PMHOME: A Database of Continuous Particle Measurements in an Occupied House for Four Years

PMHOME: A DATABASE OF CONTINUOUS PARTICLE
MEASUREMENTS IN AN OCCUPIED HOUSE FOR FOUR YEARS

LA Wallace1*, C Croghan2, C Howard-Reed3, A Persily3
National Exposure Research Laboratory, US EPA, Reston VA, USA
2National Exposure Research Laboratory, US EPA, Research Triangle Park, NC, USA
National Institute of Standards and Technology, Gaithersburg, MD, USA
ABSTRACT

Although considerable data exist on 24-hour integrated measurements of fine and coarse
particles indoors, much less information is available on moment-to-moment variation for a
full range of particle sizes including ultrafme particles. Also, information is limited on the
relationships between air change rates, temperature, humidity, indoor-outdoor concentration
ratios, indoor source strengths due to various activities such as cooking and cleaning,
penetration factors, and deposition rates under realistic conditions. Therefore EPA and NIST
have collaborated on a four-year (October 1, 1996 through Dec. 31, 2000) study of particle
concentrations in an occupied townhouse.

Target pollutants included ultraflne, fine, and coarse particles from 10 nm to 20 urn in
diameter; black carbon (BC); and particle-bound polyaromatic hydrocarbons (PAH).
Ancillary measurements included air change rates, wind velocity, temperature, and relative
humidity. Measurements were made continuously and the final database (PMHOME) is on a
5-minute basis. PMHOME is available to researchers in Statistica or SAS format. Types of
investigations that can be done using PMHOME include calculation of the relative
contribution of outdoor air particles to indoor air concentrations, effects of indoor sources
such as cooking and candle burning, and relationships of air change rates to outdoor
temperature and wind speed.

INDEX TERMS

Particles, air change rates, ultrafine particles, residential concentrations, cooking.

INTRODUCTION

Outdoor particles have been associated with mortality in many studies worldwide. However,
most people spend a majority of their time indoors. They breathe a mixture of particles from
outdoor and indoor sources. Little is known of the relative toxicity of particles from outdoor
and indoor sources, but initial findings suggest they are of roughly equal toxicity (Long, Suh,
Kobzik et al., 2001). Therefore it is of interest to measure total human exposure to particles
and apportion that exposure between outdoor and indoor sources. It is also of interest to
determine how such sources as cooking and burning candles, as well as ancillary factors such
as air change rates, affect particle composition and concentrations.

Most existing studies of indoor and outdoor particle concentrations have employed
gravimetric monitors. These have the advantage of being well understood with excellent
* Contact author email: wallace.lance@,epa.gov

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precision, often on the order of 5%. Their main disadvantage is that they provide only
average concentrations over fairly long periods of 8-24 hours. This does not allow
unambiguous identification of sources or estimation of peak concentrations. Also, ultrafine
particles, which may have health effects more in proportion to their number than their mass,
are difficult to detect with gravimetric monitors. Newer monitors are available that are able to
estimate particle number on a semicontinuous or continuous basis. Although less precise than
gravimetric monitors, they offer the chance of learning more about various indoor sources,
peak concentrations, and ultrafine particle numbers.

Therefore a four-year study was begun in the fall of 1996 to investigate the ability of the
newer monitors to provide useful data on a short (5-minute) time scale. The objective of the
study was twofold: to provide methodological information on the performance of a set of
state-of-the-art instruments; and to provide a database of particle concentrations and ancillary
information that would be made widely available to researchers. Indoor air quality models
require knowledge of how personal activities, indoor air change rates, frequency of cooking
and other particle-producing activities, frequency of window opening and fan use, and
meteorological phenomena affect indoor air quality year-round. As a result, the study was
designed to extend over several years.

