Chamber bioaerosol study
Bhangar et al.
Online Supporting Information for the following article published in Indoor Air
DOI: 10.1111/ina.12195
Chamber bioaerosol study: Human emissions of size-resolved fluorescent
biological aerosol particles
Seema Bhangar1,*, Rachel I. Adams2, Wilmer Pasut3, J. Alex Huffman4, Edward A. Arens3, John
W. Taylor2, Thomas D. Bruns2, and William W Nazaroff1
1
Department of Civil and Environmental Engineering, University of California, Berkeley, CA,
USA
2
Department of Plant and Microbial Biology, University of California, Berkeley, CA, USA
3
Center for the Built Environment, University of California, Berkeley, CA, USA
4
Department of Chemistry and Biochemistry, University of Denver, CO, USA
*
Corresponding email: bhangar@gmail.com
S1. Temperature and relative humidity trends during basic and supplementary treatments
During the basic treatments indoor temperature was successfully controlled (to 22 °C),
and varied across a small range within and between treatments, with the exception of the 8people treatments when the higher interior heat load caused the indoor temperature to drift
upward to 23 or 24 °C. The outdoor temperature varied across a wider range (9-20 °C) and was,
on average, a few degrees higher during the second (covered-floor) week. The supply air
temperature was cooler by an average 2 °C during the higher occupancy or occupant activity (8seated or 2-walking) treatments to compensate for the greater heat load in the room. Unlike
temperature, indoor relative humidity was not controlled and varied substantially among
treatments (range: <15% to 36%), reflecting differences in the outdoor absolute humidity and
interior metabolic loads, combined with the applied thermal control of the supply air.
Temperature and RH trends during the supplementary treatments showed some
differences compared to the basic set. Rather than tracking occupancy changes, supply air
temperatures varied as a function of HVAC fan speed and humidification conditions, varying on
average from 18 °C for reduced fan/no humidification, to 20 °C for normal fan/no
humidification, and to 21-23 °C for normal fan/humidification. The average temperature within
the chamber was higher on average, and spanned a wider range (22-26 °C) than for the basic set.
In contrast, the outdoor RH was higher and less variable, so indoor RH values ranged within 2134%, except when RH was deliberately manipulated.
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Chamber bioaerosol study
Bhangar et al.
S2. Preliminary explorations of the influence of relative humidity on FBAP emissions
The potential influence of relative humidity on bioaerosol emissions was explored by
conducting a few seated and walking treatments with the chamber air humidified at two levels
(40% and 80%) and the floor exposed. Results were close to or within the normal range, except
for emissions during walking at 80% RH, which were about 2.5× higher, for both FBAP and
highly fluorescent particles, than the base case of walking on the exposed floor with no
humidification. Note that the enhanced emissions were expected to have occurred as the
byproduct of RH effects on particle adhesion/detachment dynamics. The time scale of the
elevated RH conditions in the chamber was not sufficient to influence FBAP emissions indirectly
through an effect on microbial activity and growth. Note also that in the absence of deliberate
humidification, the RH level in the chamber remained below 40%, and was not thought to be a
variable directly influencing particle emission dynamics (i.e., for treatments 1-41). The
relationship between relative humidity and human particle emissions is not yet well understood.
Previous empirical findings have been inconsistent, and it has been hard to predict the expected
effect deterministically due to the simultaneous influence of RH on competing adhesion and
resuspension processes, as reviewed by Qian et al. (2014).
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Bhangar et al.
