Ventilation Challenges in Costa Rican Urban Public Transport: Implications for Health and Sustainable Mobility

Public transport is essential for achieving net-zero emissions and sustainable urban growth. Yet, the health implications of indoor air quality (IAQ) in these vehicles are often overlooked, especially as passengers may spend hours in these enclosed spaces each day. We assessed IAQ in air-conditioned buses and trains in the metropolitan region of San Jose, Costa Rica. The tropical climate of San Jose means that high temperatures and humidity drive energy-intensive cooling on buses and trains, which rely on fossil fuels. To conserve energy, vehicle windows remain sealed, and air is mostly recirculated, undermining ventilation requirements. Our measurements revealed CO₂ concentrations reaching up to 5000 ppm during a 45 min bus ride. This far exceeds recommended thresholds and highlights significant ventilation deficits. These elevated CO₂ levels are indicative of potential health risks, particularly during prolonged travel. Our findings emphasize the urgent need to redesign air circulation strategies in urban public transport, especially in air-conditioned vehicles, to safeguard public health without undermining sustainability goals. Future research should focus on innovative ventilation solutions that reconcile energy efficiency with occupant well-being, supporting the transition to truly sustainable, net-zero urban mobility.