Tracy L. Thatcher

Deposition, resuspension, and penetration of particles within a residence

Aerosol concentrations and particle size distributions were measured indoors and outdoors at a two-storey residence in California during the summer months. A single central sampling point in the downstairs living area was used for all indoor samples. The deposition rate for supermicron particles was measured by raising the particle concentration indoors and simultaneously measuring air infiltration rates and particle concentration decay rates. For particles between 1 and 5 μm diameter, the deposition velocity closely matched the calculated settling velocity. For particles larger than 5 μm the deposition velocity was less than the calculated settling velocity, probably due to the nonspherical nature of these particles. The penetration factor for supermicron particles, a measure of the amount of filtration achieved by the building shell, was calculated using the experimentally determined deposition velocities and indoor/outdoor particle ratios when no resuspension or generation activities were present. A penetration factor of one was found, indicating that the building shell was not effective at removing infiltrating particles. Resuspension was measured under several different conditions and was found to have a significant impact on indoor particle concentrations. Just walking into a room can increase the particle concentration by 100% for some supermicron particle sizes. For light activity with four people in the residence, a resuspension rate between 1.8 × 10−5 and 3.8 × 10−4 h−1 was found for supermicron particles assuming a particle density of 1 gm−3. These calculated rates may be lower than the actual rates due to assumptions made about the particle size distribution of the floor dust.

A Concentration Rebound Method for Measuring Particle Penetration and Deposition in the Indoor Environment

Continuous, size resolved particle measurements were performed in two houses in order to determine size-dependent particle penetration into and deposition in the indoor environment. The experiments consisted of three parts: (1) measurement of the particle loss rate following artificial elevation of indoor particle concentrations, (2) rapid reduction in particle concentration through induced ventilation by pressurization of the houses with HEPA-filtered air, and (3) measurement of the particle concentration rebound after house pressurization stopped. During the particle concentration decay period, when indoor concentrations are very high, losses due to deposition are large compared to gains due to particle infiltration. During the concentration rebound period, the opposite is true. The large variation in indoor concentration allows the effects of penetration and deposition losses to be separated by the transient, two-parameter model we employed to analyze the data. For the two houses studied, we found that as particles increased in diameter from 0.1 to 10 w m, penetration factors ranged from ∼1 to 0.3 and deposition loss rates ranged from 0.1 and 5 h m 1 . The decline in penetration factor with increasing particle size was less pronounced in the house with the larger normalized leakage area.

Inhalation Transfer Factors for Air Pollution Health Risk Assessment

ABSTRACT To facilitate routine health risk assessments, we develop the concept of an inhalation transfer factor (ITF). The ITF is defined as the pollutant mass inhaled by an exposed individual per unit pollutant mass emitted from an air pollution source. A cumulative population inhalation transfer factor (PITF) is also defined to describe the total fraction of an emitted pollutant inhaled by all members of the exposed population. In this paper, ITFs and PITFs are calculated for outdoor releases from area, point, and line sources, indoor releases in single zone and multizone indoor environments, and releases within motor vehicles. Typical PITFs for an urban area from emissions outdoors are ~10-6–10-3. PITFs associated with emissions in buildings or in moving vehicles are typically much higher, ~10-3–10-1.

Particle Deposition from Natural Convection Enclosure Flow Onto Smooth Surfaces

ABSTRACT Deposition can be an important fate for airborne particles in indoor environments. The effects of particle size (diameters: 0.1, 0.5, 0.7, 1.3, and 2.5 μm), surface orientation, and surface-air-temperature difference (±10 K and ±1.5 K) on particle deposition velocity have been studied experimentally in a 1.22 m × 1.22 m × 1.22 m aluminum chamber. Monodispersed ammonium fluorescein particles were deposited onto the chamber surfaces under natural convection flow conditions and then extracted to determine particle deposition at seven locations along each surface. For horizontal surfaces, gravitational settling was the dominant factor for particle diameters greater than 1 μm. For vertical surfaces, several factors significantly influenced deposition. Excluding near-corner areas, the average deposition velocities on cool vertical walls varied from a maximum of 5.8 × 10−5 m s−1 for 0.1 μm particles (surface-to-air temperature difference of -10 K) to a minimum of 5.3 × 10−7 m s−1 for 1.3 μm particles (-...