Monitoring began in October of 1996 and was completed on Dec. 31, 2000. Earlier
publications from this series of studies have provided individual particle size profiles for
different types of cooking (Wallace, Quackenboss, and Rodes, 1997); estimates of deposition
rates for ultrafine, fine, and coarse particles (Howard-Reed, Emmerich, and Wallace, 2000);
identification of morning traffic and evening woodburning as major contributors of black
carbon (BC) to indoor concentrations (Wallace, 2000; La Rosa, Wallace, and Buckley, 2002);
and estimates of source strength for different types of cooking (Howard-Reed and Wallace,
1999). This paper will describe the data base (PMHOME) that is now available for use by
interested researchers.

METHODS

The study home is a three level, four-bedroom, 385-m end townhouse in Reston, Virginia, a
suburban area 40 km northwest of Washington, D.C. Two adult nonsmokers live in the house.
The house is built on a hill, such that the basement is underground at the front (west) of the
house, but opens onto a patio at the back of the house. Heating is central forced air with a gas
furnace and standard furnace filter, gas hot water heater, and a vented gas dryer. Central air
conditioning is also available with an outdoor compressor near the patio. The basement is
partially finished, with a carpeted floor in the east portion and a cement floor in the utility
room containing washer, dryer, furnace, and hot water heater. The first floor contains a
kitchen/dining area, a bathroom, and living room with fireplace (unused). The second floor
contains four rooms: a master bedroom with bath, a guest bedroom, and two rooms used as
offices.

Particle monitors included a Scanning Mobility Particle Sizer (SMPS) for ultrafine particles
(100 size categories from 10 nm to 450 nm) and an Aerodynamic Particle Sizer (APS) for fine
and coarse particles (50 size categories from 0.5 u,m to 20 jam). Both instruments are
manufactured by TSI, Inc., St. Paul, MN. Other instruments included four optical scattering
instruments with six size ranges from 0.3 um to >10 |im (Model 500-1, Climet Instruments,
Redwood City, CA), four passive nephelometers (Model pDR-1000, MIE, Inc, Bedford, MA),
two Aethalometers measuring black carbon by optical transmission (Magee Scientific,

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Berkeley, CA), and three instruments measuring particle-bound PAH by ionization by
ultraviolet light (Ecochem Analytics, West Hills, CA), SFe tracer gas was automatically
injected every 2 or 4 hours, and the resulting concentrations were measured in 10 locations
sequentially every minute using a gas chromatograph with electron capture detection to
determine whole house air change rates. A portable meteorological station (MDL 102263,
Climatronics, Inc., Bohemia, NY) was installed atop the house and measured wind velocity
and direction ultrasonically every 6 seconds.

A journal was kept to record events such as cooking, candle burning, opening windows, and
other activities that might affect particle concentrations. These entries were then used to tag
each 5-minute period with a marker indicating whether or not an indoor source was operating.
Because concentrations remain elevated for some time after the source ceases operating, these
periods of elevated concentrations were also assigned to the indoor source regime. Since
some sources affect ultrafine particles only, whereas other sources may affect fine or coarse
particles only, separate records were kept for four sizes of particles: ultrafines (<0.1 um), the
accumulation mode (0.1-1 urn), fine particles (1-2.5 um), and coarse particles (2.5-10 u.m).

The SMPS, APS, and Climet provide a primary determination of the number of particles per
unit volume. The volume of these particles was determined by assuming sphericity and
multiplying the number of particles by ncf/6. where the diameter d of the particles is the
geometric mean of the associated size range. (In the case of the Climet, which has only 6
broad size ranges, the proper value of d was determined by calculation from the concurrent
number distribution recorded by the APS.) The MIE provides an estimated mass based on a
calibration aerosol with a specific gravity of 2.5. Therefore the MIE particle volume was
calculated from the mass by dividing by this density.

RESULTS

Each instrument was found to be useful, although each had weaknesses. The SMPS
employed two nozzles allowing somewhat different size ranges to be measured. The nozzles
agreed very well for the ultrafine particles but diverged for the overlap region of 100-450 nm.
The APS showed evidence of serious overestimates for particle size ranges greater than about
5 um. The two lower size ranges of the Climet (0.3-0.5 um and 0.5-1 um) appeared to be
affected by relative humidity, as was the MIE. The Aethalometers were affected both by
relative humidity and by the operation of the automatic tape advance feature. A more
complete discussion of these effects is found in Wallace, Howard-Reed, and Emmerich
(2002).

