Air pollution reached its worst level this year with a reading of 130 at the Causeway Bay roadside station yesterday. Weather conditions were blamed for the 'very high' reading. A lack of wind and an increase in traffic had caused nitrogen dioxide to accumulate, said the Environmental Protection Department's acting principal environmental officer Yeung Mo-man. The previous highest reading this year was 118 at Causeway Bay on January 19. Elsewhere, pollution ranged from 44 in Eastern to 68 at Tap Mun. Yesterday was the 17th time air pollution has climbed above 100 since the start of the year. The area most frequently affected was Causeway Bay, followed by Central and Mongkok. Mr Yeung said the very still conditions on Thursday had led to a build-up of pollutants. However, increasing winds would disperse the particles today and lower readings were predicted, said Mr Yeung. The department is expecting air pollution to remain within the high range - 50 to 100 - at general monitoring stations and stay under 100 at roadsides today. When the index climbs above 100, elderly people and those with heart or lung diseases are advised to avoid heavy traffic areas and reduce outdoor, physical activity. Generally healthy people are also warned that they may 'notice some discomfort' at levels above 100. If exposed to levels from 50 to 100 over some time, health problems may result, according to the department. The department has faced repeated calls to act on the worsening air pollution. It is phasing in LPG taxis and has tightened emissions standards for other vehicles.