Emissions of nitrogen oxides (NOx = NO + NO2), a precursor to ozone formation and secondary aerosol formation, have decreased across the U.S. However, the rate of decrease has slowed in the past decade, and recent studies suggest that NOx emissions associated with agricultural activities, particularly cropland soils, are an increasingly important contribution to the slowing trend in NOx reductions. California's Central Valley is a hotspot for agricultural operations, predominantly associated with croplands and livestock operations, and thus nitrogenous emissions associated with agriculture are expected to be prevalent in this region. In this work, we leverage existing datasets from multiple airborne field campaigns conducted in California's Central Valley to identify sources of reactive nitrogen species from agricultural activities and quantify contributions from various agricultural and non-agricultural sources to the NOx observations in this region. A positive matrix factorization (PMF) source apportionment model is used to identify and attribute emissions associated with agricultural operations in this region. Source contributions to the NOx observations will be quantified from source factor profiles resulting from the PMF analysis. Results will be compared with national and state emissions inventories and prior reports in the literature.