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Aerosol and Air Quality Research, 15: 572–581, 2015
Copyright © Taiwan Association for Aerosol Research
ISSN: 1680-8584 print / 2071-1409 online
doi: 10.4209/aaqr.2014.10.0258
Seasonal and Diurnal Variations of Fluorescent Bioaerosol Concentration and
Size Distribution in the Urban Environment
Sampo Saari1*, JarkkoV. Niemi2,3, Topi Rönkkö1, Heino Kuuluvainen1, Anssi Järvinen1,
Liisa Pirjola4, Minna Aurela5, Risto Hillamo5, Jorma Keskinen1
1
Department of Physics, Tampere University of Technology, Tampere, Finland
Helsinki Region Environmental Services Authority (HSY), P.O. Box 100, FI-00066 HSY, Finland
3
Department of Environmental Sciences, University of Helsinki, P.O. Box 65, FI-00014 Helsinki, Finland
4
Department of Technology, Metropolia University of Applied Science, Kalevankatu 43, FI-00180 Helsinki, Finland
5
Atmospheric Composition Research, Finnish Meteorological Institute, Erik Palménin aukio 1, FI-00560 Helsinki, Finland
2
ABSTRACT
A recently introduced fluorescence based real-time bioaerosol instrument, BioScout, and an ultraviolet aerodynamic
particle sizer (UVAPS) were used to study fluorescent bioaerosol particles (FBAP) in the Helsinki metropolitan area,
Finland, during winter and summer. Two FBAP modes at 0.5–1.5 µm (fine) and 1.5–5 µm (coarse) were detected during
the summer, whereas the fine mode dominated in the winter. The concentration and proportion of the coarse FBAP was
high in summer (0.028 #/cm3, 23%) and low in winter (0.010 #/cm3, 6%). Snow cover and low biological activity were
assumed to be the main reasons for the low coarse FBAP concentration in the wintertime. Both the fine and the coarse
FBAP fraction typically increased at nighttime during the summer. Correlations between the BioScout and the UVAPS
were high with the coarse (R = 0.83) and fine (R = 0.92) FBAP. The BioScout showed 2.6 and 9.7 times higher detection
efficiencies for the coarse and fine FBAP, respectively, compared to the UVAPS. A long-range transport episode of
particles from Eastern Europe increased the fine FBAP concentration by over two orders of magnitude compared to the
clean period in the winter, but these FBAP probably also included fluorescent non-biological particles. Correlation
analysis indicates that local combustion sources did not generate fluorescent non-biological particles that can disturb fine
FBAP counting. The results provide information that can be used to estimate health risks and climatic relevance of
bioaerosols in the urban environment.
Keywords: Fluorescence; Fungal spores; Bacteria; UVAPS; BioScout.
INTRODUCTION
Bioaerosols such as bacteria and fungal spores can cause
adverse health effects for people and animals both in indoor
and outdoor environments (Burge and Rogers, 2000; Peccia
et al., 2008; Mendell et al., 2011). Atmospheric bioaerosols,
usually called primary biogenic aerosol particles (PBAP),
consist mainly of bacteria, fungal spores and fragments,
pollens, algae and plant debris (Després et al., 2012). PBAPs
have been recognized to have important influence on
climate, acting as cloud condensation nuclei (CCN) and ice
nuclei (IN) and thus contributing cloud formation and
precipitation processes (Vali et al., 1976; Bauer et al., 2002,
2003; Jaenicke, 2005; Sun and Ariya, 2006; Andreae and
*
Corresponding author.
Tel.: +358 3 311 511; Fax: +358 3 3115 2640
E-mail address: [email protected]
Rosenfeld, 2008; Pöschl et al., 2010; Després et al., 2012).
It seems clear that nature is the most important source of
PBAP on a global scale, but anthropogenic sources, such
as agriculture, waste treatment, buildings and cooking, may
also be significant in some regions. Potential health risks
of bioaerosols are especially high in urban environments
due to their dense populations. Ryan et al. (2009) reported
that a combination of bioaerosols and traffic-related emission
exposure was associated with wheezing at age 3 years.
Bowers et al. (2011) reported that the major bacteria
sources in the urban environments are soil, leaf surfaces
and dog feces. Information on concentrations, particle size
distributions and sources of bioaerosols is needed to
estimate their health risks and climatic relevance.
Various techniques have been used to collect ambient
bioaerosols, such as impactor and filter sampling (Reponen
et al., 2011). These off-line analysis methods require
separate steps before concentration can be analyzed, resulting
in relatively low time resolution. Real-time measurement
would aid in understanding regional and global emissions,
Saari et al., Aerosol and Air Quality Research, 15: 572–581, 2015
transport and abundance of PBAP (Burrows et al., 2009;
Heald and Spracklen, 2009; Huffman et al., 2010). Laser
induced fluorescence (LIF) based instruments are modern,
easy-to-use tools for real-time bioaerosol detection (e.g.,
Hill et al., 1995; Pinnick et al., 1995; Ho, 2002; Jeys et al.,
2007; Pöhlker et al., 2012). The LIF technique is an
effective method for detecting biological molecules such
as tryptophan, NADH and flavins that are present in
microbe cells (Lakowicz, 2006; Hill et al., 2009). Saari et al.
(2013) demonstrated that bacterial and fungal spores may be
distinguished from each other through their dissimilar
fluorescence spectra. The most well-known real-time LIF
instrument is the ultraviolet aerodynamic particle sizer
(UVAPS; Hairston et al., 1997, manufactured by TSI Inc., St.
Paul, Minnesota) that is able to measure both the aerodynamic
particle size and the autofluorescence of a single particle.
Compared to the UVAPS, our recent study showed that
performance of a simple, violet diode laser based bioaerosol
detector, BioScout (Environics Oy, Finland), may be even
more sensitive in measuring common bioaerosols (Saari et
al., 2014).