Table S1. UV-APS lumped size groups
Median da (m) da range (m)
1.3
1.0 – 1.5
1.7
1.5 – 2.0
2.2
2.0 – 2.5
3.0
2.5 – 3.5
4.3
3.5 – 5.0
6.1
5.0 – 7.2
8.8
7.2 – 10.4
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Table S2. Air-exchange rate (a) assessments from selected treatments (Tm).1
Tm a (h-1) Initial dCO2 HVAC fan r2
(ppm)2
Setting
1
3.1
221
Normal 0.93
2
2.9
320
Normal 1.00
4
2.9
517
Normal 1.00
5
3.2
177
Normal 0.99
6
41
Normal
8
2.9
503
Normal 1.00
9
3.0
135
Normal 1.00
10
2.5
196
Normal 1.00
11
3.1
216
Normal 0.94
12
35
Normal
13
72
Normal
14
2.9
202
Normal 1.00
16
2.6
157
Normal 0.98
17
2.8
704
Normal 1.00
19
2.7
438
Normal 1.00
20
58
Normal
21
105
Normal 0.99
23
2.6
610
Normal 1.00
24
94
Normal
25
2.7
180
Normal 0.99
26
2.6
112
Normal 1.00
27
52
Normal
28
40
Normal
29
3.0
207
Normal 1.00
31
1.9
354
Medium 0.98
33
1.6
216
Low 1.00
35
1.3
192
Low 0.99
36
1.5
197
Low 1.00
37
1.3
252
Low 0.97
39
2.8
108
Normal 1.00
40
184
Normal 0.62
41
Normal
42
2.9
192
Normal 1.00
43
2.9
124
Normal 0.99
46
3.0
119
Normal 0.99
48
2.0
256
Medium 0.99
1
Estimates are based on the first-order decay of occupant-generated carbon dioxide. Coefficients of
determination for the linear correlation between log(dCO2) and time are shown, with dCO2 evaluated as
the difference between indoor and outdoor levels. Zero-occupant treatments (N = 12), and treatments
followed by chamber maintenance (N = 2) lacked a decay period and are not included in the table.
2
The “initial dCO2” was defined as the difference between indoor and outdoor CO2 levels at the start of
the unoccupied period. Treatments with an initial dCO2 less than 105 ppm (N = 8) were excluded because
they did not support a robust decay curve. The threshold of 105 ppm was chosen based on a sensitivity
analysis that showed high a estimates (that clustered together) were obtained for dCO2 50-105 ppm;
above that range a was no longer a function of dCO2.
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Table S3. The expected mean (± standard deviation) indoor proportion of outdoor particles (IPOP),
evaluated per particle size group as the average indoor/outdoor particle number concentration (based on
data from optical particle counters) during zero occupancy basic treatments (normal fan; N = 6) and zero
occupancy supplementary treatments conducted at reduced fan speeds (reduced fan; N = 2).
IPOP,
IPOP,
da size range (m) IPOP,
normal fan reduced fan normal fan,
modeled1
0.3 – 0.5
0.8 ± 0.1
0.4
0.9
0.5 – 0.7
0.7 ± 0.2
0.5
0.9
0.7 – 1
0.7 ± 0.2
0.5
0.9
1–2
0.6 ± 0.2
0.3
0.8
2–5
0.51 ± 0.09
0.2
0.2
>5
0.17 ± 0.05
0.08
0.1
1
Modeled values were computed for each particle size group i using IPOPi = [ a × (1-i) ÷ (ki + a) ],
which is adapted from Riley et al. (2002), neglecting natural ventilation, infiltration, recirculation, and
based on a = 2.8 h-1, size-specific deposition coefficients (ki) as reported in Figure S3, and with the
filtration efficiency (i) treated as zero for particles smaller than 2 m, and 50% for particles larger than 2
m based on expectations for MERV 7 filters. There is reasonable agreement between measured and
expected values.
Table S4. Adjustment factors from OPC side-by-side tests.1,2
da size range (m) OPC1 OPC2 OPC4
0.3 – 0.5
0.99
1.2
0.98
0.5 – 0.7
0.95
1.0
0.97
0.7 – 1
0.96
0.97
0.94
1–2
0.96
0.95
0.81
2–5
0.92
0.89
0.72
>5
0.88
1.0
1.0
1
The slopes correspond to single parameter linear regressions (intercepts = 0).
