Application of New Electrostatic and Ionic Air Purification Technologies in
Eliminating PM Pollution of Indoor Ambient Air
Xu Huoju
Summary: Research on PM pollution of public building, Propose that the electrostatic and ionic purification
technology can effectively control the PM pollution, Low power consumption, small changes, flexible
application.
Keyword: PM electrostatic purifier, Ionic purifier, Photocatalytic regeneration, Activated carbon, enclose the
public building
1. Introduction
Inhalation of airborne particulate matter (PM2.5/PM10) may cause adversary health effects, including lung
cancer, asthma, allergy, heart diseases, and death (Burge, 1990; Koskinen et al., 1995; Miller, 1992; and
Spengler et al., 1993） [1]. A statistical study with a large sample size involving 550,000 cases in 151 cities of
the United States was made by American Cancer Society (ACS) from 1995 to 2002 to find out the correlation
between PM2.5 and nitrate on one side and mortality of heart disease and lung cancer on the other side,
and the results show that air PM 2.5 pollution at the level of 25μg/m³ will reduce life expectancy by 1.5
years.[2] U.S Environmental Protection Agency (EPA) analyzed in 2012 thousands of researches on PM risk,
and concluded: It has been confirmed by scientific researches that inhalation of fine particle matters might
impose many health risks[3].
EPA offered in a 2011 document titled Benefits and Costs of the Clean Air Act 1990 - 2020the following table
of PM 2.5 and ozone's effects on health (Table 1). [4]
Table 1 Effects of PM2.5 and Ozone on Health by EPA
Avoid effects on health
Pollutant(s)
Year 2010
（for PM2.5 & Ozone only）
Year 2020
PM2.5 Adult Mortality
PM
160,000
230,000
Est. total people affected
2010-2020（NRDC）**
2,145,000
PM2.5 Infant Mortality
PM
230
280
2,805
Ozone Mortality
Ozone
4,300
7,100
62,700
Chronic Bronchitis
PM
54,000
75,000
709,500
Acute Bronchitis
PM
130,000
180,000
1,705,000
Acute Myocardial Infarction
PM
130,000
200,000
1,815,000
Asthma Exacerbation
PM
1,700,000
2,400,000
22,550,000
Hospital Admissions
PM, Ozone
86,000
135,000
1,215,500
Emergency Room Visits
PM, Ozone
86,000
120,000
1,133,000
Restricted Activity Days
PM, Ozone
84,000,000
110,000,000
1,067,000,000
School Loss Days
Ozone
3,200,000
5,400,000
47,300,000
Lost Work Days
PM
13,000,000
17,000,000
165,000,000
Table 1 shows a startling scene. The United States has better air quality than ours, however its old PM2.5
standard still cause it 2.145 million premature deaths, over 200 million lost school and work days, and an
economic loss of more than 1 trillion US dollars due to health issues.
*Xu Huoju, 1951, male, with university education, senior engineer, Guangdong Association of Cleanroom
Technology, Rm. 401, 137 Jexin Road, Guangzhou, Tel: 02084341486, Postal code: 510250,
E-mail:xuhuoju@vip.sina.com.cn
1
In Jan. 2013, a large haze pollution due to PM2.5 in the air happened in China, affecting over 1 million
square kilometers of land. One of the most affected was Beijing, where PM2.5 concentration detected was
at the level of 400μg/m3, and even up to as high as 1000μg/m3 in some areas, greatly exceeding the PM2.5
standard set by the United States and our country for Class 1 air quality (15/12μg/m3). It is normal for most
cities in China nowadays to have average PM2.5 level between 50 to 100μg/m3, and it will be almost
impossible to eradicate the problem in 20 years. From the Air Pollution Control Act in 1950s, Clean Air Act in
1960s, to the Clear Skies Act in the 21st century, the United States had spent over 50 years in environment
air treatment before bringing shining stars and blue skies back to the country. The fact that a man will live
2/3 of his life in indoor environment makes improving indoor air quality and reducing PM contamination a
technical approach that will cost relative small investment and entail less alternation, but will generate
health and economic benefits beyond calculation. PM contamination in public and residential indoor air is
now the trendiest topic in health, as well as a major concern in the nation's sustainable development.
By the end of 2006, every 3 of 10 households in the United States use domestic air purifiers [5] to prevent
indoor air pollution. The household electrical appliances market in China have witnessed a general sales
wave of air purifier this year. However the cleaners can only be used for air cleaning in domestic houses, not
applicable to large spaces in public buildings where central air conditioner are used. So how do public
buildings, including entertainment locations, hotels, restaurants, office buildings, shopping malls, bus and
railway stations, and hospitals, stand in respect of indoor PM contamination? Relevant researches and
guidance needed for its prevention are still lacking.
In view of the above, we conducted, under the leadership of Guangdong Association of Cleanroom
Technology, a survey on PM and formaldehyde contamination for public buildings in some regions in
Guangdong and Macau, as wells as PM contaminant removal experiments in a non-closed test chamber of
60m³. This paper is to give a report on the survey and experiments.
