Wildfires in the western United States are large sources of particulate matter, and the area burned by wildfires is predicted to increase in the future. Some particles released from wildfires can affect cloud formation by serving as ice‐nucleating particles (INPs). INPs have numerous impacts on cloud radiative properties and precipitation development. Wildfires are potentially important sources of INPs, as indicated from previous measurements, but their abundance in the free troposphere has not been quantified. The Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen campaign sampled free tropospheric immersion‐freezing INPs from smoke plumes near their source and downwind, along with widespread aged smoke. The results indicate an enhancement of INPs in smoke plumes relative to out‐of‐plume background air, but the magnitude of enhancement was both temperature and fire dependent. The majority of INPs were inferred to be predominately organic in composition with some contribution from biological sources at modest super cooling, and contributions from minerals at deeper super cooling. A fire involving primarily sagebrush shrub land and aspen forest fuels had the highest INP concentrations measured in the campaign, which is partially attributed to the INP characteristics of lofted, uncombusted plant material. Electron microscopy analysis of INPs also indicated tar balls present in this fire. Parameterization of the plume INP data on a per‐unit‐aerosol surface area basis confirmed that smoke is not an efficient source of INPs. Nevertheless, the high numbers of particles released from, and ubiquity of western US wildfires in summertime, regionally elevate INP concentrations in the free troposphere.

中文翻译：

---

美国西部野火在对流层中冰成核颗粒的观测

美国西部的野火是颗粒物的主要来源，预计野火燃烧的面积将来会增加。野火释放的一些粒子可以充当冰核粒子（INP）来影响云的形成。INP对云的辐射特性和降水的发展有许多影响。如先前的测量所示，野火是潜在的重要INP来源，但其在对流层中的丰富度尚未量化。西方针对云化学，气溶胶吸收和氮的野火实验对来自其源头和顺风附近的烟流中的自由对流层浸没式冻结INP以及广泛的老化烟雾进行了采样。结果表明，烟羽中的INP相对于超出背景空气的浓度有所提高，但是增强的幅度与温度和着火有关。可以推断，大多数INP的成分主要是有机的，适度的过冷会导致生物来源产生某些贡献，而在深冷时会产生矿物质造成的贡献。在该运动中，主要由鼠尾草灌木林和白杨林燃料引起的大火具有最高的INP浓度，部分归因于膨松的，未燃烧的植物材料的INP特性。电子显微镜对INPs的分析还表明，这场大火中存在焦油球。以每单位气溶胶表面积为基础的羽状INP数据的参数化证实，烟雾不是INP的有效来源。尽管如此，夏季美国西部野火释放出的大量颗粒物无处不在，