Online high temporal resolution measurement of atmospheric sulfate

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Online high temporal resolution measurement of atmospheric sulfate and sulfur trioxide with a light emitting diode and liquid core waveguide-based sensor Yong Tian, Hui-Yan Shen, Qiang Wang, Aifeng Liu, Wei Gao, Xuwei Chen, Ming-Li Chen, and Zongshan Zhao Anal. Chem., Just Accepted Manuscript • Publication Date (Web): 04 Jun 2018 Downloaded from http://pubs.acs.org on June 4, 2018

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Analytical Chemistry

Online high temporal resolution measurement of atmospheric sulfate and sulfur trioxide with a light emitting diode and liquid core waveguide-based sensor Yong Tian1, Huiyan Shen2, Qiang Wang3, Aifeng Liu1, Wei Gao2, Xu-Wei Chen2, Ming-Li Chen2 and Zongshan Zhao1, *

1

CAS Key Laboratory of Biobased Materials, Qingdao Institute of Bioenergy and

Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China 2

Research Center for Analytical Sciences, and Department of Chemistry, College of

Sciences, Northeastern University, Shenyang 110819, China 3

College of Chemistry and Pharmaceutical, Qingdao Agriculture University, Qingdao

266109, China * Corresponding author: Dr. Zongshan Zhao, Fax/Tel.: +86 532-80662709, E-mail: [email protected]

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ABSTRACT High temporal resolution components analysis is still a great challenge for the frontier of atmospheric aerosol research. Here, an online high time resolution method for monitoring soluble sulfate and sulfur trioxide in atmospheric aerosols was developed by integrating a membrane-based parallel plate denuder (MPPD), a particle collector (PC) and a liquid waveguide capillary cell (LWCC) into a flow injection analysis system. The BaCl2 solution (containing HCl, glycerin and ethanol) was enabled to quantitatively transform sulfate into a well-distributed BaSO4 solution for turbidimetric detection. The time resolution for monitoring the soluble sulfate and sulfur trioxide was 15 h-1. The limits of detection were 86 and 7.3 µg L-1 (S/N = 3) with a 20 and 200 µL SO42- solution injection, respectively. Both the inter-day and intra-day precision values (relative standard deviation) were less than 6.0 %. The analytical results of the certificated reference materials ((GBW(E)08026 and GNM-M07117-2013)) were identical to the certified values (no significant difference at a 95 % confidence level). The validity and practicability of the developed device were also evaluated during a firecracker day and a routine day, obviously revealing the continuous variance in atmospheric sulfate and sulfur trioxide in both inter-day and intra-day studies.

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INTRODUCTION Sulfate and sulfur trioxide, basic pollutants in atmospheric aerosols, are well known for their seriously adverse health effects1,2 and influence on the global climate.3,4 Except naturally formatted in sea-salt particles5, the origin of these pollutants is from the combustion of fossil fuels6,7 and the oxidization of sulfur dioxide in atmospheric conditions.8 Compared with sulfur dioxide, SO3 is more corrosive and toxic, and even more difficult to remove in ordinary flue gas desulfurization.9 As the major acid component of aerosols10, SO42- can also promote the dissolution of transition metals and increase the toxicity of atmospheric aerosols11. Moreover, SO42- and SO3 are the primary precursors of the secondary aerosols, often resulting in persistent and severe haze pollution.12,13 To date, monitoring their levels in the atmosphere is still one of the most important issues in atmospheric science.9 The methods for monitoring atmospheric SO3 and SO42- can be classified into off-line and online modes. At present, the SO42- in atmospheric aerosols are mainly off-line collected on a membranous collector, extracted, and then detected by ion chromatography, optical spectrometry or mass spectrometry.14-17 The storage and transfer efficiency are the primary technical difficulties for these off-line methods. Additionally, these methods cannot meet the demand for the continuous monitoring of atmospheric chemical composition information over a period of time.18,19 As a result, methods that combine online collection and sulfate detection in atmospheric aerosols are required.19 During the past few years, a series of well-designed online collection devices for atmospheric gas and fine particulate matter have been developed by the Dasgupta group.18,20-26 By combining a membrane-based parallel plate denuder (MPPD),20-22 a wetted hydrophilic filter assembled particle collector (PC),21,27 and an ion chromatography (IC) system,22 soluble atmospheric gases and particles could be 3

