Supporting information

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1 Supporting information Light absorption and excitation-emission fluorescence of urban organic aerosol components and their relationship to chemical structure Qingcai Chen 1, Fumikazu Ikemori 1,2, Michihiro Mochida *1 1 Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan 2 Nagoya City Institute for Environmental Sciences, Nagoya, Japan *Corresponding author mochida.michihiro@g.mbox.nagoya-u.ac.jp Address: Department of Earth and Environmental Sciences, Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya , Japan Contents: Number of pages: 30 S1: Definitions of acronyms (P S1) S2: Reproducibility and blank levels of the extraction and analysis (P S1-S2) S3: Assessment of the possible influences of solvents, ph, added ammonia and ultrasonication on the optical properties of the extracts (P S2-S5) S4. The uncertainty of the Å values (P S5-S6) S5: Post-processing of the fluorescence spectra (P S6) S6: PARAFAC analysis for the EEMs (P S6-S7) S7. Estimation of the contributions of PAHs to the total light absorption of WISOM (P S7-S8) Tables: 7 Figures: 14 References: 27

2 S1. Definitions of acronyms WSOM: water-soluble organic matter WISOM: water-insoluble organic matter HULIS-n: humic like substances with neutral nature in water-soluble organic matter HULIS-a: humic like substances with acidic nature in water-soluble organic matter HP-WSOM: high-polarity water-soluble organic matter EEM: excitation-emission matrix MAE: mass absorption efficiency NFV: fluorescence volume normalized by organic mass concentration S2. Reproducibility and blank levels of the extraction and analysis The reproducibility and the blank levels of the analysis of the WISOM, WSOM, HULIS-n, HULIS-a, and HP-WSOM by the UV-visible absorption spectrophotometer and the EEM fluorescence spectrophotometer were assessed by the triplicate extraction and analysis of an identical aerosol sample and a blank filter. The relative standard deviation (RSD) of the EEM fluorescence volumes of the WISOM, WSOM, HULIS-n, HULIS-a and HP-WSOM (over the wavelength range of nm for excitation and nm for emission) varied in the range of 0.7% 5.4% and those of the absorbances of the five components (in the wavelength range of nm for the HP-WSOM and nm for the other extracts) varied in the range of 0.5% 14.3%. Note that the light-absorption of the WSOM and the summed light-absorption of the HULIS-n, HULIS-a and HP-WSOM were similar (<11% differences on average in the range of nm), which indicates that the light-absorptive compounds were largely not lost in the separation procedure using S1

3 the SPE. The blank levels of the absorbance for the WSOM, HULIS-n, HULIS-a and HP-WSOM in the wavelength range of nm were <4% of the lowest absorbance of the sample solutions. The average blank levels of the absorbance in the wavelength ranges of nm and nm for the WISOM varied in the ranges of 1% 3.3% and 7.7% 12% of the absorbance for the sample solutions, respectively. Although the relative contribution of the blank level to the absorbance of the WISOM in the visible range ( nm) was slightly higher than that in the UV-range ( nm), the absorbance of the blank was still substantially lower than that of the actual samples. The intensities of the fluorescence peaks of the blank samples for the WISOM, WSOM, HULIS-n, HULIS-a and HP-WSOM were <6.8% of the lowest fluorescence intensity of the sample solutions over the wavelength ranges of nm for excitation and nm for emission (except for the signals of the primary and secondary Raman and Rayleigh-Tyndall scattering). The fluorescence volumes ( nm for excitation and nm for emission) of those blank extracts were <3.6% of the lowest fluorescence volumes of the sample solutions. S3. Assessment of the possible influences of solvents, ph, added ammonia and ultrasonication on the optical properties of the extracts Possible dependences of the optical properties of the extracted matters on the solvent, ph, the presence of ammonia and ultrasonication were assessed. Two filter samples (collected in winter and summer) were used for the extraction and separation of the organic components. The WSOM and WISOM were extracted by ultrasonication with 10 g of Fluka water and 10 g of MeOH. The HULIS and HP-WSOM were fractionated from the WSOM extracts using an Oasis HLB by the one-step method after Varga et al. 1 Note that eluting the HULIS from the HLB cartridges was performed S2

