Estimation of Emission Sources of Trace Elements in an Atmospheric Aerosol by Particle Size Distributions

Abstract

Discussions were made on the relationship between atmospheric trace elements and their emission sources in terms of size distribution data of aerosols.
Aerosol was collected by an Andersen impactor, and was analyzed for trace elements by neutron activation analysis or atomic absorption spectrometry. Size distributions of aerosol were found to be generally bimodal instead of log-normal, as shown in Figs.1 and 2, on the basis of the continuous size distribution curves obtained by our data processing. Size distribu- tion of the elements was classified into three groups (Fig.3). At a high-way, the peak at about 4 pm was formed by sedimentation of the dust, blown up from the ground surface (Fig.4). To simplify the size distributions of elements, the aerosol samples were divided into two parts, i. e., larger and smaller particles than 2.1 fum in aerodynamic diameter. Upon plotting the ratios of fine to coarse particles of each element in the samples, the soil elements appeared at the left side, and other elements, related to artificial emission sources did at the right side of the abscissa in Fig.6. Enrichment factors of the elements in the aerosol samples against those in the crust, using aluminium concentration as a criterion, are plotted in Fig.7 in the same arrangement as that in Fig.6. They indicated that the elements rich in fine particles might be emitted from other sources than the crust and they are probably associated with artificial sources.
On the basis of the above conclusion, the amount of atmospheric aerosol should be separately measured by dividing it into two groups, separated at a saddle part of the size distribution curve. This method of evaluation would be useful to estimate the emission sources of air pollution.