Effect of an Air Cleaner with Electrostatic Filter on the Removal of Airborne House Dust Mite Allergens

Abstract

The effects of air cleaners on the removal of airborne indoor allergens, especially house dust mites (HDM), are still controversial. The objective of this study is to evaluate the effect of an air cleaner with an electrostatic filter on the removal of airborne mite allergens.
A dried HDM culture medium that contained mite body particles and excretions was dispersed in a chamber equipped with an electrostatic air cleaner. The number of airborne particles was recorded continuously by a dust spectrometer for 60 minutes. Airborne particles in the chamber were collected on a sampling filter at a flow rate of 10 L/min and the Der f 1 concentration in the filter extracts was measured by two-site ELISA.
The air cleaner efficiently removed airborne HDM particles. The air cleaner removed airborne HDM particles (size 2-12.5 µm) 11.4 ± 2.9 fold (cleaner operating for 15 minutes), 5.4 ± 0.7 fold (cleaner operating for 30 minutes), and 2.4 ± 0.2 fold (cleaner operating for 60 minutes) more than the removal of HDM particles by natural settle down. Removal kinetics differed according to the particle size of the airborne particles. The air cleaner decreased the concentration of Der f 1 in the extraction of airborne particles collected on the air sampling filter by 60.3%.
The electrostatic air cleaner can remove airborne HDM allergens and may be useful as a supplementary environmental control tool for HDM sensitized respiratory allergic patients.

Full text

Yonsei Med J http://www.eymj.org Volume 51 Number 6 November 2010
918
Indoor air quality has received increasing attention in recent years due to the global
increase in allergic diseases. Researchers have investigated the relationship
between the level of environmental exposure to house dust mites (HDM) and
sensitization to and development of certain allergic diseases.1,2 Although naturally-
occurring aeroallergens are difficult to avoid, exposure to these allergens may be
reduced, often substantially, by environmental control measures such as encasing
bedding materials and pillows, air cleaners, and ventilation.3Use of an high
efficiency particle arrest (HEPA) air cleaner to reduce airborne allergens in the
indoor environment may provide clinical benefits for patients with respiratory
allergies; these HEPA air cleaners have been demonstrated to reduce levels of
Original Article DOI 10.3349/ymj.2010.51.6.918
pISSN: 0513-5796, eISSN: 1976-2437 Yonsei Med J 51(6):918-923, 2010
Effect of an Air Cleaner with Electrostatic Filter on the
Removal of Airborne House Dust Mite Allergens
Santosh Rani Agrawal,1* Hak-Joon Kim,2* Yong Won Lee,1Jung-Ho Sohn,1Jae Hyun Lee,1
Yong-Jin Kim,2Sung-Hwa Lee,3Chein-Soo Hong,1and Jung-Won Park1
1Division of Allergy and Immunology, Institute of Allergy, Department of Internal Medicine, Yonsei University College of Medicine, Seoul;
2Aerosol Laboratory, Environmental Machinery Research Division, Korea Institute of Machinery and Materials, Daejeon;
3Digital Appliance Company Research Laboratory, LG Electronics, Changwon, Korea.
Purpose: The effects of air cleaners on the removal of airborne indoor allergens,
especially house dust mites (HDM), are still controversial. The objective of this
study is to evaluate the effect of an air cleaner with an electrostatic filter on the
removal of airborne mite allergens. Materials and Methods: A dried HDM
culture medium that contained mite body particles and excretions was dispersed in
a chamber equipped with an electrostatic air cleaner. The number of airborne
particles was recorded continuously by a dust spectrometer for 60 minutes.
Airborne particles in the chamber were collected on a sampling filter at a flow rate
of 10 L/min and the Der f 1 concentration in the filter extracts was measured by
two-site ELISA. Results: The air cleaner efficiently removed airborne HDM
particles. The air cleaner removed airborne HDM particles (size 2-12.5 µm) 11.4 ±
2.9 fold (cleaner operating for 15 minutes), 5.4 ± 0.7 fold (cleaner operating for 30
minutes), and 2.4 ± 0.2 fold (cleaner operating for 60 minutes) more than the
removal of HDM particles by natural settle down. Removal kinetics differed
according to the particle size of the airborne particles. The air cleaner decreased
the concentration of Der f 1 in the extraction of airborne particles collected on the
air sampling filter by 60.3%. Conclusion: The electrostatic air cleaner can remove
airborne HDM allergens and may be useful as a supplementary environmental
control tool for HDM sensitized respiratory allergic patients.
Key Words: House dust mite, electrostatic air cleaner, environmental control
Received: March 8, 2010
Revised: May 5, 2010
Accepted: May 18, 2010
Corresponding author: Dr. Jung-Won Park,
Division of Allergy and Immunology,
Institute of Allergy, Department Internal
Medicine, Yonsei University College of
Medicine, 250 Seongsan-ro, Seodaemun-gu,
Seoul 102-752, Korea.
Tel: 82-2-2228-1961, Fax: 82-2-393-6884
E-mail: parkjw@yuhs.ac
*These authors contributed equally to this
work.
∙The authors have no financial conflicts of
interest.
© Copyright:
Yonsei University College of Medicine 2010
This is an Open Access article distributed under the
terms of the Creative Commons Attribution Non-
Commercial License (http://creativecommons.org/
licenses/by-nc/3.0) which permits unrestricted non-
commercial use, distribution, and reproduction in any
medium, provided the original work is properly cited.
INTRODUCTION

