Reno Wildfire Smoke Hides Gases the Air Index Misses

Desert Research Institute chemists found that nearly 98% of the toxic PAHs in Reno wildfire smoke sat in the gas phase, not in the particles the air index reports. The paper, published August 8, 2026, in Atmospheric Pollution Research, compared 2019 clear and 2020 smoke samples from August through October.

PM2.5 still set off the alarms. The compounds that rose hardest did not.

Fifty Smoke Days, Eighteen Particle Exceedances

Vera Samburova, an atmospheric scientist at DRI, led the work with Chiranjivi Bhattarai, Siying Lu of DRI and the University of Nevada, Reno, and Andrey Khlystov, a DRI research professor of chemistry. They measured PM2.5, organic carbon, elemental carbon, ozone, and more than 100 polycyclic aromatic hydrocarbons, the tar-like products of incomplete burning.

On 18 of 50 smoke-affected days, PM2.5 exceeded EPA standards. The daily yardstick they were breaking is the 24-hour standard of 35 micrograms per cubic meter, a limit EPA has held since 2006. On the smokiest days in the set, levels ran 1.1 to 2.8 times that standard.

The worst stretches were August 19 to 22, 2020, and September 11 to 17, 2020, when hundreds of California fires were burning. DRI notes that 2020 and 2021 brought a 10-fold increase in California fires compared with any time in the state’s history, and that Northern Nevada sits downwind of much of that smoke.

WHAT 2020 SMOKE ADDED IN RENO

Every pollutant they tracked went up. The public number that people check on their phones is built for only one of them.

Almost All the PAHs Were Invisible Gas

PAHs form when wood, brush, and other fuel burn incompletely. They exist as particles and as gases. Fine-particle monitors catch the first group. They are not built to tally the second.

In these Reno samples, particulate PAHs were about 6 times higher on smoke-affected days than on the 2019 clear days, and methyl- and dimethylnaphthalenes led that particle fraction. The gas share dwarfed it. Nearly 98% of the PAHs identified were in the gas phase, and the mean gas level was about 47 times the particle-phase level.

Naphthalene, one of those gases, is on EPA’s hazardous air pollutant list. It is also one of the few named PAHs a U.S. monitor is likely to see at all, and even that check is occasional, not a daily AQI feed.

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.

Vera Samburova, atmospheric scientist, Desert Research Institute

Samburova said the team wanted to expand knowledge of the toxic compounds in smoke, not just restock the particle file. DRI posted the same warning on September 14, 2026, two days after local recaps of the paper began to circulate.

A new study gives us a detailed look into the potentially hazardous chemicals lurking in #wildfire smoke. DRI's Vera Samburova, one of the study's lead authors, shares how challenging it can be for those impacted by wildfire smoke.

Read more: https://t.co/wYxZlgyksY#AirQuality pic.twitter.com/esWE3HPqqO

— Desert Research Institute (@DRIScience) September 14, 2026

Air alerts in Reno-Sparks still talk in particles and miles of visibility. That is the language of the index. It is not the language of naphthalene.

EPA’s Priority List Matched 3 of 16 in the Top 20

U.S. air toxics work has long leaned on 16 PAHs ranked for monitoring, a set that dates to EPA Method 610. The Reno plume did not obey that roster. Only 3 of the EPA’s 16 priority PAHs were present in the top 20 PAHs found in this study.

WHERE THE 16-COMPOUND NET TORE

• Hit rate: Only 3 of the EPA’s 16 priority PAHs were present in the top 20 PAHs found.
• Particle leaders: Methyl- and dimethylnaphthalenes were the most abundant particle PAHs on smoke-affected days.
• Listed toxin: Naphthalene, a gas-phase PAH, is a hazardous air pollutant on EPA’s Clean Air Act list.
• Heavier PAHs: Higher molecular weight classes are more toxic, bioaccumulate more, and change how aerosols absorb light.

The authors write that occasional U.S. monitoring for 16 specified PAHs is likely to produce an insufficient read of overall toxicity. Samburova has been making a version of that case for years. In a 2017 paper in Toxics, she and colleagues found that the 16 EPA particle-bound PAHs underrepresented carcinogenic potency by 85.6% relative to the total gas-plus-particle benzo(a)pyrene-equivalent toxicity of 88 PAHs across 13 projects. Gas-phase PAHs such as methylnaphthalenes contributed up to 30% of that summed toxicity.

The 2020 Reno campaign is the field test of that lab argument in a Western city that lives downwind of California fire. The list that regulators still treat as the PAH shortlist did not match the mixture that actually arrived.

Ozone Barely Moved While Particles Soared

Smoke can feed ground-level ozone when its volatile organic compounds react with nitrogen oxides in sunlight. That pathway is real, and it is also fussy. The Reno study found only a limited ozone rise, about 12% on smoke-affected days, and some of those days came in below typical ground-level ozone.

DRI reads that pattern as a local source story. Vehicle exhaust and other urban pollutants, not the imported plume, still look like the main ozone makers in the basin. Particle counts can go off the charts while the ozone needle barely twitches, which is easy to miss if every smoky day is treated as the same chemical event.

