A study of aging of lead aerosols—I

The alteration of the size distribution of lead aerosols was studied by the sensitive analytical technique of anodic stripping voltammetry and using Andersen Samplers (multistaged cascade impactors) to collect and sort the aerosol by size. It was found that lead aerosol size distributions do not vary greatly from one source area (essentially an area of heavy automobile traffic) to another, and that the lead aerosol size distribution does not respond noticeably to change of weather within a source area for 24 h sampling times. Short-term aging in clear air was studied by comparing the lead size distributions at three locations from downtown Chicago (a source area) with those found several kilometers downwind over Lake Michigan (a non-source area). Long-term aging in clear air was studied by comparing the size distributions of lead aerosols of various ages collected on Lake Michigan. Ages were assumed to be the travel time from shore to the sampling location, computed by a simple trajectory analysis. The aging studies did not show a clear-cut systematic alteration of the lead aerosol size distribution, although the large particle end of the distribution showed reduced relative concentrations for aerosols ages of 6 h or older. These results suggest very little modification of the shape of the lead aerosol size distribution by non-precipitative atmospheric mechanisms for equivalent particle radii larger than 0.2 μm.