Fine particulate matter (PM_2.5) raises human health concerns since it can deeply penetrate the respiratory system and enter the bloodstream, thus potentially impacting vital organs. Strong winds transport and disperse PM_2.5, which can travel over long distances. Smoke from wildfires is a major episodic and seasonal hazard in Southern California (SoCal), where the onset of Santa Ana winds (SAWs) in early fall before the first rains of winter is associated with the region's most damaging wildfires. However, SAWs also tend to improve visibility as they sweep haze particles from highly polluted areas far out to sea. Previous studies characterizing PM_2.5 in the region are limited in time span and spatial extent, and have either addressed only a single event in time or short time series at a limited set of sites. Here we study the space‐time relationship between daily levels of PM_2.5 in SoCal and SAWs spanning 1999–2012 and also further identify the impact of wildfire smoke on this relationship. We used a rolling correlation approach to characterize the spatial‐temporal variability of daily SAW and PM_2.5. SAWs tend to lower PM_2.5 levels, particularly along the coast and in urban areas, in the absence of wildfires upwind. On the other hand, SAWs markedly increase PM_2.5 in zip codes downwind of wildfires. These empirical relationships can be used to identify windows of vulnerability for public health and orient preventive measures.

中文翻译：

---

南加州圣安娜风在有或没有野火烟雾的情况下都会影响 PM2.5


细颗粒物 (PM _2.5 ) 会引起人类健康问题，因为它可以深入呼吸系统并进入血液，从而可能影响重要器官。强风会输送和驱散 PM _2.5 ，而 PM 2.5 可以长距离传播。野火产生的烟雾是南加州 (SoCal) 的主要偶发性和季节性危害，初秋冬季第一场雨之前的圣安娜风 (SAW) 与该地区最具破坏性的野火有关。然而，声表面波还可以提高能见度，因为它们将雾霾颗粒从高度污染的地区扫到远处的大海。先前对该地区 PM _2.5特征的研究在时间跨度和空间范围上都受到限制，并且要么仅针对时间上的单个事件，要么针对有限地点的短时间序列。在这里，我们研究了 1999 年至 2012 年南加州每日 PM _2.5水平与 SAW 之间的时空关系，并进一步确定了野火烟雾对这种关系的影响。我们使用滚动相关方法来表征每日 SAW 和 PM _2.5的时空变化。在逆风没有野火的情况下，SAW 往往会降低 PM _2.5水平，特别是在沿海和城市地区。另一方面，SAW 显着增加了野火顺风邮政编码中的 PM _2.5 。这些经验关系可用于识别公共卫生的脆弱窗口并确定预防措施。