NASA Ames Global Ecosystem Science - California

Understanding Change in the Biosphere

1.   "Development of Statewide Inventory Estimates of Ammonia Emissions from Native Soils and Crop Fertilizers in California"

Produced in collaboration with Charles Krauter, CIT California State University Fresno and Michael Benjamin, California Air Resources Board

This work is funded by the California Air Resources Board & NASA Ames Research Center.

1.1.   Introduction

Ammonia (NH₃) is the dominant gaseous base in the atmosphere and a principal neutralizing agent for atmospheric acids.

Volatilized ammonia:

• represents a reduction in fertilizer use efficiency by crops;
• acts as an atmospheric buffer by reacting with NOx and SOx from combustion.

NH₄NO_x and NH₄SO_x are components of PM_2.5, an air quality particulate problem that may require regulation.

In California, the estimated patterns of N deposition suggest that for areas close to photochemical smog areas, concentrations of the oxidized forms of N (NO₂, HNO₃) dominate, whereas in areas near agricultural activities the importance of reduced N forms (NH₃ and NH₄⁺) increases.

The magnitude and distribution of NH₃ emissions from fertilizer application and other agricultural sources are still largely undetermined.

1.2.   Objectives

Overall: To estimate NH₃ emissions from a variety of major crop-fertilizer combinations and from native soils in California.

Phase One:

1. Develop a simulation model for NH₃ emissions from native soils using satellite image drivers and other spatial data.
2. Evaluate an active sampler for monitoring NH₃ emissions from fertilized fields and background soil emission levels.

1.3.   Modeling Methods

As a regional model application to the state of California, we are building on the foundation of the NASA-CASA ecosystem trace gas model. Vegetation greenness estimates from satellite data are used as inputs to estimate productivity of ecosystems and associated nitrogen mineralization rates in soils, which provide the substrate for potential NH₃ volatilization. Predicted NH₃ fluxes from the model are constrained by a new series of field measurements from cropped areas in the Central Valley.

1.4.   Field Methods

Ammonia Trap Preparation Glass filters impregnated with 3% citric acid in 95% ethanol were assembled in the laboratory. NH3 forms ammonium citrate on the treated filter. In the lab, micrograms (µg) of NH3 on the filters were determined by: (1) dissolving the ammonium in de-ionized water and (2) measuring concentrations using Nessler reagent and a spectrophotometer.   Estimate NH3 at four heights Wind speed was monitored at each elevation and values averaged for the sampling period. Sample concentration of NH3 (µg m-3) of air multiplied by the average wind speed (m s-1) to get the NH3 flux (µg NH3 m-2s-1) during the sampling period. Determine NH3 Flux Rates

1.5.   Initial Field Results

   

   

• Time series plots show peak emissions shortly after fertilizer application (filled symbols).
• Emission factors are highly consistent among most fertilizer application forms and methods.

1.6.   Modeling Results

               

• Estimated annual emissions of N-NH3 from native soils in California are 14 x 106 kg from cropland and 16 x 106 kg from non-cropland (mainly coniferous forest) areas.
• Estimated annual emissions of N-NH3 from chemical fertilizer are 23 x 106 kg.

1.7.   Future Work

• Improve the characterization of the NH₃ flux gradients with additional crop sites.
• Technique will be used to monitor emissions from livestock operations.

Last Updated: 26 Feb 2001

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