UC Berkeley

People are a direct source of bioeffluent pollutants, mechanical air mixing, and heat, all of which lead to the formation of a unique perihuman microenvironment, and in certain environments also affect the room conditions. For indoor air quality (IAQ) research and professional work it is desirable to utilize the simplest possible conceptual model that captures the majority of the occupant exposure. In this dissertation a general process is put forth to determine how many zones an indoor space needs to be divided into, and how to model the pollutant transport within each zone simply. Exploring near-person pollutant sources, pollutant mixing in thermally stratified spaces, and optimizing CO2 demand control sensor placement in a displacement ventilation system are illustrated using a series of laboratory experiments. A short example is also presented at the end to illustrate how this process might inform professional IAQ diagnostics work, and communicate the results to a non-expert client.

Personal care products (PCP) might be a significant source of ultrafine particle exposure for users owing to the reaction of ozone with terpene ingredients. The near-person emissions associated with PCP may contribute to exposures that would not be properly accounted for with indoor microenvironmental measurements. To better understand this issue, screening experiments were conducted with 91 PCP to detect the occurrence of ultrafine particle production from exposure to common indoor levels of ozone (23 +/- 2 ppb). Twelve products generated measurable particle emissions; quantification experiments were performed for these to determine total particle production and peak particle production rate. A high-resolution, small volume reaction chamber was used with a heated sample plate to simulate conditions found in the human thermal plume. Ten of the quantified PCP exhibited total emissions of less than 10^9 particles, suggesting that they may not be significant sources of total ultrafine particle exposure as other common sources of particles indoor have emissions 1-4 orders of magnitude higher. Two samples, a tea tree oil-based scalp treatment and a white lavender body lotion, exhibited relatively elevated peak particle emission rates, 6.2 x 10^7 min^(-1) and 2.0 x 10^7 min^(-1), respectively. The use of such products in the presence of significant ozone levels might materially influence personal exposure to ultrafine particles.

The pollutant mixing time in an indoor environment may be a good characteristic for researchers to differentiate when it is appropriate to use the well-mixed assumption in exposure models and investigations. For a certain amount of time, episodic emissions of pollutants in an indoor environment will create spatial heterogeneities that are significant when compared to the mean concentration. There have only been a small number of studies that directly measure the amount of time it takes a pulse emission to become well-mixed in a typical indoor environment. To add to this body of knowledge, a series of mixing time experiments were conducted in a 1.2 m x 1.2 m x 1.2 m chamber. A vertical temperature gradient was established by symmetrically heating the ceiling and cooling the floor, a pulse release of neutrally buoyant mixture of CO2 and He was used as a tracer gas, and six CO2 sensors were used to measure when the relative standard deviation fell below 20%. Under isothermal conditions the mixing time varied between 40 and 100 minutes, the large variability suggesting that the mixing conditions were unstable. Under stratified conditions the variability was lower, indicating more stable conditions, and the mixing time was reduced to 38 to 52 min for a 0.5 to 3.0 C/m stratification. The presence of a heated object also had a strong effect on increasing the mixing within the chamber, a 5 W heated object reduced the mixing time from 40-60 min to 12 min. A heated wall has less effect on mixing than a freestanding object, and the position of the heated object may have a small effect as well.

There are no guidelines on where to located the CO2 sensor in rooms ventilated by demand control (DC) displacement ventilation (DV). Locating the CO2 sensor at the breathing height may be incorrect in such rooms because wall locations at the breathing height may be subject to enough spatial variability in concentration that the measurement will not be representative of the mean breathing height concentration. A full-sized chamber experiment was conducted with heated manikins that had a steady release of pure CO2 in the breathing zone to simulate an office environment. Vertical lines of temperature and CO2 sensors were placed in the center of the room and at two different wall locations to measure the horizontal concentration variability at different heights. 1, 3, and 5 manikins were used under low and high stratification conditions, and the chamber was allowed to stabilize overnight to obtain steady state conditions. Significant CO2 horizontal variability of the order of 50-150 ppm was found between 1.1-1.7 m, while there was low temperature horizontal variability at all heights. These results suggest that the current practice of placing CO2 DC sensors in a DV system at breathing height be changed to placing them at the ceiling or the return grille instead to reduce the likelihood that local variations in CO2 misrepresent the room conditions. The possibility of developing a correction factor to relate the ceiling CO2 level to the mean breathing height level was explored as well.