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. 2020 Jan 11;4(1):e2019GH000225.
doi: 10.1029/2019GH000225. eCollection 2020 Jan.

Santa Ana Winds of Southern California Impact PM2.5 With and Without Smoke From Wildfires

Rosana Aguilera  1 , Alexander Gershunov  1 , Sindana D Ilango  2   3 , Janin Guzman-Morales  1 , Tarik Benmarhnia  1   2
Affiliations

Santa Ana Winds of Southern California Impact PM2.5 With and Without Smoke From Wildfires

Rosana Aguilera et al. Geohealth. .

Abstract

Fine particulate matter (PM2.5) 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 PM2.5, 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 PM2.5 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 PM2.5 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 PM2.5. SAWs tend to lower PM2.5 levels, particularly along the coast and in urban areas, in the absence of wildfires upwind. On the other hand, SAWs markedly increase PM2.5 in zip codes downwind of wildfires. These empirical relationships can be used to identify windows of vulnerability for public health and orient preventive measures.

Keywords: PM2.5; Santa Ana winds; Southern California; air quality; wildfire smoke.

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Conflict of interest statement

The authors declare no conflicts of interest relevant to this study.

Figures

Figure 1
Figure 1
Mean PM2.5 and total SAWRI activity, summarized by month (a) and by calendar year (b). The annual values for PM2.5 consider the months of September to May of each calendar year.
Figure 2
Figure 2
Significant positive (red) and negative (blue) correlations in a San Diego coastal zip code (location shown in Figure S2 in the supporting information). Dates for positive correlations associated with wildfires upwind are highlighted in red; in addition, the Viejas Fire burned 11,000 acres in January 2001. Other wildfire names are also included to highlight the contribution of smoke to particular positive correlations.
Figure 3
Figure 3
Count of significant positive and negative correlations per day/zip code, summarized per (a) month and (b) calendar year. Months and years among the largest burned areas (Tables S1 and S2) are highlighted in red. Note the different scales for the positive and negative correlation counts.
Figure 4
Figure 4
Total counts of negative (a) and positive (b) significant correlations per zip code. Fire perimeters obtained from the Fire and Resource Assessment Program of the California Department of Forestry and Fire Protection (http://frap.fire.ca.gov/) display the total area burned, and the date reflects the start of the fire.
Figure 5
Figure 5
Case study highlighting significant correlation between PM2.5 and wildfires. Daily gridded SAW vectors shown were obtained from Guzman‐Morales et al., 2016. (a) The Moderate Resolution Imaging Spectroradiometer Rapid Response System (https://lance.modaps.eosdis.nasa.gov/cgi-bin/imagery/gallery.cgi) satellite image shows the smoke plumes for fires burning on 22 October, and wind vectors represent wind velocity for that same day. High positive correlations are found in coastal zip codes, which remained with poor air quality conditions after (b) 2 weeks from the onset of the first wildfire. Fire perimeters display the total area burned and the date reflects the start of the fire.
Figure 6
Figure 6
(a) PM2.5 concentrations for coastal zip codes in Long Beach (in Los Angeles County) and San Diego (in San Diego County). (b) SAWRI for the 2‐week period of active wildfires during October to November 2007.
See this image and copyright information in PMC

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