Recently, LIF based real-time instruments have been
used for detection of coarse (> 1.5 µm) PBAP in urban,
suburban, desert, tropical rainforest, high-altitude and boreal
forest environments (Pan et al. 2008; Gabey et al., 2010;
Huffman et al., 2010; Gabey et al., 2011; Huffman et al.,
2012; Toprak et al., 2012; Gabey et al., 2013, Huffman et
al., 2013; Schumacher et al., 2013). Huffman et al. (2012)
applied a UVAPS and a filter sampling technique to
measure PBAP size distributions and concentrations in the
Amazon rainforest region. They found a good correlation
between fluorescent particles (UVAPS) and filter analysis
(scanning electron microscopy as well as staining and light
microscopy). However, they concluded that only the lower
limit of PBAP concentration can be estimated with the
UVAPS because some PBAPs cannot be detected due to
weak fluorescence. This fluorescent fraction of bioaerosols
is usually called fluorescent biological aerosol particles
(FBAP).
Note that the fluorescent particle data can also include
non-biological particles that have similar fluorescence
characteristics, such as cigarette smoke or other combustiongenerated aerosols (e.g., Pinnick et al., 1998; Huffman et
al., 2010; Gabey et al., 2011). For the FBAP measurement,
these particles form an artifact that needs to be considered
when analyzing the data. Huffman et al. (2010) found a
high correlation of the number of fine fluorescent particles
with the total number of particles, concluding that a large
percentage of submicron particles exhibiting fluorescence
may have anthropogenic sources. Generally, the combustion
generated fluorescent particles are expected to be more
abundant in the fine mode. Consequently, the fluorescent
fine particles have not been much analyzed. When observed,
they have been treated as non-biological particles (Huffman et
al., 2010; Gabey et al., 2011).
In this study, we used two LIF based real-time bioaerosol
instruments, a recently introduced BioScout and a UVAPS,
to study FBAP concentrations and size distributions at urban
and suburban residential sites in the Helsinki metropolitan
573
area during winter and summer. To our knowledge, this is
the first study wherein the BioScout was used in an outdoor
environment and compared to another LIF based instrument.
We also demonstrate that comparison between the realtime LIF data and particle mass (PM2.5), black carbon (BC)
and nitrogen oxides (NOx), as well as meteorological data,
enables estimation of bioaerosol sources and transportation.
Contrary to the accepted custom, we especially extend the
analysis also to the fluorescent fine particles.
METHODS
BioScout
The BioScout (Environics Oy, Finland) uses a 405 nm
continuous wave laser diode with 200 mW optical power
to excite autofluorescence from individual bioaerosol
particles. Both the autofluorescence and the scattering light
are collected by an elliptical mirror and focused onto two
photomultiplier tubes (PMTs). The autofluorescence is
separated from the scattered light using a beam splitter and
a long-pass filter with a cut point at 442 nm, and the
fluorescence intensity is recorded by a PMT and sorted
into 16 channels. The scattering light intensity is used to
analyze the optical particle size. The time resolution of the
instrument is 1 second. The particle size calibration of the
BioScout was conducted against di-octyl sebacate (DOS)
and NaCl particles using the UVAPS (TSI Model 3314)
and the SCAR (Single Charged Aerosol Reference; YliOjanperä et al., 2010). The operating particle size range was
optimized between 0.3 and 5 µm. A laboratory study by
Saari et al. (2014) showed that detection efficiency of the
BioScout was high for fine bacterial particles (< 1 µm) that
may also have a role in the atmospheric fine FBAP mode.
UVAPS
Hairston et al. (1997) introduced the first prototype of
the UVAPS. The current version of the UVAPS (TSI
Model 3014) measures aerodynamic diameter of particles
between 0.5 µm and 15 µm with 52 channels. The UVAPS
also measures the autofluorescence emission of individual
particles using a pulsed 355 nm UV laser with 80 mW
maximum power as an excitation source. The
autofluorescence is recorded between 430 and 580 nm by a
PMT and sorted into 64 channels. In this study, the UV
pulse energy and fluorescence PMT gain were set into
their default values. The time resolution was adjusted to 5
min in this study. The performance of the UVAPS against
common bioaerosols has been reported in several studies
(e.g., Agranovski et al., 2003; Kanaani et al., 2007; Jung et
al., 2012; Saari et al., 2014).
Measurements
Two measurement campaigns were conducted at urban
and suburban residential sites in the Helsinki metropolitan
area. The measurement campaigns took place in winter and
summer during the time periods 2.2.–25.2.2012 and 16.6.–
22.8.2012, respectively. The winter campaign was performed
in a suburban residential area in Kattilalaakso, in Espoo.
The summer measurements were placed in an urban
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Saari et al., Aerosol and Air Quality Research, 15: 572–581, 2015
residential area, Kallio, beside a green sporting field in
Helsinki’s downtown area. Both the measurement locations
were influenced by local vegetation and human activity.
Helsinki is located on the southern coast of Finland and thus
the marine climate is strongly present there. The BioScout
was used in both campaigns, but the UVAPS was present
only during the summer campaign. The instruments were
placed in the measurement station, and the aerosol sample
was brought via total suspended particle inlet (TSP) on the
top of the station during the summer period. In the winter,
the BioScout was placed on the roof of the station and the
sample was brought through its own inlet, which had a cut
point at 10 µm. The sampling height was about 4 meters
from the street level in both campaigns.
The supporting PM2.5, NOx and BC data was monitored
at the measurement stations by the Helsinki Region
Environmental
Services
Authority
and
Finnish
Meteorological Institute. NOx was measured using a
chemiluminescence analyzer (model APNA 360, Horiba).
