Isotopic Characterization of Gaseous Mercury and Particulate Water-Soluble Organic Carbon Emitted from Open Grass Field Burning in Aso, Japan

Satoshi Irei

doi:10.3390/app12010109

Abstract

Biomass burning is one of the major emitters of airborne particulate matter (PM) and gaseous mercury. In order to apply the isotopic fingerprinting method to process identification and source apportionment studies, isotopic characterizations of targeted substances at emission are indispensable. Here, we report the stable isotopic composition of total gaseous mercury (TGM) and the stable and radiocarbon isotopic composition of low-volatile water-soluble nitrogen (LV-WSN) and organic carbon (LV-WSOC) in PM emitted from open grass field burning in the Aso region of Japan. The measurement results showed that TGM concentrations in the air increased during the open field burning events, indicating the presence of TGM emissions. The results of LV-WSN analysis showed very low concentrations; therefore, the stable nitrogen isotope ratios could not be measured. The stable mercury isotope ratios exhibited lighter composition than those observed during non-biomass-burning days. The analysis of LV-WSOC revealed heavy stable carbon isotope ratios (average ± SD, −18 ± 2‰), suggesting a substantial contribution from C4 plant carbon. The 14C analysis showed that more than 98% of the LV-WSOC was modern carbon, indicating the contribution of plant carbon to PM emitted from biomass burning. The findings here provide reference isotope compositions of TGM and particulate LV-WSOC from biomass burning in this region.

Highlights

Biomass burning, such as wildfires, biofuel burning, agricultural waste burning, and open field burning, is known to be among the major sources of atmospheric pollutants, including volatile species and airborne particulate matter (PM) [1,2,3,4,5,6]
Studying biomass burning emissions can contribute to evaluating the effectiveness of the Minamata Convention on Mercury, which regulates the use of man-made mercury internationally in order to mitigate global mercury pollution
To better trace the materials, isotopic compositions of elements, such as stable mercury isotope ratios, stable carbon isotope ratio (δ13 C), stable nitrogen isotope ratio (δ15 N), and radiocarbon (14 C) isotope ratio, denoted as percent modern carbon hereafter, have been drawing attention, since measurements of isotopic compositions increase the dimensions of the dataset, which allows us to objectively evaluate the mixing state and extent of processing [9,10,11,12,13,14,15,16,17]

Summary

Introduction

Biomass burning, such as wildfires, biofuel burning, agricultural waste burning, and open field burning, is known to be among the major sources of atmospheric pollutants, including volatile species and airborne particulate matter (PM) [1,2,3,4,5,6]. To better trace the materials, isotopic compositions of elements, such as stable mercury isotope ratios (denoted as δx Hg hereafter), stable carbon isotope ratio (δ13 C), stable nitrogen isotope ratio (δ15 N), and radiocarbon (14 C) isotope ratio, denoted as percent modern carbon (pMC) hereafter, have been drawing attention, since measurements of isotopic compositions increase the dimensions of the dataset, which allows us to objectively evaluate the mixing state and extent of processing [9,10,11,12,13,14,15,16,17] To accomplish such a goal, knowledge of the initial isotopic compositions of those species at emission are indispensable [18,19,20,21,22,23]. Even though this study could not distinguish the origins of Hg between plant and soil, the deposited mercury on the surface over a year still showed δx Hg values consistent with those observed by others

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Conclusion