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successfully collected and detected online. Strikingly, the temporal resolution can reach up to 4 h-1 by the usage of IC.21 This technique has gradually developed into a commercial instrument, named ambient ion monitor - ion chromatography (AIM-IC), and has been used for monitoring water soluble ions (SO42-, NO3-, NO2-, NH4+, etc.) in atmospheric aerosols with an hourly resolution28,29. Owing to the strict working conditions and high maintenance cost of IC, their applications are still limited to some extent, e.g., they are widely used in developing areas. The same problems, namely, high price and low portability, also occur with the other detectors, e.g., aerosol mass spectrometry, AMS30-33. Therein, developing high-time resolution online detection device for monitoring the atmospheric aerosol compositions is still an important issue. In this study, an online high time resolution method for monitoring soluble SO3 and SO42- in atmospheric aerosols was developed by integrating a membrane-based parallel plate denuder (MPPD), a particle collector (PC) and a liquid waveguide capillary cell (LWCC) into a flow injection analysis system. A light emitting diode (LED) and a photodiode are used as the light source and detector, which are beneficial for reducing the cost and increasing the portability of the detection system.34-37 The LWCC enhances the sensitivity of the optical detection system.38-40 The flow injection system enables the online monitoring of SO3 and SO42- in aerosols. The operating conditions and analytical performance were systemically investigated. The validity and practicability of the system were evaluated by monitoring the continuous variance in atmospheric SO3 and SO42- during a firecracker day (a festival in Qingdao, China) and a routine day.

EXPERIMENTAL SECTION Construction and assembly of the device 4

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Analytical Chemistry

The schematic diagram of SO3 and SO42- detection device is shown in Figure 1. The MPPD and PC were used for online collection of SO3 and SO42-, respectively. The MPPD20-22 and PC

21,27

were assembled by following the method developed by

the Dasgupta group. Briefly, the MPPD consisted of two polycarbonate plates, a spacer (perfluoroalkoxy (PFA) Teflon), and two pieces of dialysis cellulose acetate membranes (45.0 cm×5.0 cm; molecular weight cut-off, 8000-14000). These components were stacked and fixed with screws. Two pieces of stainless steel tubes (i.d. = 6 mm, o.d. = 8 mm, L = 50 mm) were sandwiched between the membranes as the air sample inlet and the air sample outlet of the MPPD. The particle collector was built by two plastic syringe tubes (10 mL and 5 mL). A paper filter (on top, Whatman type 1) and a hydrophilic membrane filter (in bottom, isopore polycarbonate filter, 5 µm pores, 5-20 % porosity, Millipore Corp., Germany), both 25 mm in diameter, were stacked and used for soluble SO42- collection in particulate matter. The air sample was aspirated by an air pump at a flow rate of 1.5 L min-1 to pass through the MPPD and PC sequentially. The flow rate was controlled by a mass flow controller. The experimental conditions for the collection of SO3 and soluble SO42- in atmospheric aerosols are summarized in Table S1 (in the supporting information). A peristaltic pump (LabM1, Baoding Shenchen Precision Pump Co., Ltd., China) was used to deliver the water at a flow rate of 0.25 mL min-1 for SO3 and SO42collection. Another peristaltic pump was used to deliver the acidic BaCl2 solution for turbidimetric detection. An auto reservoir (BS-30A, Shanghai Jiapeng Technology Co., Ltd., China) was used to collect the filtrates from the PC. The collected filtrates were introduced into the LWCC detection system by a 6-port injector. A three-way reactor was employed to mix the SO42- solution with the acidic BaCl2 solution (10 g L-1 BaCl2, 4 % glycerin, 4 % ethanol, 0.1 mol L-1 hydrochloric acid). After sufficient mixing in 5

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the reaction coil (PTFE tube, i.d. = 1.0 mm, o.d. = 1.6 mm, L = 80 cm), the mixture was delivered into the LWCC (LWCC-3250, World Precision Instruments, USA) for turbidimetric detection. A light emitting diode (LED, 465 nm) and a light-to-voltage converter (Photodiode, TSL257, www.ams.com) were connected to the LWCC via plastic fibers as the light source and optical detector. A 16-bit USB-based data acquisition (DAQ) board (USB-1608FS-Plus) and a laptop computer were employed for converting and recording the signals. The details of the electric circuit of the LED, light-to-voltage converter and the DAQ are shown in Figure S1 (in supporting information)34,35. Reagent and sample information, experimental procedures, data processing, and the spectrum properties of the turbid solution and LED

The details of the reagents and samples, experimental procedures, data processing and spectral properties of the turbid solution and LED (Figure S2) are shown in the supporting information.

