Comparison of Elemental Carbon in Lake Sediments Measured by Three Different Methods and 150-Year Pollution History in Eastern China

Abstract

Concentrations of elemental carbon (EC) were measured in a 150 yr sediment record collected from Lake Chaohu in Anhui Province, eastern China, using three different thermal analytical methods: IMPROVE_A thermal optical reflectance (TOR), STN_thermal optical transmittance (TOT), and chemothermal oxidation (CTO). Distribution patterns for EC concentrations are different among the three methods, most likely due to the operational definition of EC and different temperature treatments prescribed for each method. However, similar profiles were found for high-temperature EC fractions among different methods. Historical soot(TOR) (high-temperature EC fractions measured by the IMPROVE_A TOR method) from Lake Chaohu exhibited stable low concentrations prior to the late 1970s and a sharp increase thereafter, corresponding well with the rapid industrialization of China in the last three decades. This may suggest that high-temperature thermal protocols are suitable for differentiating between soot and other carbon fractions. A similar soot(TOR) record was also obtained from Lake Taihu (~200 km away), suggesting a regional source of soot. The ratio of char(TOR) (low-temperature EC fraction measured by the IMPROVE_A TOR method, after correction for pyrolysis) to soot(TOR) in Lake Chaohu shows an overall decreasing trend, consistent with gradual changes in fuel use from wood burning to increasing fossil fuel combustions. Average higher char(TOR)/soot(TOR) was observed in Lake Taihu than in Lake Chaohu in the past 150 years, consistent with the longer and more extensive industrialization around the Taihu region.

Distribution, input pathway and mass inventory of black carbon in sediments of the Gulf of Thailand, SE Asia

“…For quality assurance and quality control (QA/QC), whether the residue on the filters has an even distribution is a primary factor that markedly influences the accuracy of the BC concentration determination (Khan et al, 2009;Han et al, 2011;Fang et al, 2015). The typical filters loaded with acid-treated sediment residue are displayed in Fig.…”

“…In this study, char and soot were measured using the IMPROVE thermal optical method according to Han et al (2007b), which has been validated and successfully applied in aerosol studies (Han et al, 2010;Lim et al, 2012) and in soil and sediment studies (Han et al, 2009(Han et al, , 2011(Han et al, , 2015a(Han et al, , 2015bCong et al, 2013), in order to yield a better understanding of the distribution, sources and potential input pathways of char and soot within the tropical coastal system in SE Asia.…”

“…The char/soot varied from 3.11 to 24.75, with a mean value of 9.57 ± 5.02, indicating that char was a predominant constituent of BC in the GOT sediment samples. Char is produced mainly in a low-temperature combustion and has a large particle size (generally 1e100 mm), whereas the soot is mainly composed of submicrometer particles formed from the condensation of hydrocarbon radicals at high temperature combustion (>600 C) (Masiello, 2004;Han et al, 2011). Therefore, char is usually more related to the local biomass burning and industrial activities and is more easily incorporated into local soils and discharged into the adjacent aquatic sediments through rivers and surface run-off (Knicker et al, 2008).…”

Characteristics and Sources of Black Carbon in Atmospheric Dustfall Particles from Huangshi, China

“…Thus, it is likely that industrial emissions, especially those from coalpowered metal smelters in Huangshi, led to high accumulation rates for fossil BC over the past several decades. This type of influence can be seen in the historical variations of char/soot ratio in sediments from Lake Chaohu, eastern China (Han et al, 2011). Moreover, exhaust emissions from motor vehicles can lead to high BC deposition rates in urban areas-this has been shown in studies of both aerosols and sediments.…”

“…Moreover, exhaust emissions from motor vehicles can lead to high BC deposition rates in urban areas-this has been shown in studies of both aerosols and sediments. For example, by using the TOR method, Han et al (2011) found that the variations of soot in the sediments from Lake Chaohu increased after 1978, corresponding with the growth in the total number of motor vehicles.…”