PM2.5 was monitored with a tapered element oscillating
system microbalance (TEOM model 1400 AB, Thermo
Scientific; summer) or with a Synchronized Hybrid Ambient
Real-time Particulate Monitor (SHARP model 5030, Thermo
Scientific; winter). BC was measured using a Multiangle
Absorption Photometer (MAAP model 5012, Thermo
Scientific) with PM1 cut-off. Meteorological data was
observed by the Finnish Meteorological Institute at the
Kumpula measurement site in Helsinki.
Data Analysis
The BioScout data were analyzed using MATLAB
software. All particles in fluorescence channels 2–16 were
classified as fluorescent and particles in channel 1 as nonfluorescent. Non-fluorescent NaCl particles were used to
determine the detection limit for fluorescence. The detection
limit was adjusted so that less than 1% of NaCl particles
reached fluorescence channel 2 or above. The BioScout
settings were similar as in the study by Saari et al. (2014).
When the fluorescence data are combined with the optical
particle size data, fluorescent particle and total particle size
distributions and number concentrations can be calculated.
The UVAPS data were analyzed using a similar procedure,
and all particles in fluorescence channels 3–64 were
classified as fluorescent. The UVAPS fluorescence channel
3 was chosen as a limit for fluorescent particles, similarly as
in previous atmospheric studies by Huffman et al. (2010,
2012, 2013), whereas fluorescence channel 2 was used in
laboratory studies by Agranovski et al. (2003), Kanaani et
al. (2007) and Saari et al. (2014). Pearson’s linear correlation
coefficients between the different instruments were calculated
with one-hour time resolution.
RESULTS AND DISCUSSION
Size Distributions
Averaged FBAP and total particle size distributions over
the campaigns are shown in Fig. 1. There were typically two
FBAP modes at 0.5–1.5 µm (fine) and 1.5–5 µm (coarse)
during the summer. In winter, the fine mode was dominant,
and no clear coarse mode was observed. The weather
during the winter campaign was typically cold, the average
temperature was −3°C, and the ground was covered by
snow. We assumed that snow cover and low biological
activity were the main reasons for the vanished coarse
FBAP in the wintertime. Low FBAP concentrations measured
by the UVAPS in wintertime have been reported also at
Hyytiälä boreal forest site in Finland in the recent study by
Schumacher et al. (2013). The coarse FBAP has been
strongly linked to fungal spores that are abundant in this
size range as reported also in the previous atmospheric
FBAP studies by Huffman et al. (2010, 2012, 2013) and by
Schumacher et al. (2013).
Origin of the fine FBAP is not clear, but the size range
is typical for bacterial spores (Saari et al., 2014). The
hypothesis of bacterial presence is also supported in a
recent study by DeLeon-Rodriguez et al. (2013), wherein
viable bacterial cells were shown to represent, on average,
around 20% of the total particles in the 0.25–1 μm size range
in the middle-to-upper troposphere. Similar observations
were made during three measurement campaigns at Lake
Baikal, at an urban site in Mainz and over the South Atlantic
Ocean, where around 20% of total particles (Dp > 0.2 µm)
were detected as PBAPs (Matthias-Maser et al., 1995, 1999,
2000). They suggested that bacterial particle concentration
Fig. 1. Averaged fluorescent (left) and total (right) particle size distributions during the winter and summer periods
measured by the BioScout and the UVAPS. The cut-off point between the modes is shown at 1.5 µm.
Saari et al., Aerosol and Air Quality Research, 15: 572–581, 2015
was higher in the urban environment due to the anthropogenic
sources. The fine FBAP has also been supposed to come
from combustion sources in urban environments (Huffman
et al., 2010). This possibility is discussed more below.
However, our laboratory studies showed that single bacterial
spores are detectable with both the instruments (Saari et
al., 2014), so we assume that at least a fraction of the
observed fine FBAP are bacteria.
The size distributions measured by the BioScout and the
UVAPS were similar but not fully consistent because the
UVAPS measures particle aerodynamic size and the
BioScout measures particle optical size that depends on a
refractive index and absorption of particles. There were
also differences in fluorescence sensitivity between the
instruments. The fine mode was clearly weaker and barely
visible with the UVAPS. The modes have been separated
at a cut-off point of 1.5 µm, and concentrations of the fine
mode (0.5 < Dp < 1.5 µm) and the coarse mode (Dp > 1.5
µm) will be analyzed separately below.
Fluorescent Particle Concentrations and Fractions
To compare the response of the instruments, correlation
diagrams and averaged values of the total particle and FBAP
concentrations measured by the BioScout and UVAPS during
the summer period are shown in Fig. 2 and Table 1.
Pearson’s linear correlation coefficient (R) showed high
correlation with both total particles (0.88 and 0.89 for the
coarse and fine mode, respectively) and FBAP (0.83 for
the coarse mode and 0.92 for the fine mode) between the
instruments. Linear fit functions showed slope values close
to one for total particles (0.76 and 1.02 for coarse and fine
mode, respectively), indicating that concentrations are
consistent between the instruments despite the different
particle size measurements However, remarkably higher
slope values were observed for FBAP (2.6 and 9.7 for
coarse and fine mode, respectively). This suggests that the
BioScout had 2.6 and 9.7 times higher detection efficiencies
for the coarse and fine FBAP, respectively, compared to
the UVAPS. Similar results were found also in our laboratory
studies (Saari et al., 2014). The reason for the higher
575
detection efficiency of the BioScout is assumed to be high
excitation laser intensity and the good fluorescence signal
to noise ratio of the instrument.
Averaged coarse FBAP concentrations were 0.010 #/cm3
in the winter and 0.028 #/cm3 in the summer as measured
by the BioScout. In comparison, the UVAPS coarse FBAP
concentration was 0.013 #/cm3 in the summer period. The
BioScout coarse FBAP fraction (FPF) was high in the
summer (23%) and low in the winter (6%). The UVAPS
coarse mode FPF was 8% in the summer. Surprisingly, the
BioScout fine FBAP concentration was higher in the winter
(0.13 #/cm3) than in the summer (0.018 #/cm3), whereas
the fine FPF were lower in the winter (0.9%) than in the
summer (2.9%). The UVAPS fine FBAP concentration was
0.0025 #/cm3, and the FPF value was 0.31% in the summer.
