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<p>Tropospheric ozone (<span class="inline-formula">O₃</span>) formation depends on the relative abundance of precursor species, nitrogen oxides (<span class="inline-formula">NO_<i>x</i></span>), and volatile organic compounds (VOCs). Advancements in satellite retrievals of formaldehyde (HCHO) and nitrogen dioxide (<span class="inline-formula">NO₂</span>) vertical column densities (VCDs), and the corresponding <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">HCHO</mi><mo>/</mo><msub><mi mathvariant="normal">NO</mi><mn mathvariant="normal">2</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="61pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="2480322f9fcea5548ed140ee97ee4646"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-10363-2024-ie00001.svg" width="61pt" height="14pt" src="acp-24-10363-2024-ie00001.png"/></svg:svg></span></span> ratios (FNRs), provide the opportunity to diagnose the spatiotemporal evolution of <span class="inline-formula">O₃</span> production sensitivity regimes. This study investigates trends of Ozone Monitoring Instrument (OMI)-derived summertime VCD HCHO, <span class="inline-formula">NO₂</span>, and FNRs in the Northern Hemisphere from 2005 to 2021. FNR trends were analyzed for polluted regions, specifically for 46 highly populated cities, over the entire 17-year period and in 2020 when global anthropogenic emissions were reduced due to COVID-19 lockdown restrictions. It was determined that OMI-derived FNRs have increased on average by <span class="inline-formula">∼</span> 65 % across cities in the Northern Hemisphere. Increasing OMI-derived FNRs indicates a general transition from radical-limited to <span class="inline-formula">NO_<i>x</i></span>-limited regimes. The increasing trend is driven by reduced <span class="inline-formula">NO₂</span> concentrations because of emission-control strategies of <span class="inline-formula">NO_<i>x</i></span>. OMI FNR trends were compared to ground-based in situ measurements in US cities, and it was determined that they can capture the trends in increasing FNRs (<span class="inline-formula"><i>R</i>=0.91</span>) and decreasing <span class="inline-formula">NO₂</span> (<span class="inline-formula"><i>R</i>=0.98</span>) occurring at the surface. OMI FNRs in urban areas were higher (<span class="inline-formula">∼</span> 20 %) in 2020 for most cities studied here compared to 2019 and 2021. In addition to studying the longest period of OMI FNRs across the Northern Hemisphere to date, the capabilities and challenges of using satellite VCD FNRs to study surface-level <span class="inline-formula">O₃</span> production sensitivity regimes are discussed.</p>