Distribution of Different Sized Viable Airborne Particles in
Air-conditioned Public Vehicles in Ladkrabang District
Raivada Roobsuaydee1, Suwannee Junyapoon1* and Mongkol Phensaijai2
Department of Chemistry, Faculty of Science, King Mongkut’s Institute of Technology
Ladkrabang, Bangkok 10520, Thailand
1
2
Department of Biology, Faculty of Science, King Mongkut’s Institute of
Technology Ladkrabang, Bangkok 10520, Thailand
Abstract
We examined the distribution of viable airborne particles in air-conditioned public buses number
517 and public vans line Ladkrabang-Victory monument in Ladkrabang district. Air samples were
collected by Six-stage Cascade Impactor with difference particle size fractions, > 7.0, 7.0-4.7, 4.73.3, 3.3-2.1, 2.1-1.1 and 1.1-0.65 μm particle diameter, at a flow rate of 28.3 l/min for 10 minutes.
The numbers of airborne microbes were measured using total plate count technique. The results
showed that bacteria in public buses were mainly detected in the range of 3.3−4.7 μm particle
diameters with concentration of 582.9771.50 CFU/m3 while the highest concentrations of bacteria
in the public vans were collected in the range of 2.1-3.3 µm particle diameters with concentration
of 552.7489.02 CFU/m3. Airborne fungi were collected the most in the range of 1.1–2.1 µm particle
diameters in both public buses and public vans with concentration of 669.4722.83 CFU/m3 and
582.5366.59 CFU/m3, respectively. The concentrations of airborne microbes in air samples
collected inside the buses and vans were higher than their background air outside. In this study,
gram positive bacteria and white filamentous configuration and black spore fungi were mainly
found in both air-conditioned public buses and vans.
Keywords: viable airborne particles, airborne bacteria, airborne fungi, air-conditioned public
vehicles, Six-stage cascade impactor
1. Introduction
At present, respiratory problems of people caused by exposure to various indoor air contaminants
are of increasing concern because people in modern society spend most of their time in confined
indoor spaces such as offices, homes, commercial centers, cars and buses etc. [1]. Bioaerosols are
defined as airborne particles that are living or originate from living organisms [2]. Although
airborne bacteria and fungi are common bioaerosols found in both indoor and outdoor
environments, the exposure to indoor bioaerosols is a potential cause of respiratory diseases and
other adverse health effects such as rhinitis, asthma and pneumonia [3-5].
*Corresponding author.
Tel.: 662-329-8400-11 ext. 262 Fax: 662-329-8412
E-mail: kjsuwann@kmitl.ac.th
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Airborne particles are deposited in different sites of the respiratory system depending on
their aerodynamic diameters. The adverse effects of these particles on human heath are related to
their sizes and properties [6]. Bioaerosol particles with the diameter of 5-10 μm can adhere to the
surface of upper respiratory tract while the bioaerosol particles less than 5 μm are strongly
accompanied with gas-stream, and can reach alveoli readily causing allergic diseases and other
serious illness [7]. Bacterial and fungal aerosols can enter indoor environment either by means of
passive ventilation or ventilation systems. Many genera are also emitted by indoor sources like
animals, humans, flowerpots and wastebaskets. Many previous researches studied on level and
characteristics of bioaerosols in residential buildings [8-11] but there are few studies on
bioaerosols in vehicles [12]. The aims of this study were to examine size distributions and
concentrations of airborne microorganisms in air-conditioned public vehicles in Ladkrabang
district.
2. Materials and Methods
2.1 Air Sampling Location
Air samples were collected from three public air-conditioned buses number 517 and three public
air-conditioned vans line Ladkrabang-Victory monument at parking stations in Ladkrabang
district, Bangkok, Thailand. Factors such as type of engine and fuel are shown in Table 1. The
experiments were carried out from January to May 2010.
