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<p>HO<span class="inline-formula">₂</span> 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 HO<span class="inline-formula">₂</span> 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 HO<span class="inline-formula">₂</span> reactivities of ambient gases and aerosols and (ii) HO<span class="inline-formula">₂</span> uptake coefficients onto ambient aerosols (<span class="inline-formula"><i>γ</i></span>) during the 2019 Air QUAlity Study (AQUAS) in Yokohama, Japan. We identified the effects of individual chemical components of ambient aerosols on <span class="inline-formula"><i>γ</i></span>. The results were verified in laboratory studies on individual chemical components: transition metals play a key role in HO<span class="inline-formula">₂</span> 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 <span class="inline-formula"><i>γ</i></span> 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 <span class="inline-formula"><i>γ</i></span> 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 O<span class="inline-formula">₃</span> production rate and sensitivity regime.</p>