Please visit the [[Local Air Pollutant Dispersion|LAPD Summary Page]] for a quick description of the aims, investigators, and materials associated with the Local Air Pollutant Dispersion (LAPD) hosted project.
As the field of human exposure has grown, the realization that we need to focus on processes occurring near the person being exposed has also grown. For example, initially it was thought that measuring air pollution levels in ambient air, e.g., on top of buildings or weather stations, was sufficient to estimate people's exposure. However, investigators soon realized that measurements in backyards, or inside homes were more reflective of true exposures. Ultimately, the use of personal (mobile) monitoring devices placed on individuals was identified as the best way to accurately measure exposure.
The "personal cloud" is a phenomenon that, after it was observed, led to increased study of pollutant mixing and dispersion from sources immediately near people. The personal cloud effect is an observed elevation in human exposure when measured at a personal monitor relative to a fixed room monitor. It was attributed, in part, to cooking, smoking, or other pollutant-generating activities that occur in proximity to the subject wearing a personal monitor.
The LAPD project continues the elucidation of the personal cloud effect through systematic study of the "proximity effect", aiming to characterize and model the effect of being close to a source for a range of source types and common air flow conditions & human activities in homes and other locations. It examines sources, measures levels of pollutants, and considers human activities occurring within a few inches, feet, or yards from a subject.
Sandra McBride investigated and statistically modeled the proximity effect for continuous indoor sources as part of her Stanford University dissertation in 1999. Subsequently, Neil Klepeis, Wayne Ott, Paul Switzer, and Lynn Hildemann expanded the study to outdoor locations, along with continued study of indoor locations using custom multi-point sensor arrays, which measure real-time particle or tracer gas concentrations in 3 dimensions.