The “canyon effect”, also known as urban canyon, is where tall, packed buildings surround a street in turn creating an artificial canyon effect. It is common in Hong Kong. Pollutants coming from various infrastructure and traffic emissions tend to stay within these canyons worsening air quality. Tall buildings are essentially making it difficult for pollutants to escape the air and makes natural ventilation around cities poorer. This creates a mini multiplier effect as air is not being recycled thoroughly in the region, worsening air quality.