4 using MeOH as solvent without ammonia. For the assessment of the possible influence of ultrasonication, the WSOM and WISOM were first extracted with water and MeOH, respectively, by mechanical shaking (without ultrasonication). After the extraction, the filters were further subjected to the extraction by ultrasonication with 10 g of MeOH to assess the extraction efficiency of BrC by mechanical shaking. (1) Influence of the difference in the solvents We examined the difference in the UV-visible absorbance spectra of the WISOM and HULIS with different solvents. We added 1 ml of the WISOM solutions (solvent: MeOH) into two 15-ml vials. Whereas 2 ml of MeOH were mixed with one fraction, 2 ml of DCM were mixed with the other fraction, so as to made the sample solution is DCM/MeOH (2/1, v/v). Similarly, 1 ml of the HULIS solution (solvent: MeOH) in 15-ml vials was fully dried under a nitrogen flow and was re-dissolved with 3 ml of water, whereas 2 ml of MeOH were mixed with the other portion of 1 ml of the HULIS solution (solvent: MeOH). The prepared samples of WISOM with solvents of MeOH and DCM/MeOH (2/1, v/v), and HULIS with solvents of water and MeOH were subjected to the analysis by UV/vis spectroscopy. As shown in panels (a) and (b) in Figure S6, the UV-visible absorption spectra of the WISOM and HULIS were not substantially different (<3% in the range of nm) when different solvents were used. (2) Influence of ph We examined the differences in the UV-visible absorbance spectra of the HP-WSOM at different ph values (i.e., 2 and 7). The ph of the HP-WSOM extracts was adjusted to approximately 7 with 1 M NaOH solutions and then analyzed by UV-vis spectroscopy. The UV-visible absorption spectra of the HP-WSOM extracts at ph values of 2 and 7 are presented in Figure S6c. Although the S3

5 UV-visible absorption spectra in the wavelength range of <300 nm changed slightly (<5%) by changing the ph from 2 to 7, their absorbances were substantially lower than those of the WISOM and HULIS fractions. (3) Influence of ammonia We assessed the effect of the use of methanol containing 2 wt% ammonia as solvent on the UV-visible absorbance spectra and the EEM spectra of the aerosol HULIS. To determine the magnitude of this influence, 1 ml of methanol containing 4 wt% ammonia was mixed with 1 ml of the HULIS solution (solvent: MeOH) in 15 ml vials, and the mixture was dried under a nitrogen flow and re-dissolved with 3 ml of MeOH (referred to as HULIS-Amm). Furthermore, as controls, 2 ml of MeOH without ammonia was mixed with the other 1 ml HULIS solution. Figures S7 and S8 present the UV-visible absorbance spectra and the EEM spectra of the HULIS and HULIS-Amm extracts, respectively. Although the absorbance of the HULIS extracts increased slightly, the changes were less than 10%. Furthermore, no substantial differences in the EEM spectra were observed for the HULIS and HULIS-Amm. These results indicate that it is unlikely that ammonia changed the optical properties of the HULIS under our experimental conditions. Further experimentation and analysis regarding the possible influence of ammonia on the chemical structures (i.e., chemical groups, ion-groups and elemental ratio) of the HULIS was found to be insignificant based on the HR-AMS and FT-IR spectra, as described elsewhere. 2 Possible explanations for this observation are as follows: (1) the contact times during the handling of the samples (including the drying process using N 2 ) were significantly shorter than the time scale of BrC formation, which typically requires days in laboratory-generated solutions; 3-5 (2) the carbonyl groups in the HULIS in MeOH are less reactive to ammonia compared with those in water; and (3) the carbonyl groups form primary imines by the S4

