Sulfur dioxide was used as an indicator of the occurrence of air pollution episodes in a rural area of Belgium. Provided air particulates sampling operations are strictly synchronized with SO/sub 2/ immission episodes, correlations appeared between the levels in air of sulfur and the levels of some toxic metals. Comparing the relative proportions of sulfur and metals in air with emission data for combustion sources in Belgium (coal especially) leads to the conclusion that combustion is probably the main source of toxic elements likely to contaminate rural atmospheres. On the other hand, it appears that industrial zone characterization is feasible by comparing the relative proportions of some specific metals in air.
Navarre, J. L., Priest, P., & Ronneau, C. (1981). Relations between sulfur and heavy elements in rural atmospheres. Atmospheric Environment, 15(3), 221-227. https://doi.org/10.1016/0004-6981(81)90022-6 (Original work published 1981)