Removal of Airborne Mite Allergens by an Air Cleaner
Yonsei Med J http://www.eymj.org Volume 51 Number 6 November 2010
919
airborne pet allergens.4,5 However, the ability of air clea-
ners to remove HDM and other allergens is still controver-
sial.4,5,6-10 Electrostatic air cleaners remove airborne parti-
cles by charging the airborne particles and then trapping
them on oppositely charged metal plates. The efficiency of
the HEPA air cleaner has been reported to be better than
electrostatic air cleaners, and most clinical studies with
allergic patients were done with HEPA air cleaners. How-
ever, HEPA cleaners are noisy and require regular chang-
ing of expensive HEPA filters. The objective of this study
was to evaluate the ability of an air cleaner equipped with
electrostatic filter to remove airborne HDM particles.
Study design
We evaluated the efficiency of electrostatic air cleaner by
comparing the concentrations of HDM particles in the
closed chamber measured by spectrophotometer and the
amount of HDM particles in the glass filter collected by
constant flow air sampler in the chamber. We compared
these two parameters measured at the on and off statuses
of the air cleaner.
Air cleaner and sample preparation
To create a source of house dust mite particles, we dried 30
g of culture medium containing Dermatophagoides farinae
at room temperature for 24 hours. D. farinae was cultured
at 25 ± 3˚C and 75 ± 2% relative humidity. One gram of
the culture medium contained 9.6 µg of Der f 1. An LG air
cleaner with an electrostatic filter (LG Electronic, Chang-
won, Korea), embedded into an air conditioner, was used
in this study. However, the air conditioner was off during
the experiment. The airflow of the air cleaner was 10
m3/min and it was equipped with two different filters: an
electrostatic filter and a fine mesh mechanical pre-filter.
The dust removal efficiency of the electrostatic filter and
fine mesh mechanical pre-filter was about 50% and 35%,
respectively, as calculated by the one-pass method using a
particle counter (PM2.5) at the velocity of 5.3 cm/sec.
Measurement of airborne particles using dust
spectrometer
A closed stainless steel chamber (30.4 m3) was first cleared
by air circulation and a HEPA filter system and the particle
concentration was monitored until it reached a baseline of
less than 104 particle/m3for 2-12.5 µm size range. A total
of 150 mg of the allergen particles were loaded into a
suction type particle feeder and then dispersed at 30 L/min
spraying velocity for 1 minute. The number of airborne
particles during each experiment was measured using a
particle sampling unit installed 1 m above the chamber
floor at the center of the chamber. The unit was connected
to an optical particle counter (Portable Aerosol Spectro-
meter, Model 1.109, Grimm Aerosol Technik, Ainring,
Germany) and data was analyzed using a particle concentra-
tion analyzing program (Version 3.20 build 6, Grimm Aero-
sol Technik, Germany). Distribution of the particles imme-
diately after dispersion of 0.15 gm of the medium is shown
Fig. 1. The distribution was expressed as a volume (µm3/m3)
or number of particles (/m3) per volume of the chamber. The
number of the airborne particles was recorded every minute
for 60 minutes. These experiments were done triplicate.
Calculation of Clean Air Delivery Rates (CADRs)
The air cleaning performance with the LG air cleaner was
represented by a Clean Air Delivery Rate (CADR) which
determines how well an air cleaner reduces airborne part-
icles.11,12 The CADR of the air cleaner to remove the air-
bone particles is based on the below formula.
Ct,i = Cie-kt
Abbreviations; where Ct, = concentration at time t
(particles/m3), k= decay rate constant (min-1), and t = time
MATERIALS AND METHODS
Volume concentration (µm3/m3)
0.1 1 10 100
Particle size (µm)
0
2
4
6
8
10
12
14
Particle number (×103/m3)
0.1 1 10 100
Particle size (µm)
0.1
1
10
100
1,000
10,000
Fig. 1. Distribution of airborne particles per size immediately after dispersion of the 150 mg of culture media at the closed chamber. It was
expressed with the volume of the particles (A) or number of particles (B) per m3according to the size of the particles.
AB