6 reaction with ammonia through the following reciprocal reactions: 5 R 1 R 2 C=O + NH 3 R 1R 2 C(OH)NH 2 R 1R 2 C=NH + H 2 O, (S1) where the primary imines are not stable. In this case, the formed primary imines may have been converted to the original carbonyl compounds as the ammonia volatilized under a nitrogen flow. This inference is supported by the analysis of the HULIS with the repeated addition of the 2 wt% ammonia in MeOH and drying (Figure S8b). (4) Influence of ultrasonication on the extraction We examined the differences in the UV-visible absorbance spectra and EEMs of the WSOM and WISOM before and after treatment with ultrasonication. As presented in Figures S9 and S10, ultrasonication did not change substantially the absorbance and fluorescence intensities of the extracts. Note that the extracts from the ultrasonication of the same filter punches after the extraction by mechanical shaking show only a weak light absorption (<8% of total light absorption by extracts in the wavelength range nm), suggesting the extraction efficiency of BrC by mechanical shaking is comparable to ultrasonication. S4. The uncertainty of MAE and Å values The absorbance of the studied extracts at 700 nm was from 7.16% to 7.33% (or from 0.46% to 0.50%) of that at 400 (or 250) nm of the respective extracts. The percentages serve as a guide to estimate the uncertainty of the MAE values on the assumption that the variation of the absorbance at 700 nm was mainly originated from a wavelength-independent absolute error. To assess the uncertainty of the Å values, baseline adjustment was performed by the subtraction of the absorbance values at 700 nm those in the wavelength ranges of nm. The resulting changes of the Å S5

7 values for nm, nm, nm, nm and nm are in the ranges of 10.5% to +9.8%, 1.4% to +1.5%, 6.0% to +5.3%, 13.2% to +16.8% and 38.2% to +31.3%, respectively. The ranges serve as a guide to estimate the uncertainty of Å values. S5. Post-processing of the fluorescence spectra The EEMs collected using a fluorescence spectrophotometer were calibrated according to the procedures described in Lawaetz and Stedmon 6 and Murphy 7. The spectral correction factors were acquired from the manufacturer of the spectrometer (JASCO), which were used for the first calibration of the EEMs. This was followed by an inner filter correction based on the corresponding UV-visible absorbance spectra of the extracts. The highest light absorbance in the calibrated wavelength range was not greater than 2 (mostly below 1 at 235 nm), which is appropriate for the inner filter corrections of the EEMs. 8 Then, the EEMs were normalized so that their unit is RU. 6 This was performed by using the Raman peak of water, which was extracted from the EEMs of the water at an excitation wavelength of 348 nm over the emission wavelength range from 380 nm to 410 nm. S6. PARAFAC analysis for the EEMs The PARAFAC model was used to resolve the EEM compounds and to analyze the chromophores in the aerosol samples. The dreem toolbox version for MATLAB was used for the PARAFAC model, which was downloaded from 9 The details of the data analysis are given in the tutorial of PARAFAC and in literature Briefly, the EEMs (n = 12) of the extracts in the respective types of fractions and the EEMs of all of the extracts (n = 60) were used for the PARAFAC analysis. Using all 60 EEMs in the analysis, a 5-component PARAFAC solution was S6

8 adopted by comparisons of the residual errors, by split-half analysis and by visual inspection for the 2- to 7- component PARAFAC model (Figures S11 and S12). 9 The 5-component model explains >98.8% of the variations within the dataset. Although the model has low core consistencies (8.8%), it should be acceptable for models with five or more components. 9, 12 One of the PARAFAC components (compound 5 in Figures S11 and S12) is similar to those reported previously by Murphy 12 et al. and Mendoza and Zika 13, which have been identified as a component from an instrument artifact. 12 In this study, this component (which contributes to 14.8% of the total variations) was excluded from the analysis. The high contribution of the remaining four components to the total variation (84.2%) suggests that they explain most of the fluorescence from the extracted organics. To classify the fluorescence peaks in the EEMs to more clusters, the PARAFAC components derived from the respective groups of the extract samples were also derived (Figure S13). The peaks of the PARAFAC component for different fractions of the extracts were then divided into ten clusters based on the consideration of the similarity of the peak positions (Figure 14a). The relative intensities of the clusters are summarized in Figure S14. S7. Estimation of the contributions of PAHs to the total light absorption of WISOM The contributions of polycyclic aromatic hydrocarbons (PAHs) to the total light absorption of the WISOM (f PAHs ) were estimated by f PAHs = ε 10 1 MM C PAHs MAE WISOM, (S2) where MAE WISOM is the mass absorption efficiency of the organics in the WISOM, C PAHs is the mass fraction of PAHs in the WISOM, MM is the average molar mass of the PAHs, which herein is S7

