**2. Indoor particulate matter decay**

456 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

portion of their time in indoor environment [13].

g.m-3 in 2009 [4].

2.107 particles in 1 m3. In the polluted urban air the particle concentrations are higher than 1011 particles in 1 m3 and their mass concentrations may be higher than 100 g.m-3 [1,3]. In the Slovak Republic, the average annual outdoor PM10 concentrations ranged from 11.6 –18

Danger of toxic inhalation exposure depends on both the physical and chemical characteristics of particulate matter and thus the study of its properties is essential to assess the health risks. Exposure to PM in ambient air has been linked to a number of different health outcomes, ranging from modest transient changes in the respiratory tract and impaired pulmonary function, through increased risk of symptoms requiring emergency room or hospital treatment, to increased risk of death from cardiovascular and respiratory diseases or lung cancer. The elderly, children, and people with chronic lung disease, influenza, or asthma, are especially sensitive to the effects of particulate matter [5]. Multiple studies have showed that a short-term exposure to particulate matter may associated with increased cardiovascular mortality [6-8]. The occurrence of particulate matters in the air interferes with human health not only due to its composition but also due to its specific properties. The large specific particle surface takes a share on the catalysis of heterogeneous

chemical reactions and on adsorption of other pollutants and their transport [9].

Sources of particulate matter occur in the outdoor air as well as in the indoor environment. Ambient air concentrations are strongly dependent on meteorological factors in contrast to the indoor environment which is much more stable. The suspended particulate matter present in the indoor air is cumulated and as reported by [10-12] the indoor particulate concentrations are often measured to be higher than those outdoors. With the emphasis on both energy conservation and efficiency, mainly new home construction can create the problem of indoor air pollution. Vapour barriers, tight windows, weather-stripping and caulk have reduced or stopped fresh air from infiltrating and replacing stale air. Special attention must be paid to indoor air contamination because people spend a substantial

If indoor air pollution is investigated, both outdoor and indoor sources have to be considered, because the outdoor air is an important source of indoor particles pollution. Indoor particle concentration depends on penetration of outdoor particles into the indoor environment and on intensity of indoor aerosol sources [2]. Indoor particulate matter sources include building materials, cooking, heating and all activities related to combustion processes, smoking, cleaning and moving of inhabitants [14,15]. The importance of indoor sources depends significantly also on the number and habits of the inhabitants. It was noted [16] that the concentration of PM2.5 was 2.8 times higher in houses where people smoked.

The behaviour of indoor aerosols is affected by the structural system of a building, material characteristics, the way of air exchange, the operating mode of indoor environment in the presence of inhabitants. The structural systems of a building along with the physical properties of the outdoor air (wind direction and intensity, the difference in the density of the indoor/outdoor air, the difference in the indoor/outdoor air temperatures etc.) determine interzonal transport of pollutants [17]. In multi-floor buildings, the flow induced by The aerosol particulate decay in indoor environment occurs by two mechanisms ventilation and deposition. In general, ventilation is a positive mechanism for the loss of particles from indoor air. However, in real conditions, it often may cause entering the outdoor pollutants with supplied air into the indoor environment. The extent which ventilation contributes to the reduction of the indoor concentrations depends on the way of air exchange which can be carried out by natural air change, infiltration or ventilation systems. If the ratio of indoor and outdoor concentrations I/O reaches a value more than 1, the positive venting mechanism will result in a reduction of particulate matter concentration due to dilution. Otherwise, the contamination of indoor air increases by addition of outdoor particulate matter, mainly by natural air change. Ventilation systems should ensure the particulate matter concentration in the indoor environment is not increasing due to utilization of special filters in the inlet. In addition, coarse particles in ventilation system are often deposited by gravitational process which also leads to the removing of particles from the air supplied. On the other hand, particles deposited in the pipes can be re-suspended in dependence on the air flow speed [21].