That split matters for alerts. Ozone and PM2.5 both have public indexes. Gas-phase PAHs do not. A day that looks merely “unhealthy for sensitive groups” on particles can still be a high-PAH day in the gases nobody scores.

Reno Hospitals Already Saw the Asthma Cost

The chemistry paper does not count hospital visits. Earlier DRI work in the same city already tied wildfire particles to extra asthma traffic, which is why the 2020 samples were never an abstract exercise.

HOW RENO’S SMOKE FILE GREW

1. 2013 to 2018: Records 188 wildfire-smoke days and 18,836 asthma emergency and urgent care visits in Reno.
2. August through October 2019: Collects the smoke-free baseline later used in the PAH paper.
3. August 19 to 22, 2020, and September 11 to 17, 2020: Takes the season’s heaviest smoke as hundreds of California fires burn.
4. May 27, 2025: Publishes a 19-month particle study of more than 106 wildfires that reached Reno.
5. August 8, 2026: Publishes the PAH comparison in Atmospheric Pollution Research.

Daniel Kiser, a data scientist with DRI and the Renown Institute for Health Innovation, led the hospital analysis with Washoe County’s health district. On smoke days, a 5 µg/m3 rise in PM2.5 lined up with a 6.1% increase in asthma visits compared with days that had similar particle levels from traffic and industry. “Wildfire PM is more hazardous than non-wildfire PM for patients with asthma,” Kiser said.

Lu and Khlystov’s 2025 particle-size paper, built from roof instruments at DRI and a downtown EPA station, found that wildfire smoke made up 56% to 65% of PM2.5 in Reno during fire-prone late summer months, and 18% to 26% of carbon monoxide. Potassium from burning wood, satellite plumes, and NOAA back-trajectories were used to tag smoke hours. The PAH paper is the chemical sequel to that mass budget.

What the Monitors Still Do Not Count

EPA’s own teaching materials admit the gap even as they stay with particles. The EPA wildfire smoke health course describes smoke as a mix of carbon monoxide, nitrogen oxides, PAHs, other volatile organics, and PM, then focuses on PM2.5 because it is a main component and because decades of studies tie those particles to serious health effects. Gases, the course adds, can also harm, and ozone downwind of fires is highly variable.

Supplemental federal gear sent to fire country follows the same bias. EPA’s Wildfire Smoke Air Monitoring Response Technology loans still center on PM2.5, with carbon monoxide and a few other gases on some units. They are not a PAH network.

WHERE EXPERTS DISAGREE

• EPA’s teaching line: The smoke course keeps the public-health weight on PM2.5, citing long evidence that those particles drive heart and lung harm, while treating gases as a secondary, less mapped risk.
• DRI’s measurement line: Khlystov said regions frequently hit by wildfire smoke need regular monitoring for a range of PAHs, not occasional checks of 16 specified compounds.

In late August 2026, the Hawk Fire again sent smoke across the Reno-Sparks metro area. Bridger Aerospace, flying air attack on the fire, said on August 22 that the burn had topped over 15,000 acres with no containment. Forecasts talked visibility and the index. They did not talk methylnaphthalenes.

Khlystov said further health studies and regular air monitoring for a range of PAHs are needed, especially in regions frequently impacted by wildfire smoke. The network that feeds Reno’s alerts still does not provide it.

Frequently Asked Questions

Which Other Chemicals Did the 2026 Study Measure?

Organic carbon and elemental carbon, which also rose on smoke-affected days, sat alongside PM2.5, ozone, and the suite of more than 100 PAHs. Those carbon fractions help separate wood smoke from traffic soot, but they are not reported to the public the way the particle index is.

Does EPA’s 16-PAH List Include Naphthalene?

Yes. EPA Method 610 lists naphthalene first among the 16, followed by acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, dibenzo(a,h)anthracene, benzo(ghi)perylene, and indeno(1,2,3-cd)pyrene. The Reno samples still placed only 3 of those 16 in the top 20 PAHs found, which is why a named-list check can miss the mixture.

What Are EPA’s Current PM2.5 Numeric Standards?

The 24-hour primary standard is 35 µg/m3, unchanged since 2006, and that is the yardstick for daily spikes such as the 18 of 50 smoke-affected days in this study. On February 7, 2024, EPA lowered the annual primary standard to 9.0 µg/m3 from 12.0 µg/m3; that annual form was not the exceedance count used here.

How Many Fires Fed Reno in DRI’s Particle Study?

More than 106 wildfires sent smoke into Reno during a 19-month stretch from 2017 to 2020 in Lu and Khlystov’s particle-size paper. Smoky days in that campaign also carried aerosols likely to act as cloud nuclei at concentrations up to 13 times higher than average, a weather effect outside the 2026 PAH paper.

Disclaimer: This article is news reporting on a published air-quality study and is for information only. It is not medical advice, a diagnosis, or a guide to whether any person should stay indoors, use a mask, or change medication during smoke. Readers with lung or heart disease, and parents of children who wheeze, should consult a physician or local public-health department before changing care. Figures describe measurements from 2019 and 2020 samples and from later DRI papers as of the article’s date, and later fire seasons can differ.