The BioScout showed higher FPF value for both the coarse
and the fine FBAP compared to the UVAPS, which is in
line with the laboratory studies of the common fungal
spores and bacteria (Saari et al., 2014).
A comprehensive comparison of the averaged PBAP
concentrations and fractions between this study and the
previous studies is represented in Table 1. All the
fluorescence based studies of PBAP coarse mode (measured
by BioScout, UVAPS and WIBS) in urban environments are
well in line: Concentrations vary from 0.01 #/cm3 to 0.10
#/cm3, and fractions were between 3% and 23% (this study;
Huffman et al., 2010; Gabey et al., 2011; Toprak et al., 2012).
Interestingly, the results of the off-line staining method
showed similar values for coarse PBAP concentration,
ranging from 0.026 #/cm3 to 0.8 #/cm3 (Chi and Li, 2007;
Bauer et al., 2008).
Seasonal variations of the concentrations and FPF
values of coarse FBAP are well in line with the previous
studies. Matthias-Maser et al. (2000), Toprak et al. (2012)
and Schumacher et al. (2013) reported the highest coarse
PBAP concentration in summer and the lowest values in
winter, which was observed also in this study. Seasonal
behavior of our fine mode results was also similar with the
previous study by Matthias-Maser et al. (2000), except our
winter period, when a long-range transport episode (LRT)
Fig. 2. Correlation diagrams of the total (NTOT; left) and fluorescent particle (NFL; right) concentrations measured by the
BioScout and UVAPS during the summer period. Black circles represent the coarse mode (Dp > 1.5 µm), and grey triangles
represent the fine mode (Dp < 1.5 µm). Pearson’s linear correlation coefficients (R) and linear fit functions (y = kx) are
shown in diagrams.
Saari et al., Aerosol and Air Quality Research, 15: 572–581, 2015
576
Table 1. The comparison between the results of this study and the previous studies. Coarse and fine PBAP represent
supermicrometer and submicrometer bioaerosol particles, respectively. PBAP concentrations are shown as (#/cm3) and
fractions as (%).
Coarse Fine Coarse Fine
PBAP PBAP PBAP PBAP
Comments
(#/cm3) (#/cm3) (%)
(%)
Urban (Helsinki)1
winter
BioScout
0.010
0.13
6
0.9 suburban
summer
BioScout
0.028 0.018
23
2.9 urban
summer
UVAPS
0.013 0.002
8
0.3 urban
Urban (Mainz)2
autumn
UVAPS
0.03
4
Urban (Manchester)5
winter
WIBS-3
0.1
7
Urban
winter
WIBS-4
0.03
4
(Karlsruhe)8
spring
WIBS-4
0.029
7
summer
WIBS-4
0.046
11
autumn
WIBS-4
0.029
7
Urban (Mainz)9
spring
EDX + staining
3.1
24 fine + coarse
Urban (Vienna)12
summer
staining
0.026
40
fungal spores
Urban (Taipei)13
summer
staining
0.8
bacteria and fungal spores
Marine (Atlantic)10
winter EDX + staining
0.6
17 fine + coarse
Rural (Baikal)11
winter EDX + staining 0.0005 0.03
15
15
spring
EDX + staining 0.0015
1
30
20
summer EDX + staining 0.01
1
60
20
autumn EDX + staining 0.001
0.03
20
20
Tropical (Amazonia)3
winter
UVAPS
0.07
24
High-altitude (Colorado)4
summer
UVAPS
0.03
10
Tropical (Borneo)6
summer
WIBS-3
1.5
28
under the canopy
WIBS-3
0.2
55
above the canopy
High-altitude (France)7
summer
WIBS-3
0.1
35
bacteria and fungal spores
staining
0.017
Boreal forest (Finland)14
winter
UVAPS
0.004
1.1
spring
UVAPS
0.015
4.4
summer
UVAPS
0.046
13
Rocky Mountains
autumn
UVAPS
0.027
9.8
(Colorado)14
winter
UVAPS
0.0053
3.0
spring
UVAPS
0.015
2.5
summer
UVAPS
0.030
8.8
autumn
UVAPS
0.017
5.7
1
This study; 2,3,4 Huffman et al. (2010, 2012, 2013); 5,6,7 Gabey et al. (2011, 2010, 2013); 8 Toprak et al. (2012);
9,10,11
Matthias-Maser et al. (1995, 1999, 2000); 12 Bauer et al. (2008); 13 Chi and Li (2007); 14 Schumacher et al. (2013).
Environment
(Location)
Season
Measurement
method
of particles from Eastern Europe had an influence on the
results. Effects of the LRT are discussed more below.
Temporal Variations
In this section, the FBAP concentrations are analyzed as
a function of time and compared to PM2.5, NOx and BC
concentrations. Concentrations of the coarse and fine
FBAP and their FPF values measured by the BioScout as
well as PM2.5, NOx and BC concentrations in the winter are
shown in Fig. 3. Based on the PM2.5 data from other
measurement stations of the Helsinki Region Environmental
Services Authority, high concentrations during February
15–19, 2012, were caused by the long-range transportation
of aerosol particles, due to prevailing meteorological
conditions (Niemi et al., 2009). Back-trajectory analysis of
air masses (HYSPLIT Model; Draxler and Rolph, 2014;
Rolph, 2014) showed that air flows arrived from Eastern
Europe during the LRT episode, and clean air during
February 20–28 was coming from the direction of the
Atlantic Ocean and Greenland. During the LRT episode,
concentration of the coarse mode was only elevated a bit,
but the fine FBAP concentration was over two orders of
magnitude higher compared to the clean period. PM2.5 and
BC concentrations during the LRT episode were high. The
correlation analysis between the variables is discussed
more below.