Particle deposition is an important factor affecting indoor particle concentrations in all types of buildings and is considered to be a dominant mechanism of the aerosols concentration level decreasing [22-23]. The largest incidental losses occur as a result of particle deposition onto the surfaces. Due to the relatively large surface-to-volume ratio indoors, deposition has a much larger effect on reducing concentrations indoors than it does outdoors [19].

Particle deposition on indoor surfaces strongly depends on particle size and is governed by the processes of particle diffusion toward the surfaces, which is of particular significance for very small particles, and of gravitational sedimentation, which is significant for larger particles. In addition, the presence of airflows induced by convection currents or the action of fans, as well as air turbulence, can increase particle transport towards the surface a thus the deposition. Deposition is also dependent on the surface area and on its characteristics, with sticky surfaces resulting in higher deposition than smooth one. The larger surface area, the higher probability of particle deposition, and therefore furnished rooms, with lots of surface area, will have a higher deposition rate than bare rooms. Additional factors affecting particles deposition are: the presence of surface charge, which leads to the deposition rate increasing; temperature gradient, resulting in convective currents and thermophoretic deposition; and room volume [2].

Aerosol particles adhere when they collide with a surface. The aerosol concentration at the surface is zero and the concentration gradient is established in the region near the surface. The concentration gradient causes a continuous diffusion of aerosol particles to the surface, which leads to a gradual decay in concentration. Applying Fick´s first law of diffusion, deposition rate J is defined as a number of particles depositing per unit surface area per unit time and is given by equation (1)

$$J = n\_0 \left(\frac{D}{\pi t}\right)^{1/2} \tag{1}$$

Investigation of Suspended and Settled Particulate Matter in Indoor Air 459

where A*w*, A*h* and A*d* are the total areas for the vertical wall, upward-facing and downwardfacing horizontal surfaces, respectively. V*dw*, V*du* and V*dd* are the deposition velocities for the vertical wall, upward-facing and downward-facing horizontal surfaces, respectively, and

Diffusion deposition is primaryly observed on vertical and downward-facing surfaces (ceilings). Deposition induced by gravitational force is observed onto upward-facing surfaces (wear layer of floor constructions, upward-facing areas of furnishing). Air drag force compared with settling particle is determined by airflow. For settling observed in still air (i.e. Re < 1 laminar airflow) the Stoke´s low is valid. If airflow is turbulent (Re > 1000), Newton resistant low is valid for settling particle. Terminal settling velocity VTS of the particle settling due to gravitational force is results of balance drag and gravity. V*TS* is

, for Re 1 laminar airflow

<sup>4</sup> , for Re 1000 turbulent airflow

where η is the viscosity of the air, ρ*p* a ρ*g* are the density of the particle and the density of the air, d*p* is the particle diameter, g is the gravitational acceleration and C*D* the drag coefficient. Indoor particle deposition can be induced also by thermophoretic forces which results in thermoprecipitation, or by ventilation and air conditioning use which lead to the eddy diffusion. Thermoprecipitation may be significant in the winter season because of heating. The presence of a heating device seems to be related to lower concentrations of a number of components, such as particle mass, Cr, Zn, Ca2+, SO42- and NO3- and other as noted in

Particles deposited on indoor surfaces create a potential reservoir from where they can be re-suspended whereby the secondary contamination is increased. This re-suspension effect

The monitoring of aerosol particulate matter (PM) was carried out in three rooms of the selected flat building in the city of Košice, Slovakia. Kitchen, living room and working room as representative indoor environments with different indoor sources were chosen for PM monitoring. Environmental tobacco smoke was considered a major source of the particles in the living room; cooking on the gas stove was considered a major indoor source of particulate matter in the kitchen. None significant indoor source was identified in the working room. However, a penetration of outdoor particles through large openings (windows, doors) or cracks and gaps through building envelope and interzonal transport

(4)

(5)

2

1/2

can be caused by mechanical vibration, aerodynamic or electrostatic forces.

18 *p p*

*TS d g <sup>V</sup>* 

> 3 *p p*

*d g <sup>V</sup> C* 

*D g*

*TS*

**3. Indoor air monitoring – A case study** 

from other rooms cannot be neglected.

