• Non-vertical air supply slightly reduces cabin temperature and pollutant concentration but significantly worsens thermal comfort and air quality.
• Draught rate and non-uniformity coefficient increase, with about 5% and 15% more measurement points violating micro-wind speed and temperature difference requirements.
• Longitudinal pollutant penetration increases by a factor of about 5, and pollutant 'locking regions' appear at the cabin ends.
• Changing the deflection pattern only shifts the deterioration region; it does not fundamentally improve the cabin air environment.