Impacts of Soil NOxEmission on O3Air Quality in Rural California

Nitrogen oxides (NOx) are a key precursor in O3formation. Although stringent anthropogenic NOxemission controls have been implemented since the early 2000s in the United States, several rural regions of California still suffer from O3pollution. Previous findings suggest that soils are a dominant source of NOxemissions in California; however, a statewide assessment of the impacts of soil NOxemission (SNOx) on air quality is still lacking. Here we quantified the contribution of SNOxto the NOxbudget and the effects of SNOxon surface O3in California during summer by using WRF-Chem with an updated SNOxscheme, the Berkeley Dalhousie Iowa Soil NO Parameterization (BDISNP). The model with BDISNP shows a better agreement with TROPOMI NO2columns, giving confidence in the SNOxestimates. We estimate that 40.1% of the state’s total NOxemissions in July 2018 are from soils, and SNOxcould exceed anthropogenic sources over croplands, which accounts for 50.7% of NOxemissions. Such considerable amounts of SNOxenhance the monthly mean NO2columns by 34.7% (53.3%) and surface NO2concentrations by 176.5% (114.0%), leading to an additional 23.0% (23.2%) of surface O3concentration in California (cropland). Our results highlight the cobenefits of limiting SNOxto help improve air quality and human health in rural California.