RESULT AND DISCUSSION The collection mechanism and conditions of the MPPD and PC The collection efficiency and mechanism of the MPPD and PC have been thoroughly studied by Dasgupta et al.20,21 The common soluble atmospheric trace gases and mist/hydrates could quantitatively diffuse into the flushing solution of the MPPD plates through the membranes. Herein, the SO3 gas and hydrate (SO3·nH2O) are dissociated into SO42- in the flushing solution (the chemical reactions are shown in Figure S3). The collection efficiency of MPPD could achieve 99% for the gases and mist/hydrates at air flow rates less than 1.7 L min-1. The particles are capable of 6

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Analytical Chemistry

passing through the MPPD and then entering into the PC. The particles are efficiently captured by a polycarbonate filter that is continuously wetted by de-ionized water mist. The soluble ions (e.g., SO42-) are dissolved and dissociated into the flushing water. The particle collection efficiency could reach 98 % for particle aerodynamic diameters larger than 0.28 µm at an air flow rate of 1.5 L min-1. By referring to the reported results,20,21 the experimental conditions of the MPPD and PC, such as an air flow rate of 1.5 L min-1 and a water flow rate of 0.25 mL min-1 for the flushing denuder and PC are used (Table S1). The effects of the experimental conditions on SO42- detection The concentration of BaCl2 directly influences the precipitation equilibrium of BaSO4. The solubility product (Ksp) of BaSO4 in water is 1.0×10-10 at 25°C41. When ethanol and glycerin are added into the solution, the solubility of BaSO4 is not increased. Approximately 1.5 g L-1 of Ba2+ is sufficient to initiate 1.0 µg L-1 of SO42precipitation. In this study, 5.0 – 40.0 g L-1 of BaCl2 was investigated to detect 1.0 mg L-1 of SO42- in this study. There was no significant difference obtained in the results shown in Figure S4. To ensure the precipitation efficiency of SO42- and to avoid wasting BaCl2, 10.0 g L-1 of BaCl2 was chosen for the following experiments. The proportion of ethanol and glycerin in the BaCl2 solution are both important for the stability and homogeneity of the emulsion of BaSO4. The ethanol prevents bubble production. The glycerol is used as dispersant to prevent the rapid accumulation of the precipitated particulates. In this study, 0 – 15.0 % of ethanol and glycerin were tested for SO42- detection (Figure S5 and S6). The results indicate that 4.0 % of ethanol and glycerin are suitable for SO42- detection. Less than 4.0 % ethanol and glycerin should be insufficient for the satisfactory distribution of the BaSO4, and 7

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greater than 4.0 % ethanol and glycerin can increase the detection noise by raising the viscosity of the BaCl2 solution. As shown in Figures S5 and S6, 4.0 % ethanol and 4.0 % glycerin are used in the following study. Hydrochloric acid is an essential factor in the turbidimetric determination of SO42-. This acid eliminates the interference effects from common coexisting ions, such as CO32- and SO32-. However, a high level of hydrochloric acid causes acid waste and extra signal noise. As a result, 0.0050 to 0.30 mol L-1 HCl was investigated. The result shown in Figure 2A indicates that 0.10 mol L-1 hydrochloric acid is appropriate for the turbidimetric determination of SO42-. The length of the reaction coil directly affects the homogeneity and stability of the barium sulfate in this study. With the length of the reaction coils (PTFE tube, i.d. = 1.0 mm, o.d. = 1.6 mm, coil diameter = 10 mm) increasing from 20 to 80 cm, the signals are continually increased (Figure 2B). The result indicates that a PTFE tube size of less than 80 cm is not sufficient for a Ba2+ and SO42- reaction. However, when the length reaches 100 cm, the signals dramatically decrease. This decrease can be attributed to BaSO4 deposition on the inner surface of the lengthy coil42. In addition, the higher pressure and longer analytical time are inevitable with the increasing length of the coil. In this study, an 80-cm-length PTFE tube is employed as the reaction coil. The solution flow rates of BaCl2 and SO42- are closely associated with their online reaction efficiency. The results showed that the best reaction efficiency can be achieved with a flow rate of 1.0 mL min-1 in the range from 0.20 to 2.0 mL min-1. (Figure 2C) The BaSO4 precipitate might be adsorbed by the reaction coil with a lower flow rate. However, the BaCl2 solution and SO42- might not completely react in the reaction coil at a higher flow rate. 8