2. Survey on PM contamination of public ambient air
1）Indoor contaminant sources
Indoor contaminant, including particulate matter, formaldehyde, TVOC, and micro-organism, may have
indoor as well as outdoor sources. In public buildings where central air conditioning system is used and are
separated from outdoor air to an extent, it will be easier to prevent PM contaminant in atmosphere air from
affecting indoor air quality, but there still may exist other sources, including chemical contamination,
biological contamination, and cigarette smoke contamination deriving from indoor decoration and activities.
Figure 1: Some important indoor air pollution. (Data from Environmental Protection Agency)
2
As shown in Figure 1, there are many indoor air pollution sources. Closed doors and windows will lead to
higher contaminant concentration level, and adversary health effects on inhabitants. By opening windows, it
may reduce the sources and indoor contamination, but at the same time will expose indoor air quality to
particulates from outdoor air. Table 2 show standards of China and World Health Organization on indoor air
quality. Engineers and technicians shall combine this standard or guideline with the actual situation in which
they work when they make comprehensive analysis and design for air quality improvement in public
buildings where multiple contaminant sources exist, including PM2.5. Specific purification objective, air
change rate, fresh air flow, and energy efficiency are design parameters that deserve particular attention.
China’s and WTO’s Standards for Indoor Air Quality
Air pollutants
WTO Guidance
GBT 18883-2002
PM2.5
10g/μg/m3
150μg/m3
PM10
20μg/m3
0.1 mg/m3
Formaldehyde
0.1 mg/m3
0.16 mg/m3
Ozone
17mg/m3
0.11 mg/m3
Benzene
7 mg/m3
10 mg/m3
Carbon monoxide
0.1
0.1
Carbon dioxide
1.2 ng/m3
1.0 ng/m3
Benzopyrene
17μg/m3
0.2 mg/m3
Nitrogen dioxide
40μg/m3
240μg/m3
Germs
700cfu/m3
2500 cfu/m3
So we conduct a survey on indoor and outdoor contamination of PM and formaldehyde for some public
buildings in Guangzhou, Foshan, Zhuhai, and Macau, intending to derive from our survey on current
situations some guidelines which can be used in design of indoor air cleaning plans for public buildings.
2）Testing instruments
Home-made DT 9881 particle counter and formaldehyde meter; their parameters are as followed:
Channels: 0.3, 0.5, 1.0, 2.5, 5.0, 10μm
Flow rate: 0.1ft3(2.83L/min), controllable with built-in sensor
Counting functions: Accumulated value, difference value, concentration value
Tolerance: 5%, 2000000 particles/ft3
HCHO testing range: 0.01 ~ 5.00ppm; testing precision: ±5%± 0.01ppm
Homemade HPC-3000A PM2.5/PM10 testing meter range: 0-999μg/m³
3) Testing methods
Concentrations of PM2.5 and PM2.5 (at μg level) and that of formaldehyde inside and outside the public
building in question were measured. Testing instruments were held by standing inspectors.
For some public locations, 6-channel particle counters were used to verify the corresponding relationship
between high μg concentration and high particle number concentration of PM2.5.
For cleanroom operation, PM and formaldehyde concentrations were tested with and without air purifier
running, in order to determine whether there is PM and/or formaldehyde contaminant in the operation
room.
Cigarette smoke tests were made in the PM test chamber simulating residential space at Guangdong
Association of Cleanroom Technology to measure PM2.5 contamination due to indoor smoke.
3
4）Results
Table 1-3 show our results in testing PM and formaldehyde concentrations at some public places in
Guangzhou, Foshan, Zhuhai, and Macau; and Table 4 shows the data for the same period from National PM
2.5 Monitoring Network. Results for the tests of PM2.5 contamination from cigarette smoking can be found
in Figure 2.
