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Title: Synthesizing evidence for the external cycling of NOx in high- to low-NOx atmospheres

External cycling regenerating nitrogen oxides (NOx ≡ NO + NO2) from their oxidative reservoir, NOz, is proposed to reshape the temporal–spatial distribution of NOxand consequently hydroxyl radical (OH), the most important oxidant in the atmosphere. Here we verify the in situ external cycling of NOxin various environments with nitrous acid (HONO) as an intermediate based on synthesized field evidence collected onboard aircraft platform at daytime. External cycling helps to reconcile stubborn underestimation on observed ratios of HONO/NO2and NO2/NOzby current chemical model schemes and rationalize atypical diurnal concentration profiles of HONO and NO2lacking noontime valleys specially observed in low-NOxatmospheres. Perturbation on the budget of HONO and NOxby external cycling is also found to increase as NOxconcentration decreases. Consequently, model underestimation of OH observations by up to 41% in low NOxatmospheres is attributed to the omission of external cycling in models.

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Author(s) / Creator(s):
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Publisher / Repository:
Nature Publishing Group
Date Published:
Journal Name:
Nature Communications
Medium: X
Sponsoring Org:
National Science Foundation
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