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California Wildfires' Effect on Bay Area Air Quality

Updated: Mar 20, 2021

Early autumn, I woke up to what looked like hell on earth. From San Francisco to Dublin, the Bay Area was shrouded in a thick, blood-red haze. One step outside and you’d be met with a suffocating, malodorous smog. The culprit? California’s perennial wildfires. For residents of Alameda County, the smoke was likely a result of the SCU Lightning Complex fire.

——Photo courtesy of ABC7 News

Although California experiences many wildfires annually due to its dry summer climate, the issue has worsened as of late. There were over 9,000 wildfires in 2020 alone totaling in at over 4.3 million acres of land burnt, 10,000 buildings destroyed, and $12 billion worth of damages (3rd costliest on record). The August Complex fire alone—which burned from August 16th to November 12th—was the largest wildfire to ever be recorded at an astounding 1,032,648 acres of land—spanning across the Glenn, Lake, Mendocino, Tehama, Trinity, and Shasta counties.

Using air quality index data provided by the Bay Area Air Quality Management District (BAAQMD), we quantified the negative effects of these wildfires on air quality and health for the San Francisco Bay Area. In total, we analyzed 2020 weekly air quality index (AQI) datasets for six cities: Hayward, Pleasanton, San Jose, San Ramon, and San Francisco. The AQI was measured in either ozone concentration or PM2.5 (the concentration of atmospheric particulate matter with a diameter under 2.5 micrometers). The following plots below show data for seven AQI-measuring sites across six cities (two for San Jose).

Taking a look at some of the plots of AQI vs Time, we notice sharp spikes around certain time frames. To name a few: Hayward and San Ramon around the beginning of May; and nearly every single city analyzed from mid-August to November. Interestingly enough, I can't seem to explain the sharp jump in AQI for Hayward and San Ramon. The three wildfires in May collectively burned less than 10,000 acres of land, and two of the three occurred much later in the month. Although the AQI data is scaled relative to its own city's maximum, as you will see later in the article, there is a small yet noticeable AQI spike around the beginning of July. What we can explain, however, is the spike in AQI seen across all cities right around August-November.

To investigate this common trend around autumn, we plotted the start and containment dates for the four largest wildfires last year alongside the AQI data for easier comparison. See the graph below:

Looking at the plot, we see that the August Complex, SCU Lightning Complex (1st and 2nd largest) fires started right around mid-August—explaining the common trend mentioned earlier. Following this timeframe, there is a large, sudden jump in AQI—peaking near 200 right after the 3rd largest fire (Creek) began. The four largest fires of 2020 account for an approximate 250% jump in AQI.

As per, 0-50 in AQI is indicative of satisfactory air quality; at these levels, air pollution poses little to no health risk. However, From 151-200, air pollution becomes a serious health hazard. Members of sensitive groups—the elderly, people with pre-existing lung conditions—are highly likely to experience dire health effects: decreased lung function, aggravated asthma, development of chronic respiratory disease in children (e.g. chronic bronchitis or obstructive lung disease)—the most fatal among them being premature death in people with heart or lung disease.

Last September, a study conducted by Stanford researchers discovered that in 2020 alone, over 1,200 deaths have been a result of poor air quality. This a fairly conservative estimate; the number could be as high as 3,000 according to their calculations. The evidence is clear. If we continue to neglect our duties as stewards and stewardesses of our planet, congestion and smog will be the least of our worries in the near future.

GitHub repo for this project:


  1. Burke, Marshall. Indirect Mortality from Recent Wildfires in CA, 1 Jan. 1970,

  2. BAAQMD. Bay Area Air Quality Management District A Healthy Breathing Environment For Every Bay Area Resident,

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