The fine FBAP during the LRT may have been influenced
by several anthropogenic sources, including the biomass
burning in fireplaces that is popular in Eastern Europe
during the cold season. However, bacteria emissions would
be also higher in Eastern Europe than in Finland due to
temperature and snow cover differences during the winter
Smith et al. (2013) reported high concentrations of bacteria
taxa in the transpacific plumes from Asian to North.
America and showed that long-range transport is possible
for bacteria particles.
Saari et al., Aerosol and Air Quality Research, 15: 572–581, 2015
577
Fig. 3. Concentrations of PM2.5, NOx, BC and fluorescent coarse (solid) and fine (dashed) modes and their fractions
(NFL/NTOT) measured by the BioScout during the long-range transport episode (LRT; February 15–19) and clean condition
in the winter of 2012.
Time series of FBAP concentrations and averaged daily
variations of the FPF values for the modes measured by the
BioScout and the UVAPS during the summer are shown in
Fig. 4. Both the coarse and fine FPF were typically increased
at night time, which is reported to be a characteristic time
for the natural emission of fungal spores (e.g., Huffman et
al., 2012). Sometimes, e.g., on June 26, the concentrations
were high also in the daytime, which indicates the presence of
different sources. The fine FBAP showed some short peaks
at nighttime during June 27–29, which indicates the
presence of a strong local source. The source may be either
natural, such as bacteria, or anthropogenic. Similar trends
during the measurement period were shown with both the
BioScout and with the UVAPS. The FBAP concentrations
were lower with the UVAPS than with the BioScout, and
the difference was especially high for the fine mode. This
comes from the different bioaerosol detection efficiencies
between the instruments, which are also discussed above.
Correlation Analysis
Correlations between the FBAP and total particles
measured by the BioScout as well as PM2.5, NOx and BC
were analyzed in Fig. 5. To our knowledge, this is the first
study wherein FBAP concentrations were compared to the
PM2.5, NOx and BC values. In the winter, correlations were
shown separately during the LRT episode and the clean
period.
During the LRT, the fine FBAP correlated well with the
total particle concentration (R = 0.93), whereas correlation
was low between the coarse particles (R = 0.35). Similar
results were reported in the previous study by Huffman et
al. (2010). High correlations, Rcoarse = 0.71 and Rfine = 0.73,
were found between the FBAP and the PM2.5 during the
LRT, indicating high FBAP content in the transported
PM2.5 fraction. Correlations between BC and FBAP were
the highest during the LRT episode (Rcoarse = 0.60 and Rfine
= 0.65). This indicates that aged BC-containing particles
may have influenced the FBAP values acting as nonbiological fluorescent particles. Condensation and cloud
processes can increase the size of BC-containing particles
in the atmosphere, and therefore, BC also can present in
larger particle sizes in LRT aerosols (Niemi et al., 2006).
Correlations between FBAP and total particles were low
with both modes (Rcoarse = 0.15 and Rfine = 0.29) during the
clean period in winter, indicating random emission of
FBAP. Interestingly, coarse particles correlated better in
the summer (Rcoarse = 0.61 and Rfine = 0.10). This indicates
regular local emission of coarse FBAP (presumably fungal
spores) and random fine FBAP emission in summertime.
The results showed that correlations between the FBAP
and NOx were low during the all measurement periods
(0.01 < Rcoarse < 0.54 and 0 < Rfine < 0.07). This indicates
that local vehicle traffic, the dominant NOx source in the
Helsinki metropolitan area, did not disturb FBAP counting
at these measurement sites. Fine FBAP correlations with
BC were low during the clean period in the winter (R = 0.32)
and in the summer campaign (R = 0.09). This indicates that
local BC related combustion sources did not disturb the
fine FBAP analysis during these periods and that most of the
fine FBAPs counted by the BioScout were real bioaerosols.
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Saari et al., Aerosol and Air Quality Research, 15: 572–581, 2015
Fig. 4. Time series of fluorescent particle concentrations and averaged daily variations of the fluorescent particle fractions
(NFL/NTOT) for the coarse mode (Dp > 1.5 µm; above) and fine mode (Dp < 1.5 µm; below) measured by the BioScout and
the UVAPS during the summer campaign of 2012.
Fig. 5. Correlation scatter diagrams of fluorescent (NFL) coarse (Dp > 1.5 µm) and fine (Dp < 1.5 µm) particle and total
particle concentrations (NTOT) measured by the BioScout, PM2.5, NOx and BC during the winter and the summer periods.
Pearson’s correlation coefficients (R) are shown in diagrams.
Saari et al., Aerosol and Air Quality Research, 15: 572–581, 2015
579
The previous studies typically treated fine FBAP as nonbiological particles (Huffman et al., 2010; Gabey et al.,
2011), but this study showed that this is not necessarily the
case. The types and sources of fine FBAP should be studied
more and compared with other analyzing techniques such
as microscopy and quantitative polymerase chain reaction
(qPCR).
the measurements. The authors gratefully acknowledge the
NOAA Air Resources Laboratory (ARL) for the provision
of the HYSPLIT transport and dispersion model and
READY website (http://www.ready.noaa.gov) used in this
publication.
CONCLUSIONS
Agranovski, V., Ristovski, Z., Hargreaves, M., Blackall, P.
and Morawska, L. (2003). Real-time Measurement of
Bacterial Aerosols with the UVAPS: Performance
Evaluation. J. Aerosol Sci. 34: 301–317.
Andreae, M. and Rosenfeld, D. (2008). Aerosol-cloudprecipitation Interactions. Part 1. The Nature and Sources
of Cloud-active Aerosols. Earth Sci. Rev. 89: 13–41.