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Interferences The potential interference of coexisting ions in soluble particulate matter was tested at a SO42- concentration of 1.0 mg L-1. The results, summarized in Table S2, indicate that within a ± 5 % error range, 100-fold of 11 common ions do not interfere with the SO42- determination, e.g., Na+, K+, Al+, Mg2+, Ca2+, Br-, Cl-, SO32-, PO43-, CO32- and NO3-. Notably, the concentration level of HCl is highly important to the interfering tolerance. SO32- and CO32- might interfere with SO42- detection when the HCl content is lower than 0.10 mol L-1. In this study, even higher concentration levels of the cations are not tested. Generally, the coexisting ions in the particulate matter samples will not exceed the tolerant concentration levels in SO42- detection. Therefore, the present method can be directly employed, and no further treatment or masking reagents are needed. Performance Under optimized experimental conditions, the analytical performance of sulfate detection by the present method is summarized in Table S3. In the case of a 20 µL sample loop, 0.50 to 25 mg L-1 of the standard sulfate solutions is rapidly detected. The linear range could extend to 25 mg L-1 with a coefficient of determination (R2) of 0.9935 (Figure S7). A limit of detection (LOD, S/N = 3) of 86 µg L-1, a relative standard deviation (RSD) of 4.5 % for the nine successive determinations of 10 mg L-1 SO42-, and an inter-day precision of 5.7 % (n = 3 per day for 3 days, c = 5 mg L-1) are achieved. As the data acquisition time is approximately 3.0 min, in addition to approximately 1.0 min for sample loading and background stability, each run of the device for the detection of SO42- in air could be finished in 4.0 min, i.e., the temporal resolution for sample monitoring is 15 h-1, which is approximately 3 times higher than 9

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the methods based on IC21. To acquire a high sensitivity performance, 200 µL of the sample injection loop is also tested in this study (Figure S8). Briefly, a LOD of 7.3 µg L-1, a linear range of 50 to 1000 µg L-1, an intra-day precision of 3.7 %, and an inter-day precision of 6.0 % can be obtained. In consideration of the low price and simple construction of the developed detector, i.e., assembled by an LED, a photodiode and a LWCC, the system performance matches well with the MPPD and PC, which is satisfactorily comparable to AIM-IC and other commercial instruments.21,28,29 Applications Because the MPPD20-22 and PC21,27 for the collection of gases, hydrates and particulate matter have been well certified, SO3 gas, the hydrates and SO42- in particulate matter are all dissociated into SO42- in water, and the detection accuracy is validated by an analysis of SO42- in standard water samples (GBW(E)08026 and GNM-M07117-2013). The analytical results are summarized in Table 1. The results showed that the determined results are identical to the certified values with a relative standard deviation less than 2.2 %. The F-test and t-test results confirmed that there is no significant difference between the determined and certified values at a 95 % confidence

level.

The validity and practicability were evaluated by monitoring the continuous variance in atmospheric SO3 and SO42- during a firecracker day and a routine day. Soluble SO3 and SO42- in atmospheric aerosols were detected from 18:00 p.m. to 20:30 p.m. on Sept. 6, 2017 (a routine day) and from 18:00 p.m. to 21:00 p.m. on Sept. 13, 2017 (a firecracker day) respectively (Figure 3). No obvious correlation relationships between the concentration level of gaseous SO3 and soluble SO42- in the 10

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Analytical Chemistry

atmospheric aerosols have been found in these both days. On Sept. 6, the levels of SO3 were all below 60 µg m-3, except at the time of 18:20 to 18:44, 19:00 to 19:04 and 19:48 to 19:52 (Figure 3A). The maximum concentration level of SO3 could reach to 181.6 µg m-3 at 18:40 p.m. The levels of the soluble SO42- in the atmospheric aerosols were all below 40 µg m-3, except 19:00 to 19:12. The average levels of SO3 and SO42were 65.8 and 24.7 µg m-3 respectively. On Sept. 13, 2017, the residents in Qingdao City in China set off fireworks for blessings, and the air was full of smoke. The levels of SO3 and soluble SO42- in the atmospheric aerosols were all higher than those on Sept. 6, 2017. In addition, the variation in SO3 and SO42- was irregular and frequently changed due to the fireworks (Figure 3B). Between 18:00 and 21:00 on Sept. 13, 2017, the average levels of SO3 and SO42- were 94.0 and 61.2 µg m-3, respectively. The convenient identification of the inter-day and intra-day difference of SO3 and SO42- suggests that the developed device is a promising strategy.

