Air quality in Guangdong has worsened despite the efforts of the province's leaders and the Hong Kong government to cut pollution in the Pearl River Delta.
The province's latest environmental report shows the daily average concentration of sulfur dioxide reached 0.03 milligrams per cubic metre in Guangdong last year, up 11 per cent from a year earlier.
In Shenzhen, the level shot up 42 per cent year on year; in Maoming it rose 47 per cent and in Zhaoqing 31 per cent.
The province-wide concentrations of nitrogen dioxide and respirable suspended particulates also rose slightly.
Overall emissions of sulfur dioxide fell 2.1 per cent, the first such drop in at least a decade.
The Guangdong Environmental Protection Bureau admits in the report that 'the air quality in some urban regions has declined a bit compared with the year before', while saying it was 'still good in general'.
Green groups said the figures showed the province would have difficulty achieving its targets, agreed with Hong Kong, to slash levels of the four key pollutants by 2010. But scientists said Guangdong's air quality was still acceptable.