Soils are a source of atmospheric nitrogen oxides (NO_x), especially in regions with significant cropland where nitrogen (N) fertilizers are used to enhance crop yields. The magnitude of soil NO_x emissions, however, varies substantially by region, depending on the local land use pattern and management activities. We estimated soil NO_x emissions in California based on the DeNitrification‐DeComposition (DNDC) biogeochemical model, linked to a detailed spatial‐temporal differentiated California‐specific database. The DNDC‐generated surface fluxes were used in the Community Multiscale Air Quality (CMAQ) model to evaluate impacts of soil NO_x emissions on formation of ambient particulate (PM_2.5) nitrate in the San Joaquin Valley (SJV) where cropland is the dominant land use. The DNDC‐generated soil NO_x emissions contribute approximately 1.1% of total anthropogenic NO_x emissions in California, at an emission rate of roughly 24 t day⁻¹ (as NO₂) statewide and 9 t day⁻¹ in the SJV. Cropland is the dominant source of soil NO_x emissions in California, contributing nearly 60% of statewide soil NO_x emissions, driven principally by fertilizer use. The PM_2.5 nitrate concentrations simulated by CMAQ using the DNDC‐generated soil NO_x emissions are compatible with those observed in the SJV, suggesting that soil NO_x emissions have limited impacts on PM_2.5 nitrate formation in the atmosphere. Our emission and air quality modeling results are further supported by long‐term ambient NO_x‐to‐carbon monoxide (CO) and satellite NO₂ data analyses in the SJV, which showed diurnal, monthly, and annual trends consistent with characteristics of NO_x sources dominated by traffic combustion in both urban and agricultural regions.

中文翻译：

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加利福尼亚土壤中氮氧化物的排放和圣华金河谷PM2.5的影响评估

土壤是大气中氮氧化物（NO _x）的来源，尤其是在耕地面积较大的地区，其中氮（N）肥用于提高农作物的产量。土壤NO的大小_X的排放量，但是，通过区域变化很大，这取决于当地土地利用图案和管理活动。我们估计土壤NO _X在加利福尼亚州的排放基础上，反硝化分解（DNDC）生物地球化学模型，链接到一个详细的时空差异加州特定的数据库。所述DNDC生成的表面通量是在社区多尺度空气质量（CMAQ）模型用于评估土壤NO的影响_X上形成大气颗粒的PM排放（_2.5）是圣华金河谷（SJV）的硝酸盐，其中农田是主要的土地用途。所述DNDC生成的土壤NO _X排放量有助于总人为NO的大约1.1％_X在加利福尼亚州的排放量，在大致24吨天的发射率^-1（如NO ₂）全州和9吨天^-1在SJV。农田土壤是NO的主要来源_X排放量在加州，贡献了近60％，全州土壤NO的_X排放量，通过化肥的使用主要驱动。CMAQ使用DNDC产生的土壤NO _x模拟PM _2.5硝酸盐浓度排放是与那些在SJV观察兼容，表明土壤NO _X排放物具有有限的影响PM _2.5硝酸盐的形成在大气中。我们的排放和空气质量模拟结果进一步得到了SJV中长期环境NO _x到一氧化碳（CO）和卫星NO ₂数据分析的支持，这些数据显示了与NO _x特征一致的每日，每月和年度趋势在城市和农业地区，交通燃烧占主要来源。