Table 3 PM in Air at Entertainment locations in Macau
Location
Corridor, Holiday Inn Macau
Lobby, Holiday Inn Macau
Guest room, Holiday Inn Macau
Lobby, Conrad Hotel Macau
Corridor, Conrad Hotel Macau
Guest room, Conrad Hotel Macau
Corridor, Sheraton Macau Hotel,
Guest room, Sheraton Macau Hotel,
Inside, Sands Macau
Outside, Sands Macau
Smoke area, City of Dreams Macau
Corridor, City of Dreams Macau
Outside, City of Dreams Macau
Lobby, Venetian Macau
Entertainment place, Venetian Macau
PM2.5
(μg/m³)
PM10
(μg/m³)
Time
29
7
22
2
6
4
5
8
1
14
38
75
15
13
9
59
15
43
4
13
11
11
16
3
35
76
160
32
34
21
2013-8-21
2013-8-21
2013-8-21
2013-8-20
2013-8-20
2013-8-20
2013-8-20
2013-8-19
2013-8-19
2013-8-19
2013-8-19
2013-8-19
2013-8-19
2013-8-19
2013-8-18
Table 4 Air PM and formaldehyde at Public Places of Guangzhou
Location
Outside, Canton Fair Complex
Inside Hall B, Canton Fair Complex
Platform, Guangzhou South Railway Station
Inside train, Guangzhou South Railway Station
Lobby, Asia International Hotel
Crowne Plaza Hotel Guangzhou
Inside Guangzhou Metro train
Outdoor square, Guangzhou Railway Station
Ticket Office, Guangzhou Railway Station
Outside, Guangzhou Orthopaedic Hospital
Lobby of Building A, Guangzhou Orthopaedic Hospital
Lobby of Building B, Guangzhou Orthopaedic Hospital
Class 100 operation room (cleaner on), Guangzhou
Orthopaedic Hospital
Class 1000 operation room (cleaner on)
Class 10000 operation room (cleaner on)
Class 100 operation room (cleaner off)
Class 1000 operation room (cleaner off)
4
PM2.5
(μg/m³)
PM10
(μg/m³)
Formaldehyde
Time
96
34
140
41
10
12
13
31
33
34
23
24
0
196
66
278
88
20
25
26
66
66
69
46
50
0
0.186
0
0
0
0
0
0.149
0.089
0
2013-8-21
2013-8-21
2013-8-21
2013-8-21
2013-8-24
2013-8-24
2013-8-24
2013-8-24
2013-8-24
2013-8-24
2013-8-24
2013-8-24
2013-8-24
0
0
7
6
0
0
14
12
0
0
0.030
0.007
2013-8-24
2013-8-24
2013-8-24
2013-8-24
（mg/ m³)
Class 10000 operation room (cleaner off)
Lobby, Guangdong Women And Children Hospital
Outside, Guangdong Women And Children Hospital
5
67
83
10
133
166
0
0.022
0
2013-8-24
2013-8-22
2013-8-22
Table 5 Air PM and formaldehyde at Public Places of Foshan and Zhuhai
Location
Lobby, Foshan Yingbai Hotel
Guest room corridor
Outdoor, Foshan
Ticket Office, Hengdian Movieland
Cinema Hall No. 4
Cinema Hall No. 5
Cinema Hall No. 2, Times Movie Theater
Ticket Office
Outdoor, Chancheng Central Hospital
Outpatient Hall
Treatment room
Hospital office
Corridor
Maintenance office
Outside, Gongbei Port of Entry in Zhuhai
Waiting lounge, Gongbei High-speed Railway Station
Table 6
PM2.5
(μg/m³)
PM10
(μg/m³)
Formaldehyde
31
17
95
28
18
12
5
9
20
17
16
24
29
32
351
63
64
36
187
59
40
24
11
20
44
40
39
49
61
66
726
124
0
时间
（mg/ m³)
0．067
0
0．089
0．044
0．030
0
0．081
0
0
0
0．060
0．090
0．299
0
0
2013-8-19
2013-8-19
2013-8-19
2013-8-19
2013-8-19
2013-8-19
2013-8-19
2013-8-19
2013-8-19
2013-8-19
2013-8-19
2013-8-19
2013-8-19
2013-8-19
2013-8-21
2013-8-21
PM2.5 Particle Number and Mass Concentrations
Location
PM2.5μg/
m³
Outside the Outpatient Hall, Guangdong Women And Children Hospital
Inside the Outpatient Hall, Guangdong Women And Children Hospital
Outside, Times Movie Theater in Foshan
Inside, Times Movie Theater in Foshan
Outside, Foshan Hospital
Outpatient Hall, Foshan Hospital
Class 100 operation room (cleaner on), Guangzhou Orthopaedic Hospital
Class 100 operation room (cleaner off), Guangzhou Orthopaedic Hospital
Class 1000 operation room (cleaner on), Guangzhou Orthopaedic Hospital
Class 1000 operation room (cleaner off), Guangzhou Orthopaedic Hospital
Class 100000 operation room (cleaner on), Guangzhou Orthopaedic Hospital
Class 100000 operation room (cleaner off), Guangzhou Orthopaedic Hospital
83
67
95
9
20
17
0
7
0
5
0
6
5
≥ 0.3 ≤ 2.5 μ m
particles/m³
360757528
338481463
377195679
52676072
97465419
94341721
4942
53585047
2227430
34719315
4454507
49556611
Table 7 PM 2.5 values of the cities tested and Beijing as provided by the national PM monitoring Network
for the same day of the test（μg/m³）
Time
Guangzhou
Foshan
Zhuhai
Beijing
2013-8-19
2013-8-20
2013-8-21
2013-8-22
2013-8-24
50
99
78
88
40
58
88
84
81
47
35
71
104
75
26
44
107
130
146
53
Figure 2 Effects of cigarette smoking on indoor PM2.5 pollution
Excellent
Good
Medium pollution
Slight pollution
Heavy pollution
Severe Pollution
Initial indoor level
After 2 cigarettes
After 4 cigarettes
After a person smoke 2 cigarettes
Indoor Air PM2.5 Concentration (μg/m3)
PM2.5 level in the space of a 60m2 room
Time (seconds)
5）Analysis of the test results
An analysis of the PM and formaldehyde contamination testing results in Table 1 and 3 shows that:
1) According to GB3095-2012, annual PM2.5/PM10 limit for Class 1 ambient air quality is 15/40μg/m³, and
24-hour average is 35/50μg/m³; 24-hour averages of Guangzhou, Foshan, Zhuhai, and Beijing as provided by
the PM2.5 monitoring network nearly all fail the standard.PM2.5 on Aug. 20, 2013: Guangzhou 99μg/m³,
Foshan 88μg/m³, Zhuhai 71μg/m³, and Beijing107μg/m³. Such failure in meeting PM standard for ambient
air quality will affect indoor air quality both in closed and non-closed spaces. The test PM2.5/PM10 value at
the waiting lounge of Gongbei High-speed Train Station in Zhuhai was 63/124μg/m³, and the corresponding
outdoor value was 351/726μg/m³, which was far above the standard limit.