V is the volume of the enclosure [13].

expressed in equations (4, 5) [1].

reference [45].

where no is the uniform initial concentration and D is the particle diffusion coefficient [12]. The deposition can be also characterized in terms of deposition velocity V*dep*, which is defined as the deposition rate divided by concentration in the equation (2)

$$V\_{dep} = \frac{\text{J}}{\text{m}\_0} = \frac{\text{number deposited } / \text{m}^2 \text{.s}}{\text{number } / \text{m}^3} = m \text{ / s} \tag{2}$$

The number of particles depositing on the total surface per unit time is expressed by the deposition loss rate coefficient β [1/s, 1/h]. This coefficient includes all the processes that remove the particle in enclosure (e.g. diffusion loss, gravitational settling loss and other loss mechanisms by external forces). In the context of regular geometry, β can be evaluated from the deposition velocity on different orientation of surfaces and their particular surface area, and can be expressed as

$$\mathcal{B} = \frac{V\_{dvv}A\_w + V\_{du}A\_h + V\_{dd}A\_d}{V} \tag{3}$$

where A*w*, A*h* and A*d* are the total areas for the vertical wall, upward-facing and downwardfacing horizontal surfaces, respectively. V*dw*, V*du* and V*dd* are the deposition velocities for the vertical wall, upward-facing and downward-facing horizontal surfaces, respectively, and V is the volume of the enclosure [13].

Diffusion deposition is primaryly observed on vertical and downward-facing surfaces (ceilings). Deposition induced by gravitational force is observed onto upward-facing surfaces (wear layer of floor constructions, upward-facing areas of furnishing). Air drag force compared with settling particle is determined by airflow. For settling observed in still air (i.e. Re < 1 laminar airflow) the Stoke´s low is valid. If airflow is turbulent (Re > 1000), Newton resistant low is valid for settling particle. Terminal settling velocity VTS of the particle settling due to gravitational force is results of balance drag and gravity. V*TS* is expressed in equations (4, 5) [1].

$$V\_{\rm TS} = \frac{\rho\_p d\_p^{\prime 2} \text{g}}{18\eta}, \text{ for Re } < 1 \text{ laminar airflow} \tag{4}$$

$$V\_{\rm TS} = \left(\frac{4\,\rho\_p d\_p g}{3C\_D \rho\_\mathcal{g}}\right)^{1/2}, \text{for Re } > 1000 \text{ turbulent airflow} \tag{5}$$

where η is the viscosity of the air, ρ*p* a ρ*g* are the density of the particle and the density of the air, d*p* is the particle diameter, g is the gravitational acceleration and C*D* the drag coefficient. Indoor particle deposition can be induced also by thermophoretic forces which results in thermoprecipitation, or by ventilation and air conditioning use which lead to the eddy diffusion. Thermoprecipitation may be significant in the winter season because of heating. The presence of a heating device seems to be related to lower concentrations of a number of components, such as particle mass, Cr, Zn, Ca2+, SO42- and NO3- and other as noted in reference [45].

Particles deposited on indoor surfaces create a potential reservoir from where they can be re-suspended whereby the secondary contamination is increased. This re-suspension effect can be caused by mechanical vibration, aerodynamic or electrostatic forces.

## **3. Indoor air monitoring – A case study**

458 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

deposition; and room volume [2].

time and is given by equation (1)

and can be expressed as

Particle deposition is an important factor affecting indoor particle concentrations in all types of buildings and is considered to be a dominant mechanism of the aerosols concentration level decreasing [22-23]. The largest incidental losses occur as a result of particle deposition onto the surfaces. Due to the relatively large surface-to-volume ratio indoors, deposition has