Factors affecting the concentration of outdoor particles indoors (COPI): Identification of data needs and existing data

The process of characterizing human exposure to particulate matter requires information on both particle concentrations in microenvironments and the time-specific activity budgets of individuals among these microenvironments. Because the average amount of time spent indoors by individuals in the US is estimated to be greater than 75%, accurate characterization of particle concentrations indoors is critical to exposure assessments for the US population. In addition, it is estimated that indoor particle concentrations depend strongly on outdoor concentrations. The spatial and temporal variations of indoor particle concentrations as well as the factors that affect these variations are important to health scientists. For them, knowledge of the factors that control the relationship of indoor particle concentrations to outdoor levels is particularly important. In this report, we identify and evaluate sources of data for those factors that affect the transport to and concentration of outdoor particles in the indoor environment. Concentrations of particles indoors depend upon the fraction of outdoor particles that penetrate through the building shell or are transported via the air handling (HVAC) system, the generation of particles by indoor sources, and the loss mechanisms that occur indoors, such as deposition. To address these issues, we (i) identify and assemble relevant information including the behavior of particles during air leakage, HVAC operations, and particle filtration; (ii) review and evaluate the assembled information to distinguish data that are directly relevant to specific estimates of particle transport from those that are only indirectly useful and (iii) provide a synthesis of the currently available information on building air-leakage parameters and their effect on indoor particle matter concentrations.

Effect of small scale obstructions and surface textures on particle deposition from natural convection flow

ABSTRACT To increase knowledge of particle dynamics in indoor environments, we have conducted experiments on the effects of small surface discontinuities and roughness on deposition from natural convection flow. Measurements were made in a half-height (1.22 m) aluminum test chamber and in a full-scale experimental room. In the test chamber, air flow was induced by uniformly heating the floor and one wall while cooling the ceiling and opposite wall to a constant temperature difference of 3 K. In the full-scale room, one wall was heated and the opposite wall was cooled to a constant wall-to-wall temperature difference of 3 or 7 K. Other surfaces in both experiments were approximately adiabatic. Near-monodispersed fluorescent particles (diameters 0.1, 0.5, or 1.3 μm in the half-height experiments and 0.2 or 1.0 μm in the full-scale experiments) were injected into the chamber. Following an exposure period, the mass of fluorescent particles deposited on sections of the walls and/or plates mounted on the walls ...

Protecting buildings from a biological or chemical attack: Actions to take before or during a release

This report presents advice on how to operate a building to reduce casualties from a biological or chemical attack, as well as potential changes to the building (e.g. the design of the ventilation system) that could make it more secure. It also documents the assumptions and reasoning behind the advice. The particular circumstances of any attack, such as the ventilation system design, building occupancy, agent type, source strength and location, and so on, may differ from the assumptions made here, in which case actions other than our recommendations may be required; we hope that by understanding the rationale behind the advice, building operators can modify it as required for their circumstances. The advice was prepared by members of the Airflow and Pollutant Transport Group, which is part of the Indoor Environment Department at the Lawrence Berkeley National Laboratory. The groups expertise in this area includes: tracer-gas measurements of airflows in buildings (Sextro, Thatcher); design and operation of commercial building ventilation systems (Delp); modeling and analysis of airflow and tracer gas transport in large indoor spaces (Finlayson, Gadgil, Price); modeling of gas releases in multi-zone buildings (Sohn, Lorenzetti, Finlayson, Sextro); and occupational health and safety experience related to building design and operation (Sextro, Delp). This report is concerned only with building design and operation; it is not a how-to manual for emergency response. Many important emergency response topics are not covered here, including crowd control, medical treatment, evidence gathering, decontamination methods, and rescue gear.

