With Western wildfires increasing in size, duration, and intensity, millions of Americans are now exposed to wildfire smoke each year. In California, the years 2020 and 2021 were particularly challenging, with a ten-fold increase in fires compared to any time in the state's history. Northern Nevada is positioned to receive much of the smoke from California wildfires, and Reno residents experienced months of smoke-shrouded skies during this time. Now, a new study gives us a deeper look into the potentially hazardous chemicals lurking in this smoke.
The research was published August 8th in the journal Atmospheric Pollution Research . Led by a team of DRI researchers, the study examines air quality collected during smoke-free days from August-October 2019 and compares it to smoke-affected days in August-October 2020. The research examined particulate matter (PM 2.5), organic carbon, elemental carbon, ozone, and a wide range of more than 100 toxic compounds known as polycyclic aromatic hydrocarbons (PAHs). The results showed elevated levels of all pollutants. PM2.5 exceeded EPA standards on 18 of 50 smoke-affected days, demonstrating substantial exposure relevant to public health concerns. Ozone was found to increase by about 12% on smoky days, and PAHs ranged from 6.3 times higher to 47 times higher.
"We wanted to expand our knowledge on the range of toxic compounds present in smoke," said Vera Samburova , atmospheric scientist at DRI and one of the study's lead authors. "The smoky summers are difficult for everyone in Reno, but they are challenging for sensitive groups, including children, older adults, people with preexisting health conditions, athletes, and outdoor workers. With limited monitoring on the contents of smoke, we don't yet have a great understanding for the full range of public health impacts, and this study can help us identify which air pollutants are most important to monitor closely in the future."
Examining these compounds is important because many of them are known to be hazardous to human health. Previous research has found a strong association between elevated PM 2.5 levels from wildfire smoke and an increase in emergency room visits for asthma in Reno and Sparks hospitals. On the smokiest days identified in this study, concentrations were 1.1 to 2.8 times higher than the EPA National Air Quality standard. Wildfire smoke was found to have the most severe effect on the region's air quality from August 19-22, 2020 and September 11-17, 2020, when hundreds of damaging wildfires were burning in California.
Wildfire smoke can also contribute to the formation of ground-level ozone as chemical reactions occur between the smoke's volatile organic compounds (VOCs) and free radicals in the presence of nitrogen oxides (NOx) and sunlight. This study identified a limited increase in ozone of 12% on smoke affected days, with some days actually measuring lower than average ground-level ozone. These results suggest that vehicle exhaust and other pollutants are the main sources of ground-level ozone in the region.
The study also examined the presence of PAHs, which result from incomplete combustion and can be present in smoke in both gas and particulate forms. These compounds are not regularly monitored the way PM 2.5 is, but are known to be toxic to be human health. Concentrations of particulate forms of PAH were found to be approximately six times higher on smoke-affected days, with methyl- and dimethylnaphthalenes found to be most abundant. The study team notes that certain classes of PAHs, such as those with a higher molecular weight, are known to be more toxic and have a greater ability to bioaccumulate. They can also impact the light absorption of aerosols, making their monitoring important for measuring their overall climate impact.
Overall, nearly 98% of the PAHs identified were in the gas-phase, with the mean concentration found to be approximately 47 times higher than particle-phase concentrations. Naphthalene, one of these gas-phase PAHs, is identified as a hazardous air pollutant by the U.S. EPA. Although the EPA recognizes 16 priority PAHs for air quality monitoring, only three from that list were present in the top 20 PAHs found in this study. The researchers say that this demonstrates that only occasional monitoring for 16 specified PAHs in the U.S. is likely to cause an insufficient assessment of their overall toxicity in air quality samples.
"Our study shows that further health studies and regular air monitoring for a range of PAHs are needed, especially in regions frequently impacted by wildfire smoke," said Andrey Khlystov , research professor of chemistry at DRI and study author.
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More information: The full study, The effects of smoke from wildfires in the Western US on urban air quality in Northern Nevada, is available from Atmospheric Pollution Research at https://doi.org/10.1016/j.apr.2026.103168
Study authors include: Vera Samburova (DRI), Chiranjivi Bhattarai (DRI), Siying Lu (DRI/UNR), and Andrey Khlystov (DRI)
