**2. Experimental set up for PM precipitation**

#### **2.1. About particulate matter in the indoor air environment**

Indoor particulate matter is a mixture of substances including carbon (soot) emitted by combustion sources, tiny liquid or solid particles in aerosols, fungal spores, pollen, and toxins present in bacteria (endotoxins). In many homes, most of the airborne particulate matter comes from the outside. However, some homes do have significant sources of indoor particulate matter that comes from various sources: cigarette smoking is the greatest single source of particulate matter in homes and buildings where people smoke; cooking: especially frying and sautéing; combustion appliances: for example, furnaces without a proper air filter; non-vented combustion appliances like gas stoves; wood-burning appliances like wood stoves and fireplaces: especially if the smoke leaks or *backdrafts* into the home; and mold growth [7]. buildings where people smoke; cooking: especially frying and sautéing; combustion appliances: for example, furnaces without a proper air filter; non-vented combustion appliances like gas stoves; wood-burning appliances like wood stoves and fireplaces: especially if the smoke leaks or *backdrafts*

sources, tiny liquid or solid particles in aerosols, fungal spores, pollen, and toxins present in bacteria (endotoxins). In many homes, most of the airborne particulate matter comes from the outside.

Since indoor air contains various types of particulate matter, improving air quality requires a combination of high performance filters and active treating devices such as electrostatic precipitators and atmospheric plasma devices [8, 9]. into the home; and mold growth [7]. Since indoor air contains various types of particulate matter, improving air quality requires a combination of high performance filters and active treating devices such as electrostatic precipitators

#### **2.2. Electrodes for particulate matter collection** and atmospheric plasma devices [8, 9].

incubate bacteria. So the other sterilization method is required for living microorganisms or

Finally, while sterilization devices for indoor air may be commonly used in medical facilities (hospitals, clinics, etc.), these devices are uncommon for use in homes and general office buildings. While these issues could be eliminated by natural air flow, this method is energy inefficient and many houses cannot use this method. Because we spend most of our time

From these points of view, there is a need for reliable devices for the home that can remove organic pollution and that can sterilize indoor air. Devices using atmospheric pressure plasma

This chapter deals with improving indoor air quality using atmospheric plasma treatment [6]. Discussed are the results of a series of experiments on particulate matter (PM) precipitation and removal, odor control targeting ammonia and sterilization of *E. coli.* While such experi‐ ments are often performed in a small experimental chamber, these experiments were carried

) shown in Fig. 1. These results reveal the performance

indoors, indoor air quality is an important factor for healthy and comfortable lives.

**Figure 1.** The experimental room for measuring indoor air quality improved by atmospheric plasma.

Indoor particulate matter is a mixture of substances including carbon (soot) emitted by combustion sources, tiny liquid or solid particles in aerosols, fungal spores, pollen, and toxins present in bacteria (endotoxins). In many homes, most of the airborne particulate matter comes from the outside. However, some homes do have significant sources of indoor particulate matter that comes from various sources: cigarette smoking is the greatest single source of particulate matter in homes and buildings where people smoke; cooking: especially frying and

**2. Experimental set up for PM precipitation**

**2.1. About particulate matter in the indoor air environment**

technologies, especially microplasmas, are very promising.

out in the relatively large space (23.4 m3

of commercially available air treatment devices.

virus.

472 Current Air Quality Issues

The reactor shown in Fig. 2 consisted of a corona discharge needle type electrode system, a ground electrode, and a mesh filter electrode for collecting particulate matter. The needle type electrode system shown in Fig. 2 consisted of 5 parallel wires to which 4 needle type electrodes were attached to each wire. The diameter of the electrode assembly was 55 mm. The ground electrode consisted of parallel wires positioned at a discharge gap of about 5mm from needle type electrodes. At the outlet, a mesh filter placed 5mm from grounded electrode captured particles. **2. 2 Electrodes for particulate matter collection**  The reactor shown in Fig. 2 consisted of a corona discharge needle type electrode system, a ground electrode, and a mesh filter electrode for collecting particulate matter. The needle type electrode system shown in Fig. 2 consisted of 5 parallel wires to which 4 needle type electrodes were attached to each wire. The diameter of the electrode assembly was 55 mm. The ground electrode consisted of parallel wires positioned at a discharge gap of about 5mm from needle type electrodes. At the outlet, a mesh filter placed 5mm from grounded electrode captured particles.