A fine particle indoor source was evident 12.2% of the time and a coarse particle source was
apparent 14.5% of the time. Similarly, a source of ultrafine particles (<0.1 um) was evident
22.0% of the time, and of particles in the accumulation mode (0.1-1 u.m) 7.2% of the time.
The remainder of the time should represent the infiltration of outdoor particles. If we subtract
the average concentration due to outdoor particles from the observed concentration while
indoor sources were operating, we can estimate the relative contribution of indoor and
outdoor sources. Indoor sources were responsible for 50-80% of the ultrafine particles but
only about 40-50% of the accumulation mode particles. Then the indoor contribution rose
again to 75-90% for the particles >1 um (Figure 1).

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Relative Contribution of Indoor Sources to Observed Volumes
« 0.9
Q)
i o-s
o
W 0.7

§ 0.6
| 0.5

§ 0.4
Q
B 0.3
o
1 0.2
£
"- 0.1
0
SMPS
APS
N^
IF iSr

Size Range (SMPS: nm; APS:
Figure 1. Relative contribution of indoor sources to total indoor particle volume
concentrations, by particle diameter.

A database (PMHOME) was created to organize all data by 5-minute intervals. Data
collected at shorter time intervals (e.g., every minute) were averaged for 5-minute entries. At
present, only the last 18 months (July 1999 through December 2000) are included. The earlier
years are being prepared for entry. The APS and SMPS had a completeness percentage of
88% and 89%, respectively. The Climets and MIEs were operating only during January
through May 2000, and had a comparable completeness percentage over that time period.
There were approximately 6000 measured air change rates for each of the 10 indoor locations
over the 18-month period. The instruments employed and the rough number of measurements
made by each instrument over the four-year period are summarized in Table 1.

Table 1. Continuous methods employed in townhouse study.
Instrument
SMPS
APS
Climets (4)
MIE (4)
Aethalometers
PAS (3)
GC/ECD
Climatronics
Transducers
HS-3 sensors
Parameter
Ultrafmes
Fine, coarse
Fine, coarse
Fine, coarse
Black carbon
PAH
SF6
Wind
Temperature
Rel humidity
Site
Basement
Basement
3 floors, out
3 floors, out
In, out
In, out
Basement
Rooftop
1 0 rooms
6 rooms
Frequency
5 min
1 min
5 min
1 min
5 min
1 min
10 min
6 sec
10 min
10 min
Start date
11/97
4/98
10/96
12/98
7/98
10/96
12/98
12/98
12/98
12/98
Observations
250,000
1,000,000
1,500,000
500,000
400,000
2,000,000
600,000
4,000,000
600,000
360,000

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DISCUSSION

The SMPS and APS proved highly reliable, operating continuously for a full year at near-90%
completeness. Most of the missing values were due to scheduled interruptions or operator
errors rather than equipment malfunction. The indoor MIE also provided generally trouble-
free operation, but the outdoor MIE attracted spiders and had to be cleaned often. The
Climets were slightly less reliable, requiring a number of repairs at the manufacturers'
facility.

Several recent studies have employed continuous instruments to measure indoor particles.
Abt, Suh, Catalano et al (2000) employed an SMPS and APS in four Boston homes for 2-
week periods. The authors estimated the indoor contribution of particles from 100-500
nanometers to range between 5% and 65%, compared to our estimates of 30-50%. Their
estimate of the contribution of indoor sources to the larger size range from 1-10 fim was 40-
80%, compared to our estimate of 70-90%. The wider range of their estimates could be due to
increased variability represented by four homes compared to our single home. Long, Suh, and
Koutrakis (2000) and Long, Suh, Catalano et al (2001) used the same instrumentation to study
a broader sample of nine Boston homes (five over two seasons) for 6-12 days per visit.

CONCLUSION AND IMPLICATIONS

All instruments employed were extremely useful in identifying indoor sources, recording peak
concentrations, and making possible estimates of the relative importance of indoor and
outdoor sources. However, all instruments also had weaknesses that must be accounted for in
interpreting the results.