CONCLUSION A SO3 and SO42- detector that is compatible with online atmospheric aerosol collection was developed by assembling a light emitting diode, a liquid waveguide capillary cell, and a photodiode into a flow injection system. The inexpensive and easy-to-assemble developed device presented comparable performance to ion chromatography methods for monitoring SO3 and SO42-. The high precision and sensitivity, i.e., inter-day/intra-day precision and limit of detection, was also obtained. Moreover, the validity and practicability of the system was evaluated during a firecracker day and a routine day by continuously monitoring the variance in atmospheric SO3 and SO42-. As a highly needed technique, the developed device should be a promising strategy for monitoring SO3 and SO42-.

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ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. The contents of the Supporting Information include reagents and samples, experimental conditions for SO3 and soluble SO42- collection in atmospheric aerosols, experimental procedures for standard SO42- detection, experimental procedures for the analysis of SO3 and soluble SO42- in atmospheric aerosols, data analysis, spectral properties of the turbid solution and LED, additional figures and tables.

AUTHOR INFORMATION Corresponding Authors *

Fax/Tel.: +86 532-80662709, E-mail: [email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS

The present study was supported by the National Natural Science Foundation of China (No. 21607161), the Primary Research & Development Plan of Shandong Province (No. 2016GSF117039), the Instrument Developing Project of the Chinese Academy of Sciences (No. YZ201642), the Livelihood Science and Technology Program of Qingdao City (No. 15-9-2-123-ns), and the State Key Laboratory of Environmental

Chemistry

and

Ecotoxicology, 12

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Eco-Environmental Sciences, Chinese Academy of Sciences (No. KF2015-10).

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(21) Takeuchi, M.; Ullah, S. M. R.; Dasgupta, P. K.; Collins, D. R.; Williams, A. Anal. Chem. 2005, 77, 8031-8040. (22) Ullah, S. M. R.; Takeuchi, M.; Dasgupta, P. K. Environ. Sci. Technol. 2006, 40, 962-968. (23) Boring, C. B.; Al-Horr, R.; Genfa, Z.; Dasgupta, P. K.; Martin, M. W.; Smith, W. F. Anal. Chem. 2002, 74, 1256-1268. (24) Ito, K.; Chasteen, C. C.; Chung, H. K.; Poruthoor, S. K.; Zhang, G. F.; Dasgupta, P. K. Anal. Chem. 1998, 70, 2839-2847. (25) Samanta, G.; Boring, C. B.; Dasgupta, P. K. Anal. Chem. 2001, 73, 2034-2040. (26) Simon, P. K.; Dasgupta, P. K. Anal. Chem. 1995, 67, 71-78. (27) Fuller, S. J.; Wragg, F. P. H.; Nutter, J.; Kalberer, M. Atmos. Environ. 2014, 92, 97-103. (28) Markovic, M. Z.; VandenBoer, T. C.; Murphy, J. G. J. Environ. Monitor. 2012, 14, 1872-1884. (29) Beccaceci, S.; McGhee, E. A.; Brown, R. J. C.; Green, D. C. Aerosol Sci. Tech. 2015, 49, 793-801. (30) Guo, S.; Hu, M.; Shang, D. J.; Guo, Q. F.; Hu, W. W. Acta Chim. Sin. 2014, 72, 145-157. (31) Parshintsev, J.; Hyotylainen, T. Anal. Bioanal. Chem. 2015, 407, 5877-5897. (32) Duarte, R. M. B. O.; Duarte, A. C. TrAC, Trends Anal. Chem. 2011, 30, 1659-1671. (33) Hao, L.; Romakkaniemi, S.; Kortelainen, A.; Jaatinen, A.; Portin, H.; Miettinen, P.; Komppula, M.; Leskinen, A.; Virtanen, A.; Smith, J. N.; Sueper, D.; Worsnop, D. R.; Lehtinen, K. E. J.; Laaksonen, A. Environ. Sci. Technol. 2013, 47, 2645-2653. (34) Tian, Y.; Dasgupta, P. K.; Mahon, S. B.; Ma, J.; Brenner, M.; Jian, H.; Boss, G. R. Anal. Chim. Acta 2013, 768, 129-135. (35) Tian, Y.; Zhang, X.; Shen, H.; Liu, A.; Zhao, Z.; Chen, M.-L.; Chen, X.-W. Anal. Chem. 2017, 89, 13064-13068. (36) Ratcliff, E. L.; Veneman, P. A.; Simmonds, A.; Zacher, B.; Huebner, D.; Saavedra, S. S.; Armstrong, N. R. Anal. Chem. 2010, 82, 2734-2742. (37) Toda, K.; Yoshioka, K. I.; Ohira, S. I.; Li, J. Z.; Dasgupta, P. K. Anal. Chem. 2003, 75, 4050-4056. (38) Dallas, T.; Dasgupta, P. K. TrAC, Trends Anal. Chem. 2004, 23, 385-392. (39) Gimbert, L. J.; Worsfold, P. J. TrAC, Trends Anal. Chem. 2007, 26, 914-930. (40) Páscoa, R. N. M. J.; Tóth, I. V.; Rangel, A. O. S. S. Anal. Chim. Acta 2012, 739, 1-13. (41) Christian, G. D.; Dasgupta, P.; Schug, K. Analytical chemistry, 7th edition: seventh edition, 2013, 14