9 assumed to be 250 g mol 1 (typical molar mass based on Dzepina et al.: g mol 1 ), and ε is the average molar absorption coefficient of the PAHs, which herein is assumed to be l mol 1 cm 1 at 245 nm (typical molar absorption coefficient based on Zhan et al.: 15 (1 10) 10 4 l mol 1 cm 1 ). The maximum contribution of the PAHs to the light absorption of the WISOM was calculated with the maximum of ε of l mol 1 cm 1 and the minimum of MM of 200 g mol 1 for the PAHs. S8

10 Figure S1. Calculated wavelength-resolved contributions of the aerosol extracts and BC to the light-absorption of the studied atmospheric aerosols in (a) summer/early-autumn and (b) winter. The bars indicate the standard deviation. S9

11 Figure S2. Backward trajectories of air masses for each sampling period (start time: 14:00 Japan Standard Time (every day); start height: 500 m above ground level; duration: 120 h) were calculated using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model version S10

12 Figure S3. Pearson s correlation coefficients between the MAEs at different wavelengths and the relative intensities of the AMS ions. S11

13 Figure S4. Pearson s correlation coefficients between the MAEs at different wavelengths and the relative intensities of the chemical groups in the FT-IR spectra of the WISOM, HULIS-n and HULIS-a (n = 36). S12

14 Figure S5. Pearson s correlation coefficients between the fluorescence volumes of four fluorescent components (C1, C2, C3 and C4) normalized by the organic mass concentrations and the mass absorption efficiencies of the extracts. S13

15 Figure S6. UV-visible absorbance spectra of the (a) WISOM, (b) HULIS and (c) HP-WSOM with different solvents and ph. S14

16 Figure S7. (a) Scatterplot of the absorbance of the HULIS with the addition of 2 wt% ammonia in MeOH against that of the HULIS without the addition. (b) Absorption spectra of the HULIS from Sample before and after the addition of 2 wt% ammonia with repeated drying ("+NH 3 " in the annotation) and re-dissolution in MeOH ("+dried" in the annotation). The red and blue solid lines in panel (a) represent regression lines constrained to origin for samples 1 and 2, respectively. The black dotted line in panel (a) represents 1:1 line. S15

17 Figure S8. EEM spectra of the MeOH-elutable HULIS (a) before and (b) after the addition of 2 wt% ammonia in MeOH. (c) Scatterplot of the fluorescence intensity of the HULIS-Amm versus that of the HULIS-Amm for different emission/excitation wavelengths. The solid lines in panel (c) represent regression lines. S16

18 Figure S9. (a and b) Absorption spectra of the WSOM and WISOM extracted with mechanical shaking with and without treatment by ultrasonication. (c) Percent of the total light-absorption by the residual matter extracted by ultrasonication of the filter samples for which the extraction of the WSOM and WISOM were performed by mechanical shaking. S17

19 Figure S10. EEM spectra (fluorescence intensity in A.U.) of (a) the WSOM and WISOM extracted by mechanical shaking, and (b) those further processed by ultrasonication. (c) Scatterplot of the fluorescence intensity of the WSOM and WISOM extracted by mechanical shaking versus those after ultrasonication. The solid lines in panel (c) represent linear regression lines. S18

20 Figure S11. Results of the 4- to 7-component PARAFAC solutions for the EEMs of all of the aerosol extracts. S19

21 Figure S12. Split half validation of the 5-component solutions obtained by the split style of S 4 C 6 T 3 for the entire dataset (n = 60). The solid and dashed lines represent the spectra against excitation and emission wavelengths respectively. S20

22 Figure S13. PARAFAC components from the 5-component model for the sets of EEMs from the respective types of extracts (n =12). The solid and dashed lines represent the spectra against excitation and emission wavelength respectively. S21

23 Figure S14. (a) EEM clusters identified by the PARAFAC analysis for the EEMs of the respective groups of the extract samples. (b) The proportion of the averages of the integrated relative fluorescence intensities in the areas of the rectangles in panel (a) to the sum of the fluorescence intensities of clusters in respective areas. S22

24 Table S1. Mass concentrations of organics and organic carbon in different fractions and mass concentration of EC in total suspended particulates over Nagoya, Japan (μg m 3, after Chen et al., 2016). 2 WISOM WSOM HULIS-n HULIS-a HP-WSOM WINSOC WSOC OC in HULIS-n OC in HULIS-a HP-WSOC EC 26 July 2 August, August, August, August, August, August 6 September, December, January, January, January, January, January, January 7 February, S23