Bauer, H., Giebl, H., Hitzenberger, R., Kasper-Giebl, A.,
Reischl, G., Zibuschka, F. and Puxbaum, H. (2003).
Airborne Bacteria as Cloud Condensation Nuclei. J.
Geophys. Res. 108: 4658.
Bauer, H., Kasper-Giebl, A., Löflund, M., Giebl, H.,
Hitzenberger, R., Zibuschka, F. and Puxbaum, H. (2002).
The Contribution of Bacteria and Fungal Spores to the
Organic Carbon Content of Cloud Water, Precipitation
and Aerosols. Atmos. Res. 64: 109–119.
Bauer, H., Schueller, E., Weinke, G., Berger, A.,
Hitzenberger, R., Marr, I.L. and Puxbaum, H. (2008).
Significant Contributions of Fungal Spores to the Organic
Carbon and to the Aerosol Mass Balance of the Urban
Atmospheric Aerosol. Atmos. Environ. 42: 5542–5549.
Bowers, R., Sullivan, A., Costello, E., Collett Jr, J., Knight, R.
and Fierer, N. (2011). Sources of Bacteria in Outdoor
Air across Cities in the Midwestern United States. Appl.
Environ. Microbiol. 77: 6350–6356.
Burge, H.A. and Rogers, C.A. (2000). Outdoor Allergens.
Environ. Health Perspect. 108: 653–659.
Burrows, S.M., Elbert, W., Lawrence, M.G. and Pöschl, U.
(2009). Bacteria in the Global Atmosphere- Part 1:
Review and Synthesis of Literature Data for Different
Ecosystems. Atmos. Chem. Phys. 9: 9263–9280.
Chi, M.C. and Li, C.S. (2007). Fluorochrome in Monitoring
Atmospheric Bioaerosols and Correlations with
Meteorological Factors and Air Pollutants. Aerosol Sci.
Technol. 41: 672–678.
DeLeon-Rodriguez, N., Lathem, T.L., Rodriguez-R, L.M.,
Barazesh, J.M., Anderson, B.E., Beyersdorf, A.J., Ziemba,
L.D., Bergin, M., Nenes, A. and Konstantinidis, K.T.
(2013). Microbiome of the upper Troposphere: Species
Composition and Prevalence, Effects of Tropical Storms,
and Atmospheric Implications. Proc. Nat. Acad. Sci. U.S.A.
110: 2575–2580.
Després, V.R., Alex Huffman, J., Burrows, S.M., Hoose,
C., Safatov, A.S., Buryak, G., Fröhlich-Nowoisky, J.,
Elbert, W., Andreae, M.O., Pöschl, U. and Jaenicke, R.
(2012). Primary Biological Aerosol Particles in the
Atmosphere: A Review. Tellus Ser. B 64: 15598.
Draxler, R.R. and Rolph, G.D. (2014). HYSPLIT (HYbrid
Single-Particle Lagrangian Integrated Trajectory) Model
access via NOAA ARL READY Website (http://www.
arl.noaa.gov/HYSPLIT.php). NOAA Air Resources
Two fluorescence based real-time instruments were used
to measure bioaerosol concentrations and size distributions
in the two different case studies in urban environments
during winter and summer. Two FBAP modes at 0.5–1.5
µm (fine) and 1.5–5 µm (coarse) were detected during the
summer, whereas the fine mode dominated in the winter.
Correlations between the BioScout and the UVAPS were
high with the FBAP coarse mode (R = 0.83) and fine mode
(R = 0.92). The BioScout showed 2.6 and 9.7 times higher
detection efficiencies for the coarse and fine FBAP,
respectively, compared to the UVAPS. This is the first study,
wherein the BioScout was used in outdoor environment and
compared to another LIF based instrument.
The coarse FBAP concentrations and fractions were the
highest in summer (0.028 #/cm3, 23%) and the lowest in
winter (0.010 #/cm3, 6%). Snow cover and low biological
activity were assumed to be the main reasons for low
coarse FBAP concentration in the wintertime. Both the fine
and the coarse FBAP fraction typically increased at night
during the summer; that is characteristic for natural fungal
spore emission. Various factors suggest that at least a
fraction of the observed fine FBAP were bacteria.
The long-range transport episode of particles from
Eastern Europe increased the fine FBAP concentration
over two orders of magnitude compared to the clean period
in the winter, but these FBAP probably also included
fluorescent non-biological particles. The potential sources
of fluorescent fine particles during the long-range transport
episode might be bacteria and/or anthropogenic emissions
such as biomass burning. Low correlations between FBAP
and NOx and BC indicate that local traffic emissions and
biomass burning are not considerable sources for fluorescent
particles at the measurement sites. The previous studies
typically treated fine FBAP as non-biological particles, but
this study showed that this is not necessarily the case, and
fine FBAP should be studied more and compared with
other analyzing techniques such as microscopy and qPCR.
The results provide information that can be used to
estimate health risks and climatic relevance of bioaerosols
in urban environments.
ACKNOWLEDGMENTS
The study was a part of the MMEA research program of
Cleen Ltd, supported by funding of Tekes (MMEA WP
4.5.2.). The support of Doctoral School of TUT, Jenny and
Antti Wihuri Foundation and Eemil Aaltonen Foundation
are also gratefully acknowledged. Special thanks are given to
Ms. Katri Pihlava and Mr. Anders Svens for their help during
REFERENCES
580
Saari et al., Aerosol and Air Quality Research, 15: 572–581, 2015
Laboratory, College Park, MD.
Gabey, A., Gallagher, M., Whitehead, J., Dorsey, J., Kaye,
P. and Stanley, W. (2010). Measurements and Comparison
of Primary Biological Aerosol above and below a Tropical
Forest Canopy Using a Dual Channel Fluorescence
Spectrometer. Atmos. Chem. Phys. 10: 4453–4466.