2
Comparisons were conducted with 1-min particle number concentrations (with the exception of one test,
when 5-min data were used).
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Figure S1a. The chamber interior (volume ~75 m3) showing sampling equipment, desks and chairs (with
casters) for up to 8 seated occupants, inoperable windows along the south and west walls, the carpeted
floor, and floor-level air supply vents.
Figure S1b. The chamber exterior south wall, showing its location on the building’s second story. The
outdoor sampling inlets are adjacent to the mechanical air handling system air intake. The vegetation is
eucalyptus trees, with foliage at least two meters from the exterior wall.
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Bhangar et al.
Figure S2. Mean concentrations of particles (excluding those with fluorescence intensity = 1) in the
chamber air during two representative treatments conducted with the floor exposed: (a) 8 seated
occupants (treatment 8), and (b) Zero occupants (treatment 7). Particle concentrations are shown as a
function of particle size (0.5 – 20 m) and autofluorescence intensity (2 to 64).
In the present analysis particles with fluorescence intensity 1-2 are designated as non-fluorescent, greater
than 2 as fluorescent biological aerosol particles or FBAPs, and greater than 20 as highly fluorescent. The
concentration of highly fluorescent particles is not strongly sensitive to the specific choice of threshold
level for denoting particles as highly fluorescent, because a large fraction of the highly fluorescent
particles are in the “saturated” channel (with intensity 64).
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Chamber bioaerosol study
Bhangar et al.
Figure S3. A comparison between empirical estimates (means ± standard deviations, N = 3-9) of sizespecific deposition loss rate coefficients (k), and values from Thatcher et al. (2002) for conditions that
match the airspeed (14 cm/s) measured in the core of the chamber. The range of values reported by
Thatcher et al. (2002) for conditions ranging from “fans off, bare room surfaces” to “airspeed = 19 cm/s,
fully furnished room” are shown as a shaded band.
Only a few empirical estimates are included in the means presented because the net-NF levels in the room
at the end of each treatment were typically too low to support a decay curve that met the criteria for
inclusion. These criteria were related to the number of minutes before levels returned to the baseline, and
the coefficient of determination of the linear correlation between log(net-NF) and time.
The mean airspeed measured in the core of the room was 0.14 ± 0.04 cm/s under sedentary conditions. It
increased only slightly to 0.15 ± 0.06 cm/s with one occupant walking. Consequently, a single set of
deposition loss rates was used as input for treatments that included both sedentary and ambulatory
conditions.
Thatcher et al. (2002) report k values for discrete particle aerodynamic diameters. The k for each lumped
size group was estimated by linearly interpolating between the Thatcher et al. (2002) estimates
corresponding to diameters just less than and just greater than the midpoint diameter of each lumped
group. The upper bound of the largest OPC size bin was assumed to be 10 m for the purposes of
interpolation.
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Chamber bioaerosol study
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Figure S4. UV-APS size calibration curve. The x-axis shows equivalent aerodynamic diameters for
polystyrene latex particles (PSL). The parameter da* plotted on the y-axis is the median UV-APS
response (i.e., 50% of sampled particles were smaller than da*). The best-fit line was da* = 0.99 (PSL da)
+ 0.04 m. Results based on the response to monodispersed fluorescent particles (green markers) are
shown on the curve for comparison but were not included in the regression used to generate the
calibration equation. (The accuracy of fluorescent particles of these sizes is not certified by NIST.)
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Figure S5. Mean (± standard deviation) estimated emission rates of total particles 2-5 m (ERT2), from
basic treatments, when occupants (number = 0, 1, 2, 8) were seated and engaged in normal desk work,
with the carpeted floor exposed or with the floor covered with clean plastic sheeting. Error bars show
standard deviations. The large range in control (i.e. zero occupancy) results and the large coefficients of
variation show that our methods are not adequate to resolve emissions for this particle-size group under
these experimental conditions. Hence, total particle emissions are reported only for particles larger than 5
m in the main manuscript.
