Decarbonized ammonia production through photocatalytic nitrogen fixation is appealing, as it may allow for farm-scale fertilizer production using earth-abundant feedstocks, energy, and catalysts. Yet, the viability of decentralized ammonia production systems is largely dependent on the cost of a complete photocatalytic system reaching a Haber–Bosch parity point. Here, we demonstrate that an air separation unit for a farm-scale low-cost photocatalytic ammonia synthesis system can account for 70% of the total system cost. This high cost depends on the type of air separation unit and the purity of nitrogen. This promotes the need for a catalyst, which can tolerate trace oxygen or can even operate under aerobic conditions to attain Haber–Bosch cost parity. We further demonstrate the change in catalytic activity of prototypical undoped and metal-doped titania photocatalysts under aerobic and anaerobic conditions. Among various metal-doped titania photocatalyst, vanadium- and ruthenium-doped titania demonstrated no performance decline under aerobic conditions.