A Simple Method for Evaluating Photochemical Dependencies in the Atmosphere

Džepina, Katja; Madronich, Sasha (2025) A Simple Method for Evaluating Photochemical Dependencies in the Atmosphere. Croatica Chemica Acta, 97 (4). pp. 275-283. ISSN 00111643

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Abstract

This work examines the photochemistry of the lower troposphere for clean high latitudes in spring 2000 during the Tropospheric Ozone Production about the Spring Equinox (TOPSE) experiment. TOPSE measurements included the short-lived quantities [OH], [HO₂] + [RO₂], and [NO]/[NO₂] as well as those slow varying ones that, according to photo-chemical theory, control them, e.g. [H₂O], [O₃], [NOₓ], [CO], temperature T, pressure p, and photolysis rate coefficients (J-values). We examine this control using a simple scaling equation, which we term local sensitivity function (LSF), to correlate simultaneous measurements: [X] ∝ [H₂O]ᵅ [O₃]ᵝ [NOₓ]ᵞ [CO]ᵟ [J]ᵋ [T]ᵠ [p]ˣ where X = OH, HO₂ + RO₂, or NO/NO₂ ratio, and the exponents α, β, γ, δ, ε, φ, and χ are estimated with box model. We first test this correlation using the output from a regional chemistry-transport model (CTM) and find a remarkable improvement in the correlation between X and the LSF, compared to correlations of X with any single parameter (e.g., J values). When using actual observations, the correlations for OH remain unchanged, those for HO₂ + RO₂ improve significantly, but the correlation of the observed NO/NO₂ ratio with its LSF is sharply worse than simple correlations (e.g. vs. J value). This surprising result suggests that neither the box model nor the CTM are representing the chemistry of NO and NO₂ correctly in the polar troposphere, and points to the importance of other reactions, e.g., BrO + NO → Br + NO₂ and aerosol heterogeneous chemistry ones, that are not currently in the models.

Item Type:	Article
Uncontrolled Keywords:	TOPSE experiment; polar troposphere; photochemistry; box model Master Mechanism; chemistry-transport model HANK
Subjects:	NATURAL SCIENCES > Chemistry
Divisions:	Division of Physical Chemistry
Depositing User:	Sofija Konjević
Date Deposited:	31 Dec 2025 10:08
URI:	http://fulir.irb.hr/id/eprint/10713
DOI:	10.5562/cca4143

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