2) The test result show that in closed spaces inside a public building where central air conditioner is applied
the 24-hour average PM2.5 level is 35μg/m³, which is within the Class 1 ambient air quality limit, but fails to
meet the annual limit of 15μg/m³; what is more, there is still risk of excessive chemical pollution, including
that of formaldehyde. Formaldehyde level in the air was found beyond the limit at two hospitals and one
hotel in Foshan and Guangzhou.
3) Hilton's high-end Conrad Hotel in Macau , and Sands Macau recorded satisfying PM2.5 values, reading
only 1~8μg/m³; the author even found that the particle number concentration in their guest rooms reach
that of a Class 100000 clean room.
It suggests that risk of PM contamination can be eliminated by a proper central air conditioning system.
4) There is no PM contamination in a clean room equipped with three-step filtration system. PM2.5 and
6
PM10 values of three different class operation theaters at Guangzhou Orthopaedic Hospital all recorded 0
when cleaner were on, and all meet Class 1 ambient air quality standard of the country when cleaners were
off.
5) PM contaminant may have both indoor and outdoor sources. Figure 2 PM measurements done in test
chamber in which someone is smoking or lighting cigarettes give startling results. The previous good indoor
air quality (average PM2.5 at 10μg/m³) worsening quickly; the average PM2.5 went beyond 100μg/m³ when
the second cigarette was lighted, and reached 308μg/m³ after the fourth one; however, when one person
was smoking in the chamber, the PM value reached as high as 1000μg/m³, which is over 60 times that of
annual PM2.5 limit of 15μg/m³ for the country Class 1 ambient air quality standard. Our tests in other rooms
where people smoked found that when there was cigarette smoking, the PM2.5 level of the room could
easily exceeded 100μg/m³.
6) There is a link between PM2.5 mass concentration and particle number concentration of particles ≥0.3
μm≤2.5μm; the high the mass concentration, the higher the particle number concentration (Table 6).
3. Cleaning technologies for ambient air PM contamination control in public buildings
There are three basic ways to reduce PM contaminant in indoor air: 1) source control, 2) ventilation, and 3)
air purification.
1) Source control
Remove sources of specific contaminants, or reduce their emission. This is usually the most effective way in
reduce contaminants. For PM contaminant coming from outdoor air, enclosed space with central air
conditioning system is an effective way of control.
2) Ventilation
In most cases, the best way to address risks of biological or chemical pollution is to control and eliminate
contaminant sources, and at the same time introduce fresh outdoor air by keeping good ventilation. But the
approach of ventilation may be limited by weather conditions or polluted outdoor air.
3) Air purification
Air-cleaning devices will come to help when pollution of ambient air makes ventilation impossible. Air filters
and other air-cleaning devices are designed to remove specific pollutants in indoor air.
Commonly used air-cleaning device for central air conditioning system usually adopt one or more of the
following air purification technologies:
1) Filtration and electrostatic adsorption technologies: particle filter (primary efficiency filters for 5
micrometer particles, medium efficiency filters for 1~2 micrometer particles, and high efficiency filters for
0.1~0.5 micrometer particles ) ; F9 filters have a removal rate of over 95% for 1~3μm particles and can be
used to treat PM2.5/PM10 pollution. But F9 filters' air resistance of 100~200pa make it impossible for them
to be used in ordinary public buildings without purification. 2) Ion purification: aggregation and deposition
of plasma or polarized ions of high concentration are used to remove PM contaminants. 3) Activated carbon
absorption, photocatalytic oxidation, and other technologies for chemical pollution control. 3) Disinfection
technologies: ultraviolet light, ions, and photocatalysis can be used to restrain or kill various kinds of
microorganisms, including germs, viruses, molds, and dust mite. 4) Combined purification technologies:
Technologies that combined the use of filtration, electrostatic adsorption, odor removal, photocatalysis with
titanium dioxide, ultraviolet light, and ions.
There are big differences between technologies for purification of public ambient air and those for industrial
use (see Table 5). And that is why people in industrial purification field, from authoritative technical experts
to ordinary technicians, remained silence when the haze swept over 1 million square kilometers of land in
the country. In contrast to this, it was people in public opinion area and consumers' associations among
others who took an active role and offered many advices.
