4 days into the traffic restrictions, today is even worse than yesterday, with an API of 113 for 24 July- this is equivalent to a PM10 value of about 175 micrograms/m3. Let’s go back to the World Health Organisation (WHO) Air Quality Guidelines of 2005 (AQG) to understand this number. For PM10 they suggest on page 10:
- annual mean: 20 micrograms/m3
- 24-hour mean: 50 micrograms/m3
The 24-hour average from 23 July noon to 24 July noon in Beijing was 175 micrograms/m3, that is 250% higher than the WHO guideline. The Chinese authorities are saying that level 2 (API up to 100 = PM10 of 150 micrograms/m3) is safe for athletic competition (’blue sky day’). The WHO guideline for short exposure is a PM10 of 50 micrograms/m3, which corresponds to an API of 50. We have only had 2 days like that in July until now: 6 and 15 July.
On page 13 of the WHO document it says what short exposure to an API of 100 does to you:
Therefore, a PM10 concentration of 150 μg/m3 would be expected to translate into roughly a 5% increase in daily mortality, an impact that would be of significant concern, and one for which immediate mitigation actions would be recommended.
The annual average API in Beijing is around 100 = PM10 of 150 micrograms/m3, which is 650% higher than the WHO guideline for long-term exposure. The WHO’s first ‘interim target’ for long-time exposure starts at 70 micrograms/m3 (API of 60) so no further comment on this.
Also check out this recent comment by Dr. George D. Thurston, Professor at the NYU School of Medicine:
…All in all, anything above Chinese API=50 is very unhealthy. Even if it is at API=50, that is still more than double New York City usual levels, so that is not acceptable either. They really need to get the API down to 25 or below to call the air acceptable for Olympic competition. It seems only strong (clean) winds from the North can provide lowered concentrations, and this just doesn’t happen often enough in Beijing.
The Beijing Environmental Protection Bureau is providing daily reports of SO2, PM10, NO2 levels on a special section of their website, even in English, screenshot below. It seems these numbers are already converted to the API scale, so that makes it quite confusing; actual values in micrograms/m3 are higher for the 3 pollutants, as described here.
Also interesting to see how the interpretations of the API levels has shifted a bit (upper left box on the above screenshot, compared to the same 2007 document):
1 = API 0-50 = excellent (old) => good (new)
2 = API 51-100 = good => moderate
3A = API 101-150 = slightly polluted => unhealthy for sensitive groups
3B = API 151-200 = light polluted => unhealthy
4A = API 201-250 = moderate polluted => very unhealthy
4B = API 251-300 = moderate-heavy polluted => hazardous
Especially the re-classification of ‘light polluted’ to ‘unhealthy’ is remarkable; the new classification is in fact very similar to the US-EPA.