Gabey, A.M., Stanley, W.R., Gallagher, M.W. and Kaye,
P.H. (2011). The Fluorescence Properties of Aerosol
Larger than 0.8 μm in Urban and Tropical Rainforest
Locations. Atmos. Chem. Phys. 11: 5491–5504.
Gabey, A.M., Vaitilingom, M., Freney, E., Boulon, J.,
Sellegri, K., Gallagher, M.W., Crawford, I.P., Robinson,
N.H., Stanley, W.R. and Kaye, P.H. (2013). Observations
of Fluorescent and Biological Aerosol at a High-altitude
Site in Central France. Atmos. Chem. Phys. 13: 7415–
7428.
Hairston, P.P., Ho, J. and Quant, F.R. (1997). Design of an
Instrument for Real-time Detection of Bioaerosols Using
Simultaneous Measurement of Particle Aerodynamic Size
and Intrinsic Fluorescence. J. Aerosol Sci. 28: 471–482.
Heald, C. and Spracklen, D. (2009). Atmospheric Budget
of Primary Biological Aerosol Particles from Fungal
Spores. Geophys. Res. Lett. 36: L09806.
Hill, S.C., Mayo, M.W. and Chang, R.K. (2009).
Fluorescence of Bacteria, Pollens, and Naturally Occurring
Airborne Particles: Excitation/Emission Spectra (No.
ARL-TR-4722). Army Research Lab Adelphi Md
Computational and Information Sciences Directorate.
Ho, J. (2002). Future of Biological Aerosol Detection.
Anal. Chim. Acta 457: 125–148.
Hill, S.C., Pinnick, R.G., Nachman, P., Chen, G., Chang,
R.K., Mayo, M.W. and Fernandez, G.L. (1995). Aerosolfluorescence Spectrum Analyzer: Real-time Measurement
of Emission Spectra of Airborne Biological Particles.
Appl. Opt. 34: 7149–7155.
Huffman, J., Treutlein, B. and Pöschl, U. (2010). Fluorescent
Biological Aerosol Particle Concentrations and Size
Distributions Measured with an Ultraviolet Aerodynamic
Particle Sizer (UV-APS) in Central Europe. Atmos. Chem.
Phys. 10: 3215–3233.
Huffman, J.A., Sinha, B., Garland, R.M., Snee-Pollmann,
A., Gunthe, S.S., Artaxo, P., Martin, S.T., Andreae,
M.O. and Pöschl, U. (2012). Size Distributions and
Temporal Variations of Biological Aerosol Particles in
the Amazon Rainforest Characterized by Microscopy
and Real-time UV-APS Fluorescence Techniques during
AMAZE-08. Atmos. Chem. Phys. 12: 11997–12019.
Huffman, J.A., Prenni, A.J., Demott, P.J., Pöhlker, C., Mason,
R.H., Robinson, N.H., Fröhlich-Nowoisky, J., Tobo, Y.,
Després, V.R., Garcia, E., Gochis, D.J., Harris, E., MüllerGermann, I., Ruzene, C., Schmer, B., Sinha, B., Day, D.A.,
Andreae, M.O., Jimenez, J.L., Gallagher, M., Kreidenweis,
S.M., Bertram, A.K. and Pöschl, U. (2013). High
Concentrations of Biological Aerosol Particles and Ice
Nuclei during and after Rain. Atmos. Chem. Phys. 13:
6151–6164.
Jaenicke, R. (2005). Abundance of Cellular Material and
Proteins in the Atmosphere. Science 308: 73.
Jeys, T.H., Herzog, W.D., Hybl, J.D., Czerwinski, R.N.
and Sanchez, A. (2007). Advanced Trigger Development.
Lincoln Laboratory J., 17: 29–62.
Jung, J.H., Park, S.Y., Lee, J.E., Lee, B.U. and Bae, G.N.
(2012). Distinguishing Biotic and Abiotic Particles Using
an Ultraviolet Aerodynamic Particle Sizer for Real-time
Detection of Bacterial Bioaerosols. Environ. Eng. Sci.
29: 866–874.
Kanaani, H., Hargreaves, M., Ristovski, Z. and Morawska,
L. (2007). Performance Assessment of UVAPS: Influence
of Fungal Spore Age and Air Exposure. J. Aerosol Sci.
38: 83–96.
Lakowicz, J.R. (2006). Principles of Fluorescence
Spectroscopy, 3rd edn., Springer, Berlin, p. 205–231.
Matthias-Maser, S. and Jaenicke, R. (1995). The size
Distribution of Primary Biological Aerosol Particles
With radii 0.2 µm in an Urban/Rural Influenced Region,
Atmos. Res. 39: 279–286.
Matthias-Maser, S., Brinkmann, J. and Schneider, W. (1999).
The Size Distribution of Marine Atmospheric Aerosol
with Regard to Primary Biological Aerosol Particles over
the South Atlantic Ocean. Atmos. Environ. 33: 3569–3575.
Matthias-Maser, S., Obolkin, V., Khodzer, T. and Jaenicke,
R. (2000). Seasonal Variation of Primary Biological
Aerosol Particles in the Remote Continental Region of
Lake Baikal/Siberia. Atmos. Environ. 34: 3805–3811.
Mendell, M.J., Mirer, A.G., Cheung, K. and Douwes, J.
(2011). Respiratory and Allergic Health Effects of
Dampness, Mold, and Dampness-related Agents: A
Review of the Epidemiologic Evidence. Environ. Health
Perspect. 119: 748–756.
Niemi, J.V., Saarikoski, S., Tervahattu, H., Mäkelä, T.,
Hillamo, R., Vehkamäki, H., Sogacheva, L. and Kulmala,
M. (2006). Changes in Background Aerosol Composition
in Finland during Polluted and Clean Periods Studied by
TEM/EDX Individual Particle Analysis. Atmos. Chem.