Particle deposition on indoor surfaces strongly depends on particle size and is governed by the processes of particle diffusion toward the surfaces, which is of particular significance for very small particles, and of gravitational sedimentation, which is significant for larger particles. In addition, the presence of airflows induced by convection currents or the action of fans, as well as air turbulence, can increase particle transport towards the surface a thus the deposition. Deposition is also dependent on the surface area and on its characteristics, with sticky surfaces resulting in higher deposition than smooth one. The larger surface area, the higher probability of particle deposition, and therefore furnished rooms, with lots of surface area, will have a higher deposition rate than bare rooms. Additional factors affecting particles deposition are: the presence of surface charge, which leads to the deposition rate increasing; temperature gradient, resulting in convective currents and thermophoretic

Aerosol particles adhere when they collide with a surface. The aerosol concentration at the surface is zero and the concentration gradient is established in the region near the surface. The concentration gradient causes a continuous diffusion of aerosol particles to the surface, which leads to a gradual decay in concentration. Applying Fick´s first law of diffusion, deposition rate J is defined as a number of particles depositing per unit surface area per unit

> 0 *<sup>D</sup> J n t*

defined as the deposition rate divided by concentration in the equation (2)

0

where no is the uniform initial concentration and D is the particle diffusion coefficient [12]. The deposition can be also characterized in terms of deposition velocity V*dep*, which is

> / *dep <sup>J</sup> <sup>V</sup> m s <sup>n</sup>*

The number of particles depositing on the total surface per unit time is expressed by the deposition loss rate coefficient β [1/s, 1/h]. This coefficient includes all the processes that remove the particle in enclosure (e.g. diffusion loss, gravitational settling loss and other loss mechanisms by external forces). In the context of regular geometry, β can be evaluated from the deposition velocity on different orientation of surfaces and their particular surface area,

> *V A VA VA dw w du h dd d V*

*number deposited / m .s*

1/2

*2*

*3*

(1)

*number / m* (2)

(3)

a much larger effect on reducing concentrations indoors than it does outdoors [19].

The monitoring of aerosol particulate matter (PM) was carried out in three rooms of the selected flat building in the city of Košice, Slovakia. Kitchen, living room and working room as representative indoor environments with different indoor sources were chosen for PM monitoring. Environmental tobacco smoke was considered a major source of the particles in the living room; cooking on the gas stove was considered a major indoor source of particulate matter in the kitchen. None significant indoor source was identified in the working room. However, a penetration of outdoor particles through large openings (windows, doors) or cracks and gaps through building envelope and interzonal transport from other rooms cannot be neglected.

Settled particulate matter sampling was carried out by passive methods during 28 days. The adjusted sampling method for ambient air was used for indoor environment. The aerosol particulates were captured into Petri dishes (8.5 cm diameter), installed at three height levels: on the floor, at height of 0.8 m from the floor and at height of 2.2 m from the floor. The settling of particles proceeded onto both by water filled Petri dishes (wet gravitational settling) and empty Petri dishes (dry gravitational settling) at each monitored level. The particle total mass was calculated by gravimetric method from the Petri dish mass increases; the surface particle concentrations were determined by standard way.

Investigation of Suspended and Settled Particulate Matter in Indoor Air 461

0.0 m 0.8 m 2.2 m

The highest total deposited mass was detected in the kitchen, the lowest in the working room (Table 2). The highest non-dissolved mass was expected as well. However, there was detected the highest percentage of non dissolved particulate matter in the living room. Fibres from carpets, textile and upholstered furniture represented the essential part of non-

The results of indoor particle deposition monitoring considering the three high levels in all monitored rooms are summarized in Table 3. Besides the standard wet deposition, the dry deposition was included in the study in order to investigate the re-suspension processes. The surface concentrations of particles ranged from 21.0 to 86.6 μg.cm-2 by wet gravitational settling and from 7.0 to 39.5 μg.cm-2 by dry gravitational settling in all monitored rooms.

wet gravitational settling 86.62 53.50 51.59 dry gravitational settling 39.49 27.39 24.84

wet gravitational settling 42.68 38.22 32.48 dry gravitational settling 27.39 21.02 14.01

wet gravitational settling 47.77 29.29 21.02 dry gravitational settling 17.19 15.92 7.01

The highest surface concentrations of particulate matters were measured in the kitchen at all monitored levels. The surface concentration values were expected to be the highest in the kitchen because of the most intensive indoor particulate sources. The surface concentrations

The particles surface concentration was found to be decreased with the height of the room from the floor to the ceiling construction at wet gravitational settling in all monitored rooms

Surface concentration [μg.cm-2] Distance from the floor

dissolved from the total deposited mass (Figure 1).

