Wildfire emissions affect downwind air quality and human health. Predictions of these impacts using models are limited by uncertainties in emissions and chemical evolution of smoke plumes. Using high-time-resolution aircraft measurements, we illustrate spatial variations that can exist horizontally and vertically within a plume due to differences in the photochemical environment. Dilution-corrected mixing ratio gradients were observed for reactive compounds and their oxidation products, such as nitrous acid, catechol, and ozone, likely due to faster photochemistry in optically-thinner plume edges relative to darker plume cores. Mixing ratio gradients in midday plumes, driven by j_HONO gradients, are often steepest in the freshest transects, and become flatter with chemical aging. Gradients in plumes emitted close to sunset are characterized by titration of O₃ in the plume and little to no gradient formation. We show how gradients can lead to underestimated emission ratios for reactive compounds and overestimated emission ratios for oxidation products.