Apportioning Sources of Nitrogen Oxides in California's San Joaquin Valley Using Observations From Three Airborne Field Campaigns
Journal Article
Overview
abstract
Abstract; ; Emissions of nitrogen oxides (NO; x; = NO + NO; 2; ), a precursor to ozone and secondary aerosol formation have become increasingly important to understand as ozone production transitions to NO; x; limited in most regions of the US. Recent studies suggest that NO; x; emissions associated with agricultural activities, particularly cropland soils, are an increasingly important contributor. California's San Joaquin Valley (SJV) is a prominent agricultural region, with large‐scale cropland and livestock operations that are known sources of nitrogenous emissions. In this work, observations from six summertime research flights, two each from three airborne field campaigns conducted in 2010, 2019, and 2023, are used to identify sources and quantify contributions from various agricultural and non‐agricultural sectors to airborne observations of NO; x; in the SJV. This analysis utilizes measurements of total reactive nitrogen oxides (NO; y; ; a more conserved tracer than NO; x; ), nitrous oxide, ammonia, ammonium, methane, ethane, carbon monoxide, sulfur dioxide, and select volatile organic compounds and applies two source receptor models to separate abundances of NO; y; into source contributions. Both approaches identify and attribute NO; y; observations in the SJV to the same four source sectors. Results varied for each individual flight. The basin‐wide average (1σ standard deviation) percent contribution from six flights to the regional NO; y; observations were 24.9(10.3)% for fertilized soils, 25.3(9.6)% for livestock operations, 40.8(13.9)% for mobile combustion, and 2.9(2.7)% for stationary combustion sources indicating that agriculture can be a larger contributor to nitrogenous emissions in the SJV compared with a California‐based emissions inventory.;