Measurements and modeling of deposited particle transport by foot traffic indoors.

Deposited particles are transported into and within buildings by adhering to and releasing from peoples shoes. To better understand transport of deposited particulate contaminants and exposures to these materials, experimental data on tracking by foot traffic are needed. Laboratory experiments measured uptake and downlay mass transfer efficiencies of particles between shoes and floors in a step-simulation chamber. Equilibrium uptake transfer fractions, the net mass fraction transferred from floors to shoes after several steps, were also measured. Single-step uptake and downlay transfer efficiencies ranged from 0.02 to 0.22 and equilibrium uptake transfer fractions were 0.10-0.40. Particle size, particle loading, shoe type, floor type, step pressure, and step sequence were all investigated. Experiments demonstrated that single-step downlay transfer efficiencies decrease with each successive step onto clean floors. A simple empirical model is proposed to estimate these transfers as a function of step number. Simulations using the transfer efficiency values measured here illustrate the spread of deposited particles by people walking in a hypothetical hallway. These simulations show that in locations where a few people walk over the same area each minute, tracking can spread deposited material over length scales comparable to building dimensions in just a few hours.

Simplifying the assessment of building vulnerability to chemical,biological and radiological releases

The intentional or accidental release of airborne chemical, biological, or radiological materials can pose a significant threat to the health of building occupants. Pre-planning and emergency response measures, such as HVAC system manipulation and sheltering during an event, can significantly reduce the exposure of building occupants. A straightforward and comprehensive vulnerability assessment methodology is an essential tool for assisting building managers and operators in preparing for airborne hazards.

Progress on building a predictive model of indoor concentrations of outdoor PM-2.5 in homes

The goal of this project is to develop a physically-based, semi-empirical model that describes the concentration of indoor concentration of PM-2.5 (particle mass that is less than 2.5 microns in diameter) and its sulfate, nitrate, organic and black carbon constituents, derived from outdoor sources. We have established the methodology and experimental plan for building the model. Experimental measurements in residential style houses, in Richmond and Fresno, California, are being conducted to provide parameters for and evaluation of this model. The model will be used to improve estimates of human exposures to PM-2.5 of outdoor origin. The objectives of this study are to perform measurement and modeling tasks that produce a tested, semi-mechanistic description of chemical species-specific and residential PM-2.5 arising from the combination of outdoor PM and gas phase sources (HNO{sub 3} and NH{sub 3}), and indoor gas phase (e.g. NH{sub 3}) sources. We specifically address how indoor PM is affected by differences between indoor and outdoor temperature and relative humidity. In addition, we are interested in losses of particles within the building and as they migrate through the building shell. The resulting model will be general enough to predict probability distributions for species-specific indoor concentrations of PM-2.5 based on outdoor PM, and gas phase species concentrations, meteorological conditions, building construction characteristics, and HVAC operating conditions. Controlled intensive experiments were conducted at a suburban research house located in Clovis, California. The experiments utilized a large suite of instruments including conventional aerosol, meteorological and house characterization devices. In addition, two new instruments were developed providing high time resolution for the important particulate species of nitrate, sulfate, and carbon as well as important gaseous species including ammonia and nitric acid. Important initial observations include the result that, with rare exceptions, there is virtually no nitrate found inside the house. This nitrate appears to dissociate into ammonia and nitric acid with the nitric acid quickly depositing out. Initial model development has included work on characterizing penetration and deposition rates, the dynamic behavior of the indoor/outdoor ratio, and predicting infiltration rates. Results from the exploration of the indoor/outdoor ratio show that the traditional assumption of steady state conditions does not hold in general. Many values of the indoor/outdoor ratio exist for any single value of the infiltration rate. Successful prediction of the infiltration rate from measured driving variables is important for extending the results from the Clovis house to the larger housing stock.