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

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 m) 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 1.65e−2A□m/kg and 2.28e−2A□m/kg 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.

Barking up the Right Tree: Using Tree Bark to Track Airborne Particles in School Environment and Link Science to Society

“… Box plot for calculated xARM/SIRM ratio in both school bio‐sensors (indoor and outdoor) and bibliographical values (for natural iron oxides (Dankers, 1978 ); PM10 and total PM (Mitchell & Maher, 2009 ) and PM2.5 (Leite et al., 2021 )). Data points in black dots, outliers in red dots, median is the horizontal line inside the box, the interquartile range by the size of the box, maximum and minimum values are the vertical whiskers.…”

“…The covariation found between PM2.5 and NO 2 indicates that vehicle exhaust is the main source of PM2.5 in the city of Toulouse. The presence of iron‐rich fly ash spherules among soot carbon chains (Figures 5a and 5b ), on the PM1 filters, is also an indicator of internal combustion engine emissions found both indoors and outdoors (Leite et al., 2021 ; Shi et al., 2015 ). The presence of magnetite in PM is often linked to combustion and traffic sources, in line with the shapes detected for some iron oxides on the PM 1 filters (Figures 5a and 5b ) by the SEM microscopy (spherules—Bardeli et al., 2011 ; Castañeda‐Miranda et al., 2014 ; Gonet & Maher, 2019 ; Gonet et al., 2021 ; Leite et al., 2021 ; Liati et al., 2015 ; Sagnotti & Winkler, 2012 ; Winkler et al., 2021 ).…”

Tracking Airborne Pollution with Environmental Magnetism in A Medium-Sized African City

“…The burning of wood and coal in connection with cooking on an open stove next to the street (and trees) could represent an additional provider of magnetite particles, thus explaining the higher values. Indeed, coal generally contains a high Fe content [60], which results in a high iron oxide content in the fly ashes from coal combustion [17,61]. As the building material of the stove contains iron itself, it may also contribute to the magnetic particle load.…”

“…As the building material of the stove contains iron itself, it may also contribute to the magnetic particle load. Urban wood burning can release a substantial quantity of PM2.5 particles [13,62] containing magnetite [17,63]. For example, it has been shown that winter wood burning for indoor heating represents an important part of the total suspended particles in some North American cities [62].…”

“…Over the last decade, environmental magnetism has proven its cost-effectiveness for the monitoring of atmospheric pollution [16]. Magnetic properties of pumped-air filters are related to the atmospheric PM2.5 [17] or the nitrogen oxides (NOX) concentrations [18]. Biocollectors-based environmental magnetism is a rapid and non-destructive way to monitor emitted particle dispersion in various environments ( [16] and reference therein).…”