The collision complex formed from a vibrationally excited reactant undergoes redissociation to the reactant, intramolecular vibrational relaxation (randomization of vibrational energy), or chemical reaction to the products. If attractive interaction between the reactants is large, efficient vibrational relaxation in the complex prevents redissociation to the reactants with the initial vibrational energy, and the complex decomposes to the reactants with low vibrational energy or converts to the products. In this paper, we have studied the branching ratios between the intramolecular vibrational relaxation and chemical reaction of an adduct HO(v)-CO formed from OH(X(2)Π(i)) in different vibrational levels v = 0-4 and CO. OH(v = 0-4) generated in a gaseous mixture of O(3)/H(2)/CO/He irradiated at 266 nm was detected with laser-induced fluorescence (LIF) via the A(2)Σ(+)-X(2)Π(i) transition, and H atoms were probed by the two-photon excited LIF technique. From the kinetic analysis of the time-resolved LIF intensities of OH(v) and H, we have found that the intramolecular vibrational relaxation is mainly governed by a single quantum change, HO(v)-CO → HO(v-1)-CO, followed by redissociation to OH(v-1) and CO. With the vibrational quantum number v, chemical process from the adduct to H + CO(2) is accelerated, and vibrational relaxation is decelerated. The countertrend is elucidated by the competition between chemical reaction and vibrational relaxation in the adduct HOCO.
The
change in the ozone production rate on reducing its precursors,
namely, ozone production sensitivity, is important information for
developing a strategy to reduce ozone. We expanded a conventional
sensitivity analysis theory by including peroxy radical loss by uptake
onto particle surfaces in the aim of examining their potential impact.
We also propose a new concept of absolute sensitivity that enables
us to evaluate the quantitative effectiveness of precursor reduction
toward mitigating ozone production over a given period and area. This
study applies the theory to observations in Tsukuba, a city in Japan.
The relative sensitivity analysis shows that ozone production was
more sensitive to volatile organic compounds (VOCs) in the morning
and evening, and it became more sensitive to NO
x
in the afternoon. NO depletion was a main trigger in this
sensitivity regime transition. The absolute sensitivity analysis indicates
that the VOC-sensitive period in the morning determines the total
ozone production sensitivity in a day. While particles did not have
significant impact on regime classification in Tsukuba, they have
a potential to decrease the mitigating effect of VOC reduction on
ozone production and to moderate the enhancement effect of NO
x
reduction depending upon uptake coefficients.
A further study will benefit from a combination with an observation-constrained
box model simulation or chemical transport modeling system, which
may provide sensitivity analysis over a large spatial and temporal
range.
Abstract. HO2 uptake kinetics onto ambient aerosols play pivotal roles in
tropospheric chemistry but are not fully understood. Field measurements of
aerosol chemical and physical properties should be linked to molecular-level kinetics; however, given that the HO2 reactivity of ambient aerosols is
low, traditional analytical techniques are unable to achieve this goal. We
developed an online approach to precisely investigate the lower-limit values of (i) the HO2 reactivities of ambient gases and aerosols and (ii) HO2 uptake coefficients onto ambient aerosols (γ) during the 2019 Air QUAlity Study (AQUAS) in Yokohama, Japan. We identified the effects of individual chemical components of ambient aerosols on γ. The results were verified in laboratory studies on individual chemical components: transition
metals play a key role in HO2 uptake processes, and chemical components indirectly influence such processes (i.e., by altering
aerosol surface properties or providing active sites), with smaller
particles tending to yield higher γ values than larger particles
owing to the limitation of gas-phase diffusion being smaller with micrometer particles and the distribution of depleting species such as transition metal
ions being mostly distributed in accumulation mode of aerosol. The modeling of γ utilized transition metal chemistry derived by previous studies,
further confirming our conclusion. However, owing to the high NO
concentrations in Yokohama, peroxy radical loss onto submicron aerosols has
a negligible impact on O3 production rate and sensitivity regime.
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