The resulting database (PMHOME) has been used in several journal articles, but is
sufficiently rich that a number of other statistical approaches could be supported. It is hoped
that researchers will avail themselves of this opportunity.

ACKNOWLEDGEMENTS

We would like to thank Dan Greb, Stuart Dols, and Steve Nabinger of the National Institute
of Standards and Technology NIST for technical help.

REFERENCES

Abt E, Suh H, Catalano P. and Koutrakis, P. 2000. Relative contribution of outdoor and
indoor particle sources to indoor concentrations, Environ Sci Technol 34:3579-3587.

Howard-Reed C, and Wallace LA. 1999. Continuous measurement of particles (0.01 fim to 20
fj.m) in an occupied home. Presented at the 18th Annual American Association for Aerosol
Research, Tacoma, Washington, October 1999.

Howard-Reed CH, Emmerich SJ, and Wallace LA. 2000. Determination of particle
deposition rates for cooking and other indoor sources. Presented at AAAR Annual
Conference, St. Louis, MO, November, 2000.

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La Rosa LE, Buckley T, and Wallace LA. 2002. Real-time indoor and outdoor measurements
of black carbon and particle-bound PAHs: an examination of sources. JAir Waste Manage
Assoc 52:114-1*5.

Long CM, Suh HH, and Koutrakis P. 2000. Characterization of indoor particle sources using
continuous mass and size monitors. J Air Waste Manage Assoc. 50:1236-1250.

Long CM, Suh HH, Catalano PJ, and Koutrakis P. 2001. Using time- and size-resolved
particulate data to quantify penetration and deposition behavior. Environ Sci Technol 35
(10):2089-2099.

Long CM, Suh HH, Kobzik L, Catalano PJ, Ning YY, and Koutrakis P. 2001. A pilot
investigation of the relative toxicity of indoor and outdoor fine particles: in vitro effects of
endotoxin and other particulate properties. Environ Health Perspectives 109:1019-1026.

Wallace LA, Quackenboss J, and Rodes C. 1997. Continuous measurements of particles,
PAH, and CO in an occupied townhouse in Reston, VA. In: Measurement of Toxic and
Related Air Pollutants, Proceedings ofEPA-AWMA Symposium on Toxic and Related
Compounds, Research Triangle Park, NC, April 29-May 1, 1997, pp. 860-871. Air & Waste
Management Association, Pittsburgh, PA. VIP-74.

Wallace LA. 2000. Real-Time monitoring of particles, PAH, and CO in an occupied
townhouse, Applied Occup Environ Hygiene 15:1-9.

Wallace LA, Howard-Reed C, and Emmerich SJ. 2002. Continuous monitoring of particles
in a residence for 18 months in 1999-2000. Submitted to J Air Waste Manage Assoc.
DISCLAIMER

This study was partially funded by an EPA Internal Grant to the first author. It has been
reviewed and cleared for publication. However, it is not necessarily reflective of EPA policy.
Mention of brand names is not to be understood as endorsement.

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DISCUSSION

Several recent studies have employed continuous instruments to measure indoor particles.
Abt, Suh, Catalano et al (2000) employed an SMPS and APS in four Boston homes for 2-
week periods. The authors estimated the indoor contribution of particles from 100-500
nanometers to range between 5% and 65%, compared to our estimates of 30-50%. Their
estimate of the contribution of indoor sources to the larger size range from 1-10 um was 40-
80%, compared to our estimate of 70-90%. The wider range of their estimates could be due to
increased variability represented by four homes compared to our single home. Long, Suh, and
Koutrakis (2000) and Long, Suh, Catalano et al (2001) used the same instrumentation to study
a broader sample of nine Boston homes (five over two seasons) for 6-12 days per visit.

CONCLUSION AND IMPLICATIONS

ACKNOWLEDGEMENTS

We would like to thank Dan Greb, Stuart Dols, and Steve Nabinger of the National Institute
of Standards and Technology NIST for technical help.