**Figure 1.** Non-dissolved particles captured on the filter

**Table 3.** Surface concentration of particulate matter

determined in the other rooms reached the comparable values.

Kitchen

Living room

Working room

Suspended particulate matter investigation was focused on total suspended particles (TSP) and thoracic fraction PM10. Investigation was carried out in the same rooms in the investigated flat building in the city of Košice. Measurement have included integral particles sampling onto a collection material (membrane filter Synpor 0.83 m pore size, 35 mm in diameter and PTFE filter for TSP and PM10, respectively) by sampling equipment VPS 2000 (Envitech, Trenčín) at the constant air flow of 600 litres/hour during a sampling period of approximately 24 hours. Because of minimization of humidity interference and volatile organic matters elimination, the filters were dried at a temperature of 105C for 8 h before sampling than equilibrated at a constant temperature and humidity (e.g. 20C and 50% RH) for 24 h before and after sampling. The particulate mass concentrations were determined by gravimetric method from the increase of filter weight (measured by analytical balance fy Mettler Toledo within 0.00001 g). The average concentrations of measured particulate matter in studied rooms are presented in Table1.


**Table 1.** The mean concentrations of settled and suspended particulate matter

The surface concentrations of settled particulate matter measured in selected rooms were in the range 7.0 to 86.6 μg.cm-2 while the average surface concentrations for the rooms were calculated from 32.7 to 63.9 μg.cm-2 (Table 2). The percentage of non-dissolved portion of settled particulate matter was calculated by dividing of the non-dissolved mass separated by filters by total deposited mass [47].


**Table 2.** Settled particulate matter and percentage of non-dissolved particles in total deposited mass

The highest total deposited mass was detected in the kitchen, the lowest in the working room (Table 2). The highest non-dissolved mass was expected as well. However, there was detected the highest percentage of non dissolved particulate matter in the living room. Fibres from carpets, textile and upholstered furniture represented the essential part of nondissolved from the total deposited mass (Figure 1).

**Figure 1.** Non-dissolved particles captured on the filter

460 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

in studied rooms are presented in Table1.

by filters by total deposited mass [47].

Total deposited mass [μg]

Room

the surface particle concentrations were determined by standard way.

Settled particulate matter sampling was carried out by passive methods during 28 days. The adjusted sampling method for ambient air was used for indoor environment. The aerosol particulates were captured into Petri dishes (8.5 cm diameter), installed at three height levels: on the floor, at height of 0.8 m from the floor and at height of 2.2 m from the floor. The settling of particles proceeded onto both by water filled Petri dishes (wet gravitational settling) and empty Petri dishes (dry gravitational settling) at each monitored level. The particle total mass was calculated by gravimetric method from the Petri dish mass increases;

Suspended particulate matter investigation was focused on total suspended particles (TSP) and thoracic fraction PM10. Investigation was carried out in the same rooms in the investigated flat building in the city of Košice. Measurement have included integral particles sampling onto a collection material (membrane filter Synpor 0.83 m pore size, 35 mm in diameter and PTFE filter for TSP and PM10, respectively) by sampling equipment VPS 2000 (Envitech, Trenčín) at the constant air flow of 600 litres/hour during a sampling period of approximately 24 hours. Because of minimization of humidity interference and volatile organic matters elimination, the filters were dried at a temperature of 105C for 8 h before sampling than equilibrated at a constant temperature and humidity (e.g. 20C and 50% RH) for 24 h before and after sampling. The particulate mass concentrations were determined by gravimetric method from the increase of filter weight (measured by analytical balance fy Mettler Toledo within 0.00001 g). The average concentrations of measured particulate matter

