Santa Ana Winds of Southern California Impact PM_2.5With and Without Smoke From Wildfires

Abstract

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.

Global climatology of synoptically‐forced downslope winds

“…From a societal perspective, the seasonal and geographic distribution of downslope winds helps to identify potential risks to infrastructure and other wind‐related hazards, including those tied to wind energy, power outages, transportation, and fire ignitions. Finally, meteorological downslope winds have also been shown to impact air quality (Li et al ., 2015; Aguilera et al ., 2019), and pose an array of adverse effects to human health via entrainment and transport of dust (Evan, 2019), smoke transport downwind of wildfires fanned by the same winds (Delfino et al ., 2009; Leibel et al ., 2019), and heat impacts on valley and coastal populations at the terminus of downslope winds (Schwartz et al ., 2019). Our database and conceptual model set the stage for evaluating downslope windstorm impacts and physical mechanisms, as well as plausible changes in downslope winds simulated by global models under a warming climate.…”

Wildfire smoke impacts respiratory health more than fine particles from other sources: observational evidence from Southern California

“…Daily-, zip code-specific concentrations of PM 2.5 were estimated from 1999 through 2012 31 using 24-h daily means sampled and analyzed by the US EPA Air Quality System ( https://www.epa.gov/aqs ) at ground monitoring stations within a 20 km radius of each population-weighted zip code centroid. Values were interpolated using an inverse distance weighting approach 31 , which gives greater importance to monitoring stations closer to the point of interest. These PM 2.5 values, coming from monitoring station data, represent fine particulate matter from all sources, including ambient levels and wildfire smoke.…”

“…We collected hourly data from NOAA’s National Centers for Environmental Information Integrated Surface Database (NCEI ISD; https://www.ncdc.noaa.gov/isd ) and calculated 24-h daily means for wind speed, temperature, and humidity. Values were interpolated using an inverse distance weighting approach 31 and considering the daily observations from monitoring stations within a 20 km radius of each population-weighted zip code centroid.…”

“…These SAW-driven wildfires can spread faster and burn longer than fires at other times of the year 30 . Furthermore, recent work has shown that PM 2.5 tends to increase with strong SAWs in the presence of wildfire burning upwind 31 .…”

“…The Santa Ana wind season extends liberally from September to May 26 and therefore the summer months of June, July, and August were excluded from our analyses. Daily-, zip code-specific concentrations of PM 2.5 31 represent fine particulate matter from all sources, including ambient levels and wildfire smoke. Daily hospital admissions for respiratory diseases ( n = 1,655,011), which include pulmonary diagnoses such as asthma, chronic obstructive pulmonary disease (COPD), pneumonia, and interstitial lung disease were aggregated at the daily level by zip code.…”