MDPI Impacts on Urban VOCs and PM2.5 during a Wildfire Episode
Overview:
During the 2018 Camp Fire (November 8–25), dangerous pollutants traveled roughly 240 km to the San Francisco Bay Area. There, volatile organic compounds (VOCs) were measured at 3–4 times their normal concentrations, PM2.5 reached an hourly peak of 270 μg/m³, and black carbon briefly spiked to nearly 13 times its usual background level. A persistent temperature inversion (warm air over cool air) prevented the smoke from dispersing, causing pollution to linger in the region for about three weeks. Even after the fire ended on November 25, it took 17–25 days for most pollutant levels to return to normal. While VOC levels at 240 km away remained below acute risk thresholds, measurements in Davis - about 100 miles from the fire - exceeded health guidelines. This illustrates that wildfire emissions can pose significant health risks, especially when exposure lasts for extended periods, even at considerable distances from the source.
By December 12 (17 days after the Camp Fire ended), VOC concentrations in the Bay Area had returned to near-baseline levels. PM2.5 also normalized in early December, though the exact date for all pollutants fully returning to baseline is not specified.
Relationship To AQI:
Based on the paper's data, here's how these pollutants relate to AQI:
- Partially - AQI only directly measures some components:
- PM2.5: Yes - this is a major component of AQI calculations
- PM10: Yes - also included in AQI
- Black Carbon: Indirectly - it's a component of PM2.5
- NOT captured in AQI:
- VOCs (volatile organic compounds) like benzene, toluene, etc.
- Many other specific toxic compounds from fires
This is important because during the Camp Fire, while AQI readings would have shown the dangerous particulate matter levels (the paper mentions PM2.5 reaching 270 μg/m³), they wouldn't have reflected the 3-4× increase in toxic VOCs that the researchers measured.
So while AQI readings during wildfires are definitely useful warning indicators, they don't tell the complete story about air toxicity since they don't measure many of the harmful compounds identified in this study.
Takeaways:
The paper suggests that measuring and monitoring both particulate matter (which AQI captures) AND gas phase composition (which AQI doesn't capture) would be more informative for public health during wildfire season.
We need local VOC measurements to help aid in public guidance.
The Camp Fire was about four times larger than the fires that broke out in Los Angeles.
We’d like to see data about VOCs directly at the Camp Fire. If anyone has an analysis of a paper that documents these, please be in touch.
Use this information at your own risk. Please consult with local agencies regarding laws and regulations. This information is provided without warranty or guarantee. Your safety comes first. Be careful, be empathetic, and please don’t be an asshole.