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Nitrogen Deposition:
Measurement Techniques
and Field Studies
AT 621 Special Lecture
November 26, 2012
Ashley Evanoski-Cole
Atmospheric Nitrogen Pathways
May increase with climate change (Civerolo, 2007)
Eutrophication
Decrease biodiversity
Acidification
- Cation exchange in soils
- Lakes/streams acidification
http://nadp.sws.uiuc.edu/lib/brochures/nitrogen.pdf
Pathways for Ammonia (NH3)
NH3 Sources
Particle Formation
Chemical Processing
1. Livestock
NH3(g) → NH3(aq)
2. Ammonification
of Humus
NH3(aq) + H+ ↔ NH4+(aq)
3. Emission from
Soils
4. Fertilizer
5. Industrial
Emissions
NH4+(aq) + NO3-(aq) ↔
NH4NO3(aq)
Dry or Wet Deposition
Transport
τ ~ 10 days
Dry Deposition
Pathways for NOx
Chemical Processing (day)
NOx Sources
1. Fossil fuel
combustion
2. Biomass
Burning
3. Soils
NO2(g) + OH → HNO3(g)
Chemical Processing (night)
NO2 + NO3 ↔ N2O5
N2O5(g) H2O(aq) → HNO3(aq)
Ozone Formation
4. Lightning
Transport
(lifetime highly variable)
HNO3 dry and wet
deposition
HNO3 dry and wet
deposition
Wet Deposition
• Particles and gases that
deposit to the surface
via rain, snow or fog
– In cloud nucleation
– Particle / gas scavenging
How is it measured?
• Analyze species in
precipitation samples
Dry Deposition
• Gases and particles that directly transfer to the surface by
diffusion (gases and small particles) or gravitational settling
(larger particles)
How is it measured?
• Directly: Measure the vertical flux of species of interest or
measuring amount of species collected on a surface, such as
on a filter
• Indirectly: Flux measurements are derived from
measurements of mean concentration or vertical gradients of
mean concentrations (this method requires more
assumptions)
CASTNet site at Penn State University
NADP Monitoring Network
• National Atmospheric
Deposition Program
– Started measurements in
1978 measuring only weekly
precipitation data in the
National Trends Network
(NTN).
– Now monitoring sites for
daily precipitation, mercury
in precipitation (wet
deposition), atmospheric
mercury (dry deposition),
and ammonia
Weekly precipitation monitoring sites (NTN)
CASTNet Monitoring Network
• Clean Air Status and
Trends Network
• Established in 1991 to
measure acid deposition
• Measure ambient
concentrations and dry
deposition of SO2, HNO3,
(gases) and SO42-, NH4+,
NO3-, (particles)
• Use indirect method by
measuring concentration
and estimated deposition
velocities
H+
NO3-
NH3
http://nadp.sws.uiuc.edu/ntn/annualmapsbyyear.aspx
Percent Change in N deposition
Ammonia
Lehmann et al., 2005
Nitrate
Inorganic Nitrogen
(Ammonium and nitrate)
ROMANS Field Campaigns
• Rocky Mountain Atmospheric Nitrogen and Sulfur
(RoMANS) study
• Multi-year study between 20062010
• Collaboration between CSU,
CIRA, NPS, many other groups
• Main Objectives were to:
• Measure N and S deposition
• Characterize meteorological
conditions associated with
high N and S concentrations
• Identify source regions and
emissions within Colorado
and out of state transport
Measurements
• Gas and Particle Chemistry
– 24 hr gaseous species: NH3, HNO3, SO2
– 24 hr Particle Chemistry: Na+, NH4+, K+,
Mg2+, Ca2+, Cl-, NO3-, SO42– 15 min. Particle Chemistry: same as
above
– Weekly PM2.5 water soluble organic
nitrogen
• Precipitation Chemistry
– ions above and organic nitrogen
• In RMNP - meteorological
measurements from the National
Park Service Air Resources Division
• In GTNP – we operated three
different met. stations
[slide from K. Benedict]
Brush
Loveland
RMNP
Concentrations
Across Colorado
Concentration
(µmol/m3)
1.0
NH3
0.8
0.6
0.4
0.2
0.0
0.02
Concentration
(µmol/m3)
HNO3
0.06
0.04
0.02
NO3-
0.06
0.05
0.04
0.03
0.02
0.01
12/1/09
11/1/09
10/1/09
9/1/09
8/1/09
7/1/09
6/1/09
5/1/09
4/1/09
3/1/09
2/1/09
0.00
1/1/09
[slide from K. Benedict]
0.04
12/1/08
NH3(g) + HNO3 (g) ⟺ NH4NO3 (p)
0.06
0.00
0.07
Concentration
(µmol/m3)
f(T, RH)
0.08
0.00
Large differences between
sites for gas phase species
Concentrations are more
similar of aerosol species –
often concentrations at
RMNP are similar to those
on the plains
NH4+
0.10
11/1/08
Seasonal trends
Concentration
(µmol/m3)
0.12
Winds and Concentrations
SO4
1.2
NH4
NO3
Rain Event
Wind Direction
1.0
0.8
0.6
0.4
0.2
0.0
5/26/09
Concentration
5.0
SO4
5/28/09
NH4
5/29/09
NO3
5/30/09
Rain Event
5/31/09
6/1/09
Wind Direction
4.0
3.0
2.0
1.0
0.0
10/6/09
[slide from K. Benedict]
10/10/09
10/14/09
10/18/09
10/22/09
360
270
180
90
0
-90
-180
-270
-360
Wind Direction
(µg/m3)
Fall
5/27/09
360
270
180
90
0
-90
-180
-270
-360
6/2/09
Wind Direction
Concentration (µg/m3)
Spring
Critical load describes the point at which a natural system is impacted by
air pollution. They can be used to assess ecosystem health, guide
resource management decisions, and evaluate the effectiveness of
emissions reduction strategies.
http://nadp.sws.uiuc.edu/lib/brochures/criticalloads.pdf
http://www.nature.nps.gov/air/Studies/criticalloads/criticalLoadExplain.cfm
Nitrogen Deposition & Critical Load
• All Pathways Annual Deposition: 3.46 kg N·ha-1
Set
Critical Load
2008-2009
Critical Load Comparison
2008-2009
Dry NH3 and Wet ON
1.5
1.97
1.37
(Wet deposition of NH4+ + NO3-)
• Are dry deposition of NH3
and wet deposition of ON
important in other areas?
[slide modified from K. Benedict]
Dry
NO3
Dry 1%
Dry
NH4
HNO3
2%
5%
Dry
ON
1%
Dry
NH3
17%
Wet
ON
17%
Wet
NO3
20%
Wet
NH4
37%
Results and Potential Future Research
• Results of RMNP study were used to form a
nitrogen deposition reduction plan for the state
of Colorado
In Future Studies:
• Determine importance of each contribution to
dry and wet deposition in other sites
– Grand Teton NP (agricultural emissions to the east)
– Theodore Roosevelt NP in North Dakota (oil and gas
drilling emissions)