1. Nitrogen Deposition: Measurement Techniques and Field Studies
AT 621 Special Lecture
November 26, 2012
Ashley Evanoski-Cole

2. Atmospheric Nitrogen Pathways
May increase with climate change (Civerolo, 2007)
Eutrophication
Decrease biodiversity
Acidification
- Cation exchange in soils
- Lakes/streams acidification

3. Pathways for Ammonia (NH3)
NH3 Sources
1. Livestock
2. Ammonification of Humus
3. Emission from Soils
4. Fertilizer
5. Industrial Emissions
Chemical Processing
NH3(g) → NH3(aq)
NH3(aq) + H+ ↔ NH4+(aq)
Particle Formation
NH4+(aq) + NO3-(aq) ↔ NH4NO3(aq)
Dry or Wet Deposition
Transport
τ ~ 10 days
Dry Deposition

4. Pathways for NOx NOx Sources 1. Fossil fuel combustion
2. Biomass Burning
3. Soils
4. Lightning
Chemical Processing (day)
NO2(g) + OH → HNO3(g)
HNO3 dry and wet deposition
Chemical Processing (night)
NO2 + NO3 ↔ N2O5
N2O5(g) H2O(aq) → HNO3(aq)
Ozone Formation
Transport
(lifetime highly variable)

5. 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
Explain precip bucket (and dry dep bucket)

6. 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)
Direct methods include measuring deposition on surrogate surfaces (filter) or natural surfaces such as leaf-washing, snow analysis, a “chamber,” eddy correlation using vertical winds, also eddy accumulation (one filter or chamber right side up, one upside down, to measure both the flux up and flux down to get the next flux of a species)
CASTNet site at Penn State University

7. 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)

8. 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

9. H+
Mention acid sensitive areas (NE) because of low acid neutralizing capacity

10. NO3-

11. NH3

12. Percent Change in N deposition
Ammonia
Lehmann et al., 2005

13. (Ammonium and nitrate)
Inorganic Nitrogen
(Ammonium and nitrate)

14. ROMANS Field Campaigns
Rocky Mountain Atmospheric Nitrogen and Sulfur (RoMANS) study
Multi-year study between
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

15. Measurements Gas and Particle Chemistry Precipitation 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]

16. Concentrations Across Colorado
Seasonal trends
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
f(T, RH)
NH3(g) + HNO3 (g) ⟺ NH4NO3 (p)
[slide from K. Benedict]

17. Winds and Concentrations
Spring
Fall
[slide from K. Benedict]

18. 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.

19. Nitrogen Deposition & Critical Load
All Pathways Annual Deposition: 3.46 kg N·ha-1
Set
Critical Load
Critical Load Comparison
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]

20. 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)