Optical Method for Measuring Deposition Amount of Black Carbon Particles on Foliar Surface

Abstract

To perform quick measurements of black carbon (BC) particles deposited on foliar surfaces of forest tree species, we investigated an optical method for measuring the amount of BC extracted from foliar surfaces and collected on quartz fiber filters. The seedlings of Fagus crenata, Castanopsis sieboldii, Larix kaempferi and Cryptomeria japonica were exposed to submicron BC particles for one growing season (1 June to 7 December 2009). At the end of the growing season, the leaves or needles of the seedlings were harvested and washed with deionized water followed by washing with chloroform to extract the BC particles deposited on the foliar surfaces. The extracted BC particles were collected on a quartz fiber filter. The absorption spectrum of the filters was measured by spectrophotometer with an integrating sphere. To obtain the relationship between the absorbance of the filter and the amount of BC particles on the filter, the amount of BC particles on the filter was determined as that of elemental carbon (EC) measured by a thermal optical method. At wavelengths below 450 nm, the absorption spectrum of the filter showed absorption by biological substances, such as epicuticular wax, resulting in the low coefficient of determination (<TEX>$R^2$</TEX>) in the relationship between the amount of EC on the filter (<TEX>$M_{EC}$</TEX>, <TEX>${\mu}g\;C\;cm^{-2}$</TEX> filter area) and the absorbance of the filter. The intercept of the regression line between <TEX>$M_{EC}$</TEX> and the absorbance of the filter at 580 nm (<TEX>$A_{580}$</TEX>) was closest to 0. There was a significant linear relationship between the <TEX>$A_{580}$</TEX> and <TEX>$M_{EC}$</TEX> (<TEX>$R^2$</TEX>=0.917, p<0.001), suggesting that the amount of BC particles collected on the filter can be predicted from the absorbance. This optical method might serve as a simple, fast and cost-effective technique for measuring the amount of BC on foliar surfaces.