Two-thirds of the regional air quality index recorded by the Pearl River Delta Regional Air Quality Monitoring Network last year was in Grade I or II, meaning pollutant concentrations were within Class 2 National Ambient Air Quality Standards, the Environmental Protection Department says.

Intermittent high levels of pollutants exceeding Class 2 National Ambient Air Quality Standards (applicable to general residential areas) were recorded in all monitoring locations, mainly triggered by meteorological conditions hindering pollutant dispersion.

The department and Guangdong Environmental Protection Bureau today issued the 2007 report on the network's monitoring results. The network measures the concentration of four major pollutants - sulphur dioxide, nitrogen dioxide, ozone and respirable suspended particulates.

Coastal air better

Air quality was generally better in the coastal areas than in the central and northern region of the Pearl River Delta last year, which could be attributed to the relatively more favourable conditions for dispersion of pollutants.

The overall concentration of most pollutants was generally higher in winter. Apart from heavier rainfall and a higher mixing layer, the relatively clean maritime air stream prevailed in the region under the influence of southern monsoon accounting for a lower level of pollution in summer.

As the monthly variations in concentration of pollutants can change from year to year, long-term monitoring is required before a general pattern can be established.

Smooth operation

Overall the network operated smoothly during the reporting period, the department said. It comprises 16 monitoring stations, with 13 in Guangdong (Guangzhou, Shenzhen, Zhuhai, Foshan, Zhongshan, Huizhou, Dongguan, Jiangmen, Zhaoqing, Shunde, Huiyang, Panyu and Conghua) and three in Hong Kong (Tsuen Wan, Tung Chung and Tap Mun).

Changes in regional air quality will be monitored and results for the first half of this year issued in October.