The Impact of Precipitation Cell Morphology on Mercury Wet Deposition in Michigan
Pamela D.
1
Eck ,
1
Alexandra L.
2
Caruthers ,
and Frank J.
3
Marsik
Hobart and William Smith Colleges, Geneva, New York
2 Valparaiso University, Valparaiso, Indiana
3 University of Michigan, Ann Arbor, Michigan
Abstract: Recent research has suggested that levels of mercury wet-deposi/on observed in some regions of the United States could be strongly influenced by the scavenging of globally emiVed mercury in the free troposphere by tall
cumulus convec/on. This study inves/gated the rela/on between mercury wet-deposi/on at two loca/ons in Michigan and precipita/on cell morphology. While some correla/on was observed between mercury wet-deposi/on
amount and maximum echo top and convec/ve available poten/al energy at one of the sites, mercury wet-deposi/on at these loca/ons otherwise showed liVle correla/on with precipita/on cell morphology for the period studied.
3. Data Analysis
Fig. 7
Fig. 4
DXT FRT 500.00
400.0
450.00
350.0
400.00
300.0
Deposi/on (ng/sq m)
350.00
300.00
250.00
200.00
R² = 0.00289
150.00
100.00
200.0
150.0
R² = 0.18814
50.0
0.00
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
0.0
maxET (k_)
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
maxET (k_)
500.00
400.0
450.00
350.0
Fig. 6
400.00
300.0
350.00
Deposi/on (ng/sq m)
2. Methodology
300.00
250.00
R² = 0.00798
200.00
250.0
200.0
150.0
150.00
R² = 0.0098
100.0
100.00
50.0
50.00
0.00
0.00
10.00
20.00
30.00
40.00
50.00
0.0
60.00
0.0
10.0
20.0
max reflec/vity (dBZ)
30.0
40.0
50.0
60.0
max reflec/vity (dBZ)
500.00
400.0
450.00
350.0
400.00
300.0
350.00
Fig. 3 and 4
In both DXT and FRT, the overwhelming majority of events were
convec/ve (isolated cells (IC), cluster of cells (CC), linear nonstra/form (LNS), trailing stra/form (TS), or other). Deposi/on (ng/sq m)
Based on the work of Gallus et al (2008) and Nair et al. (2013) , this study analyzed the
meteorological features of precipita/on cells that passed through urban Fort Street, Detroit, MI
(FRT) and rural Dexter, MI (DXT) during the convec/ve season (June-August) of 2005. Radar
images collected in Detroit, Michigan were taken from the Na/onal Clima/c Data Center and
viewed on GR2Analyst so_ware. Only events with >20dBZ were considered. Days were defined
from 1300Z to 1300Z. Events were categorized into one of eight types (Fig. 2). Upper air
soundings taken at 1200Z from the Iowa State GEMPAK archive were used in addi/on to radar
images to determine all of the variables listed below:
250.0
100.0
50.00
Deposi/on (ng/sq m)
300.00
250.00
R² = 0.00646
200.00
150.00
250.0
R² = 0.24144
200.0
150.0
100.0
100.00
50.0
50.00
Fig. 7
Correla/ons between maximum echo top height, maximum
reflec/vity, CAPE, surface to 6km shear and mercury deposi/on
were inves/gated. Coefficient of correla/on (R^2) values ranged
anywhere from less than 0.01 to 0.24, none of which are
sta/s/cally meaningful. 0.00
0.00
0.0
500.00
1000.00
1500.00
2000.00
2500.00
500.0
1000.0
3000.00
1500.0
2000.0
2500.0
3000.0
CAPE (J/kg)
CAPE (J/kg)
500.00
$400.00 450.00
$350.00 400.00
$300.00 350.00
Deposi/on (ng/sq m)
Fig. 2
Fig. 5 and 6
Though most of the summer/me events were convec/ve,
approximately half of the events that occur each year are nonconvec/ve, thus that a large por/on of annual mercury deposi/on
may come from the more frequent non-convec/ve events
0.0
Deposi/on (ng/sq m)
Mercury is a toxic, bioaccumula/ve pollutant that has both natural and anthropogenic sources.
Mercury exists primarily in three forms within the atmosphere: gaseous elemental mercury Fig. 3
(GEM), reac/ve gaseous mercury (RGM), and par/culate bound mercury (PBM) (Schroeder and
Munthe, 1998). Despite con/nued reduc/ons in the levels of anthropogenic emissions of
mercury na/onally, some regions of the United States con/nue to experience elevated levels of
mercury deposi/on from rainfall (wet-deposi/on). Recent research has suggested that one
explana/on for this observa/on may be that a significant frac/on of mercury wet-deposited is
scavenged from the free-troposphere by tall, cumulus convec/on (Nair et al., 2013) and thus a
significant frac/on of the deposited mercury may come from global sources. If such a
rela/onship can be verified, such findings could have significant implica/ons on federal policy
seeking to limit the emissions of mercury from U.S. anthropogenic sources. This study
inves/gated the rela/on between observed mercury wet-deposi/on at two loca/ons Michigan Fig. 5
and precipita/on cell morphology. Deposi/on (ng/sq m)
Deposi/on (ng/sq m)
1. Mo/va/on
300.00
250.00
200.00
$250.00 $200.00 $150.00 150.00
R² = 0.00956
$100.00 100.00
R² = 0.06109
50.00
0.00
0.00
$50.00 $- 10.00
20.00
30.00
Surface to 6km Shear (kts)
40.00
50.00
60.00
$- $10.00 $20.00 $30.00 $40.00 $50.00 $60.00 Surface to 6km Shear (kts)
4. Conclusions and Future Research
Summer/me wet-deposi/on events at two loca/ons in southern Michigan were analyzed to determine if a rela/onship exists
between mercury wet-deposi/on and precipita/on cell morphology. While some correla/ons were noted, there was limited
evidence of significant rela/ons between mercury wet-deposi/on and precipita/on cell morphology. Further research will focus on
expanding the inves/ga/on to addi/onal years, as Calendar Year 2005 may not be representa/ve of average condi/ons.
5. References
Gallus, W. A., N. A. Snook, and E. V. Johnson (2008): Wea. Forecas+ng, 23, 101-113.
Schroeder, W. H. and J. Munthe (1998): Atmospheric Environment, 32, No. 5, 809-822.
Nair, U. S., et al. (2013): Atmos. Chem. Phys. Discuss., 13.
6. Acknowledgments This research was completed as part of the 2013 Research Experience for Undergraduates (REU) at
the Department of Atmospheric, Oceanic, and Space Sciences at the University of Michigan in Ann
Arbor, Michigan. Funding for this project was provided by the Na/onal Science Founda/on (NSF).