Settled particulate matter - surface concentration [μg.cm-2] 44.8 Total suspended particulates - mass concentration [μg.m-3] 84.7 PM10 - mass concentration [μg.m-3] 45.4 PM10 / TSP ratio 0.5

The surface concentrations of settled particulate matter measured in selected rooms were in the range 7.0 to 86.6 μg.cm-2 while the average surface concentrations for the rooms were calculated from 32.7 to 63.9 μg.cm-2 (Table 2). The percentage of non-dissolved portion of settled particulate matter was calculated by dividing of the non-dissolved mass separated

> Average surface concentration [μg.cm-2]

Kitchen 44.8 x 103 63.9 17.06 x 103 38.1 Living room 27.6 x 103 37.8 19.70 x 103 71.4 Working room 21.7 x 103 32.7 7.36 x 103 33.9 **Table 2.** Settled particulate matter and percentage of non-dissolved particles in total deposited mass

**Table 1.** The mean concentrations of settled and suspended particulate matter

Mean

Non-dissolved mass [μg]

Percentage of non-dissolved [%]

The results of indoor particle deposition monitoring considering the three high levels in all monitored rooms are summarized in Table 3. Besides the standard wet deposition, the dry deposition was included in the study in order to investigate the re-suspension processes. The surface concentrations of particles ranged from 21.0 to 86.6 μg.cm-2 by wet gravitational settling and from 7.0 to 39.5 μg.cm-2 by dry gravitational settling in all monitored rooms.


**Table 3.** Surface concentration of particulate matter

The highest surface concentrations of particulate matters were measured in the kitchen at all monitored levels. The surface concentration values were expected to be the highest in the kitchen because of the most intensive indoor particulate sources. The surface concentrations determined in the other rooms reached the comparable values.

The particles surface concentration was found to be decreased with the height of the room from the floor to the ceiling construction at wet gravitational settling in all monitored rooms

(Figure 2), as well as at dry gravitational settling (Figure 3). That means the lowest surface concentrations of particulates were measured at the height level of 2.2 m in all monitored rooms.

Investigation of Suspended and Settled Particulate Matter in Indoor Air 463

The proportion of particles (re-suspended) released into the air after sedimentation settling was calculated as a difference between surface concentrations at both wet and dry settling for each height level and all monitored rooms [48]. The particles portions in relation to the

The values of re-suspension particles portions ranged from 45.6 to 58.7% in monitored rooms. The results of particles re-suspension effect were not consistent with our expectations. None trend of particles release in relation to the height level was confirmed (Figure 4). The wide differences in particle re-suspension portions were achieved at monitored height levels in studied rooms: from 35.8 to 64 % on the floor and from 56.8 to 66.7 % at the height level of 2.2 m from the floor. The comparable portions for particles release was achieved only at the height level of 0.8 m from the floor (48.8, 45.0 and 45.7 %).The average values of re-suspended particles portion in all monitored rooms are

Room Re-suspended portion [%]

Kitchen 51.69 Living room 45.89 Working room 58.77

**Table 4.** The re-suspended portions of particulate matter in monitored rooms

height level in monitored rooms are illustrated in Figure 4.

**Figure 4.** The particles portions in relation to the height level

presented in Table 4.

**Figure 2.** Particles surface concentration versus height level at wet gravitational settling

**Figure 3.** Particles surface concentration versus height level at dry gravitational settling

Particles re-suspension effect was studied in real conditions without boundary conditions providing for any effect elimination. The particles release was expressed in percentage; the amount of particulates settled into water filled Petri dishes was represented by 100%.

The proportion of particles (re-suspended) released into the air after sedimentation settling was calculated as a difference between surface concentrations at both wet and dry settling for each height level and all monitored rooms [48]. The particles portions in relation to the height level in monitored rooms are illustrated in Figure 4.

**Figure 4.** The particles portions in relation to the height level

462 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

rooms.

