440
420
400
380
Excitation Wavelength, nm
360
340
320
300
280
260
300
350
400
450
500
550
600
300
350
400
450
Emission Wavelength, nm
500
550
600
300
350
400
450
Emission Wavelength, nm
500
550
600
300
350
400
450
500
550
600
240
440
420
400
380
Excitation Wavelength, nm
360
340
320
300
280
260
240
440
420
400
380
360
340
320
300
280
260
240
440
420
400
380
360
340
320
300
280
260
240
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.06
0.05
0.04
0.03
0.02
0.01
0
0.55
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.1
0.15
0.05
(a)
(b)
(d)
(c)
Whole Water
HPIA
TPIA
HPOA
Plate 2. Excitation–emission spectra for the (a) whole water, and mass normalized EEMs for the (b)
hydrophobic organic acid, (c) transphilic organic acid, and (d) hydrophilic fractions of a water sample from the Yukon River at Pilot Station, Alaska.