Expanding the horizons of the Visibility Assessment Scoping Model (VASM) Page: 4 of 7
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
mountainous sites may be above the regional mixed
layer part of the time, particularly during the cooler
portion of the year, and thus may experience typically
lower particle concentrations and better visibility than
sites at lower elevations. To some extent, elevation
differences may be confounded with urban-rural
differences, because urban areas tend to be at lower
elevations, while much of the IMPROVE monitoring
occurs at elevated sites in the mountains. As will be
seen, our interpolation example is affected by both
urban-rural differences and elevation differences.
VASM results are usually presented as seasonal
distributions of daily visual range (km) or haziness
(deciviews). Such presentations are also suitable for
demonstrating the results of interpolation to a single
location, as will be the case in the example to follow. If
results were presented for a grid of interpolated points
across the region, however, a single parameter such as
the median visual range or haziness value would be
more suitable for two-dimensional contouring.
A significant advantage of the VASM approach has
been its ease of use and speed on a desktop computing
platform, but combining that ease of use with a spatially
broader application is not a simple matter. In an
integrated assessment, the Tracking and Analysis
Framework (Henrion et aL., 1997),VASM simulations of
the seasonal distributions of daily noontime haziness
for all four seasons and two emission scenarios, at 5-y
intervals from 1980 to 2030 and at seven locations,
required about three minutes on a Power Mac 6100/60.
Because all calculations are saved during an application
of a model in the AnalyticaTM language (in which this
version of VASM is written), the effect of a modeling
change, such as a different optical extinction formula
for sulfate, can be calculated quickly, because only the
internal variables affected by that change are
recalculated. Such temporal efficiencies come at a cost
in required computer memory, however, so the number
of receptor haziness distributions that can be examined
in a single model run is limited. While ultimately a cost-benefit analysis might require use of only a single
parameter of the haziness distribution, such as the
mean or median value, determination of a parameter of
the distribution currently requires VASM calculation of
the entire distribution.
Inspection of a plot of the eastern IMPROVE
monitoring sites reveals that the Washington, DC, site is
convenient for testing the interpolation methods,
because there are surrounding stations at Shenandoah
National Park, VA; Dolly Sods in the Monongahela
National Forest, WV; and Brigantine National Wildlife
Reserve, NJ. Several factors confound the
interpolation, however. Both Shenandoah and Dolly
Sods are rural sites at elevations above 1 km, while the
DC urban site is near sea level. The Brigantine site, also
rural, is near the Atlantic Ocean and thus would
experience greater concentrations of sea salt particles
than the other sites.
For an initial evaluation of the urban perturbation in
particle concentrations, we compare the concentration
averages at the three surrounding sites with
concentration averages for Washington, as shown in
Table 1. The urban-rural differences in concentrations
of elemental carbon and nitrate fine particles are most
pronounced and consistent through the year, with the
urban concentration averages 2.5 to 3.0 times higher for
nitrate and 3.5 to 4.0 times higher for elemental carbon.
The ratios for organic carbon fine particles show a
strong seasonal trend ranging from 2.8 in winter to 1.4 in
summer, perhaps due to the larger role of natural
emissions in the warm season. Except for winter, the
urban-rural differences for sulfate, fine dust, and coarse
dust may well lie within the uncertainty (unquantified,
but presumably large) of this analysis approach. The
implication of the results in Table 1 is that if urban
concentrations are interpolated from measurements at
the predominantly rural IMPROVE monitoring sites for
subsequent VASM simulations, urban concentrations
are likely to be significantly underestimated unless the
urban-rural difference is parameterized.Table 1: Comparison of seasonal average particle concentrations prior to 1994 at an urban site (Washington, DC)
with the average of rural sites at Shenandoah National Park, VA; Dolly Sods, WV; and Brigantine, NJ (pg m3).season
locale
urban
winter rural
ratio
urban
spring rural
ratio
urban
summer rural
ratio
urban
autumn rural
ratiosulfate
5.92
3.93
1.5nitrate organic C elemental C fine dust coarse dust
3.40
1.19
2.93.32
1.19
2.81.85
0.50
3.72.51
0.92
2.719.84
3.84
5.27.38 2.52 2.66 1.50 2.83 8.63
5.98 0.90 1.48 0.39 1.85 5.82
1.2 2.8 1.8 3.8 1.5 1.4
10.46 1.36 3.04 1.82 4.52 8.74
11.35 0.48 2.23 0.43 5.25 6.92
0.9 2.8 1.4 4.2 0.9 1.3
6.95 2.07 3.12 1.9 2.42 7.30
5.83 0.79 1.82 0.5 1.83 5.14
1.2 2.6 1.7 3.8 1.3 1.43. RESULTS
Lognormal means and standard deviations of
concentration, together with the average between-
species correlation matrix (all averaged for the threerural sites) are combined with RH climatology specific
to Washington in VASM simulations in one approach
to VASM interpolation. An alternate interpolation
averages the haziness distributions simulated by
VASM for each of the rural sites. (NOTE: the
Upcoming Pages
Here’s what’s next.
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
Shannon, J.D. Expanding the horizons of the Visibility Assessment Scoping Model (VASM), report, December 31, 1998; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc689665/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.