Figure S6. Size distributions of weighted mean (± standard deviation) occupant emissions of highly
fluorescent particle numbers normalized by the mass of carbon dioxide emitted (EF20), shown as a
function of particle aerodynamic diameter (da) during basic treatments when 1-8 occupants were sitting
and engaged in normal desk work, with the carpeted floor (a) exposed or (b) covered (N = 9 treatments
and 31-33 subjects per floor condition). The mode, geometric standard deviation (GSD), and amplitude
(A) of lognormal distributions that provide the best fit to emissions of particles larger than 2 m are
shown on each panel.
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Bhangar et al.
Figure S7. Size distributions of weighted mean (± standard deviation) normalized occupant emission
rates of (a) FBAP numbers (EF) and (b) highly fluorescent numbers (EF20) during basic (N = 9) versus
supplementary treatments (N = 3) when 1-8 occupants were sitting and engaged in normal desk work with
the carpeted floor exposed. Basic treatments utilized 20 female subjects and 11 male subjects.
Supplementary treatments utilized 6 female subjects.
Figure S8. Size distributions of weighted mean (± standard deviation) normalized occupant emission
rates of (a) FBAP numbers (EF) and (b) highly fluorescent numbers (EF20) during basic (N = 3) versus
supplementary (N = 1) treatments when 2 occupants walked on the exposed carpeted floor. All subjects
were female.
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Bhangar et al.
Figure S9. Time-series of (a) size-integrated (2.5-10 m) NF20 and NF concentrations, and NF/NT
concentration ratios, and of (b) size-resolved NF concentrations, during a treatment with a choreographed
series of upper body movements. The periods labeled 1-6 represent the following activities conducted
repetitively by two seated occupants who did not vary the contact of their feet with the floor: (1) walk into
room, normal computer work; (2) brush hair; (3) take outer wear clothing layers off and put back on; (4)
read a book, deliberately flipping pages more than needed; (5) stretch; and (6) rub bare arms and face.
Occupants exited the room at 12:17.
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Figure S10. Supply-air levels of total particles larger than 2 m (PN2), evaluated with optical particle
counters, for the non-RH treatments, comparing baseline and treatment periods. Results show that the
mean PN2 baselines generally agreed well with treatment mean PN2 concentrations, with the exception of
treatments 40-41. The mean baselines for these treatments were skewed high because of one very high
baseline concentration estimate (post-40, pre-41). However, using only the more representative pre-40
baseline to evaluate emissions for Tm40 (supplementary walking/floor-exposed) led to a relatively small
(<10%) increase in the response.
As a second potential indicator of the potential of temporal changes to influence emission estimates, we
evaluated a signal-noise (S/N) ratio per treatment as the treatment mean, NF or NF20, divided by the
absolute value of the difference between the pre-baseline and post-baseline mean values (for all
treatments except Tm30 and Tm47 for which post-baseline means were unavailable). The median
estimated S/N ratios for FBAP (and highly fluorescent particles) for treatments with more than one
occupant (i.e., that were associated with higher treatment mean concentrations) were reasonably high: 19
(45), 4 (7), and 7 (8) for exposed floor, covered floor, and supplementary treatments, respectively.
References for Supporting Information
Qian, J., Peccia, J. and Ferro, A.R. (2014) Walking-induced particle resuspension in indoor
environments, Atmospheric Environment, 89, 464-481.
Riley, W.J., McKone, T.E., Lai, A.C.K., and Nazaroff, W.W. (2002) Indoor particulate matter of
outdoor origin: importance of size-dependent removal mechanisms, Environmental Science
and Technology, 36, 200–207.
Thatcher, T.L., Lai, A.C.K., Moreno-Jackson, R., Sextro, R.G. and Nazaroff, W.W. (2002)
Effects of room furnishings and air speed on particle deposition rates indoors, Atmospheric
Environment, 36, 1811-1819.
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