This week’s unprecedented Hong Kong air pollution: explanation & consequences
How bad is it out there?
The current levels are the highest ever recorded since the EPD began monitoring air quality in 1995. Particulate matter (PM) today has been around 700 micrograms per cubic meter, 14x the levels recommended under the WHO Air Quality Guidelines (AQGs). Even by the HK Government’s very lax, outdated Air Quality Objectives (AQOs), the current levels of PM are 4 times greater than the AQO for PM10. Finally, we would like to point out that, as of 7 pm, all the EPD monitoring stations showed readings of API 500, meaning they were probably maxed out and not calibrated to take readings above 500. (N.B. the API is an averaged index of pollutants which is NOT correlated to micrograms per cubic meter, so do not try to compare the API with the AQOs or AQGs.) Schools and other institutions canceled outdoor activity today because of the dangerous levels of pollution. This Businessweek article provides a good overview. http://www.businessweek.com/news/2010-03-22/hong-kong-pollution-hits-record-levels-above-300-update2-.html
Explanation from HKUST’s Alexis Lau of the sources of this week’s unprecedented pollution
The following is a direct copy and paste from Alexis’ email to us of this morning: “Up to about 4pm yesterday, the pollution was dominated by NO2 and was locally generated. I was asked by two newspapers yesterday whether the pollution was sandstorm related and I said, no, because the dominating pollutant was NO2. However, the sandstorm came over Hong Kong at about 5pm with strengthing easterlies and we are now seeing the worst air pollution I’ve seen in Hong Kong.”
The sandstorm is an aberration, but our daily levels of extremely high roadside pollution are not
Note that, at 7 am, we noted that, while the Central ambient general API was “only” 70, the roadside API was already at 200+, meaning that roadside pollution is still the determining factor in creating levels of pollution hazardous to human health.
What are the health impacts of such high levels of air pollution?“The last few days will predictably have had a major impact on local health; many of those who have not so far become sick will have sustained significant injury and now have to contend with a new intense insult to cardiopulmonary systems. Unfortunately there is very little one can do for health protection apart from (i) avoidance of lifestyle risks such as tobacco smoke and low antioxidant diet; (ii) avoidance of increased exposure through vigorous exercise; (iii) indoors may be marginally safer and certainly roadside exposures potentially lethal for some,” wrote Professor Anthony Hedley of Hong Kong University this morning.
On the “bright” side, Professor Wong Tze Wai of Chinese University of Hong Kong pointed out that the coarse size and crustal source of the particles may make them less harmful than respirable particles from man-made sources. “We must make a distinction between particulates from vehicular, industrial and power plant sources and crustal PM, which is largely composed of silica. Whereas crystalline silica is a well-known cause of important lung diseases – silicosis, the impact of desert sandstorms as a health threat has been reported much less often. Toxicologically, there is a great difference between PM that contains a carbon core coated with nasty PAHs (polycyclic aromatic hydrocarbons) and toxic heavy metals (PM2.5 generated from local vehicular sources) and PM generated from crustal sources (from the Gobi Desert for example).” Now, of course, this hardly means that these particles are harmless: “Apart from possible cardiorespiratory effects, eye and skin disease are triggered by coarser particles. Another factor of concern is that we have had several intense exposures to PM10, NO2, SO2 and ozone in the days leading up to the sandstorm. The induction of inflammation by these pollutants may make many individuals more susceptible to this new insult. Better knowledge about the chemistry of the “sandstorm” material would help us interpret its significance.”
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The particulate matter monitoring instrument of the Central/Western general station was broken during Sunday night and Monday morning, therefore the reading of API 70 did not reflect the actual situation. The Kwai Chung and Sham Shui Po general station also had the same problem at the onset of the sand storm.