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Analytical Chemistry

p803. (42) Fang, Z. L.; Sperling, M.; Welz, B. J. Anal. Atom. Spectrom. 1991, 6, 301-306.

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Table 1. The determination of SO42- in certified reference materials GBW(E)080267 and GNM-M07117-2013 (n = 3, ± standard deviation).

Materials GBW(E) 080267 GNM-M07117 -2013

Certified values

This method

(mg L-1)

(mg L-1)

100.0 ± 1.0

100.2 ± 2.2

100.0 ± 1.4

100.0 ± 1.5

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Analytical Chemistry

Figure legends Figure 1. The diagram of the online detection system coupled with the membrane-based parallel plate denuder and particle collector for the determination of SO3 and SO42- in atmospheric aerosol. PP: Peristaltic pump; MPPD: Membrane-based parallel plate denuder; PC: Particle collector; WTF: Water trap filter; AP: Air pump; MFC: Mass flow controller; AR: Auto reservoir; R: Reservoir; SI: Sample injector; W: Waste; TR: Three-way reactor; RC: Reaction coil; A: H2O; B: reagent: 0.01 g mL-1 BaCl2, 4 % glycerin, 4 % ethanol, 0.1 mol L-1 hydrochloric acid; LWCC: Liquid waveguide capillary cell; LED: Light emitting diode; PD: Photodiode. Figure 2. The effects of the concentration level of hydrochloric acid (A), the length of the reaction coil (B), and the flow rates of the BaCl2 and sample solutions on SO42detection (C). (SO42-: 1 mg L-1) Figure 3. The concentration levels of SO3 and SO42- detected in the air of the QIBEBT campus (A) from 18:00 pm to 20:30 pm on September 6, 2017 and (B) from 18:00 pm to 21:00 pm on September 13, 2017.

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Figure 1.

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Figure 2. B. Length of reaction coil (cm) 0

40

80

120

0.0025

A B C

0.002

0.0015

Signal

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Analytical Chemistry

0.001

0.0005

0 0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

A. Concentration of HCl (mol/L) 0

0.5

1

1.5

2

2.5

C. Flow rates of the BaCl2 solution and sample (mL/min)

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Analytical Chemistry

Figure 3. 200

200

SO3 SO42-

A

SO3 SO42-

160

B

160 -3)-3 Concentration µg mm Concentration((µg )

-3)-3 Concentration µg mm Concentration((µg )

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120

80

40

120

80

40

0

0

18:00

18:30

19:00

19:30

20:00

20:30

Determination of SO3 and SO42- On Sep. 6th 2017

18:00

18:45

19:30

20:15

21:00

Determination of SO3 and SO42- On Sep. 13th 2017

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Analytical Chemistry

For TOC only SO42SO3

SO3

SO42-

LWCC SO42SO4

H2O

2-

PD

H2O H 2O

LED

SO42-

W

BaCl2

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