Numerical Simulation of Atmospheric Loadings of Mercury from a Coal Fired Power Plant to Lake Erie

S. M. Daggupaty, C. M. Banic and P. Blanchard

Air Quality Research Division, Science and Technology BranchEnvironment Canada.

Presented at 11th Conference on Atmospheric Chemistry11-15 January 2009. Phoenix, AZ.

Dry deposition flux (g m-2 s-1), is given by F(x, y)d = c(x,y,z1.5) vd

eff (x, y)

Ra bulk aerodynamic resistance is function of u*, z0 ,L. Rd quasi-

laminar or surface resistance, Rc overall canopy resistance and Vg

gravitational settling velocity. 

gv

cReff

dReffaR

1effdv

BLFMAPS – Mesoscale Boundary Layer Forecast Model with Air pollution Prediction system. (Daggupaty. et al 2006) was used for simulations.

Deposition Fluxes: - Dry and Wet processes are formulated following Ma and Daggupaty (2000), Daggupaty et al (2006) and Zhang et al (2001, 2003).

Wet deposition flux (g s -1/ m2) :

zt

zbz)dzy,C(x, Iy)(x,

wF

•For P-Hg the wet deposition flux is followed as in Daggupaty (2006).

is the normalised scavenging coefficient (s-1 /mm hr-1) I is precipitation intensity (water equivalent in mm/hr).

• For RGM (as of HNO3) =6* 10-4

• For GEM with its low solubility =3.0*10-6

• These are in agreement with Berg(2001), Petersen et al (1998) and Ryaboshapko et al (2004).

Adsorption at air – water interface was also estimated.

3. The chemical transformation of the plume Hg. species over the travel period (~ 10 hr) of study domain is hard to anticipate and is not modeled in this study. Thus the plume could be undergoing different combinations of species strength over the travel period. The different scenarios considered here could be mimicking the plume evolution in time.

1. The annual average total Hg emission rate for the Nanticoke power plant varies between 4 to 8 mg/s (i.e., 130 to 240 kg/y) from NPRI data (National pollutant release inventory, http://www.ec.gc.ca/pdb/npri/npri_home_e.cfm).

In the year 2005 the annual average emission rate is 5 mg/s.

2. Particulate Hg mass is assumed to be in large, medium and small particle size bins with respective fraction of 80%, 5% and 15%.

Table 1. Proportionate Hg species emission rates.

Scenario GEM RGM P-Hg

A 45% 45% 10%

B 5% 90% 5%

C 90% 5% 5%

D 10% 45% 45%

15.Urban

14.

13.Inland Water

12.

11.Wet land with plants

10.

9.

8.

7.Crops,mixed farming

6.Grass

5.Mixed leaf trees

4.Decds brdleaf trees

3.Decds Ndle Lf trees

2.Evergrn BrdLf trees

1.

GEM emission rate of 4.5mg/s (Scenario C)

RGM emission rate of 0.25mg/s (Scenario C)

GEM with emission rate of 1 g/s.

RGM with emission rate of 1 g/s.

Fig. 4a.

Fig. 4c.

Fig. 4b.

.

.

. Figure 5a

Figure 5b

Figure 5c

Table 2. Mercury loading (g) to Lake Erie as per scenarios A to D. for April and May 2005

Scenarios with 5 mg/s of total Hg emission

GEM RGM GEM+ RGM

P-HgLarge Medium Small

P-Hg Total

Total Hg (GEM+RGM+ P-Hg)

Dry 0.00161 473.4 473.4 91.1 0.3 2.2 93.6 567.0

A Wet 332.3 2797.8 3130.1 646.5 24.3 28.5 699.3 3829.4

45,45,10 Adsorption 7.33 865.5 872.8 872.8

A Total 339.6 4136.7 4476.3 737.6 24.6 30.7 792.9 5269.2

Dry 0.00018 946.7 946.7 45.6 0.2 1.1 46.9 993.6

B Wet 36.9 5595.5 5632.4 323.2 12.1 14.2 349.5 5981.9

5,90,5 Adsorption 0.81 1731.0 1731.8 1731.8

B Total 37.7 8273.2 8310.9 368.8 12.3 15.3 396.4 8707.3

Dry 0.0032 52.6 52.6 45.6 0.2 1.1 46.9 99.5

C Wet 664.5 310.8 975.4 323.2 12.1 14.2 349.5 1324.9

90,5,5 Adsorption 14.6 96.2 110.8 110.8

C Total 679.2 459.6 1138.8 368.8 12.3 15.3 396.4 1535.2

Dry 0.00036 473.4 473.4 410.2 1.6 9.9 421.7 895.1

D Wet 73.8 2797.8 2871.6 2909.1 109.4 128.2 3146.7 6018.3

10,45,45

Adsorption 1.63 865.5 867.2 867.2

D Total 75.5 4136.7 4212.2 3319.3 111.0 138.1 3568.4 7780.6

Total Hg deposited to Lake Erie in the percentage of total Hg emission (26.4 kg) in 61 days of April and

May 2005.

Scenario Modeled value (kg)

In percentage of total Hg emission

A (45, 45,10) 5.3 20.

B (5, 90, 5) 8.7 33.

C (90, 5, 5) 1.5 6.

D (10, 45, 45) 7.8 29.

Wet deposition flux of total Hg to the lake as monitored at MDN

site Erie was 9 µg/m2/year.

Scenario Modeled value (µg/m2/y)

In percentage of annual MDN value

A (45, 45,10) 0.89 10

B (5, 90, 5) 1.39 15

C (90, 5, 5) 0.31 3

D (10, 45, 45) 1.40 15

Model vs MDN value:

CONCLUSIONS1. RGM is found to be the dominant contributor of the three species

of Hg to the Lake Erie loading.

2. The scenario B (with 90% as RGM) emissions gives highest loading and it was about 15% of observed MDN value to the Lake Erie.

3. 98% of GEM emissions and 93% fine particulate Hg emissions were transported out of the circular area with 100km radius from the power plant.

4. Our experiments also suggest that a case with a larger GEM portion of emission (about 90% of total Hg emission) will have the least amount of total Hg loading to the Lake Erie.

5. It is prudent to mention that out of the four scenarios the aircraft measured Hg species configuration in the plume is that of scenario C and it has least impact with 3% of the observed total Hg wet deposition to Lake Erie.

Thank you.

Any comments or ?