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2019 California Climate and Agriculture SummitUC Davis
Estimating Nitrogen Emissions fromCalifornia’s Agricultural Lands
March 5, 2019
Michael FitzGibbon, ChiefAtmospheric Science and Climate Strategies Branch
Research [email protected]
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Outline
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• Background and motivation• Methods• Preliminary results • Summary and next steps
The Nitrogen Cycle
**Nitrogen is an important element in our lives ! 3
(N2,NH3, NOx, and N2O)
Agriculture
Farming Freshwater
What Contributes to Nitrogen in the Air?
**Mobile sources dominate NOx emissions while fertilizers dominate N2O emissions!4
• Mobile sources• Fuel combustion• Wastewater management• Industrial processes• Fertilizer use• Manure management• Other land use
Emission Trends of Nitrogen Species
5
0
100
200
300
400
500
600
700
0
1
2
3
4
5
6
7
8
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
NO
xE
mis
sion
(ton
s pe
r day
)
PM
2.5
Nitr
ate
(µg/
m3 )
NO
x(p
pb x
0.2
)
PM2.5 Nitrate
Ambient NOx
NOx Emission
• NOx emission controls in the mobile source sector has significantly improved air quality in the San Joaquin Valley over the past decades
• Reduction of N2O emissions from California croplands resulted from decreased cropland acreage and increased irrigation efficiency
0
2
4
6
8
10
12
14
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
N2O
em
issi
ons
(kilo
met
ric to
n)
Three-year average trends of ambient PM2.5 nitrate, NOx, and NOx emissions (CARB, 2019)
Year
Three-year average trend of N2O emission from California cropland
Year
Motivation to Study Nitrogen
**Reducing nitrogen emissions into our air will improve our environment! 6
Air Quality• NOx contributes to the formation of ozone (O3)
• NOx and NH3 contributes to the formation of
fine particulate matter (PM2.5)
• The San Joaquin Valley (SJV) continues to
exceed the National Ambient Air Quality
Standards (NAAQS) for both O3 and PM2.5
• CARB is required to develop State
Implementation Plans (SIPs) to achieve
NAAQS attainment
Climate Change• AB 32 and SB 32: California Global
Warming Solutions Act of 2006 and its
extension
o Reduce California’s greenhouse gas (GHG)
emissions to 1990 levels by 2020
o Reduce GHG emissions to 40% below 1990
levels by 2030
• N2O is a potent GHG that has global
warming potential of 265 times greater than
that of carbon dioxide (AR5)
Study Objective
**Study emphasis is on soil NOx
• As NOx emissions from the mobile sector decreases, other sources may become more important.
• The use of chemical nitrogen fertilizers and manure results in soil NOx emissions.
• CARB has taken a multi-tiered approach to evaluate the importance of soil NOx emissions in California, with an emphasis in the San Joaquin Valley.
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CARB’s Multi-tiered Approach to Study
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• Modeling methodso Biogeochemical modeling (DNDC)o CMAQ regional air quality modeling
• Measurement methodso Satellite o Surface monitoring
Satellite Surface monitoring network
Field measurements
Modeling
Modeling Methods: DNDC
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• Denitrification-Decomposition (DNDC) biogeochemical model, is used by CARB to estimate N2O and NOx emissions from cropland.
• DNDC derived soil N2O and NOx emissions are correlated with measurements well.
Y = 0.95X+0.08, R² = 0.77
0
0.5
1
1.5
2
2.5
3
0.0 0.5 1.0 1.5 2.0 2.5 3.0
DNDC
est
imat
es, k
g N
/ha
Field measurements, kg N/ha
N2O
NOx
Y = 1.00X, R² = 0.87
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
DNDC
est
imat
es (N
kg/
ha)
Field measurements (N kg/ha)
DNDC Results
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0.0E+0
5.0E+5
0 1 2 3 4 5 6 7 8 9 10 11 12
NO
E
mis
sion
(k
g N
)
Month
NO
0.0E+0
1.0E+8
2.0E+8
0 1 2 3 4 5 6 7 8 9 10 11 12Ferti
lizer
Inpu
t (k
g N
)
Month
Fertilizer
0.0E+0
5.0E+5
1.0E+6
0 1 2 3 4 5 6 7 8 9 10 11 12
N2O
E
mis
sion
s(k
g N
)
Month
N2O
0
10
20
30
0 1 2 3 4 5 6 7 8 9 10 11 12W
ater
Inpu
t(c
m)
Month
Precipitation and Irrigation
• Monthly soil NOxemissions peaked in May, consistent with seasonality of fertilizer use.
• Soil NOx emissions are mainly controlled by nitrogen input as opposed to soil N2O emissions, which were also affected by soil moisture.