7
Table 7 Difference of technologies of industrial purification and public ambient air cleaning
Characteristics
and
technical requirements
Normal industrial purification
Public ambient air cleaning
Air changes
20~500
2~8
Air flow direction
Controllable
Not Controllable
Air flow design
Supply at upper side and
return at lower side
Not applicable
Positive pressure
Air pressure gradient control
Not applicable
Purification facilities space
Yes
No
Comprehensive
electric
power for purification
50~500W/m²
5~20W/ m²
Stories and
building
High buildings, easy for
installation of purification
device
Low in height In most places, with
limited space.
Enclosure of the building
Good
Bad
Noise
≤65dB(A)
45~55 dB(A)
Maintenance and change
of filters
Professional service
Difficult
height
of
Traditional air purification technologies used in industrial area, biological safety, hospital, and
pharmaceutical industry usually apply multi-step filtration, especially high performance filters at room
terminals, to achieve purification of air. Either from the points of view of investment, power consumption,
and resistance or from facility space required and noise, a three-step filtration approach will be impractical
for PM contamination treatment in ordinary public buildings where multi-step filtration system is not in
place. What is suitable for treatment of PM pollution in public buildings are electrostatic and ion purification
technologies that require no plant room, nor major alternation to existing air conditioning systems, and are
low in power consumption and resistance.
4) Electrostatic Purifier for duct
An electrostatic absorption air purifier (Figure 3) has an ionizing part and a collection plate part, both of
which use external power. An electrostatic absorption air purifier will suck indoor air into its ionizing part, in
which particles are charged. When the charged particles move through the collector, them will be collected
to an array of collection plates that are oppositely charged. To keep good performance of the air purifier, the
collection plates shall be regularly cleaned. Due to electrostatic power, the particles will be firmed attached
to the collection plates and will not peel off even when there is power interruption. Traditional manual
cleaning may not thoroughly clean the plates, while ultrasonic cleaning may do the job. Electrostatic
absorption air purifier can achieve high dust removal rates, which may vary according to designs of different
manufacturers.
National Center of Quality Supervision and Inspection and Testing for Air Conditioning Equipment once
tested the performance of an electrostatic absorption air purifier made by a domestic producer, and the
results show that its removal rate for particles ≥0.5μm is over 93%. Electrostatic air purifiers can effectively
remove and collect airborne particles and smoke pollutants; when airflow rate is low, its initial ASHRAE
dust-spot efficiency can be as high as 98%. U.S. EPA takes this as the highest efficiency of an electrostatic air
8
purifier. Electrostatic air purifiers have high initial air purification efficiency. But as particles accumulate on
the collection plates, or when airflow rate increase or become uneven, its efficiency will decline.
The high voltage required for an electrostatic air purifier to produce the electric field will result in ozone,
which may be an intended product of the designer or a byproduct. When the plates are collecting particles,
there will be cracking noise as one may hear from a mosquito zapper at work.
Figure 3 Electrostatic absorption air purifier
Latest electrostatic air purifiers can eliminated the ozone produced by certain technical measures.
Figure 4 shows an experiment of 6-channel particle counting and PM2.5 concentration reduction by
Guangdong Association of Cleanroom Technology using an electrostatic air purifier produced by a U.S
manufacturer. We can see that the results are remarkable: in merely 10 minutes, particles of 0.3~10μm were
nearly 100% removed, and PM2.5 concentration dropped from the initial 20μg/m³ to 0μg/m³, The tests
made on an electrostatic air purifier of the same type for its efficiency on particles of different equivalents
size by National Center of Quality Supervision and Inspection and Testing for Air Conditioning Equipment
shows that it has an efficiency higher than 96% for particles ≥0.5μm (Table 8).
9
In a typical enclosed room of 60m3, air change rate at 8 per hour,
Total purification effect on PM in the Air (%)
Run a highly efficient electrostatic purifier made by US
manufacturer
Outdoor PM2.5 level: 24μg/m3
Initial indoor PM2.5 level: 20μg/m3
Indoor PM2.5 level in 10 minutes: 0μg/m3
Time (minutes)
Figure 4 Performance test on U.S F9 electrostatic air purifier
National Center of Quality Supervision and Inspection and Testing for Air Conditioning Equipment
Inspection Report
Report No.: 2013ac31-1
Page 2 of 4
1. Particle efficiency
The respective particle efficiencies of the electrostatic purifier at 500m3/h, 1000m3/h, 3000m3/h are listed in
Table 1
Table 1 Electrostatic Purifier’s Efficiency on Particles of Different Sizes
Particle efficiency (%)
Airflow rate(m3/h)
500
≥0.3μm
97.1
≥0.5μm
97.8
≥1.0μm
98.4
1000
95.6
96.6
97.8
3000
80.3
89.2
96.1
Since the combined resistance of F9 electrostatic air purifier and F4 electret filter at 1000m³/h flow rate is
only about 25pa, which makes it possible for it to be used with existing fan coil units without changes to the
units. (Table 9)
Table 2 Table 1 Electrostatic Purifier’s Resistance at Different Airflow Rates
Airflow rate(m3/h)
850
1700
2550
3400
4250
Resistance (Pa)
17.8
48.9
92.3
144.5
210.3
6) Ionic air purification
Ionic air purifiers are generally welcomed and were increasingly used in various settings to remove dust,
10
VOCs, airborne allergen, and micro-organisms in the air. Although the performance of commercial ionic air
purifiers are still open to discussion (both in and against it), available researches show that devices of high
output power have rather high efficiency in removing particles, killing germs, and eliminating odors and
VOCs.
