Last updated: April 30, 2010
Source: South China Morning Post
Environment officials have been told not to rejoice over remarkable improvements in regional air quality last year, since roadside air pollution continues to worsen and remains at health-threatening levels.
Hong Kong and Guangdong yesterday jointly released monitoring results that showed sulphur dioxide and nitrogen dioxide levels fell 26 and 7 per cent respectively last year, some of the biggest reductions recorded in four years.
But roadside figures quietly published on the government website two days ago showed annual average concentrations of nitrogen dioxide at the roadside in Causeway Bay, Central and Mong Kok all rose by up to 13 per cent.
The figures, the worst in at least five years, show concentrations of the key pollutant exceeded 100 micrograms per cubic metre of air – more than double the World Health Organisation guideline of 40.
The Clean Air Network, an independent group that encourages public comment about air pollution, said officials would be “grossly disingenuous and misleading” if they were to call the regional improvement a victory, as many people were still being exposed to excessive local pollution.
“Roadside pollutant concentrations are critical when assessing harm to human health,” network chief executive Joanne Ooi said. “What matters is the level of pollution to which people are actually exposed to at street level.” She noted that all the regional monitoring stations were well above that level.
Environment officials pledged to continue tackling roadside air pollution from vehicles.
The encouraging regional readings come from a network of 16 air quality monitoring stations in various cities in the Pearl River Delta including Hong Kong. They measure four key air pollutants. The results have been published since late 2005.
The report says the number of days with better air quality rose to 75 per cent last year, compared to 68 per cent in 2006 – in line with local improvement in ambient air quality last year.
Environment officials dismissed suggestions that the good result was attributatble to a drop in industrial production caused by the 2008 credit crunch. They said power consumption in Guangdong rose only modestly last year despite strong economic growth in the province.
They put the improvements down to emission control programmes in Guangdong, such as power plant desulphurisation, and to the use of cleaner vehicle fuel. These, they said, had led to cumulative reductions in the sulphur dioxide level of 38 per cent and of 9 per cent in nitrogen dioxide.
Both pollutants mainly come from combustion in power generation, industrial boilers and the millions of vehicles in the region.
There was similar progress on respirable suspended particles, with the concentration falling 7 per cent since 2006 and remaining roughly the same last year as in 2008. The officials admit, however, that regional ozone pollution has shot up, rising 10 per cent over 2008 and 17 per cent over 2006 – reflecting a similar deterioration in Hong Kong.
Ozone is a secondary pollutant formed through chemical reaction mainly between two pollutants – nitrogen dioxide and volatile organic compounds, such as solvents used in industrial production – under strong sunlight.
The officials blamed stronger solar radiation last year. “There has been fluctuation of the radiation level over the years, and we need more time to observe that,” one said. The official said increased cloud cover earlier this year had led to a decrease of 20 per cent in solar radiation, and the ozone concentration had fallen by roughly the same extent.
Officials also warned that there were signs that ambient ozone pollution had influenced the formation of nitrogen dioxide at the roadside.
They said ozone could react with nitrogen oxides emitted from vehicles and turn the latter into nitrogen dioxide – which has been found to have increased by up to 16 per cent between 2005 and 2009 at the three roadside monitoring stations.
Professor Alexis Lau Kai-hon, an atmospheric scientist from the Hong Kong University of Science and Technology, said while officials’ theory on ozone and nitrogen dioxide was correct, it did not suggest vehicle emissions should not be blamed.
He said it would take a long time to address the complicated ozone pollution and no matter how much the ozone could be suppressed, the presence of nitrogen oxide emissions from vehicles would still contribute to more roadside pollution.
“After all, vehicle emissions remain excessive and dirty enough to threaten our health. There is no excuse not to clean them up,” Lau said.
Lau said the government should take roadside air pollution seriously and implement more transport management measures on top of controlling exhaust emissions.
Professor Wang Tao, a scientist specialising in air pollution research at the Polytechnic University, said ozone pollution was a worldwide issue and the most difficult to deal with. He said his research suggested that volatile organic compounds, such as solvents found in paints and protective coatings, were the main driver of ozone pollution.
“Unlike controlling sulphur dioxide and particulate matter, for which one can target a relatively smaller number of power plants, the volatile organic compounds are being emitted from thousands of factories in the region, many of which are small and medium-sized,” he said.
Wang said improvement in regional air quality did not guarantee better roadside air, and it was advisable for the government to tackle vehicle pollution at the same time.
Ooi of the Clean Air Network said roadside pollution had a greater direct health impact than regional pollution. “The lowest pollution monitor included in the sampling network was five metres above the ground, far above pedestrian height, with all other monitoring stations at nine metres or higher,” she said.
She also noted that while levels of roadside respirable suspended particles fell last year, concentrations were still several times higher than WHO guidelines.
Read the full reports on Hong Kong and Pearl River Delta air pollution.
http://www.epd-asg.gov.hk/english/report/files/AAQS09e.pdf
http://www.gdepb.gov.cn/gsgg/200710/P020100429536280667936.pdf
Written by Cheung Chi-fai