**Figure 2.** Schematic diagram of the needle electrodes and the reactor system with the mesh filters.

**Figure 3.** Mesh filter used for collecting dust. (x100)

Mesh filters like the one in Fig. 3 were used in this study. One side of the filters were coated by metal. The characteristics of the mesh filters are given in Table 1.


**Table 1.** Characteristic of mesh filters.

We used the large, experimental room in Fig. 1 to carry out our indoor air quality experiments using the reactor in Fig. 2. We measured particulate matter collection, and ammonia removal from the indoor air. The fan in the corner of the experimental room shown in Fig. 4 circulated indoor air at a flow rate of 4.6 m3 / min.

**Figure 4.** A reactor and a fan arrangement in the experimental room.

The reactor was placed 30 cm above the floor and 100 cm from fan. The gas flow through the reactor was about 112 L / min. The reactor was driven by a negative DC voltage of 5 kV.

To evaluate the collection of particulate matter, we took particle measurements at three locations #1, #2 and #3 in Fig. 4. We measured the number of particles using an optical particle counter (SHIMADZU, MODEL 3886). The diameter of the measured particles was 0.5 µm. During the measurement time of 2 hours, the relative humidity was 67% and the temperature was 23.7 C.

#### **2.3. Microplasma generation for indoor air treatment**

The microplasma electrode has been described in previous publications [6, 10]. In this study, the volume of the experimental room shown in Fig. 1 (23.4 m3 ) was much larger that the experimental chambers used in previous studies. So the microplasma electrode in Fig. 5 was enlarged corresponding to the area.

The microplasma electrodes consisted of a high voltage electrode and a grounded electrode separated by a discharge gap in the range 30 to 100 m. Both electrodes were coated with dielectric materials. When an AC voltage in the range from several hundred volts to 1 kV was

**Figure 5.** Microplasma electrodes utilized in this study.

Mesh filters like the one in Fig. 3 were used in this study. One side of the filters were coated

Aperture size [mm] 0.1 Wire diameter [mm] 0.06 Mesh count [mesh /inch] 150

We used the large, experimental room in Fig. 1 to carry out our indoor air quality experiments using the reactor in Fig. 2. We measured particulate matter collection, and ammonia removal from the indoor air. The fan in the corner of the experimental room shown in Fig. 4 circulated

The reactor was placed 30 cm above the floor and 100 cm from fan. The gas flow through the reactor was about 112 L / min. The reactor was driven by a negative DC voltage of 5 kV.

To evaluate the collection of particulate matter, we took particle measurements at three locations #1, #2 and #3 in Fig. 4. We measured the number of particles using an optical particle counter (SHIMADZU, MODEL 3886). The diameter of the measured particles was 0.5 µm. During the measurement time of 2 hours, the relative humidity was 67% and the temperature

The microplasma electrode has been described in previous publications [6, 10]. In this study,

experimental chambers used in previous studies. So the microplasma electrode in Fig. 5 was

The microplasma electrodes consisted of a high voltage electrode and a grounded electrode separated by a discharge gap in the range 30 to 100 m. Both electrodes were coated with dielectric materials. When an AC voltage in the range from several hundred volts to 1 kV was

) was much larger that the

by metal. The characteristics of the mesh filters are given in Table 1.

/ min.

**Figure 4.** A reactor and a fan arrangement in the experimental room.

**2.3. Microplasma generation for indoor air treatment**

enlarged corresponding to the area.

the volume of the experimental room shown in Fig. 1 (23.4 m3

**Table 1.** Characteristic of mesh filters.

474 Current Air Quality Issues

indoor air at a flow rate of 4.6 m3

was 23.7 C.

applied to the high voltage electrode, numerous streamers were generated between the electrodes as shown in fig. 6 [11].

**Figure 6.** Generation of micro streamers (a); cross section, (b) front view.

The basic characteristics of a microplasma are similar to that of a typical dielectric barrier discharge (DBD) that typically has a discharge gap of 1mm or more. However, the diameters of streamers in microplasmas were observed to be in the range 10-20 um, which is narrower than that of DBD streamers [11]. The numerous microplasma streamers generate various active species, such as radicals, ions, and ozone that enhance the chemical reactions in the gas phase describing the next section.