DNDC Results
**Soil NOx emissions are a minor fraction of the total NOx emissions in California. 11
• Annual soil NOx emissions averaged 15 ton/day statewide using 2012 data.• The DNDC-derived soil NOx fluxes were consistent with recent estimates by
Rasool (2019), and lower than Almaraz (2018) estimates.
Air Quality Modeling
**Impact of soil NOx emissions on ambient NO2 and PM2.5 is not significant. 12
• CARB’s regional air quality model showed that both PM2.5 and NO2 concentrations were simulated reasonably well at an urban site in Fresno and at a rural site in Madera using soil NOx emissions comparable to the DNDC output.
Surface Monitoring
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• NOx and CO correlations and ratios were explored at 132 surface monitoring sites in California over the past 10 years
• Correlations and ratios of NOx and CO at urban and non-urban sites were statistically very similar, and its ratios closely represent combustion emissions
**High/low soil NOx sites classified based on IMAGE model
This suggests that NOx sources at non-urban locations are similar to urban locations
Urban vs. non-urban SOURCE characteristics
Surface Monitoring
Urban emissions (i.e., mobile sources) dominate NOx emissions! 14
• NOx diurnal trends at agricultural site (Madera, CA) paralleled urban NOx diurnal trends in all seasons
• Surface monitoring data at remote site do not reflect diurnal NOx emission patterns from cropland
Urban vs. non-urban DIURNAL characteristics
Remote monitoring site in Madera, CA Aggregated normalized diurnal/ seasonal NOx mixing ratios at Madera, CA
Diurnal NO emissions from cropland (Matson and Firestone, 1997)
Satellites
**Urban emissions dominate spatiotemporal pattern of NO2! 15
Annual and Monthly Satellite OMI NO2 Data in SJV Satellite TROPOMI NO2 Data (unit: 10-5 mol/m2 )
• Satellite NO2 data shows high NO2 levels in highly populated and traffic areas
• NO2 patterns are similar in urban and rural areas, indicating similar emission sources
Unit: x1015 molecules/cm2
Summary and Next Steps
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Summary
• DNDC model results suggest that soil NOx emissions from agricultural cropland are a minor fraction of the total NOx emissions in California
• Regional air quality modeling results showed that the impact of soil NOx emissions on ambient NO2 and PM2.5 is not significant.
• Surface and satellite data showed no differences between NOx observed over agricultural and non-agricultural areas which points to vehicular emissions dominating NOx emissions.
Next Steps
• Several other potential sources of soil NOx were excluded in this study but will be considered for future research, including urban landscape, such as lawn fertilizers, and forest lands.
• Future air quality model simulations will be performed using the DNDC estimated soil NOxemissions.
CARB’s Nitrogen Research Projects
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Funding Source Title Air Pollutants PI Funding Period
CARB
Agricultural Systems in the San Joaquin Valley:
Development of Emissions Estimates for Nitrogen
Oxides
NOxPamela Matson and Mary Firestone,
UC Berkeley1994-1995
CARB, SJVAPCD, and CSU Agricultural
Research Initiative
Dairy Air Quality Monitoring of ROG and Ammonia
in the Central Valley of CaliforniaVOCs and NH3 Charles Krauter, CSU Fresno 2006-2007
CARB, CDFA, and Ag Air Research
Council
National Air Emissions Monitoring Study (NAEMS):
Air Emissions from California DairiesVOCs, NH3, H2S, and PM Frank Mitloehner, UCD 2007-2010
CARBDetermining NOx Emissions from Soil in California
Cropping Systems to Improve Ozone ModelingNOx Will Horwath and Martin Burger, UCD 2010-2012
CARB, EDFAssessment of Baseline Nitrous Oxide Emissions in
California’s Dairy FarmsN2O Will Horwath and Martin Burger, UCD 2010-2012
CARBQuantification of the Emission Reduction Benefits
of Mitigation Strategies for Dairy SilageVOCs, NOx, NH3, and N2O Frank Mitloehner, UCD 2011-2016
CARB
Evaluation of Dairy Manure Management Practices
for Greenhouse Gas Emissions Mitigation in
California
CH4, N2O, NOx Stephen Kaffka, UCD Completed 2016
CARB
Improving DNDC Modeling Capability to Quantify
Mitigation Potential of Nitrous Oxide from
California Agricultural Soils
N2O Changsheng Li and Jia Deng, UNH 2014-2017
CARBMultiple polluant mitigation strategies for dairy
sources CH4, N2O, NH3, NOx, and VOCs Frank Mitloehner, UCD 2018-2021
CARB Monitoring Ammonia at California Dairies NH3 Mark Zondlo, Princeton University 2019-2021
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