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The ozone air quality standard is regularly surpassed in the Los Angeles air basin, and efforts to mitigate ozone production have targeted emissions of precursor volatile organic compounds (VOCs), especially from mobile sources. In order to assess how VOC concentrations, emissions, and chemistry have changed over the past decade, VOCs were measured in this study using a Vocus‐2R proton‐transfer reaction time‐of‐flight mass spectrometer in Pasadena, California, downwind of Los Angeles, in summer 2022. Relative to 2010, ambient concentrations of aromatic hydrocarbons have declined at a similar rate as carbon monoxide, suggesting reduced overall emissions from mobile sources. However, the ambient concentrations of oxygenated VOCs have remained similar or increased, suggesting a greater relative importance of oxidation products and other emission sources, such as volatile chemical products whose emissions are largely unregulated. Relative to 2010, the range of measured VOCs was expanded, including higher aromatics and additional volatile chemical products, allowing a better understanding of a wider range of emission sources. Emission ratios relative to carbon monoxide were estimated and compared with 2010 emission ratios. Average measured ozone concentrations were generally comparable between 2022 and 2010; however, at the same temperature, daytime ozone concentrations were lower in 2022 than 2010. Faster photochemistry was observed in 2022, with average hydroxyl radical exposure being ∼68% higher during midday (statistically significant at 95% confidence), although this difference reduces to ∼35% when comparing observations at ambient temperatures of 25–30°C only. Future trends in temperature are important in predicting ozone production. Plain Language Summary: Gas‐phase organic molecules are emitted from many sources including vegetation, cars, cooking, industries, and chemical products (paints, inks, pesticides, deodorant, shampoo, etc.), among others. These emissions oxidize in the atmosphere and contribute to the formation of particles and ozone, which are harmful to human health. To improve air quality, the behavior of these molecules in the atmosphere must be understood, and their sources must be identified, before effective emission reduction policies can be established. In summer 2022, we measured atmospheric concentrations of such molecules in Pasadena, California, downwind of Los Angeles, California, to investigate fresh, unreacted emissions as well as aged, oxidized emissions. Compared to similar measurements made in 2010, emissions from vehicle sources appear to have declined while chemical products have become relatively more important. Atmospheric oxidation of these emissions also appears to have increased relative to 2010, in part due to higher average temperatures and related meteorology. Despite reduced emissions from vehicles, unregulated emissions from chemical products and faster oxidation yielded similar concentrations of secondary products such as ozone. Future air quality improvements will likely require further emission reductions, particularly for chemical products, and such improvements may be offset by rising temperatures due to climate change. Key Points: Concentrations of aromatic hydrocarbons in Los Angeles have declined since 2010 while those of oxygenated volatile organic compounds (VOCs) are similar or higherMidday photochemistry was ∼68% faster in 2022 than 2010 possibly due to higher average temperatures and changes in the NOx‐VOC regimeOzone concentrations were similar between 2010 and 2022 due to the combination of changes in emissions, photochemistry, and meteorology [ABSTRACT FROM AUTHOR]