(minutes).
The decay constant, k, is obtained by fitting a linear
regression line to the slope of-ln(C(t)/C0), which is the
negative of the natural log of the time-varying particle
concentration (C(t)) normalized by the initial concentration
at the time the incense was extinguished (C0), versus time
(h). The CADR of airborne particles was calculated by the
below formula.
CADR = V×k
Abbreviations; V = volume of test chamber (m3), k=
measured decay rate, min-1.
Measurement of the concentration of Der f 1 from the
air sampling filters
Airborne particles in the closed chamber were collected on
glass fiber filter paper (Model GF/C Φ47 mm, Whatman,
UK, pore size; 1.6 µm) at a flow rate of 10 L/min for 30 mi-
nutes after the concentrations of HDM particles reached
the maximum values. During the experiments, the air clea-
ner and the air sampler worked simultaneously. The HDM
allergens were extracted from the filter paper with borate
buffered saline (BBS) (170 mM boric acid, 125 mM NaCl,
pH 7.0) for 18 hr at room temperature with gentle shaking.
The Der f 1 concentrations in each extracted solution were
measured by 2-site ELISA (Indoor biotechnologies, Man-
chester, UK) following the manufacturer’s recommenda-
tions, except that 3,3’-5,5’-tetramethylbenzidine (TMB,
Kirkegaard & Perry Laboratories, Gaithersburg, MD,
USA) were used as a substrate instead of ABTS. The
detection limit for Der f 1 was 60 pg/mL. These experi-
ments were done triplicate.
Statistical analysis
The Mann-Whitney U-test was used to compare the Der f
1 level or CADR value between the samples. The Wilcoxon
Sign Ranked test was used to compare the fold-removal
rate in comparison with the baseline. Significance was set
up at p< 0.05. All statistical analysis was performed with
SPSS 12.0 (SPSS Inc., Chicago, IL, USA). Bars in the
figures indicate the standard error of the mean.
Removal efficiency of the air cleaner measured by dust
spectrometer
HDM airborne particles between the size ranges of 10.0-
12.5, 5.0-6.5, and 2.0-2.5 µm were rapidly removed by the
Santosh Rani Agrawal, et al.
Yonsei Med J http://www.eymj.org Volume 51 Number 6 November 2010
920
RESULTS
Particle/m3
0 10 20 30 40
AC on
AC off
50 60
Time (min)
0
5,000
10,000
15,000
20,000
Particle/m3
010 20 30 40
AC on
AC off
50 60
Time (min)
0
5,000
10,000
15,000
Particle/m3
0 10 20 30 40
AC on
AC off
50 60
Time (min)
0
5,000
10,000
15,000
20,000
20,000
Particle/m3
0 10 20 30 40
AC on
AC off
50 60
Time (min)
0
5,000
10,000
15,000
Fig. 2. Removal efficiency of the split electrostatic and fine mesh mechanical pre-filter air cleaner. The size and number of HDM particles were
measured using a dust spectrometer. (A) HDM particles in the size range 10.0 - 12.5 µm. (B) HDM particles in the size range 5.0 - 6.5 µm. (C) HDM
particles in the size range 2.0 - 2.5 µm. (D) HDM particles in the size range 0.25 - 0.28 µm. The bars in these figures represent standard error of the
mean. HDM, house dust mites.
AB
CD