Air ionization is a physical chemical phenomenon commonly found in the nature world. Ionization is a
process, or rather the result of the process; neutral atoms or molecules obtain positive or negative charge
through the ionization process. When an atom absorbs energy and exceeds the threshold of ionization
energy, it will release free electrons and positive ions, and this is called ionization. Small ions and ion groups
have numerous chances to bump and react with impurities and gases in the air to produce chemical
reactions or to aggregate small particles into large aerosol particles, which will make particles more easily be
captured by high or medium efficiency filters, or cause them to precipitate under the influence of gravity. In
this way VOCs, and dusts in the air will be removed and the air cleaned. At the same time, micro-organisms,
being surrounded by hydroxyl ions, die when their DNA or RNA is destroyed as the hydrogen atoms inside
them are combined with the ions and turned into water.
Low temperature ionic air purifiers (or Ionizers, of single polar or bipolar, Figure 5) dissipate charged ions
into the air by changing frequency, voltage, and flow. This makes them similar to electrostatic air purifier, but
ionizers do not have collection plates. Ionizers usually apply corona discharge or ultraviolet light to generate
ions. Ions will charge dust particles and aggregate fine airborne particles of about 0.3 micrometer into larges
one over 2 micrometers, which will greatly increase primary or medium efficiency filters' efficiency in
removing particles of small size. Studies and researches show that hospital operating theaters equipped with
2-step filtration system and nonthermal plasma air cleaning device can achieve air cleanliness up to Class
10000 or even Class 1000 clean room level. Dust particles that are charged will attach themselves to nearby
surface, including that of walls, floor, or to other particles to form a large one before precipitate onto room
surface. Ionic air purifiers, depending on what kind of ionizing approach they adopt, may produce ozone
problems as electrostatic air purifiers do, or have the ability to eliminate ozone.
Figure 5 Nonthermal plasma air purifier with air outlets
One type of high concentration ionic air purifier produced by a U.S company can release in one second over
4.5 trillion negative ions or plasma, giving it excellent ability in removal of PM and smoke pollution in the air.
Ionic air purifiers are of the type of concentration oriented, or active air purifiers as someone calls them.
Active air purifiers means the device will search on its own and eliminate pollution, leaving no blind spot.
Passive air purifiers are those into which air must be sucked in and treated before being discharged from the
11
Total purification effect on PM in the Air (%)
outlet as fresh air. But for air near a pollution source, say a cigarette smoking point, even the passive cleaner
is placed at a distance of 2 meter to the source point, there will be no reduction of smoke within 1 meter
around the smoke, and any people close to him will be a victim of second hand smoke.
Ionic air purifiers are effective in reduce Pm2.5 and smoke in a room; see Figures 6 and 7.
In a typical enclosed room of 60m3, run 2 NS100A purifiers
Outdoor PM2.5 level: 34μg/m3
Initial indoor PM2.5 level: 24μg/m3
Indoor PM2.5 level in 1 hour: 1μg/m3
Time (minutes)
Figure 6 Particle removal rate of U.S NS1000A plasma air purifier with air outlets
Initial indoor PM2.5 level
PM2.5 level with 2 cigarettes burning and 2 NS1000A running
Indoor PM2.5 level (μg/m³)
PM2.5 level in a 60m3 chamber simulating residence house
End of cigarette burning
Time (minutes)
Figure 7 Smoke removal rate of NS1000A plasma air purifier with air outlets
Most of the users of ionic air purifiers reported that air in the room were fresher, and smell of cigarette
smoke nearly all gone. Even smokers themselves reported that the smoke was reduced.
The tests as shown above confirms their report: in 14 minutes high level of smoke concentration drop from
160μg/m³ when a cigarette was lighted to 10μg/m³. For PM pollution the sources of which are mainly
smoking rooms inside public buildings, this kind of active cleaners enjoy irreplaceable technical advantages
due to their effective removal of smoke without entailing modification of air conditioning system.
Ionic air purifiers have the highest energy efficiency in all kinds of air cleaning devices; 1W power
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consumption can achieve a clean air delivery rate of 187m³/h. This makes them a perfect choice for PM
pollution treatment in public buildings where existing air conditioning systems are difficult to change (Table
10).
