Magnetic properties of PM in relation to combustion sources from west Africa.

The particulate matter (PM) presents in air has well known health hazards, finer fractions being particularly harmful. The magnetic methods present advantages in PM investigation, being quick and cost effective, and also sensible enough to investigate finer fractions of the iron oxides. West African cities are being subject to increasing air pollution problems, which are expected to get worse in the coming decades. In order to address the evolution of air quality in two major West African cities (Cotonou and Benin) an extensive monitoring campaign was conducted by Djossou et al. (2018) for about two years. Sites with different combustion sources were chosen in order to address the impacts in air quality. We present here the use of environmental magnetism methods in the air filters previously collected. The magnetic protocol includes the acquisition of anhysteretic remanent magnetization (ARM), saturation isothermal magnetization (SIRM) and the calculation of the S ratio in order to assess concentration, mineralogy and grain size of the iron oxides captured by the filters. Volume (air pumped in the filter) normalized ARM and SIRM data present a temporal variation that seems to be related to the season, increasing in the dry seasons, and decreasing in the wet seasons, especially on the traffic and waste burning sites. The magnetic properties are mainly dominated by high coercive magnetite-like grains.