dust concentration and airborne dust individual fractions. It can be assumed that the high concentrations of PM 2.5 and PM 1 fractions achieved in this research (Table 3) are caused by high temperatures and low relative air humidity when measured in the summer period in the Czech Republic.
If it is an assessment of the cleanliness of the air in the barn from the point of view of occupational health [35], the occupational exposure limits important for animal houses, which are for feather (4 mg·m −3 ), wool, fur, and other animal dust (6 mg·m −3 ), straw, and cereals (6 mg·m −3 ), were not exceeded in any measurement, even in the case of total dust mass concentration results.
Considering the current trend in livestock breeding to strive for the most favorable animal welfare, which will be close to the natural conditions of animals kept in the wild, it is interesting to compare the internal environmental conditions in the barns in terms of air pollution by airborne dust with the limits recommended for the stay of people in the outdoor environment. However, these data are also interesting from the point of view of the stay of people in the relevant premises as part of their work activities and duties.
When comparing the measured values with the limit value of recommended air quality standards for PM 10 = 50 µg·m −3 for the outdoor environment for a 24 h exposure period [31][32][33][34][35], the lower value was only in cowshed without straw bedding LC 210 (46.51 ± 5.38 µg·m −3 ) and maternity cowshed MC 27 (30.86 ± 4.09 µg·m −3 ), and significantly lower compared to other barns was in large-capacity cowshed without straw bedding LC 440 (20.91 ± 5.24 µg·m −3 ). This cowshed was the only one of the investigated barns that would also meet the requirement of PM 10 = 25 µg·m −3 for an annual exposure period. The requirement for an annual exposure period [37] of PM 10 = 40 µg·m −3 would also be met for cowshed MC 27.
The recommended air quality standards are slightly different. According to [37]

Conclusions
From the results presented in the tables, it follows that dairy cattle barns equipped with laying stalls with straw bedding cause higher indoor air dust pollution than barns without straw bedding.
A comparison of the measurement results presented in the tables showed that increased ventilation has a positive effect on reducing the concentration of airborne dust particles.
A comparison of the measurement results presented in the tables shows that in modern, uninsulated cowsheds with a large proportion of open walls made of woven fabric mesh and variable side curtains, the concentration of airborne dust was lower than in modernized massive brick barns with a smaller proportion of open parts of the building, which would allow ventilation.
From the results presented in tables and figures, it follows that in the summer season, a large proportion of airborne dust particles in most dairy cattle barns are the smallest PM 1 particles, regardless of the type of construction and technology of housing with straw bedding or without straw. For this reason, attention should also be paid to these smallest airborne dust particles in further research.
Funding: This research received no external funding.

Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.

Data Availability Statement:
The farmers gave consent for the raw data to be used by the researcher only, but any queries involving the processing of these data can be directed to the corresponding author.