National Center of Quality Supervision and Inspection and Testing for Air Conditioning Equipment
Inspection Report
Report No.: 2013AC40
1. Test standard
GB/T18801-2008 Air Purifier
2. Test results
1) Purification effect on particles
Results of purification effect on particles are shown in Table 1
Page 2 of 4
Table 1 Results of Purification Effect on Particles
Test item
Resulting value
Initial PM level (particle/L)
1770432
PM level in 20 minutes (particle/L)
460943
Purified airflow rate
(m3/h)
125.46
Measured power (W)
Purification efficiency
0.67
[m3/(h-W)]
187.25
Class decision
A
Class A: η≥2.00
Class B: 1.50≤η＜2.00
Class standard
Class C: 1.00≤η＜1.50
Class D: 0.50≤η＜1.00
Negative ions, health preserving vitamin in the air as someone calls them, has influence on health. In forest,
negative ions have density as high as 1500~20000 ions/cm³, but in a closed building, the number drops to as
low as 100~300 ions/cm³. Application of ionic air purification technology in a room can not only reduce PM
pollution, but also increase negative ion density to 10000~20000 ions/cm³.
Medical evidences show that negative ions result in (1) improved sleep; negative ions can refresh and excite
one, increase work efficiency, improve sleep quality, and are effective in pain soothing.
(2) more reactive oxygen species; oxygen ions can effectively activate oxygen molecules in the air, making
them more easily to be absorbed by human body and prevent illness related to air conditioning. (3)
improved lung health; with the help of oxygen carrying ions, the lung may inhale 20% more oxygen, and
exhale 15% more carbon dioxide. (4) Better metabolism; ions can activate multiple enzymes in the body to
promote metabolism. (5) Increased body resistance to illness; ions can improve body's reaction ability, make
the reticulo-endothelial system more active, and enhance body immunity. (6) Germ killing. (7) Fresh air, free
of dust and smoke; ions with negative charge will neutralize airborne smoke and dust particles with positive
charge, making them precipitate on their own. (8) Protection; neutralize high voltage static electricity of TV
sets and computers and form before them a protective layer of ions, which can effectively reduce harms of
high voltage static electricity from TV sets or computers on human eyes, while at the same time also protect
TV sets and computers from dust.
University of Cincinnati once made an experiment to study the protection provided by ionized air against
hazardous respiratory viruses. The results show that when mask is used, negative ions reduce the number of
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hazardous viruses on the other side of the mask is reduced by a factor of 45~450 (Table 3).
Table 3 Test results of negative ions' ability in killing highly hazardous virus
NS 1000A’s efficiency on killing microorganism
Pathogenic
Microorganism 50%
Infection Test Chamber Number of hazardous microorganism
Hazardous
type
Dosage
Aerosol
inhaled in 1 hour
Microorganism
(ID50%)
Microorganism 30L/hour
(inhalation)
Level (M3)
No
Surgical mask Surgical mask
protection
+ NS1000A
2
Venezuelan equine Virus
10-100
10
180
45
1
2
encephalitis)
10
1800
450
10
Coxsachie virus A21 Virus
18
102
10
Influenza A
Influenza A2-MAX
Bacillus anthracis
Virus
Virus
Bacterium
80
790
8000-15000
2
180
450
1
1800
450
10
x102
350
90
2
102
1800
450
10
2X102
3600
900
20
102
18000
4500
100
4X102
72000
18000
400
102
180000
45000
1000
Remarks: Red background indicates that the number of hazardous microorganism inhaled exceed the 50% infection dosage;
while the green background indicates that the number is far below the 50% infection dosage.
7) Activated carbon air purification technology
Closed doors and windows help in one hand prevent outside PM contaminants from coming in, but one the
other hand may contribute to indoor gaseous pollution as shown in Figure 1. Indoor air pollutants in Figure
1 include formaldehyde, benzene, xylene, chloroform, tetrachloroethylene, TCOC, particles matters such as
asbesto, dust, and other health affecting physical or chemical pollutants. In places of high foot traffic, there
is also pollution arising from airborne microorganisms and droplets that are associated with respiratory
diseases.
For this kind of gaseous pollution, sorbents, including activated carbon, are usually used to absorb pollutants
and clean them from the air. All of the above mentioned filters are designed for one or at best a limited
number of specific gaseous pollutants, they are of no avail in reducing pollution caused by other sources. No
single gas-phase air filter can eliminate all gaseous pollutants commonly found in a building. In contrast to
particle air filters, gas-phase filters are less commonly used in public buildings. One of the reasons is that the
working capacity of this kind of absorption filter can be easily used up, and regular change or cleaning is
needed.
There are various gas-phase filters to choose from, but as there exists no test standards, it will be difficult to
evaluate, or to compare the effectiveness of the sorbent filters installed.
Gas-phase air filters depend on physical or chemical ways to remove gases or odors. This kind of filters are
usually used to remove one or more low concentration gaseous pollutants in the airflow after the air is
treated with mechanical filters. But none of them can remove all gaseous pollutants.
