Oil & Natural Gas Projects
Exploration and Production Technologies
A Predictive Model for Determining Indoor Concentrations of Outdoor Volatile
Organic Compound Air Toxics
This project was funded through DOE's Natural Gas and Oil Technology Partnership
Program. The program establishes alliances that combine the resources and experience
of the nation's petroleum industry with the capabilities of the national laboratories
to expedite research, development, and demonstration of advanced technologies
for improved natural gas and oil recovery.
The goal of this project is to develop a model to estimate concentrations of
indoor concentrations of outdoor volatile organic compounds (VOCs) from outdoor
measurements. The approach will be to integrate existing models with information
derived from experiments to provide essential data required for environmental
Lawrence Berkeley National Laboratory (LBNL)
A model to estimate indoor VOC concentrations from outdoor VOC concentrations
has been developed. Outdoor samples of ambient air were measured to provide
the data for modeling.
This research will provide a model that can provide a quantitative estimate
of indoor inhalation exposure to hazardous air pollutants (HAPs). Putting the
HAP standard on a risk basis will significantly restrict the number of compounds
regulated and will target concentrations of those deemed to pose significant
risk. This is especially critical for refiners faced with ever-tightening fuel
emissions standards that may not be based on sound science.
Congress has directed the Environmental Protection Agency to establish and promulgate
emission standards for HAPs. This is consequential for refineries and may require
refineries to change the composition of fuels produced for mobile and stationary
combustion sources and to reduce their fugitive emissions.
When suitable tools are available to assess health risks associated with specific
HAPs, EPA plans to base HAP standards on achieving risk reduction rather than
applying a mandated reduction level for all HAPs. If risk is to be assessed
reliably, exposure must be known.
Key to quantifying risk is determining actual exposure of the population to
the air toxics. This requires determining the quantitative relationship between
air toxic concentrations measured at stationary outdoor monitoring sites and
the actual exposures of individuals to them. One of the key exposure pathways
is inhalation. Determining indoor concentrations of outdoor HAPs is particularly
crucial for quantifying the inhalation exposure pathway because individuals
spend, on average, about 90% of the time indoors (70% in homes).
A model is being developed to estimate indoor VOC concentrations from outdoor
VOC concentrations determined from outdoor measurements. The approach is to
integrate existing models (e.g., LBNL infiltration model and gas-phase reaction
models) with information derived from experiments to provide essential data
required for risk assessment.
Ambient air concentrations of VOCs vary temporally and often exhibit a diurnal
pattern in response to changes in source terms and atmospheric processes. When
these compounds enter buildings from outdoors by infiltration, they interact
with indoor surfaces. Thus, when ambient concentrations are high, indoor concentrations
may be reduced relative to outdoor values due to sorption. Conversely, re-emission
from surfaces can result in higher indoor concentrations after outdoor concentrations
have decreased. To capture this, design and coding have been completed for a
coupled outdoor/indoor air model.
For the outdoor portion of the model, a Lagrangian photochemical box model
is used. The chemical mechanism SAPRC-99 has been implemented into the model
because it is the best representation of atmospheric VOC chemistry. A set of
diurnally varying emissions representative of an urban area is used as model
input. Dilution and entrainment of air aloft due to cell height variations induced
by a temporally varying mixing height are included in the model to generate
representative VOC concentrations. A state-of-the-art radiation model will be
included to calculate actinic flux that will drive the photochemistry.
Outdoor air concentrations of VOCs will be computed for several days for different
seasons and for different spatial locations. The project model then has the
outdoor air flow into an indoor space of specific volume at a fixed infiltration
rate, which is an input parameter. Calculations have revealed that the photochemistry
ceases indoors because there is insufficient actinic flux to support photochemistry.
However, the VOC reactions continue to occur because they are driven by reactions
with ozone. Physical loss via sorption and gain via desorption also are represented
in the model, and appropriate rate parameters required to evaluate them is to
be evaluated experimentally or taken from the literature.
Current Status (October 2005)
The project is complete, but final results have not been submitted.
Project Start: April 12, 2001
Project End: April 11, 2005
Anticipated DOE Contribution: $435,000
Performer Contribution: $120,000 (22% of total)
NETL - Kathy Stirling (firstname.lastname@example.org or 918-699-2044)
LBNL - Nancy Brown (email@example.com or 510-486-4241)