(Figure 2), as well as at dry gravitational settling (Figure 3). That means the lowest surface concentrations of particulates were measured at the height level of 2.2 m in all monitored

**Figure 2.** Particles surface concentration versus height level at wet gravitational settling

**Figure 3.** Particles surface concentration versus height level at dry gravitational settling

Particles re-suspension effect was studied in real conditions without boundary conditions providing for any effect elimination. The particles release was expressed in percentage; the

amount of particulates settled into water filled Petri dishes was represented by 100%.

The values of re-suspension particles portions ranged from 45.6 to 58.7% in monitored rooms. The results of particles re-suspension effect were not consistent with our expectations. None trend of particles release in relation to the height level was confirmed (Figure 4). The wide differences in particle re-suspension portions were achieved at monitored height levels in studied rooms: from 35.8 to 64 % on the floor and from 56.8 to 66.7 % at the height level of 2.2 m from the floor. The comparable portions for particles release was achieved only at the height level of 0.8 m from the floor (48.8, 45.0 and 45.7 %).The average values of re-suspended particles portion in all monitored rooms are presented in Table 4.


**Table 4.** The re-suspended portions of particulate matter in monitored rooms

The non-expected conclusion has resulted from comparison of the average values of resuspension portions in monitored rooms. The highest portions of released particles were found out in the working room with a minimum operating mode (minimum people activity).

Investigation of Suspended and Settled Particulate Matter in Indoor Air 465

**Figure 5.** Settled particulate matter morphology

**Figure 6.** Settled particulate matter morphology

The mass concentrations of total suspended particulate matter (TSP) in studied rooms were detected in the range 59.028 to 114.583 μg.m-3; PM10 mass concentrations measured ranged from 31.94 to 55.56 μg.m3 (Table 5). Unlike settled particulate matter monitoring, the highest concentration of total suspended particles as well as PM10 fraction were measured in the living room.


**Table 5.** Suspended particulate matter concentration

The PM10 hygienic limit (50 μg.m-3) for indoor air in the Slovak Republic was exceeded in one measured room; the mean mass concentration detected was close to the limit. PM10 concentration values reached about half of TSP concentration values (PM10/TSP ratio 0.48 for the living room, 0.60 for the kitchen and 0.54 for the working room).

The similar mean concentration value of 63.3 μg m−3 monitored in 34 homes in Hong Kong has been reported in [25]. The lower indoor PM10 concentration levels were measured in Athens (mean values for all residences was 35.0 ± 10.7 g.m-3 during the warm period and 31.8 ± 7.8 g.m-3 during the cold period), presenting no exceedance above the 50 g.m-3 limit value [26]; whereas the authors in the study [27] referred much higher mean concentrations of 202 and 215 g.m-3 in poor Bangladeshi households. The very high PM10 levels were caused by using wood, dung and other biomass fuels for cooking.

## **4. The morphology of settled and suspended particulate matter**

The morphology of settled as well as suspended particulate matter was investigated by electron scanning microscopy (SEM) with equipment Jeol JSM-35CF (Japan) at various extensions ranging from 90 to 5500. The scanning electron microscopy (SEM) micrographs represent the morphology of selected particles. As shown in Figures 5 to 9, the particles of irregular shapes and various sizes were observed in the sample of settled particulate matter.

**Figure 5.** Settled particulate matter morphology

Room TSP

**Table 5.** Suspended particulate matter concentration

activity).

living room.

cooking.

matter.

The non-expected conclusion has resulted from comparison of the average values of resuspension portions in monitored rooms. The highest portions of released particles were found out in the working room with a minimum operating mode (minimum people

The mass concentrations of total suspended particulate matter (TSP) in studied rooms were detected in the range 59.028 to 114.583 μg.m-3; PM10 mass concentrations measured ranged from 31.94 to 55.56 μg.m3 (Table 5). Unlike settled particulate matter monitoring, the highest concentration of total suspended particles as well as PM10 fraction were measured in the

Kitchen 80.556 48.611 0.60

Living room 114.583 55.556 0.48

Working room 59.028 31.944 0.54

The PM10 hygienic limit (50 μg.m-3) for indoor air in the Slovak Republic was exceeded in one measured room; the mean mass concentration detected was close to the limit. PM10 concentration values reached about half of TSP concentration values (PM10/TSP ratio 0.48 for