Gas-phase air filters with sorbent can be installed in existing HVAC system, usually at the downstream of a
particle air filter. Air filters reduce the number of particles which may reach sorbent, and the sorbent in turn
absorbs vapor coming out of the liquid drops collected by the particle filters.
Some gas-phase filters may remove, or at least temporary remove, part of the gaseous pollutants in the air.
Although some gas-phase air filters, depending on their design, use, and maintenance, may effective clean
specific pollutants in indoor air, but none of them can sufficiently remove all gaseous pollutants in a typical
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room. For example, physical or chemical absorption will be ineffective in capture carbon monoxide. In
addition, a typical cleaning system for gaseous pollutants can operate effective for a limited period of time
before its sorbent be replaced. It gives rise to concern that when sorbent of the filters becomes saturated,
previously captured pollutants may be release again into the air. [6] Service life of gas-phase air filters may
vary by concentration of and exposure to indoor pollutants. If timely changes are not made, it may happen
that pollutants reenter the room after penetrating filtering layers imbued with sorbent. Therefore it can be
concluded that this kind of device has only limited effect on odor removal.
Gaseous pollutants used in all tests conducted on the efficiency of activated carbon in removing them are of
high concentration, and there is no evidence yet on activated carbon's performance in treating chemicals
which are usually found in indoor air at low concentration (at ppt level) . In an experiment made by US
Environmental Protection Agency, three activated carbon samples are used to determine the adsorption
isotherms of three Volatile Organic Compounds (VOC) at the concentration level of 100ppb~200ppb. In
estimation of thickness of filtering layer that is needed for compounds removal, it has been taken as givens
that concentration of compounds is 150 ppb in the air and 50 ppb at the outlet, airflow rate is 100 cfm, and
section area of the filter is 2'X2'. The results suggested that chemical compounds in question can quickly
penetrate a 6-inch carbon filter that is designed for odor control. [7]
In recent years, there emerges in the United States a kind of automatic regeneration gas phase air purifier
for ducts that combines activated carbon and photoactive substances such as titanium dioxide. This kind of
purifier consists of two parts: 1) A matrix of activated carbon mixed with certain portion of titanium dioxide,
which is used to absorb chemical pollutants; 2) UVC photocatalytic device, which is used to turn the
chemical pollutants absorbed by activated carbon into harmless water and CO2.
Figure 7 Photocatalytic regeneration activated carbon air purifier
A photocatalytic auto regeneration activated carbon air purifier can be installed in air ducts (Figure 8) to
capture with its activated carbon formaldehyde, TVOC and other gaseous pollutants in the return wind that
flows through the purifier, and make them harmless. This kind of purifiers eliminates the need to change
activated carbon because the carbon can be automatically regenerated and keeps the absorption
performance, so it has a technical advantage over traditional filters available in the market.
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Figure 8 A photocatalytic regeneration activated carbon air purifier installed in air duct
Guangdong Detection Center of Microbiology's test on this kind of purifier shows that after a run of 24 hours,
it eliminated over 95% of high concentration TVOC and benzene, and over 62% of high concentration
formaldehyde.
Analysis and Test Results
Test value (mg/m3)
Item
Reduction under
test conditions (%)
Test methods
Sample
concentration at 0
hour
Sample
concentration at 24
hour
Benzene
2.67
0.127
95.2
QB/T 2761-2006
Formaldehyde
0.952
0.358
62.4
QB/T 2761-2006
TVOC
14.4
0.614
95.7
QB/T 2761-2006
Conclusion
Given the fact that there is serious PM pollution of ambient air in the country, enclosed public buildings with
central conditioning systems are subject to PM pollution, gaseous pollution of formaldehyde and others, and
biological pollution, with both indoor and outdoor sources.
Various types of air purification technologies are needed to control pollution and protect people's health.
Newly developed electrostatic air purification, ionic air purification, and medium efficiency filtration are
effective ones with which to improve indoor air quality in public buildings.
References:
[1] http://www.epa.gov/pm/2012/decfshealth.pdf
[2] LONG-TERM HEALTH EFFECTSOF PM2.5: Air resources Board California Environmental Protection Agency
2002
[3] Quantitative Health Risk Assessment for Particulate Matter US Environmental Protection Agency
Office of Air and Radiation Office of Air Quality Planning and Standards 06，2010
[4]The Benefits and Cost of the Clean Air Act from 1990 to 2020 US Environmental Protection Agency
Office of Air and Radiation Office 03，2011
[5] R. J. Shaughnessy and R. G. Sextro. What Is an Effective Portable Air Cleaning Device? A Review[J]
Journal of Occupational and Environmental Hygiene, 3: 169–181, 2006
[6] Keller, G.H. 1991. Benzene adsorption onto activated carbon and benzene destruction by potassium
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permanganate-loaded alumina. Union Carbide Chemicals and Plastics Company. South Charleston, WV.
[7] Ramanathan, K., Debler, V.L., Kosusko, M., Sparks, L.E. 1988. Evaluation of control strategies for volatile
organic compounds in indoor air. Environmental Progress. Vol. 7, No. 4, pp. 230-235
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