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From Ammonia to PM2.5
Brent AuvermannTexas Cooperative ExtensionTexas Agricultural Experiment
StationAmarillo, TX
Acknowledgments
• Spyros Pandis, atmospheric chemist, CMU
• Rich Scheffe, USEPA-OAQPS• N. Andy Cole and Rick Todd, USDA-
ARS• David Parker, agricultural engineer,
TAMU• Saqib Mukhtar, agricultural engineer,
TAMU
NH3 – What’s the Big Deal?
• Superfund/EPCRA – Federal litigation on broad CAFO front– Multiple species– Multiple states– Do the math
• NH3 + (SO4, NO3 or Cl) >> PM2.5
• NH3 + PM >> synergistic effect on animal pulmonary health >> effect on human health?
0
200
400
600
800
1,000
0 20 40 60 80 100
N Use Efficiency
CE
RC
LA
Th
resh
old
Cap
acit
y
Y
0
200
400
600
800
1,000
0 20 40 60 80 100
Aggregate N Efficiency (%)
CE
RCL
A T
hre
shold
Cap
aci
ty
Y
Open-Lot Systems
• Beef feedyards– Animal spacing 75-250
ft2/hd– Excreted N 90% of N
consumed in feed (Bierman et al., 1996)
• Open-lot dairies– Animal spacing 200-
400+ ft2/hd– Excreted N 70% of N
consumed in feed (Van Horn et al., 1996)
Fate of Excreted N in Open-Lot Systems
• Collected in solid manure– Spread– Stored (stockpiles, mounds,
other)– Composted and spread
• Remains on corral surface– Stable if it remains dry– Runs off into holding pond
• Volatilized as NH3(g) directly– Increases with wet/dry cycling
Extinction efficiencies for ubiquitous particle types (Malm, 1999)
Particle TypeDry Extinction
Efficiency (m2/g)Sulfates 3.0
Organics 3.0
Elemental Carbon 10.0
Nitrates 3.0
Soil Dust 1.25
Coarse Particles 0.6
Feedyard PM10/TSP 0.5-0.6/0.3-0.4
Air Pollution in Pittsburgh
July 2, 2001
PM2.5=4 g m-3
July 18, 2001
PM2.5=45 g m-3
(Adapted from Pandis, 2003)
Nucleation
• In aqueous solution, two or more species react to form a low-solubility product known as a precipitate
• Because the precipitate has relatively low solubility, it immediately forms a solid particle in aqueous suspension
• The particle provides a surface on which more of these reactions can occur
Interactions between Fine PM and Their Precursors
NOx emissions
SO2 emissions
VOC emissions
NH3 emissions
Primary Organic emissions
Primary Inorganic PM emissions
0
5
10
15
20
25
30
35
40
Co
nce
ntr
atio
n
CrustalAmmonium
EC
Nitrate
Sulfate
Organics
PM2.5 Composition during the Winter
(Adapted from Pandis, 2003)
The Sulfuric Acid/Ammonia System (Pandis, CMU)
02468
101214161820
0 1 2 3 3.6 5 10
Ammonia
Ammonium
Sulfate
Bisulfate
Sulfuric acid
Total Available Ammonia (g m-3)
Co
nc
entr
ati
on
(g
m-3)
2 Ammonia:1 Sulfate
(Adapted from Pandis, 2003)
Ammonium Nitrate Formation
• The formation of ammonium nitrate requires– Nitric acid (major sources of NOx in the US are
transportation and power plants)
– Free ammonia (ammonia not taken up by sulfate)
• The formation reaction is favored at:– Low temperatures (night, winter, fall, spring)
– High relative humidity
• Hypothesis: A significant fraction of the sulfate reduced will be replaced by nitrate when SO2 emissions are reduced.
(Adapted from Pandis, 2003)
Fine PM CompositionP
M2
.5 (
g/m
3)
0
5
10
15
20
25
30
35
Organic matter Elemental carbon Sulfate Nitrate Ammonium Crustal components
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
2001 2002
PM2.5 mass
(Adapted from Pandis, 2003)
Which is the Limiting Reactant?
0 10 20 30 40
0
20
40
60
80
10
30
50
NH4NO3 (g m-3)
To
tal N
itri
c A
cid
(g
m-3)
Total Ammonia (g m-3)
A
B
A:Ammonia limited
B: Nitric acid limited
(Adapted from Pandis, 2003)
Reductions in Ammonia(July 2001)
0 10 20 30 40 50
0
10
20
30
40
Inorg
an
ic P
M2
.5 R
ed
uct
ion
(%
)
Ammonia Reduction (%)
20% Sulfate Reduction
(Adapted from Pandis, 2003)
Reducing Inorganic PM2.5
• Controls of SO2 will reduce sulfate and PM2.5 in all seasons.
• A fraction of the now existing sulfate will be replaced by nitrate.
• For Pittsburgh, ammonia controls in all seasons can minimize the replacement of sulfate by nitrate.
• For Pittsburgh, NOx controls will help reduce the nitrate during the winter but they will have a small effect during the summer.
(Adapted from Pandis, 2003)
Nucleation and Ultrafine Particles
• The model was successful in reproducing the observed behavior (nucleation or lack of) in all simulated dates in July (10) and January (10)
• Strong evidence that the nuclei are sulfuric acid/ammonium/water clusters– Growth with the help of organics
• Discrepancies in the nucleation rates– the model tends to predict higher rates
• Ammonia appears to be the controlling reactant !– Small to modest reductions of ammonia can turn off the
nucleation in the area especially during the summer
(Adapted from Pandis, 2003)
CMAQ Ammonia Sensitivity Runs- 50% NH3 Reduction- January
Basecase Nitrate Nitrate with 50% Ammonia Reduction