Distribution of aerosol paint droplets in open- and closed-space environments: Towards activity level evaluation

One way to determine the presence of a suspect on the scene of graffiti sprayed public territory, is by seeking the presence of aerosol paint droplets transferred to his clothing and accessories. Previous studies have evaluated the distribution of spray paint droplets in closed space, on clothing, and its persistence following washing. Yet, due to the difficulty in observing and counting them under a stereomicroscope, the previous studies had to limit the tests conducted and limit the amount of data collected. In this paper, we perform simulations of spraying using a fluorescent paint and a computer-automated extraction of features and counting of the droplets. With these tools we were able to perform many different tests in a relatively small amount of time and gather data about the density, distribution, and size of the droplets transferred. We discuss the obtained results and hypothesize that such evaluations of the transferred droplets would permit to distinguish between different scenarios at an activity level, such as the presence on the scene as a simple witness or bystander, versus the illicit action of spraying a graffiti or a tag.