Oil & Natural Gas Projects
Exploration and Production Technologies
A Predictive Model of Indoor Concentration of Outdoor PM2.5 in Homes
This is a Natural Gas and Oil Technology Partnership project initiated in FY1998.
The purpose is to determine impacts of particulate matter (PM) on indoor air
The San Joaquin Valley has some of the country's highest PM2.5 (PM less than
2.5 microns) concentrations. A large percentage is NH3NO3. This study utilizes
species- and size-specific residential PM2.5 measurements as input into a model.
The validated, semi-mechanistic model is general enough to predict probability
distributions for species-specific indoor PM2.5 concentrations based on outdoor
PM, gas-phase species and concentrations, weather conditions, building characteristics,
and heating, ventilation, and air conditioning. This model is a component in
understanding human exposure to airborne particulate matter.
Lawrence Berkeley National Laboratory (LBNL)
Analyses show relationships between indoor and outdoor particle chemistries.
Chemical and time-resolved data are necessary to understand the transport and
fate of indoor particles of outdoor origin. Results suggest that significant
differences exist among chemical constituents. Exposure assessments based on
total outdoor particle mass measurements may obscure causal relationships for
indoor exposure of outdoor origin. For example, results indicate indoor exposure
to ammonium nitrate (NH3NO3) is much smaller than outdoor concentrations suggest.
These results could impact future PM2.5 standards.
Because ambient-air PM2.5 standards are based on health risk, population exposure
to PM2.5 is an important issue. Individuals spend about 90% of their time indoors
(70% in homes). To date, standards have focused on outdoor suspended particle
mass because there is no scientific evidence to implicate any particular mass
component(s). Exposure evaluation is a critical element for apportioning particulate
characteristics to health risks.
This new predictive model is a tool for relating indoor PM2.5 concentrations
of outdoor origin to measurements at central monitoring stations. It is based
on mass balance principles, where the residential building is treated as a single,
well-mixed zone. By bringing sound science to regional air quality regulation,
such research helps refiners avoid needlessly stringent emissions standards
for their operations and products.
San Francisco Bay area refineries are subjected to strict NOx rules because
they are believed to be contributors to San Joaquin Valley particle loading.
This research provides sound science for possible future regulatory frameworks.
Exposures must be quantified to eliminate arbitrary control decisions that could
be ineffective. Project findings suggest a methodology to minimize conflict
between ozone and PM control strategies.
The health research community is also faced with understanding causes, if any,
of adverse health effects resulting from exposure to ambient PM2.5. Current
correlations between adverse health effects and PM concentration are based upon
short-term increases in outdoor particle concentrations, not on indoor exposure.
An essential component to determine PM2.5 exposure is to establish the fate
and transport of outdoor particles crossing the building shell and becoming
resident indoors. Understanding processes affecting indoor concentrations of
outdoor PM is required. Although indoor sources and resuspended particles also
may have an influence on human health, it is unlikely that particles of indoor
origin would track outdoor particle concentration changes.
During fall 2000 and winter 2001, experiments were conducted at an unoccupied
suburban Clovis, CA, research house located in the San Joaquin Valley. This
is the first such experiment to characterize time- and chemically resolved PM2.5
Researchers sought to determine that:
- Data analysis and model building showed that indoor/outdoor concentration
relationships depend on particle chemistry.
- Chemical and time-resolved data that were necessary to understand transport
and fate of indoor particles of outdoor origin.
- A mechanistic understanding could be achieved for individual chemical particle
species transformations of physical loss of PM indoors and for infiltration
- Results could be extended to other locations and housing types using the
LBNL infiltration model.
Results showed that concentrations of atmospheric aerosols, nitrate sulfate,
and carbonaceous matter are variable both within a single day and between days.
Aerosol constituents behave differently upon entrance into a building. On average,
indoor sulfate aerosol concentrations are about half of those outdoors. However,
when the house air exchange rate is elevated, indoor sulfate aerosol levels
can approach those outdoors. Measured indoor sulfate aerosol concentrations
can be predicted using a mass-balance model and knowledge of penetration loss
through the building shell, deposition loss rate within the building, and air
Results indicate that indoor exposure to NH3NO3 in the San Joaquin Valley is
small. In contrast to sulfate aerosol, chemically resolved data revealed that
indoor NH3NO3 concentrations are much less than predicted. Additional reductions
were attributed to indoor transformation of NH3NO3 into NH3 and nitric acid
gasses, which are subsequently lost by deposition and surface sorption.
Current Status (August 2005)
The first-generation model is nearing completion. Recent analysis of time-resolved
organic carbon data shows that, even at high air exchange rates, indoor concentrations
are lower than outdoor values. Differences between predicted and measured concentrations
correlate with temperature and sulfate air change rates. This is not true for
NH3NO3. Results suggest that gas-to-particle partitioning of organic gases is
an important factor controlling indoor aerosol concentrations.
Lunden, M.M., Revzan, K.L., Fischer, M.L., Thatcher, T.L., Littlejohn, D., Hering,
S.V., and Brown, N.J., 2003, The Transformation of Outdoor Ammonium Nitrate
Aerosol in the Indoor Environment, invited paper, Atmospheric Environment, 37,
5633-5644 (LBNL Report No. 52795).
Lunden, M.M., Thatcher, T.L., Hering, S.V., and Brown, N.J., 2003, The Use
of Time- and Chemically Resolved Particulate Data to Characterize the Infiltration
of Outdoor PM2.5 into a Residence in the San Joaquin Valley, Environmental Science
and Technology, 37, 4724-4732 (LBNL Report No. 52221).
Thatcher, T.L., Lunden, M.M., Revzan, K.L., Sextro, R.G., and Brown, N.J., 2003,
A Concentration Rebound Method For Measuring Particle Penetration And Deposition
In The Indoor Environment, Aerosol Science and Technology, 37, 847-864 (LBNL
Report No. 51631).
Fischer, M.L., Littlejohn, D., Lunden, M.M., and Brown, N.J., 2003, Automated
Measurement of Ammonia and Nitric Acid in Indoor and Outdoor Air, Environmental
Science and Technology, 37, 2114-2119 (LBNL Report No. 51385).
Project Start: January 15, 1999
Project End: September 30, 2005
DOE Contribution: $2,291,000
Performer Contribution: $290,000 (11.2% of total)
$75,000 from American Petroleum Institute in 2005
NETL - Betty Felber (firstname.lastname@example.org or 918-699-2031)
LBNL - Nancy J. Brown (email@example.com or 510-486-4241)
A schematic of indoor/outdoor particle chemistry.
Time- and chemically resolved indoor/outdoor particle data.