25 353 Table S2. Summary of the MAE and AAE values of BrC. a Wavelength (nm) This study (n = 12)* WISOM HULIS-n HULIS-a HP-WSOM WSOM References (MAE: m 2 g 1 [OC]) ±0.51 (2.18±0.64) 1.89±0.56 (2.94±0.86) 1.15±0.40 (2.09±0.69) 0.35±0.09 (0.78±0.19) 1.69±0.58 (3.23±0.99) (650 nm), 0.08 (550 nm) and 2.25 (350 nm): inputs of a global chemical transport model and a radiative transfer model; (650 nm) and 2.25 (350 nm): methanol extracts from BBOA; (370 nm), 0.63 (520 nm) and 0.32 MAE (m 2 g 1 [OM] ±0.14 (0.52±0.18) 0.43±0.15 (0.67±0.23) 0.19±0.07 (0.34±0.12) 0.05±0.02 (0.12±0.04) 0.35±0.13 (0.66±0.23) (660 nm): BrC at Beijing; (532 nm) and 2 3 (300 nm): HULIS in BBOA; (404 nm) in aerosols during a fire event; and (365 and m 2 g 1 [OC]) ±0.016 (0.037±0.020) 0.024±0.012 (0.037±0.018) 0.004±0.004 (0.007±0.007) 0.006±0.005 (0.013±0.010) 0.017±0.011 (0.031±0.021) nm): WSOM in Los Angeles and Atlanta, respectively; and 0.71 (365 nm): water-soluble BrC during winter and summer in Beijing, respectively; 25 <0.03 (532 nm), 0.32 (355 nm) and 4.9 (266 nm): HULIS of PM 1 at a rural background ±0.006 (0.010±0.008) 0.005±0.004 (0.008±0.006) BDL BDL 0.002±0.002 (0.004±0.003) site; and 1.6 (365 nm): water- and methanol-soluble BrC in Los Angeles, respectively. 27 AAE ± ± ± ± ± ± ± ±0.6 10± ± ± ± ± ± ± ± ± ±1.5 BDL 9.0± ( nm) and ( nm): MeOH extracts from BBOA; ( nm): water extracts from BBOA; ( nm): BrC in Beijing; ( nm) for HULIS in BBOA; and 3.4 ( nm): WSOM in Los Angeles and Atlanta, respectively; and 7.0 ( nm): water-soluble BrC during winter and summer in Beijing, respectively; (266/355 nm), 5.9 (355/532 nm) and 2.2 (532/1064 nm): HULIS of PM 1 at a rural background site; and 4.8 ( nm): water ± ± ± ± ±0.8 and methanol-soluble BrC in Los Angeles, respectively ** 7.2** 8.8** 5.0** 7.6** a mean ± standard deviation (except for the values with **); *The values with the brackets represent MAE in m 2 g 1 [OC]; ** The values with the double asterisks are those obtained by fitting the average spectra; BDL: below the detection limit. S24

26 Table S3. The Pearson s correlation coefficients (r) and significance levels (p, two-sided t-test) from the correlation analysis between the relative intensities of the ion-groups in the AMS spectra and the normalized fluorescence volumes for the different extracts (n = 12). a Ion-groups WISOM WSOM HULIS-n HULIS-a HP-WSOM 359 CH 0.79* 0.73* 0.80* CHN 0.82* 0.86* CHO * CHO 1 N 0.93* 0.87* 0.95* CHO > * 0.84* CHO >1 N 0.79* 0.95* 0.93* 0.80* CS 0.73* CO 0.82* 0.75* 0.92* a The r values with significance levels p greater than 0.05 are not shown. * p< Table S4. Pearson s correlation coefficients (r) and significance levels (p, two-sided t-test) from the correlation analysis between the relative intensities of the chemical groups in the FT-IR spectra and the normalized fluorescence volumes for the different extracts (n = 12). a Ion-groups WISOM HULIS-n HULIS-a All (n = 36) 366 C H 0.88* C NH * 0.73 C OH 0.83* 0.87* C ONO 2 C=O * COOH 0.62* a The r values with significance levels p greater than 0.01 are not shown. * p< S25