Table 1. Characteristics of subjects investigated in this study
characteristics
No. of
Vehicles
Types
of studied
studied
vehicles
Air-conditioned
2 doors,
Bus number
with filter
3
47 seats
517
(Euro II)
Public van
Air-conditioned
3
3 doors,
with filter
15 seats
Manufacturing
company
Fuel
injected
HINO
Diesel
TOYOTA
LPG
2.2 Sampling and analysis of aerosol samples
The sampling and analysis of aerosol samples were carried out based on procedures described by
Kim and Kim [11] with some modifications. The six-stage viable particulate cascade impactor at a
flow rate of 28.3 liters/min was used for sampling airborne bacteria and fungi. The aerodynamic
diameter ranges of each stage are as follows: stage 1 (>7.0 µm), stage 2 (7.0-4.7 µm), stage 3 (4.73.3 µm), stage 4 (3.3-2.1 µm), stage 5 (2.1-1.1 µm) and stage 6 (1.1-0.65 µm) [13]. Each air
sampling was taken for 10 mins inside the vehicles about 0.5 m above the floor. The experiments
were carried out in triplicate at the same measuring point. For comparison with the outdoor
concentration, the measurement was conducted simultaneously once at one spot located within 1
m from each vehicle. Before sampling, the inside of the impactor was disinfected with 70%
alcohol and then was inserted with the agar plate according to collection stage. Tryptione soya
agar (TSA) with 500 mg of cycloheximide to suppress the growth of fungi was used for bacterial
culture. Malt extract agar (MEA) with 100 mg of cycloheximide to suppress the growth of bacteria
was used for fungal culture. After sampling, the cultures were immediately taken to the microbe
laboratory and were cultured in the incubator at 37 C for 1-2 days for bacteria and at 20-25 C for
3-5 days for fungi. The concentration of airborne bacteria and fungi was calculated by dividing
numbers of colonies formed on the culture medium by air volume (m3) at standard conditions
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67
(25 C, 1 atm) as shown in equations 1-3. The bacteria and fungi were identified by gram stain and
colonial morphology, respectively.
CFU (Colony Forming Unit/m3) =
Colony counted on agar plate (CFU)
(1)
Air volume at standard condition (m3)
Air volume (m3)
=
28.3 l/min x sampling time (min)
103
(2)
Air volume at standard condition
=
P sampling x V sampling x 298.15 K
T sampling
1 atm
(3)
2.3 Statistical analyses
The multiple comparative analysis method of ANOVA and Duncan’s test were used to assess the
differences in concentrations of airborne bacteria and fungi between the investigated public buses
and public vans. The differences in air borne bacterial and fungal concentrations between the
indoor and outdoor air were analyzed by means of paired t-test.
3. Results and Discussion
3.1 Size distribution and concentrations of airborne bacteria inside and outside airconditioned public vehicles
The size distribution of airborne bacteria both inside and outside air-conditioned public buses and
vans are shown in Figure 1. The mean concentrations of airborne bacteria inside air-conditioned
public buses and vans were ranged from 138.4915.76 to 582.9771.50 CFU/m3. The highest
distribution appeared at stage 3 of cascade impactor (3.3-4.7 µm) with the mean concentrations of
582.9771.50 CFU/m3 for public buses whereas the lowest distribution was at the stage 5 (1.1-2.1
µm) with the mean concentrations of 395.9183.14 CFU/m3. For the public vans, the highest
distribution appeared at stage 4 of cascade impactor (2.1-3.3 µm) with the mean concentrations of
552.7489.02 CFU/m3 while the lowest distribution was at the stage 6 (0.65-1.1 µm) with the
mean concentrations of 138.4915.76 CFU/m3.
Size distribution of airborne particles outside both public buses and vans was similar. The
mean concentrations of airborne bacteria were ranged from 128.426.65 to 237.123.69 CFU/m3
as shown in Figure 1. The highest distribution appeared at stage 5 of cascade impactor (1.1-2.1
µm) with the mean concentrations of 227.4319.88 CFU/m3 for public buses whereas the lowest
distribution was at the stage 6 (0.65-1.1 µm) with the mean concentrations of 154.439.11
CFU/m3. For public vans, the highest distribution appeared at stage 3 of cascade impactor (3.3-4.7
µm) with the mean concentrations of 237.123.69 CFU/m3 whilst the lowest distribution was at
the stage 6 (0.65-1.1 µm) with the mean concentrations of 128.426.65 CFU/m3.
