[en] The applicability of proton activation analysis to the determination of the trace amounts of lead in atomospheric particulate matter and the problem of evaluating background levels for measuring the characteristic sources of emissions is discussed. The determination of background levels are extremely difficult because of the large variations in concentrations, associated to changes in meterological conditions. Not only wind direction, but meteorological parameters as variation of temperature with altitude, precipitation and humidity, are preponderant in assessing the diffusion and transport of pollutants to rather remote areas. A statistically significant number of samples treated by multicomponent statistical analysis including the different meteorological variables together with pollution indicators present an interesting alternative to describe complex pollution cases and to asses responsibility of some specific emission sources. (T.G.)