Source Apportionment, Spatial Mapping and Exposure Assessment for Ultrafine (Nano) Particles in the Atmosphere of Beijing

Ultrafine particles, also commonly referred to as nanoparticles, are defined as those with one dimension smaller than 100 nanometres. Although evidence is as yet inconclusive, they are regarded by many as having enhanced toxicity. The sources of ultrafine particles are quantitatively different from those of particulate matter mass and methods for quantification of source contributions are currently in their infancy. These are based upon application of Positive Matrix Factorization to multiple measurements of particle number size distributions collected with a Scanning Mobility Particle Sizer and this method, alongside cluster analysis of particle size distributions and identification of periods of regional nucleation from the evolution of particle size distributions will be applied to the quantitative source apportionment of particulate matter in Beijing. The sources such as regional nucleation and road traffic can be readily differentiated, and their contributions to the ambient particle loading determined. Measurements of particle number count will also be made using condensation particle counters and DiSCmini particle counters in order to gain insights into the spatial distribution of concentrations.

The combination of the mapped ultrafine particle concentrations with time-activity diaries of volunteer subjects will allow an estimation of personal exposure. Such estimates will be compared with personal exposures directly measured using the DiSCmini instruments as samplers. Once a validated personal exposure model to ultrafine particles has been developed, it will be made available to the teams running the two Beijing health studies in order to provide estimates of exposure to ultrafine particles for the subjects in both the panel study led by Kings College, London and the cohort study led by the Institute of Occupational Medicine. By use of a lung deposition model, the regional lung dose of particles associated with each source will also be estimated using approaches developed in our group