Auxiliary material for
Black carbon and other light-absorbing particles in snow of central North America
Sarah J. Doherty1, Cheng Dang2, Dean A. Hegg2, Rudong Zhang2,3 and Stephen G.
Warren2
1
Joint Institute for the Study of Atmosphere and Ocean, 3737 Brooklyn Ave NE, Seattle,
WA 98195, USA.
2
Department of Atmospheric Sciences, Box 351640, University of Washington, Seattle,
WA 98195, USA.
3
Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of
Atmospheric Sciences, Lanzhou University, Lanzhou, China.
Journal of Geophysical Research - Atmospheres
Introduction
This Word file “Dohertyetal2014_NAmerSurvey2013_SupplementalText.docx” includes
two tables: The first contains additional information on the 67 sampling sites discussed in
the main text. The second the PMF analysis results, attributing snow particulate light
absorption in surface and sub-surface layers to soil, pollution and biomass burning
sources, as summarized in Figures 9 and 10 of the main text.
Below are figure captions to accompany Supplementary Figures S1-S5.
Figure S1. Site locations on Google Earth, showing terrain variations across the different
sites. (Map data: U.S. Dept. of State Geographer, © 2014 Google, Image Landsat, Data
SIO, NOAA, U.S. Navy, NGA, GEBCO).
(file: FigureS1.pdf)
Figure S2. Average snow cover fraction (%) for February, 2013 (color scale) and the
location of our sampling sites (white dots). See Table S1 for latitude/longitude and
sampling dates for each site. Snow cover fraction data are from MODIS [Hall et al.,
2006] and are available at http://nsidc.org/data/mod10cm.
(file: Figure S2.pdf)
Figure S3. Chemical “fingerprints” of the five factors that account for variations in snow
𝑚𝑎𝑥
particulate light absorption, as measured by 𝐶𝐵𝐶
, and the fraction of that absorption
attributable to the five factors across all sites. The three fingerprints dominating
particulate light absorption were identified as being associated with soil (blue), biomass
𝑚𝑎𝑥
burning (green) and pollution (red). “BCmax” is 𝐶𝐵𝐶
from ISSW analysis. Non-crustal
sources of Mn, V and K are indicated as nonC-Mn, nonC-V and nonC-K. OC-abs is the
470-700nm particulate absorption due to organic components of the particles, as
determined by Dang and Hegg [2014] via serial extractions of sample filters. All other
constituents are measured by chemical analysis as described in the text, where “levo” is
levoglucosan and “succ-mal” is the sum of succinate and malate.
(file: Figure S3.pdf)
Figure S4. A map with markers showing the sites from the survey presented herein
(pink), and from previous surveys in 2007 (blue) and 2009 (green) [see Doherty et al.,
2010]. Figure 12 shows PMF results binned by latitude for 34 of the 46 sites inside the
red box shown here, based on availability of PMF analysis results. Two of the excluded
sites are from the 2007 survey (MS26 and MS28) and three from the 2009 survey (C8,
C20 and C23). All other excluded sites are from the 2013 survey: sites 25, 27, 37, 42, 48,
51 and 56. (Map data: U.S. Dept. of State Geographer, © 2014 Google, Image Landsat,
Data SIO, NOAA, U.S. Navy, NGA, GEBCO).
(file: FigureS4.png)
Figure S5. HYSPLIT was used to calculate 10 day back-trajectories for surface air
originating at the sites included in Figure 12 in Canada and sites directly south of these in
the U.S. (Fig. S4). Trajectories were calculated four times a day for a period of 30 days
preceding the sampling date at a given site, and cluster analysis was used to determine the
five most common airmass pathways at each site. Shown here are a sub-set of eight of
these backtrajectory cluster analyses subjectively determined to be representative of other
sites at similar latitudes.
(files: FigureS5a.pdf, FigureS5b.pdf , FigureS5c.pdf, FigureS5d.pdf, FigureS5e.pdf,
FigureS5f.pdf, FigureS5g.pdf, FigureS5h.pdf)
Reference
Hall, D. K., V. V. Salomonson, and G. A. Riggs (2006), MODIS/Aqua Snow Cover
Monthly L3 Global 0.05Deg CMG. Version 5. [February 2013, 38-60°N, 135170°W]. Boulder, Colorado USA: National Snow and Ice Data Center.