Lake Merritt at 3p.m. on the infamous "orange sky" day, September 9, 2020. Credit: Pete Rosos

Last week, to the surprise of many Oaklanders, local air quality maps glowed with ominous orange markers signifying unhealthy air quality, after a ten-week stretch in which levels were largely “moderate” or better. Residents took to social media to bemoan this fact and search for explanations. One tweeted that a “city outdoor afterschool program got canceled for the first time since the fires were so bad in September and October.” Another wondered if the smoke was coming from wildfires in Southern California. 

In fact, according to the regional air monitoring agency, last week’s culprit was residential wood burning, with more people tossing logs on firepits, wood stoves, and fireplaces as temperatures dropped. A high-pressure system across Northern California had trapped the wood smoke at ground level in and around Oakland, triggering the 50th air pollution alert of the year. Meanwhile, a red flag warning for wildfires was issued for the Oakland hills this past weekend—unusual this late in the year. 

It’s normal to wonder: how does 2020 compare to previous years when it comes to air quality?  Is the number of unhealthy air days each year increasing?

To answer these and other questions, The Oaklandside analyzed daily and annual recorded highs of PM2.5, the primary pollutant from wood smoke, wildfires, and other sources recorded in Oakland since 2010, the first full year that an air monitor operated by the Bay Area Air Quality Management District (BAAQMD) began recording PM2.5 levels in our city. Our analysis runs from the start of 2010 through December 7.

Of course, when looking at both air pollution and climate change, it’s important to study much longer time spans. But given that there is widespread scientific agreement that wildfires in California have indeed gotten worse over the past decade, and will continue to do so—“The last 10 years have shattered records. 2020 tops them all,” notes the Los Angeles Times—we felt it was worthwhile to review 10 years of air quality data in Oakland to provide some context.

Is Oakland seeing fewer “good” air days over time?

When unhealthy air settled over Oakland during this year’s wildfire season after the dry lightning storm in mid-August, the regional air monitoring agency, BAAQMD issued more than 40 Spare the Air alerts in a row, smashing the previous record of 14 consecutive Spare the Air days set in 2018 by the Camp Fire.

BAAQMD, headquartered in San Francisco, operates over 30 air monitoring sites throughout the Bay Area. Three of them are in Oakland. The East Oakland monitor, located at Roots Community Health Center, went online in late 2009. The other two, located at the EBMUD Adeline Maintenance Center in West Oakland and near downtown at Laney College, turned on in late 2012 and 2014, respectively. Our analysis primarily relies on data from the East Oakland monitor, but also considers data from the newer monitors.

Data from these monitors are uploaded to BAAQMD’s website and the EPA’s AirNow on an hourly basis, and BAAQMD averages readings over 24 hours to compute a daily value. The goal is to help residents make short-term decisions about their lives: Should you take your dog for a walk or stay home? Is it safe to pick up your medication and go grocery shopping? What might tomorrow look like?

On September 7, the monitors in East, West, and downtown Oakland recorded “very unhealthy air quality” levels for the first time this year, close to levels recorded in Oakland during the Camp Fire, which originated in Butte County. The primary pollutant in the wildfire smoke in every case was PM2.5, tiny particles that are 30 times smaller than the width of a human hair and can cause health problems if inhaled. One scientific study described PM2.5 as “small enough to invade even the smallest airways and penetrate the lungs.” 

Like aerosols that can transmit respiratory viruses, PM2.5 can stay suspended in mid-air, exposing people to dangerous pollution for weeks on end. Most climate scientists already agree that our planet is warming every year, but studies also reveal that increasing temperatures are tied to increasing PM2.5 levels. 

The Oaklandside found that while all three monitors in Oakland have recorded mostly “good” air days every year that they’ve been online, the number of days with “unhealthy” air quality, where PM2.5 was the primary pollutant, are rising.

Take a look at data for East Oakland in the chart below. Since 2010, the first full year that the East Oakland monitor began tracking PM2.5, the number of days in East Oakland with “good” and “moderate” air quality has fluctuated, with no clear trendline. But in recent years, we’ve started to see years with air that’s considered “unhealthy” for all and even “very unhealthy.” 

How many days of “moderately” poor air quality each year is too much? “Clearly we can’t have 365 days in the moderate range and still meet the annual average standard,” said Robert Harley, professor at UC Berkeley’s Department of Civil & Environmental Engineering. “But I would say having some days in the yellow [moderate] range is okay.”

If we isolate days when air quality was “moderate” or worse, we can see clearly that 2017 is the first year since it came online that the East Oakland monitor recorded AQI levels that are considered “unhealthy,” for everyone, and that 2018 was the first year with “very unhealthy” air levels. (Note that the highest and most dangerous category of air quality in the AQI scale is “hazardous,” or above 300. None of the three Oakland monitors have recorded hazardous PM2.5 air levels in the past 10 years.)

