Ozone photochemistry in fresh biomass burning smoke over the United States

Published:

Recommended citation: Jin, L., Coggon, M. M., Permar, W., Juncosa Calahorrano, J. F., Palm, B. B., Gkatzelis, G. I., Robinson, M. A., Bourgeois, I., Hall, S. R., Peischl, J., Ullmann, K., Thornton, J. A., Warneke, C., Flocke, F., Fischer, E. V., Yokelson, R. J., and Hu, L. (2026). Ozone photochemistry in fresh biomass burning smoke over the United States. Science Advances, 12(6), eads2157. https://doi.org/10.1126/sciadv.ads2157

Lixu Jin, Matthew M. Coggon, Wade Permar, Julieta F. Juncosa Calahorrano, Brett B. Palm, Georgios I. Gkatzelis, Michael A. Robinson, Ilann Bourgeois, Samuel R. Hall, Jeff Peischl, Kirk Ullmann, Joel A. Thornton, Carsten Warneke, Frank Flocke, Emily V. Fischer, Robert J. Yokelson, Lu Hu

Science Advances, 12(6), eads2157 (2026). DOI: 10.1126/sciadv.ads2157

Plots showing high hydroxyl radical concentrations early in five wildfire plumes and chemical age advancing faster than physical travel time.
Plume-center OH estimates and chemical age versus physical age across five selected daytime smoke plumes. Figure 1 from Jin et al. (2026), CC BY 4.0.

Plain-language summary

Wildfire Smoke Chemistry Runs in Fast-Forward

Aircraft observations reveal unusually rapid chemistry during the first two hours after emission.

Wildfire smoke does not carry a clock, but its chemistry does. In five selected daytime plumes, the first two hours unfolded in fast-forward: after one hour of travel, the smoke had experienced about as much oxidation as it would in three to four hours under typical background conditions. Observations from three major US aircraft campaigns captured each plume near the fire and again farther downwind, giving us snapshots of how the plume-center chemistry changed during the first five hours after emission.

Four findings

  • The source of reactive radicals changed quickly. HONO supplied most of the estimated radical production during the first hour. Oxygenated organic gases and ozone became more important as the smoke aged.
  • Chemical age organized the plume-to-plume differences. It explained about two-thirds of the variation in ozone enhancement and roughly 40%–70% of the differences in VOC loss and ozone and PAN formation.
  • Ozone control could shift within two hours. At least two of the five plumes moved from VOC-limited or transitional conditions toward NOₓ-limited conditions as they aged.
  • Models performed best with a fuller wildfire-VOC representation. Reduced VOC sets produced larger errors in OH, ozone, and organic nitrates, pointing to specific chemistry that current simplified mechanisms should improve.

中文解读

新鲜野火烟雾按下了化学“快进键”

飞机观测揭示新鲜烟羽最初两小时为何反应如此迅速。

野火烟雾没有时钟，化学反应却有自己的节奏。在我们选取的5条白天烟羽中，最初两小时仿佛按下了“快进键”：烟羽每实际传播1小时，累积的氧化程度大约相当于典型背景大气中3–4小时才能达到的水平。这些观测来自美国3次大型飞机观测项目。科研飞机在离火场不同距离的位置反复穿过这些烟羽，留下了排放后前5小时烟羽中心的一系列“化学快照”。

四个主要发现

  • 推动烟羽反应的自由基来源迅速换班。 最初1小时HONO是主力；随后含氧有机气体和臭氧逐渐接棒。
  • 化学年龄解释了不同烟羽为何表现不同。 它解释了约三分之二的臭氧增强差异，以及VOC氧化和臭氧、PAN生成差异的约40%–70%。
  • 臭氧控制条件可能在两小时内转变。 5条烟羽中至少有2条从VOC受限或过渡状态逐渐转向NOₓ受限。
  • VOCs表示越完整，模式表现越好。 精简VOC清单会放大OH、臭氧和有机硝酸盐的偏差，说明当前简化机制仍需改进野火烟雾VOCs的表示。

Official abstract

The first 5 hours of aging in biomass burning plumes can strongly affect ozone photochemistry. We examine how volatile organic compounds (VOCs), nitrogen oxides, and nitrous acid influence hydroxyl radical, ozone, and peroxyacetyl nitrate (PAN) based on three aircraft campaigns over the United States. Our analyses reveal variable, highly elevated hydroxyl radical concentrations in the first 2 hours, resulting in evident fire-to-fire variability in VOCs oxidation and in ozone and PAN production. About 40 to 70% of the variability is explained by chemical aging. Ozone production in the plumes is usually VOC-limited for the first 2 hours and then nitrogen oxide limited downwind. Box model results for hydroxyl radical, ozone, and most VOCs, using the full, explicit Master Chemical Mechanism (MCM) mechanism, suggest no major gaps in the current best knowledge of gas-phase chemistry. However, the MCM sometimes overestimates PAN due to underestimated nitrogen oxide sinks. GEOS-Chem, a widely used chemical transport model with a reduced mechanism, generally underperforms because of incomplete VOC representation. We identify these critical pathways to guide future model development.

Jin, L., Coggon, M. M., Permar, W., Juncosa Calahorrano, J. F., Palm, B. B., Gkatzelis, G. I., Robinson, M. A., Bourgeois, I., Hall, S. R., Peischl, J., Ullmann, K., Thornton, J. A., Warneke, C., Flocke, F., Fischer, E. V., Yokelson, R. J., and Hu, L. (2026). Ozone photochemistry in fresh biomass burning smoke over the United States. Science Advances, 12(6), eads2157. https://doi.org/10.1126/sciadv.ads2157