Urban ozone (O3) formation can be limited by NOx, VOCs, or both, complicating the design of effective O3 abatement plans. A satellite-retrieved ratio of formaldehyde to NO2 (HCHO/NO2), developed from theory and modeling, has previously been used to indicate O3 formation chemistry. Here, we connect this space-based indicator to spatiotemporal variations in O3 recorded by on-the-ground monitors over major U.S. cities. High-O3 events vary nonlinearly with OMI HCHO and NO2, and the transition from VOC-limited to NOx-limited O3 formation regimes occurs at higher HCHO/NO2 value (3 to 4) than previously determined from models, with slight intercity variations. To extend satellite records back to 1996, we develop an approach to harmonize observations from GOME and SCIAMACHY that accounts for differences in spatial resolution and overpass time. Two-decade (1996-2016) multisatellite HCHO/NO2 captures the timing and location of the transition from VOC-limited to NOx-limited O3 production regimes in major U.S. cities, which aligns with the observed long-term changes in urban-rural gradient of O3 and the reversal of O3 weekend effect. Our findings suggest promise for applying space-based HCHO/NO2 to interpret local O3 chemistry, particularly with the new-generation satellite instruments that offer finer spatial and temporal resolution. This dataset is not publicly accessible because: The data are publicly available on government-supported servers and are terabytes in size. It can be accessed through the following means: Please refer to the linked publication, visit archives described in the text or contact the corresponding authors for more information. Format: Data are processed as described in the linked publication - 10.1021/acs.est.9b07785 .

Data included in the analysis are from the European Quality Assurance for Essential Climate Variables project (QA4ECV; http://www.qa4ecv.eu/ecvs), and EPA/AQS and are publicly available at the time of publication.

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This dataset is associated with the following publication: Jin, X., A. Fiore, K.F. Boersma, I. De Smedt, and L. Valin. Inferring changes in summertime surface ozone-NOx-VOC chemistry over U.S. urban areas from two decades of satellite and ground-based observations. International Journal of Environmental Science and Technology. Springer, Heidelburg, GERMANY, 54(11): 6518-6529, (2020).