REFERENCES

Abt E, Suh H, Catalano P. and Koutrakis, P. 2000. Relative contribution of outdoor and
indoor particle sources to indoor concentrations, Environ Sci Technol 34:3579-3587.

Howard-Reed C, and Wallace LA. 1999. Continuous measurement of particles (0.01 um to 20
urn) in an occupied home. Presented at the 18th Annual American Association for Aerosol
Research, Tacoma, Washington, October 1999.

Howard-Reed CH, Emmerich SJ, and Wallace LA. 2000. Determination of particle
deposition rates for cooking and other indoor sources. Presented at AAAR Annual
Conference, St. Louis, MO, November, 2000.

-------
La Rosa LE, Buckley T, and Wallace LA, 2002. Real-time indoor and outdoor measurements
of black carbon and particle-bound PAHs: an examination of sources. J Air Waste Manage
Assoc 52:174-185.

Long CM, Suh HH, and Koutrakis P. 2000. Characterization of indoor particle sources using
continuous mass and size monitors. J Air Waste Manage Assoc. 50:1236-1250.

Long CM, Suh HH, Catalano PJ, and Koutrakis P. 2001. Using time- and size-resolved
particulate data to quantify penetration and deposition behavior. Environ Sci Techno! 35
(10):2089-2099.

Wallace LA. 2000. Real-Time monitoring of particles, PAH, and CO in an occupied
townhouse, Applied Occup Environ Hygiene 15:1-9.

Wallace LA, Howard-Reed C, and Emmerich SJ. 2002. Continuous monitoring of particles
in a residence for 18 months in 1999-2000. Submitted to J Air Waste Manage Assoc.
DISCLAIMER

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NERL-RTP-HEASD-02-018 TECHNICAL REPORT DATA
1. Report No. 2,
EPA/600/A-02/001
4, Title and Subtitle
PMHOME: A DATABASE OF CONTINUOUS
PARTICLE MEASUREMENTS IN AN OCCUPIED
HOUSE FOR FOUR YEARS
7. Author(s)
LA Wallace1, C Croghan2, C Howard-Reed3, A Persily3
9,Performing Organization Name and Address
N/A
12.Sponsoring Agency Name and Address
EPA
12201 Sunrise Valley Drive
555 national Center
Reston VA
3
5. Report Date
1/18/02
6. Performing Organization Code
N/A
8. Performing Organization
Report No.
N/A
1 0, Program Element No.
1 1 . Contract/Grant No.
N/A
13. Type of Report and Period
Covered
14. Sponsoring Agency Code
1 5 , Supplementary Notes
16. Abstract
Although considerable data exist on 24-hour integrated measurements of fine and coarse particles indoors, much less information is
available on moment-to-moment variation for a full range of particle sizes including ultrafine particles. Also, information is limited on
the relationships between air change rates, temperature, humidity, indoor-outdoor concentration ratios, indoor source strengths due to
various activities such as cooking and cleaning, penetration factors, and deposition rates under realistic conditions. Therefore EPA and
NIST have collaborated on a four-year (October 1, 1996 through Dec. 31, 2000) study of particle concentrations in an occupied house.
Target pollutants included ultrafine, fine, and coarse particles from 10 nm to 20 pm in diameter; black carbon (BC); and particle-bound
polyaromatic hydrocarbons (PAH). Ancillary measurements included air change rates, wind velocity, temperature, and relative
humidity. Measurements were made continuously and the final database (PMHOME) is on a 5-minute basis. PMHOME is available lo
researchers in Statistica or SAS format. Types of investigations that can be done using PMHOME include calculation of the relative
contribution of outdoor air particles to indoor air concentrations, effects of indoor sources such as cooking and candle burning, and
relationships of air change rates to outdoor temperature and wind speed.
17. KEY WORDS AND DOCUMENT ANALYSIS
A. Descriptors B. Identifiers / Open Ended C. COSATI

18. Distribution Statement 19. Security Class (This 21. No. of Pages
Report)
20. Security Class (This 22. Price
Page)

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