AIR pollution yesterday climbed to its highest levels since the publication of a daily index began three months ago, with distant Tropical Storm Janis held to blame. Readings ranged from 66 to 76, with the highest levels being recorded in industrial areas. The previous highest readings were in the mid-60s when Tropical Storm Helen was approaching. Pollution levels were classified as 'moderate' yesterday by the Environmental Protection Department. 'It is still within what we consider acceptable for short-term exposure,' senior environmental protection officer Pang Sik-wing said. Only when the reading hits 100 does the department advise people with heart or respiratory-related illnesses to reduce exertion and outdoor activities. Pollution levels rise when a tropical storm is over the South China Sea because warm air, sucked up in the middle of the storm, is forced down over the territory. This stops the air currents that usually blow away Hong Kong's pollution. The high readings were mainly due to the higher level of particles in the air. The particles, linked to lung cancer, are caused largely by vehicle emissions and construction sites. Tomorrow should see air quality improve to 'good to moderate'.