split electrostatic and fine mesh mechanical air cleaner (Fig.
2). Fig. 2 shows the efficiency of the cleaner at different
time points. The cleaner removed airborne HDM particles
(size 2-12.5 µm) in the chamber 11.4 ± 2.9 fold (cleaner
operating for 15 minutes), 5.4 ± 0.7 fold (cleaner oper-
ational for 30 minutes), and 2.4 ± 0.2 fold (cleaner operat-
ing for 60 minutes) more than particle removal by natural
settling. By running the cleaner for 30 minutes, 79.9 ±
2.6% of HDM particles (2-12 µm) were removed compared
to the 9.7 ± 5.0% of HDM particles removed by natural
settling. Approximately 64.3% of the HDM particles (size
2-12.5 µm) were still airborne 60 minutes after the concen-
tration of the HDM particles, sprayed from the particle
feeder; use of the air cleaner reduced this value to 10%
(Fig. 3).
Measurement of CADRs
Significant differences in removal kinetics were found ac-
cording to the size of airborne particles. The air cleaner com-
pletely removed larger particles between 10-12.5 µm within
30 minutes. The CADRs were particle size-dependent and
the difference between the CADRs with and without the
air cleaner operation dramatically increased as the size of
the particles were larger (Fig. 4). Particles larger than 15
µm settled down so rapidly that they could not be accurately
measured using the dust spectrometer (data not shown).
Measurement of airborne Der f 1 with or without air
cleaner
The concentration of airborne Der f 1 in the chamber was
markedly decreased by the air cleaner as shown in Fig. 5.
The Der f 1 concentration in the extract solution of the air-
sampling filter was 47.2 ± 7.5 ng/mL when the air cleaner
was used, as compared to 118.75 ± 14.12 ng/mL when the
air cleaner was not used, indicating that the air cleaner
decreased the Der f 1 concentration by 60.3%.
Our study shows that the use of an air cleaner with electro-
static filters can reduce the exposure to HDM particles of
several sizes. Air cleaners can reduce airborne Can f 1 or
Fel d 1,4-5,10 but few studies have investigated the ability of
these cleaners to remove airborne or settle down HDM
allergens, and the clinical effects of air cleaners for reduc-
ing the exposure to HDM are questionable.3,6,7 In this study,
an air cleaner with electrostatic filters removed larger
HDM particles of sizes (10-12.5 µm) within 30 minutes
and markedly reduced the concentration of smaller particles
Removal of Airborne Mite Allergens by an Air Cleaner
Yonsei Med J http://www.eymj.org Volume 51 Number 6 November 2010
921
DISCUSSION
% Removal
0.25 - 0.28
0
20
40
60
80
2.0 - 2.5
Particle size (µm)
5.0 - 6.5
10.0 - 12.5
2 - 12.5
100 Off
On
% Removal
0.25 - 0.29
0
20
40
60
80
2.0 - 2.5
Particle size (µm)
5.0 - 6.5
10.0 - 12.5
2 - 12.5
100 Off
On
% Removal
0.25 - 0.28
0
20
40
60
80
2.0 - 2.5
Particle size (µm)
5.0 - 6.5
10.0 - 12.5
2 - 12.5
100 Off
On
Fold increase for removal
0.25 - 0.29
0
5
10
15
2.0 - 2.5
Particle size (µm)
5.0 - 6.5
10.0 - 12.5
2 - 12.5
20 15 min
30 min
60 min
Fig. 3. Removal efficiency of the air cleaner expressed as the percentage removal of airborne HDM particles in the chamber. The baseline value is
the concentration of particles immediately after spraying. (A) Removal efficiency after 15 minutes. (B) Removal efficiency after 30 minutes. (C)
Removal efficiency after 60 minutes. Black bars in A-C represent the rate of settlement of HDM particles. D shows the fold-increase in HDM
removal by the cleaner compared to the natural settlement. The dotted line represents 1 fold indicating natural settlement. Bars in these figures
represent standard errors of the mean. *p< 0.05.
AB
CD