As shown in Figure 1, the mean concentrations of bacteria in both types of airconditioned public vehicles were higher than that of the outside ones. These results implied that
ventilation systems of air-conditioned public vehicles were not enough. Gram-positive rod bacteria
were found in both public buses and vans as shown in Figure 2 and Table 2.
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Figure 1. Size distribution of inside and outside airborne bacteria in types of vehicles
(A)
(B)
Figure 2. Characteristics of airborne bacteria identified in the air-conditioned public vehicles
A, B = gram-positive rod bacteria
Table 2. Characteristics of airborne bacteria in air-conditioned public buses and vans
Characteristics of airborne bacteria
Types of
vehicle
stage 1
stage 2
stage 3
stage 4
stage 5
Public buses
+
+
(rods)
(rods)
+
+
Public vans
(rods)
(rods)
(+) = gram-positive bacteria
stage 6
+
+
+
+
(rods)
+
(rods)
(rods)
+
(rods)
(rods)
+
(rods)
(rods)
+
(rods)
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3.2 Size distribution and concentrations of airborne fungi inside and outside airconditioned public vehicles
The concentrations of airborne fungi inside and outside air-conditioned public buses and vans are
shown in Figure 3. The mean concentrations of airborne fungi inside air-conditioned public
vehicles ranged from 138.0824.02 to 669.4722.83 CFU/m3. The highest distribution appeared at
stage 5 of cascade impactor (1.1-2.1 µm) with the mean concentrations of 669.4722.83 CFU/m3
for public buses whereas in the public vans, the highest distribution appeared at stage 5 of cascade
impactor (1.1-2.1 µm) with the mean concentrations of 582.5366.59 CFU/m3.
The mean concentrations of airborne fungi outside public buses and vans were ranged
from 127.2112.21 to 390.906.07 CFU/m3 as shown in Figure 3. The highest distribution
appeared at stage 4 of cascade impactor (2.1-3.3 µm) with the mean concentrations of
371.0421.57 CFU/m3 for public buses while in the public vans, the highest distribution appeared
at stage 5 of cascade impactor (1.1-2.1 µm) with the mean concentrations of 390.906.07 CFU/m3.
The lowest distribution of fungal particles inside and outside air-conditioned public vehicles
appeared at stage 6 (0.65-1.1 µm). As shown in Figure 3, the mean concentrations of fungi inside
both types of air-conditioned public vehicles were higher than that of outside ones. Figure 4 shows
the characteristics of airborne fungi by observing their forms, shapes and colors of colony through
the optical microscope. Yellow colonies and white filamentous configuration were detected.
However, fungi morphology studies are required in future work.
Figure 3. Size distribution of inside and outside airborne fungi in types of vehicles
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70
(A)
(B)
Figure 4. Characteristics of airborne fungi identified in the air-conditioned public vehicles
A = characteristics of filamentous
B = characteristics of colony
4. Conclusions
The results showed that the concentration of bacteria at stage 3 (3.3-4.7 µm) in public buses and
stage 4 (2.1-3.3 µm) in public vans and fungi at stage 5 (1.1-2.1 µm) in both pubic buses and
public vans exceed 500 CFU/m3 which is the threshold limit value of the American Conference of
Governmental Industrial Hygienist (ACGIH) [14]. The detection of high level of bacteria and
fungi concentrations implied that the air-conditioned public vehicles had inadequate air ventilation
and over-crowded. These can result in respiratory disorders and other adverse health effects. To
prevent the spread of bacteria and fungi in all types of air-conditioned public vehicles, the cleaning
of vehicles’ environment (i.e. curtains, seats, floor) and air conditioner are required.
5. Acknowledgements
The authors would like to thank Assoc. Prof. Dr. Nuanpun N Ranong and Asst. Prof. Dr. Chitti
Thawai, Department of Biology, Faculty of Science, King Mongkut’s Institute of Technology
Ladkrabang for their advice. We also grateful to Mr. Ittipol Pawarmart, Pollution Control
Department for equipment support of this work.
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