Modelling the soiling of float glass in a polluted atmosphere

Samples of float glass were exposed either sheltered or unsheltered from the rain, in the centre of Paris (background air pollution) for up to 24 months. Selected samples were withdrawn after one, two, six, 12 and 24 months. SEM observations of the exposed glass surfaces revealed the nature of the deposited particulate matter. On both sheltered and unsheltered samples, carbonaceous nanosoot particles were the most abundant type of deposited particles. On sheltered samples the soot particles were present along with soluble salts. Four soiling parameters were chosen to describe the time evolution of soiling: haze, the total mass of deposited particles, the total mass of deposited carbon and the total mass of deposited water soluble ions. For sheltered glass a general model for soiling was established: it follows a variable slope sigmoid function (Hill equation). No general equation was found that described the soiling of unsheltered samples.