(2-10 µm) within 60 minutes. These results may suggest
that electrostatic air cleaners may reduce the exposure of
inhabitants to HDM allergens. As the removal of the air-
borne particles by an electrostatic cleaner is governed by
impaction, electrical charging and interception of the air-
borne particles on the filter, efficiency of removal of air-
borne particles depends on the physical size of the parti-
cles. Generally, removal of larger particles is easier than
that of smaller particles.13 The CADR values for airborne
particles in the ranges of 5-12.5 µm, critical ranges for
HDM allergens, were superior to the values of smaller
particles in this study. It is noteworthy that 60% of airborne
Der f 1 was removed by the air cleaner within 30 minutes.
More than 80% of airborne particles, including HDM
fecal material, are usually larger than 10 µm14-16 and the fecal
material has been recognized as the major sources of the
HDM allergen.17 These findings raise a question of how
HDM aggravates asthma in patients with HDM sensitiza-
tion. Aerodynamically larger particles (> 10 µm) usually do
not reach the peripheral airway, and encasings with pore
sizes less than 10 µm are effective in blocking dust mite
allergens.18 However, Svartengren, et al.19 demonstrated that
4% to 15% of inhaled large Teflon particles ranging from
8.2 to 13.7 µm were deposited in the alveoli, confirming
that large particles can be deposited in the peripheral air-
ways. Although the majority of HDM particles in homes
are larger than 10 µm, this does not decrease the signifi-
cance of small HDM particles in asthmatic patients. Cus-
tovic, et al.20 showed that group 2 dust mite allergens are
carried not only on large particles but also on small
particles (< 5 µm). Furthermore, HDM had more than 15
major allergens, and the aerodynamic characteristics of
these allergens may be different. HDM allergens have
been shown to be present in the lower airway of most HDM
sensitized asthmatic patients. HDM allergens have been
identified in BAL fluid at low concentrations.21 De Lucca,
et al.22 demonstrated that Der p 1 is associated with parti-
cles not ranging from feces, to fibers, to flakes, which are
all sources of inhaled mite aeroallergens. The particle sizes
of the culture medium used in this study was not that
different from the HDM particles in the house dust. The
median size of the particles (in the aspect of volume concen-
tration) used in this study fell in the range of 4-8 µm, and a
considerable amount of particles were larger than 10 µm.
Although the air cleaner cannot efficiently reduce ex-
posure to HDM particles during sleep, settled dust is likely
to be disturbed by various living activities of inhabitants
during the day, and under these circumstances, the air
cleaner may protect inhabitants from exposure to HDM.
The HEPA filter can remove 99.9% of airborne particles
0.3 µm in size by passing through the filter, but the perfor-
mance of the air cleaner is expressed as the CADR that
takes into account both the flow rate through the air clea-
ner and the filter efficiency.23,24 HEPA air cleaners have
some weak points. Noise is one drawback of the HEPA air
cleaner, and it requires high energy costs. Pressure drop is
another drawback. As the air particles are deposited into
the HEPA filter, the air flow rate decreased. In spite of a
lower filtration efficiency of the electrostatic filter than that
of the HEPA, the electrostatic filter may permit higher air
flow rates due to a smaller pressure drop than that with the
HEPA filter. Furthermore, we showed that the levels of
airborne Der f 1 could be reduced using an electrostatic air
cleaner in this study.
This study has several limitations. Measurements were
taken in a closed chamber in which HDM particles from
the culture medium had been sprayed. These experimental
conditions do not reflect a real living environment. Further-
more, we only measured indirect parameters to assess the
effects of the air cleaner. Further clinical studies are need-
Santosh Rani Agrawal, et al.
Yonsei Med J http://www.eymj.org Volume 51 Number 6 November 2010
922
CADR (m3/min)
0 42 86 1210
Airborne particle size (µm)
Air cleaner on
Air cleaner off
0
1
2
3
4
5
6
7
Fig. 4. CADR values of the electrostatic and fine mesh mechanical pre-filter air
cleaner according to the size of airborne particles. CADR values are airborne
particle size dependent. The bars in this figure represent standard error of the
mean. *p< 0.05. CADR, Clean Air Delivery Rate.
Der f 1 (ng/mL)
0
20
40
60
80
Air cleaner
Off On
100
120
140
Fig. 5. Concentration of Der f 1 in extracts from the air sampling filters installed in
a closed chamber with or without air cleaner. The bars in this figure represent
standard error of the mean. *p< 0.05.

Removal of Airborne Mite Allergens by an Air Cleaner
Yonsei Med J http://www.eymj.org Volume 51 Number 6 November 2010
923
ed to determine the clinical usefulness of the air cleaner.
In conclusion, an electrostatic air cleaner can remove
airborne HDM allergens and may be useful for the mana-
gement of respiratory allergies in patients sensitized to
HDM allergens.
This study was supported by grant from LG Electronics.
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ACKNOWLEDGEMENTS
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