Leaf saturation isothermal remanent magnetization (SIRM) as a proxy for particulate matter monitoring: Inter-species differences and in-season variation

In recent studies, the saturation isothermal remanent magnetization (SIRM) of leaves has been used for monitoring of atmospheric particulate matter. This study examined leaf SIRM of tree species with different leaf surface characteristics in the urban environment of Gent (Belgium). Leaf SIRM was measured from co-located trees of Carpinus betulus (with ‘hairy’ leaves) and Tilia sp. (‘non-hairy’ leaves) at locations with contrasting traffic density (and particulate pollution level). The measurements were conducted twice during the growing season (June and September 2009). The highest SIRM values were observed for C. betulus, and the lowest for the non-hairy Tilia sp. leaves. The SIRM was significantly higher in locations with high traffic density and in September. Differences between species were independent of pollution level and sampling time, except between hairy and non-hairy Tilia sp. Monthly measurements of leaf SIRM on Tilia platyphyllos and C. betulus trees revealed high in-season variation, which may be due to a combination of short and long-term leaf surface processes. It is concluded that the leaf SIRM, a proxy for particulate matter deposition, depends on leaf surface structure, leaf maturity, and particulate pollution level.