Investigating fire-induced ozone production from local to global scales

Le résumé fourni par la source

Tropospheric ozone (O 3 ) production from wildfires is highly uncertain; previous studies have identified both production and loss of O 3 in fire-influenced air masses. To capture the total ozone production attributable to a smoke plume, we bridge the gap between near-field fire plume chemistry and aged smoke in the remote troposphere. Using airborne measurements from several major campaigns, we find that fire-ozone production increases with age, with a regime transition from NO x -saturated to NO x -limited conditions, showing that O 3 production in well-aged plumes is largely controlled by nitrogen oxides (NO x ). Observations in fresh smoke demonstrate that suppressed photochemistry reduces O 3 production by ∼ 70 % in units of ppb O x (O 3 + NO 2 ) per ppm CO in the near-field (age < 20 h). We demonstrate that anthropogenic NO x injection into VOC-rich fire plumes drives additional O 3 production, sometimes exceeding 50 ppb above background. Using a box model, we explore the evolving sensitivity of O 3 production to fire emissions and chemical parameters. We demonstrate the importance of aerosol-induced photochemical suppression over heterogeneous HO 2 uptake, validate HONO's importance as an oxidant precursor, and confirm evolving NO x sensitivity. We evaluate GEOS-Chem's performance against these observations, finding the model captures fire-induced O 3 enhancements at older ages but overestimates near-field enhancements, fails to capture the magnitude and variability of fire emissions, and does not capture the chemical regime transition. These discrepancies drive biases in normalized ozone production (ΔO3/ΔCO) across plume lifetime, though the model generally captures observed absolute O 3 enhancements in fire plumes. GEOS-Chem attributes 2.4 % of the global tropospheric ozone burden and 3.1 % of surface ozone concentrations to fire emissions in 2020, with stronger impacts in regions of frequent burning.

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