Phys. 6: 5049–5066.
Niemi, J.V., Saarikoski, S., Aurela, M., Tervahattu, H.,
Hillamo, R., Westphal, D.L., Aarnio, P., Koskentalo, T.,
Makkonen, U., Vehkamäki, H. and Kulmala, M. (2009).
Long-range Transport Episodes of Fine Particles in
Southern Finland during 1999-2007. Atmos. Environ.
43: 1255–1264.
Pan, Y., Pinnick, R., Hill, S. and Chang, R. (2008).
Particle-fluorescence Spectrometer for Real-time
Single-particle Measurements of Atmospheric Organic
Carbon and Biological Aerosol. Environ. Sci. Technol.
43: 429–434.
Peccia, J., Milton, D.K., Reponen, T. and Hill, A.J. (2008).
A Role for Environmental Engineering and Science in
Preventing Bioaerosol-related Disease. Environ. Sci.
Technol. 42: 4631–4637.
Pinnick, R.G., Hill, S.C., Nachman, P., Pendleton, J.D.,
Fernandez, G.L., Mayo, M.W. and Bruno, J.G. (1995).
Fluorescence Particle Counter for Detecting Airborne
Bacteria and Other Biological Particles. Aerosol Sci.
Technol. 23: 653–664.
Pinnick, R.G., Hill, S.C., Nachman, P., Videen, G., Chen, G.
and Chang, R.K. (1998). Aerosol Fluorescence Spectrum
Analyzer for Rapid Measurement of Single Micrometer-
Saari et al., Aerosol and Air Quality Research, 15: 572–581, 2015
Sized Airborne Biological Particles. Aerosol Sci. Technol.
28: 95–104
Pöhlker, C., Huffman, J. and Pöschl, U. (2012).
Autofluorescence of Atmospheric Bioaerosols-fluorescent
Biomolecules and Potential Interferences. Atmos. Meas.
Tech. 5: 37–71.
Pöschl, U., Martin, S.T., Sinha, B., Chen, Q., Gunthe, S.S.,
Huffman, J.A., Borrmann, S., Farmer, D.K., Garland,
R.M., Helas, G., Jimenez, J.L., King, S.M., Manzi, A.,
Mikhailov, E., Pauliquevis, T., Petters, M.D., Prenni,
A.J., Roldin, P., Rose, D., Schneider, J., Su, H., Zorn,
S.R., Artaxo, P. and Andreae, M.O. (2010). Rainforest
Aerosols as Biogenic Nuclei of Clouds and Precipitation
in the Amazon. Science 329: 1513.
Reponen, T., Willeke, K., Grinshpun, S. and Nevalainen,
A. (2011). Biological Particle Sampling, Aerosol
Measurement: Principles, Techniques, and Applications,
Third Edition, p. 549–570.
Rolph, G.D. (2014). Real-time Environmental Applications
and Display sYstem (READY) Website (http://www.re
ady.noaa.gov). NOAA Air Resources Laboratory, College
Park, MD.
Ryan, P.H., Bernstein, D.I., Lockey, J., Reponen, T., Levin,
L., Grinshpun, S., Villareal, M., Khurana Hershey, G.K.,
Burkle, J. and LeMasters, G. (2009). Exposure to Trafficrelated Particles and Endotoxin during Infancy is
Associated with Wheezing at Age 3 Years. Am. J.
Respir. Crit. Care Med. 180: 1068–1075.
Saari, S.E., Putkiranta, M.J. and Keskinen, J. (2013).
Fluorescence Spectroscopy of Atmospherically Relevant
Bacterial and Fungal Spores and Potential Interferences.
Atmos. Environ. 71: 202–209.
Saari, S., Reponen, T. and Keskinen, J. (2014). Performance
581
of Two Fluorescence Based Real-time Bioaerosol
Detectors: BioScout vs. UVAPS. Aerosol Sci. Technol.
48: 371–378.
Schumacher, C.J., Pöhlker, C., Aalto, P., Hiltunen, V.,
Petäjä, T., Kulmala, M., Pöschl, U. and Huffman, J.A.
(2013). Seasonal Cycles of Fluorescent Biological Aerosol
Particles in Boreal and Semi-arid Forests of Finland and
Colorado. Atmos. Chem. Phys. 13: 11987–12001.
Smith, D.J., Timonen, H.J., Jaffe, D.A., Griffin, D.W.,
Birmele, M.N., Perry, K.D., Ward, P.D. and Roberts,
M.S. (2013). Intercontinental Dispersal of Bacteria and
Archaea by Transpacific Winds. Appl. Environ. Microbiol.
79: 1134–1139.
Sun, J. and Ariya, P. (2006). Atmospheric Organic and
Bio-aerosols as Cloud Condensation Nuclei (CCN): A
Review. Atmos. Environ. 40: 795–820.
Toprak, E. and Schnaiter, M. (2013). Fluorescent Biological
Aerosol Particles Measured with the Waveband Integrated
Bioaerosol Sensor WIBS-4: Laboratory Tests Combined
with a One Year Field Study. Atmos. Chem. Phys. 13:
225–243.
Vali, G., Christensen, M., Fresh, R., Galyan, E., Maki, L.
and Schnell, R. (1976). Biogenic Ice Nuclei. Part II:
Bacterial Sources. J. Atmos. Sci. 33: 1565–1570.
Yli-Ojanperä, J., Mäkelä, J. M., Marjamäki, M., Rostedt,
A. and Keskinen, J. (2010). Towards Traceable Particle
Number Concentration Standard: Single Charged Aerosol
Reference (SCAR). J. Aerosol Sci. 41: 719–728.
Received for review, October 24, 2014
Revised, February 3, 2015
Accepted, February 4, 2015