27 Table S5. Pearson s correlation coefficients (r) and significance levels (p, two-sided t-test) from the correlation analysis between the relative intensities of the ion-groups in the AMS spectra and the relative contents of the EEM components derived from the PARAFAC model (n = 60). a C1 C2 C3 C4 Ion-groups HULIS-1 HULIS-2 Protein-like-1 Protein-like-2 CH 0.76* 0.93* 0.84* CHN 0.64* 0.92* CHO * 0.84* 0.54* 0.56* CHO 1 N CHO >1 0.79* 0.77* CHO >1 N CS CO 0.67* 0.74* 0.75* a The r values with significance levels p greater than 0.01 are not shown. * p< S26

28 384 Table S6. Pearson s correlation coefficients (r) and significance levels (p, two-sided t-test) from the correlation analysis between the 385 AMS-derived relative intensities of the ion-groups and EEM clusters (n = 12). a Ion-grou ps WISOM WSOM HULIS-n HULIS-a CH 0.76 (C1a); 0.73 (C1b); 0.76 (C2a); 0.89 (C1a)*; (C1c); 0.87 (C2a)*; 0.89 (C2b)*; 0.80 (C2c); 0.95 (C4a)*; (C3a); 0.79 (C2c) 0.72 (C2c); 0.78 (C3a) 0.93 (C4b)* 0.84 (C3b)* CHN 0.75 (C1b); 0.80 (C1c); 0.72 (C1b); (C1a)* 0.73 (C2a); 0.84 (C2c)* (C1c) 0.79 (C3a) CHO (C1a); 0.84 (C2a)*; 0.78 (C2b); 0.87 (C1a)*; (C4a)*; 0.90 (C4b)* (C3b)* 0.75 (C2c) 0.76 (C3a) CHO 1 N 0.75 (C3a); (C1a); 0.90 (C1b)*; (C1c)*; 0.79 (C2a); (C2b); (C1c)*; 0.84 (C2c)*; 0.83 (C3a)* 0.72 (C2c) 0.87 (C2c)*; 0.87 (C3a)*; 0.76 (C4a) 0.82 (C1a); 0.93 (C1b)*; (C1b); 0.79 (C1c); CHO > (C1a); 0.74 (C3b) (C1c)*; 0.88 (C2a)*; 0.77 (C2c); 0.86 (C2c)*; 0.92 (C3a)*; 0.79 (C4a) 0.92 (C3a)* CHO >1 N 0.76 (C1a); (C1a)*; 0.89 (C1b)*; (C2a)*; 0.86 (C3a)*; (C1b); (C1c)*; 0.83 (C4b)* 0.84 (C3a)* 0.82 (C2c)*; 0.90 (C3a)*;0.75 (C4a) HP-WSO M 0.76 (C2a); 0.73 (C2b) CS 0.73 (C2c) 0.71(C4a) 0.89(C2b)*; 0.72(C2c); 0.82(C3b);0.78(C4a) CO 0.78 (C1a); 0.80 (C1b);0.89(C2b)*; 0.85 (C2c)*; 0.72 (C3a); 0.95(C4a)* 0.90(C4b)* 0.94 (C1a)*; 0.75 (C1b); 0.81 (C3a); 0.86 (C3b)* 0.92(C1a)*;0.82(C1b);0.85(C1c)*; 0.71(C2c); 0.88(C3a)*; 0.71(C3b) 0.86(C1b)*;0.89(C1c)*; 0.93(C2a)*;0.90(2c)*; 0.96(C3a)* 386 a The r values with significance levels p greater than 0.01 are not shown. * p< S27

29 Table S7. Pearson s correlation coefficients (r) and significance levels (p, two-sided t-test) from the correlation analysis between the relative intensities of the chemical groups in the FT-IR spectra and the relative contents of the EEM components derived from the PARAFAC model (n = 36 for the WISOM, HULIS-n, and HULIS-a). a Chemical C1 C2 C3 C4 groups HULIS-1 HULIS-2 Protein-like-1 Protein-like-2 C H 0.94* 0.94* 0.78* 0.61* C NH * 0.54 C OH 0.82* 0.96* 0.90* 0.76* C ONO C=O 0.88* 0.60* COOH 0.88* 0.66* a The r values with significance levels p greater than 0.01 are not shown. * p< S28

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