Agricultural Soil Emissions of Reactive Nitrogen and their impacts on Air Quality, Health, and Climate
Daniel Cohan and Lina Luo
Rice University
Presentation to U.S. EPA
August 25, 2022
About us
Daniel Cohan
Lina Luo
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Reactive Nitrogen Emissions from Soils
Importance of Soil NOx
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BDSNP
Wang
Global Emissions
California Emissions
Sensitivity to Soil Temperature
Importance of Soil Ammonia
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Economic Damage of U.S. Emissions by Sector
Soil Ammonia Emissions
Importance of Soil N2O
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Sources of N2O
Agricultural Emissions of Greenhouse Gases
Global Mean N2O
Agroecosystem Modeling of Nitrogen Emissions
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Agroecosystem Model
Volatilization
Nitrification
Denitrification
Other processes
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Prior soil NO studies by Cohan group
(Rasool et al., 2016 and 2019)
Latest study: Soil NOx, NH3, and N2O
and their impacts
(Luo et al., 2022)
Integrated Assessment with FEST-C* and APEEP
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Enhanced Fertilizer Emissions Scenarios Tool for CMAQ (FEST-C*)
Air Pollution Emission Experiments and Policy Analysis (APEEP)
NH3
NOx
N2O
Social Cost
of N2O
Climate Impacts
FEST-C*: Agroecosystem model adapted by Rice from EPIC and DayCent
APEEP: Reduced form air quality & health model
Luo et al., Environmental Science & Technology, 2022
Emissions Estimates
Health Impacts via O3 & PM
Comparison of Estimation Approaches for Nr Emissions
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Source | U.S. EPA | U.S. EPA | U.S. EPA | This study |
Species | NOx | NH3 | N2O | NOx, NH3, N2O |
Model | BEIS YL | CMU Ammonia Model | DayCent & IPCC Tier1 | FEST-C* |
Approach | Parametric model | Emission factor method | Mechanistic model (DayCent) & Emission factor method (IPCC Tier1) | Mechanistic model |
Biome | Soil | Agricultural soil | Agricultural soil | Agricultural soil |
Variables | Soil properties, meteorological conditions | Fertilizer input | Soil properties, meteorological conditions, farming practices | Soil properties, meteorological conditions, farming practices |
*Note: U.S. EPA uses CMU Ammonia Model for NH3 estimates in 2011 and bidirectional exchange model in 2017
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Enhanced Features of FEST-C*
Enhanced Fertilizer Use Rates
(based on USGS data)
Original FEST-C
(optimized for crop N demand)
USGS fertilizer
sales data
FEST-C*: Scaled up by USGS data where applicable
Enhanced N scheme
(based on DayCent model)
Comparison of nitrogen budgets in FEST-C and FEST-C*
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Our modifications to FEST-C increased N input from fertilization by 0.13% and N loss by 14%, leading to a 7% decline in the soil N pool and a less than 1% decline in harvested N
Simulated 3 Years with Different Palmer Drought Severity Index
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National Climatic Data Center (https://www.ncdc.noaa.gov/temp-and-precip/drought/historical-palmers/)
Drought
2011
2012
2017
May
June
July
Moist
Comparison of Fertilizer Use in FEST-C & FEST-C*
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2011
2012
2017
FEST-C
(based on optimization)
FEST-C*
(adjusted by USGS sales data)
24% increase
26% increase
29% increase
Difference
(to account for overuse)
Comparisons of Soil N Emissions Estimates
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Estimated agricultural emissions in BEIS YL
County-Level Annual Emissions Estimated by FEST-C*
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NOx
NH3
N2O
2011
2012
2017
Emissions largely follow fertilizer use, but with subtle differences by species and year (e.g., drought)
Ratio of HONO Emissions to NOx (HONO + NO) from Nitrification
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Maximum HONO/NOx estimates by FEST-C* : 0.35 ~ 0.43 in Oswald et al.
2011
2012
2017
Interannual Variability of Fertilizer N & Soil Nr Emissions
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N2O
NH3
NOx
Fertilizer N
%change
2012 vs. 2011
%change
2017 vs. 2011
Interannual variability of Nr emissions cannot be fully explained by changes in fertilizer use
Pulsing factors for NOx emissions when follows dry period
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2011
2012
2017
Intense pulsing of NOx in 2012 across Corn Belt and Northeast regions
Monetized Impacts of Agricultural Soil Emissions by County
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NOx
NH3
N2O
Marginal damage
($/ton)
Total damage
($)
Luo et al., Environmental Science & Technology
In most counties, NH3 emissions have largest impact
Marginal Health Damages of NOx Emissions in 2011
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O3
PM
Health impacts via PM dwarf those via O3
Seasonality of Emissions and Impacts
Here, Winter = Q1 (January – March); Spring = Q2 (April – June); Summer = Q3 (July – September); Fall = Q4 (October – December)
Fertilizer use peaks in spring;
Emissions peak in spring & summer
Marginal impacts peak in winter, when PM is most sensitive to emissions
Total impacts by season
Regional Air Quality and Climate Impacts
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Luo et al., Environmental Science & Technology
Forthcoming work: How soil carbon amendments influence emissions
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ZVC
Potential Impacts of Soil Amendments (good or bad?)
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Air
Climate
Water
Soil
Initial Modeling of Biochar with FEST-C*
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Biochar Algorithm for FEST-C (Lychuk et al. 2014)
Simulation Configurations
How should we change this to model VACS??
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Impact of Biochar on Soil pH and Cation Exchange Capacity
Base case
Biochar (5 ton/ha)
Difference (Biochar – Base)
Soil pH
Soil CEC
Soil pH and CEC both increase with addition of biochar;
Largest impact on pH in Southeast states
Preliminary Results: Impacts may depend on dose
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% Change
Increase
Decrease
N2O
NH3
NOx
Impacts of 20 ton/ha biochar
Preliminary Results
Impacts of 5 ton/ha biochar
Preliminary finding: Emissions may increase with low dose biochar but decrease with high dose
Preliminary Results
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Further Explorations: Modeling Potential Environmental Impacts of Zero-Valent Carbon (ZVC)* Soil Amendment
Represent ZVC and its impacts on soil properties based on laboratory studies
Integrated assessment of impacts
Represent impacts of ZVC on microbial activity
*ZVC: Produced along with hydrogen from methane pyrolysis (Carbon Hub)
Conclusions
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Acknowledgements
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