Pollutant concentrations were within National Ambient Air Quality Class 2 standards for 75% of 2009, according to the latest Pearl River Delta regional air quality monitoring results.

The Environmental Protection Department and Guangdong's Department of Environmental Protection today announced the monitoring results of the Pearl River Delta Regional Air Quality Monitoring Network for 2009. The network measures concentrations of sulphur dioxide, nitrogen dioxide, ozone and respirable suspended particulates.

The concentration of most pollutants was lower from June to August, and higher from October to March, as the heavier rainfall, higher mixing layer, and the clean maritime airstream brought by the southern monsoon helped disperse pollutants during the summer.

Compared to 2008, the concentration of sulphur dioxide dropped by 26% last year, while that of nitrogen dioxide decreased by 7%. The reductions were attributable to implementation of enhanced emission-reduction measures by Hong Kong and Guangdong.

However, ozone concentration grew 10% due to stronger photochemical activities as a result stronger solar radiation and less rainfall through the year.

The report can be viewed here. Monitoring results for the first half of 2010 will be available in October.