Table S1. Site locations and date sampled.
Site
Date
latitude
Site # sampled
(°N)
Site
longitude
(°W)
Site
elevation (m)
1
1/10/13 47.3991
121.3886
787
2
1/28/13 45.9508
120.6700
838
3
1/29/13 44.8997
120.6104
1136
4
1/29/13 43.8038
120.8477
1576
5
1/30/13 43.4455
118.9911
1332
6
1/31/13 42.3231
118.7468
1715
7
1/31/13 41.3849
117.8184
1330
8
2/1/13
40.9014
115.8910
1949
9
10
2/1/13
2/3/13
42.2767
43.3495
116.0115
115.3968
1772
1538
11
2/3/13
43.5927
113.5894
1942
12
2/4/13
43.4010
111.2053
1727
13
2/4/13
42.9357
109.8576
2274
14
2/5/13
41.7297
109.3668
2223
15
16
17
18
2/5/13
2/7/13
2/8/13
2/9/13
40.7464
40.1316
40.4929
40.6695
109.4776
109.4711
107.8994
106.4158
2583
1538
1962
2512
19
2/13/13 42.0249
107.4167
1987
20
2/14/13 43.7016
108.8452
1963
21
2/14/13 45.0754
109.1313
1330
22
2/15/13 45.7980
108.4369
962
23
2/16/13 47.6249
108.6968
1090
Notes
new snow <1 day old ; Snoqualmie
pass (mountains)
new snow <1 day old ; Satus pass
(mountains)
new snow < 1 day old
drift behind sagebrush, east of Bend,
Oregon
in sage meadow on plateau above
Burns, Oregon
top layer fell ~ 3 days previous; open
grassland
top layer fell ~ 3 days previous;
melting; grassland
drift snow; many sastrugi; pass north
of Elko, Nevada
open grassland
hilly grassland
mountain foothills, near mine and lava
fields
new snow < 2 days old; on frozen
creek in forest
new snow < 2 days old; sagebrush,
pasture
in sagebrush; thin snow north of Rock
Springs, Wyoming
Uinta mountain pass; deep snow
south of Vernal, Utah; thin snow
sageland; juniper bushes
new snow <1 day old; open grassland
windy; thin, drifted snow; total snow
depth varies 0-23cm
new snow <2 days old; sampled in
drift on north-facing slope
sampled in deeper snow on slope; new
snow <1 day old
transect east of Billings, MT; all new
snow <12 hrs old
drift on north-facing slope; otherwise
region largely snow-free
24
2/17/13 48.2318
105.0949
648
25
2/17/13 47.6137
103.3555
627
26
2/18/13 47.0987
101.4700
688
27
2/18/13 45.4587
99.8113
636
28
2/19/13 45.2569
98.7477
405
29
2/19/13 44.0547
97.8803
403
30
2/22/13 43.5880
97.1759
439
31
32
2/22/13 43.1963
2/22/13 42.3145
97.4784
97.8711
414
540
33
2/22/13 42.1825
97.5657
493
34
35
2/23/13 43.0561
2/23/13 44.1535
95.6485
95.7772
451
464
36
2/24/13 45.5482
95.7252
334
37
2/24/13 46.4733
96.5378
297
38
2/27/13 45.8645
96.5744
296
39
40
41
2/27/13 46.4435
2/28/13 47.2668
2/28/13 47.8796
97.4029
98.8338
101.0000
327
448
657
42
3/1/13
48.0104
102.3245
646
43
44
45
46
47
3/1/13
3/1/13
3/2/13
3/2/13
3/3/13
48.1463
48.1197
48.8649
48.8539
48.8159
102.8639
103.2260
100.9097
99.1845
97.8797
560
560
451
465
343
48A
3/4/13
47.8910
97.0761
254
48B
3/5/13
47.8285
96.8489
257
48C
3/5/13
47.8271
96.8477
246
49
3/6/13
50.7280
97.1307
244
50
3/7/13
51.2723
98.5681
245
wind-loaded slope on farm field
Theo. Roosevelt Natn’l Park; deep
drift on N facing slope
new snow <1 day old; drift behind
bushes on farm
Ground mostly bare or ice; blowing
new snow (<1 day old) in small drifts
on frozen lake
sampled deeper part of snow; on
farmland
new snow <1.5 days old; on frozen
lake edge
new snow <1.5 days old; farmland
new snow <1.5 days old; farmland
new snow <1.5 days old; on frozen
lake
new snow <2 days old; on farmland
new snow <3 days old; on frozen lake
new snow ~3 days old; wildlife
conservation area
in wildlife conservation grass area
wildlife conservation grass/swamp
area
Sheyenne Natn’l Grasslands
grassland
grassland
new snow <3 days old; farmland;
sample between crop stubble (deeper)
new snow <3 days old; on frozen lake
new snow <3 days old; on frozen lake