The similar mean concentration value of 63.3 μg m−3 monitored in 34 homes in Hong Kong has been reported in [25]. The lower indoor PM10 concentration levels were measured in Athens (mean values for all residences was 35.0 ± 10.7 g.m-3 during the warm period and 31.8 ± 7.8 g.m-3 during the cold period), presenting no exceedance above the 50 g.m-3 limit value [26]; whereas the authors in the study [27] referred much higher mean concentrations of 202 and 215 g.m-3 in poor Bangladeshi households. The very high PM10 levels were caused by using wood, dung and other biomass fuels for

The morphology of settled as well as suspended particulate matter was investigated by electron scanning microscopy (SEM) with equipment Jeol JSM-35CF (Japan) at various extensions ranging from 90 to 5500. The scanning electron microscopy (SEM) micrographs represent the morphology of selected particles. As shown in Figures 5 to 9, the particles of irregular shapes and various sizes were observed in the sample of settled particulate

PM10 [μg.m-3]

PM10/TSP

[μg.m-3]

the living room, 0.60 for the kitchen and 0.54 for the working room).

**4. The morphology of settled and suspended particulate matter** 

**Figure 6.** Settled particulate matter morphology

Investigation of Suspended and Settled Particulate Matter in Indoor Air 467

The majority of particles are non-spherical in shape with strong division of the surface. The

Individual particles along with the aggregates of fine particles were observed in PM10 suspended particulate matter (Figure 9). The evaluation of SEM micrographs of the total suspended particulate samples showed that 80 - 90 % of the particles are smaller than 10 m. In case of some samples, the particle size distribution was even shifted in the range of particle size under 5 m. As referred by authors in the Chinese study [24], the analysis of the settled dusts collected in typical resident buildings showed that the volume percent for the

Seasonal variations and variations due to location were observed in both the morphological measurements and chemical analysis of settled dust collected inside the main foyers of three

**5. The chemical composition of settled and suspended particulate matter** 

The elemental EDX analyses were carried out on the micro-analytical system LINK AN 10 000 operating in secondary mode at a potential 25 kV. The energy-dispersion X-ray system provided preliminary information on the elemental composition of the samples. The EDX spectra were very similar for majority of collected particulate matter samples. Principal inorganic elements constituting the particles calcium, silicon, aluminium, potassium, iron, chlorine, magnesium as well as titan and manganese were confirmed. The EDX spectrum in Figure 10 represents the elemental chemical composition of the settled

fine particles (particle size < 10.5 μm) of the settled dusts ranged from 26 % - 38 %.

University buildings in Wolverhampton City Centre, U.K. [28].

occurrence of spherical as well as fibrous particles was not obvious.

**Figure 9.** PM10 particulate matter morphology

particulate matter sample.

**Figure 7.** Detail of various shapes of settled particulate matter

**Figure 8.** Detail of various shapes of settled particulate matter

The majority of particles are non-spherical in shape with strong division of the surface. The occurrence of spherical as well as fibrous particles was not obvious.

**Figure 9.** PM10 particulate matter morphology

466 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

**Figure 7.** Detail of various shapes of settled particulate matter

**Figure 8.** Detail of various shapes of settled particulate matter

Individual particles along with the aggregates of fine particles were observed in PM10 suspended particulate matter (Figure 9). The evaluation of SEM micrographs of the total suspended particulate samples showed that 80 - 90 % of the particles are smaller than 10 m. In case of some samples, the particle size distribution was even shifted in the range of particle size under 5 m. As referred by authors in the Chinese study [24], the analysis of the settled dusts collected in typical resident buildings showed that the volume percent for the fine particles (particle size < 10.5 μm) of the settled dusts ranged from 26 % - 38 %.

Seasonal variations and variations due to location were observed in both the morphological measurements and chemical analysis of settled dust collected inside the main foyers of three University buildings in Wolverhampton City Centre, U.K. [28].
