Behaviour of airborne lead and temporal variations of its source effects in Geneva (Switzerland): comparison of anthropogenic versus natural processes

Lead isotope compositions of aerosols from two Geneva stations (city and country), monitored during one year, show the existence of two main lead sources, petrol and waste incineration. A third, subordinate source is represented by coal burning and is detectable in winter. This source is believed to be of local importance due to the very low coal consumption in Geneva. Lead contributions from the three sources have been apportioned using isotopic mixing equations. During summer, petrol contributes about 70% of the total lead in the city while the incinerator contributes 65% of the total lead in the country. During winter, coal burning provides in average 15% of the total lead in the city. Atmospheric lead concentrations are mainly controlled by wind speed. As expected, wind dilution is more effective on lead aerosols originating from sources situated farthest from the monitoring stations. Thus, incinerator lead contributions at the city station decrease linearly with wind speed in winter due to their transport from a longer distance than automotive emissions. Due to the same process, during summer petrol contributions are anticorrelated with wind speed at the country. Incinerator winter contributions in the city display greater variations than in summer, suggesting a seasonal meteorological regime which enhances the wind speed control on incinerator aerosol dilution. We relate this meteorological regime to the lower mixing height typical of the cold season. Isotope-based apportionments of lead sources and their statistical comparison with particulate matter and sulfur dioxide concentrations have also allowed a qualitative assessment of the impact of traffic and coal emissions on PM and SO2 levels at the two monitored sites