PM2.5 Magnetic Properties in Relation to Urban Combustion Sources in Southern West Africa

Aruã Da Silva Leite,Jean-François Léon,Ricardo Ivan Ferreira Da Trindade,Véronique Yoboué,Cathy Liousse,Sonia Rousse,Aristide Barthélémy Akpo,Arnaud Proietti,Loïc Drigo,Melina Macouin,Paul Yves Jean Antonio

doi:10.3390/atmos12040496

Abstract

The physico-chemical characteristics of particulate matter (PM) in African cities remain poorly known due to scarcity of observation networks. Magnetic parameters of PM are robust proxies for the emissions of Fe-bearing particles. This study reports the first magnetic investigation of PM2.5 (PM with aerodynamic size below 2.5 μm) in Africa performed on weekly PM2.5 filters collected in Abidjan (Ivory Coast) and Cotonou (Benin) between 2015 and 2017. The magnetic mineralogy is dominated by magnetite-like low coercivity minerals. Mass normalized SIRM are 1.65 × 10−2 A m2 kg−1 and 2.28 × 10−2 A m2 kg−1 for Abidjan and Cotonou respectively. Hard coercivity material (S-ratio = 0.96 and MDF = 33 mT) is observed during the dry dusty season. Wood burning emits less iron oxides by PM2.5 mass when compared to traffic sources. PM2.5 magnetic granulometry has a narrow range regardless of the site or season. The excellent correlation between the site-averaged element carbon concentrations and SIRM suggests that PM2.5 magnetic parameters are linked to primary particulate emission from combustion sources.

Highlights

The physico-chemical characteristics of particulate matter (PM) in African cities remain poorly known due to scarcity of observation networks
We study PM2.5 filter samples collected through the Dynamic Aerosol–Cloud–Chemistry Interaction in West Africa (DACCIWA) research program in Africa between 2015 and 2017 to characterize the iron oxides in terms of concentration, grain size distribution and magnetic mineralogy
In this work we presented the magnetic investigation of the PM2.5 captured by air filters, previously sampled in a two year campaign on the western sub-Saharan Africa (SSA)

Summary

Introduction

The physico-chemical characteristics of particulate matter (PM) in African cities remain poorly known due to scarcity of observation networks. Magnetic parameters of PM are robust proxies for the emissions of Fe-bearing particles. This study reports the first magnetic investigation of PM2.5 (PM with aerodynamic size below 2.5 μm) in Africa performed on weekly PM2.5 filters collected in Abidjan (Ivory Coast) and Cotonou (Benin) between 2015 and 2017. The excellent correlation between the site-averaged element carbon concentrations and SIRM suggests that PM2.5 magnetic parameters are linked to primary particulate emission from combustion sources. Carbonaceous particles (elemental and organic carbon) are emitted by combustion due to transportation, the use of biofuels or agricultural waste for domestic cooking, and open-air waste burning [13]. Most of the urban areas in SSA lack an air quality network, leaving large, densely populated areas without PM observations. The Dynamic Aerosol–Cloud–Chemistry Interaction in West Africa (DACCIWA)

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