next to abandoned farmhouse
on frozen lake
wildlife conservation wetland
new snow <12hrs old; at hotel in
Grand Forks, ND
new snow <12 hrs old; farmland 20km
ESE of Grand Forks
new snow <12 hrs old; frozen river
20km ESE of Grand Forks
new snow <1 day old; on frozen bog in
wildlife park
new snow <2 days old; on frozen lake
51
3/7/13
52.5433
98.8883
248
52
3/8/13
53.8509
99.2559
282
53
3/8/13
55.1136
98.5094
222
54
3/11/13 56.0766
97.0474
192
55
3/11/13 56.5330
95.3282
138
56
3/12/13 58.7261
93.8281
17
57
3/13/13 54.5831
100.4714
278
58
3/14/13 53.6038
102.1222
272
59
60
61
62
63
64
3/14/13
3/15/13
3/18/13
3/19/13
3/19/13
3/20/13
51.7972
50.5768
52.7499
55.2484
54.7011
54.3954
102.7436
105.4384
106.6554
105.3427
107.8271
110.8437
521
588
514
381
458
550
65
3/20/13 52.7820
111.3175
697
66
3/21/13 50.9260
112.0593
729
67A
3/21/13 50.9713
113.4214
974
67B
3/21/13 50.9864
113.6108
1005
67C
3/21/13 50.9896
113.8211
1020
new snow <2 days old; power-line
clearing in trees
new snow <1 day old; clearing in trees
new snow <1 day old; on frozen lake
in forest
new snow <3 days old; on frozen
swamp in forest
new snow <3 days old; on frozen lake
in forest
new snow <3 days old; site is in
deeper area protected by trees; at
forest/tundra boundary
new snow <3 days old; on frozen
swamp in forest
new snow <2 days old; power-line
clearing in trees
new snow <2 days old; farmland
new snow <12 hrs old; farmland
new snow <3 days old; farmland
new snow <3 days old; frozen lake
new snow <3 days old; frozen swamp
new snow <1 day old; farmland
new snow <1 day old; in drift on north
slope; farmland
new snow <1 day old; grassland
new snow <1 day old; behind
farmhouse; 60km ESE of Calgary city
limit
new snow <1 day old; by grain
elevator; bare ground in area; ~45km
ESE of Calgary city limit
new snow <1day old; behind house on
farm field; 30km ESE of Calgary city
limit
Table S2. PMF analysis results, showing the fraction of 650-700nm absorption
attributed to soil, biomass burning and pollution (fossil fuel) sources. The entries in
italics are from a second PMF run with somewhat lower predictive capacity for light
absorption (i.e. lower normalized Q), but which allowed the addition of data for five sites
in the U.S. Great Plains regions. All other values are from the optimized PMF run.
Surface (1),
Site
Sub-surface (2)
FSOIL
FBB
FFF
2
2
-0.42
1.04
0.36
6
1
-0.54
1.06
-0.32
8
2
-0.35
0.86
0.50
9
1
-0.29
1.02
0.29
10
1
0.05
0.84
0.11
11
2
-0.14
0.34
0.13
14
2
0.34
0.32
0.34
15
1
-0.09
0.67
0.37
15
2
0.07
0.36
0.55
16
2
-0.18
0.28
0.86
17
1
0.25
0.29
0.44
17
2
0.28
0.20
0.42
18
1
0.61
0.15
0.12
19
1
0.81
-0.01
-0.02
20
1
0.46
0.19
0.25
20
2
0.46
0.19
0.31
26
1
0.70
0.06
0.04
26
2
0.85
0.13
0.01
28
1
0.74
0.09
0.17
28
2
0.68
0.17
0.10
29
2
0.87
0.02
0.07
30
2
0.21
0.23
0.53
31
1
0.22
0.39
0.32
35
1
0.33
0.27
0.39
35
2
0.94
0.02
0.02
36
1
-0.19
0.57
0.47
36
2
0.93
0.02
0.03
38
1
0.62
0.09
0.24
38
2
0.75
0.10
0.15
39
2
0.59
0.24
0.08
40
1
0.48
0.11
0.39
40
2
0.84
0.00
0.12
42
1
0.62
0.31
0.06
43
1
0.76
0.24
0.00
43
2
-0.04
0.17
0.83
44
2
0.46
0.08
0.45
45
45
46
49
49
50
50
52
53
54
54
55
57
58
59
60
61
61
62
63
63
64
65
66
1
2
1
1
2
1
2
1
2
1
2
2
2
1
2
1
1
2
2
1
2
1
2
2
0.23
0.23
0.30
0.20
0.27
-0.05
0.16
0.59
-0.16
0.36
0.04
-0.22
0.27
0.32
0.14
-0.19
0.30
-0.15
-0.24
0.02
-0.12
0.19
0.22
0.18
0.36
0.30
0.13
0.49
0.27
0.64
0.31
0.20
0.35
0.28
0.24
0.38
-0.04
0.12
0.22
0.83
0.41
0.16
0.47
0.32
0.55
0.30
0.22
0.29
0.35
0.44
0.54
0.30
0.45
0.38
0.52
0.20
0.74
0.30
0.70
0.53
0.38
0.24
0.64
0.31
0.30
0.80
0.29
0.64
0.56
0.49
0.56
0.53