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

Abstract

As in other parts of the world, air pollution over West and Central Africa has major health and meteorological impacts. Air quality assessment and its possible sanitary impact have become essential even in medium-sized towns, therefore amplifying the need for easy-to-implement monitoring methods with low environmental impact. We present here the potential of magnetic methods to monitor air quality at street level in the medium-sized city of Maroua (northern Cameroon) affected by dust-laden desert winds. More than five hundred (544) samples of bark and leaves taken from Neem trees in Maroua were analyzed. Magnetic susceptibility, saturation remanence, and S-ratio were found to determine the concentration and nature of magnetic particles. They are dominated by magnetite-like particle signals as a part of particulate emissions due to urban activities, including both traffic, composed of a substantial proportion of motorcycles, and wood burning for food preparation. We show that both bark and leaves from Neem trees are adequate passive bio-recorders. The use of both enables different times and heights to be sampled, allowing for the high-resolution monitoring, in terms of spatialization, of various urban environments. Particle emissions require assessment and screening that could be carried out rapidly and efficiently by magnetic methods on bio-recorders, even in cities impacted by dust-laden wind.

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

“…The capacity of bark to accumulate the airborne particles was already demonstrated for Neem trees by Dawaï et al. ( 2021 ) in Cameroon, and for various street trees by Chaprarro et al. ( 2020 ) in Buenos Aires (Argentina) and in Milan (Italy) by Vezzola et al.…”

“…Environmental magnetism methods can be applied to natural media. They have been used to monitor anthropogenic PM trapped on vegetation such as leaves, lichens and bark (Chaparro et al., 2020 ; Dawai et al., 2021 ; Limo et al., 2018 ; Moreno et al., 2003 ; Muñoz et al., 2017 ; Sagnotti et al., 2009 ; Urbat et al., 2004 ; Vezzola et al., 2017 ; Zhang et al., 2008 ). Such methods rely on tracking magnetic minerals, for example, iron oxides like magnetite, hematite and maghemite (Leite et al., 2018 ; Marié et al., 2018 ; Winkler et al., 2021 ).…”