Until three years ago, “unhealthy” levels of PM2.5 weren’t recorded by any of the three monitors in Oakland—and experts say many residents don’t understand just how bad “unhealthy” air is compared to good or even moderately polluted air.

“I don’t think it is widely understood by the general public how much worse 200 AQI is compared to 150 AQI, and how steep the slope is between these points that bracket the ‘unhealthy’ range,” said Robert Harley, professor at UC Berkeley’s Department of Civil & Environmental Engineering.

That’s because the AQI index is oversimplified. “Unhealthy” air quality ranges from 55 to 150 micrograms of pollutants found in one cubic meter of air (µg/m3), which translates to the AQI range of 151 and 199. Both an AQI of 151 and 199 are considered “unhealthy.” The problem is that an AQI of 199 is actually nearly three times more polluted than 151.

In 2018, the East Oakland, West Oakland, and Laney College monitors all recorded the highest annual average and daily average of PM2.5 pollution since they came online, as a result of the Camp Fire. That all changed in 2020. 

2019 had a much less active wildfire season, which could explain why there weren’t as many days with high PM2.5 levels. 

Overall, there isn’t a firm consensus on when wildfire season officially begins and ends in California. One academic has suggested that California has two distinct fire seasons that essentially run year-round. According to NASA, which tracks wildfire smoke from space, California’s wildfire season peaks from May to October

CalFire, the state’s wildland fire management agency, surmises that wildfire seasons are now starting earlier and ending later, with climate change mainly driving this trend. Oakland Fire Department leaders largely agree, though they cite weather and vegetation as better indicators. But there’s no hard and fast rule; in 2018, the deadly Camp Fire started in early November, and Oaklanders experienced bad air until the end of that month. 

It’s also important to note that not all PM2.5 pollution picked up by these monitors is directly tied to wildfires, as we saw with the impacts of residential wood burning last week. BAAQMD spokesperson Erin DeMerritt says each monitoring location can be affected by a number of unique factors at any given time, including emissions from background regional sources, nearby local and mobile sources (like cars, trucks, and ships), meteorology, year-to-year variability, and seasonality. 

“For example, the Laney College monitoring site is located in close proximity to a major roadway and is more directly affected by emissions from mobile sources than downwind locations in East and West Oakland,” DeMerritt said.

How does this year’s air pollution compare to past years across California?

The California Air Resources Board (CARB), the state’s air pollution regulatory agency, also analyzes PM2.5 data. A CARB report published in June revealed that PM2.5 pollution from wildfires increased significantly in 2017.

From 2001 to 2010, over three million pounds of PM2.5 emissions were generated by wildfires in California. Over the last decade, the amount of emissions have increased by more than a million pounds of PM2.5 emissions. However, in 2020 alone, wildfires produced 600 times the amount of PM2.5 emissions produced in the past 10 years. According to CARB, this year recorded two times the amount of PM2.5 emissions produced in 2008, the year of the lightning siege, and 2018 combined. 

“Wildfire acreage for this year was more than twice what burned in 2018 and more than three times the 2008 acreage,” said CARB spokesperson Amy MacPherson. 

CARB spokesperson Melanie Turner said this August and September had unprecedented levels of pollution in California, and some of the daily PM2.5 concentrations recorded were two and three times higher than the state’s air quality standards. Just days after Bay Area skies turned orange, pollution was at an all-time high.

“Nearly 95% of Californians were exposed to levels over the daily standard,” said Turner. “That [orange sky] smoke event resulted in the most widespread PM2.5 from wildfire smoke since CARB began monitoring it.”

These recent years of wildfire smoke pollution have turned back years of progress made in cleaning the state’s air, said Joshua Apte, a professor at UC Berkeley’s Department of Civil & Environmental Engineering and School of Public Health. 

“We are perhaps seeing an end of a 15-year run of steady improvements in PM2.5 air quality in many cities,” said Apte. “The effects of short, but very severe wildfire smoke episodes are washing away many years of hard work.”

The bigger picture shows some improvement though. A 2014 study found that California has made progress in reducing ambient PM2.5 levels since the 1990s, with many air monitoring sites recording pollution levels halved by 2013. In other words, in years without multiple catastrophic wildfires, the air has gotten cleaner due to tighter regulations compared to prior decades.

“I think the silver lining is further reductions in PM2.5 are very much possible and will likely result from California’s aggressive climate change policies,” said Apte.

Sarah Belle Lin is an independent journalist and photographer based in the East Bay.