| Particles and indexes comparison... |
| Thursday, 29 March 2007, Written by Julien | |
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The pollution comparator sometimes shows that "Good" air in Beijing is considered as "Very bad" by Paris criteria. It can be quite puzzling, and it is important to understand why. I'll try to explain this complex issue clearly, answering simple questions. Tell me if you want more details. 1/ What is the main pollutant that explains the differences? Particles. 2/ Is it possible to compare directly particles concentration in Paris and Beijing? Yes, mostly comparable. 3/ Does different values of particles concentration have different impact on health? Yes. Particles concentrations are directly comparable, and so is the impact on health. Chinese authorities and Paris authorities might have different views of what is acceptable for the population. What Paris considers as very bad, Beijing considers it as good! Click on [more] for details... 1/ Is the difference in index values the same for all pollutants? NO. SO2 and NO2 levels are roughly comparable in China and France, but the index values for particles are completely different. The highest particle index in Paris is 125µg/m3 while it is 600µg/m3 in China. There is thus a 4 fold difference. 2.1/ Are the indicators measuring the same thing? YES. Particles measured in Paris and Beijing are PM10, which mean particles having 10µm diameter or less. It is considered to be the particles that actually enter in our lungs. In addition, half of the measure equipments in Beijing come from France, and are the same as the one used in Paris. 2.2/ Are all PM10 the same? NO. Within PM10, it is considered that the most harmful particles are the smaller one, the particles having 2.5µm or less. They are called PM2.5 . 2.3/ Is the PM10/PM2.5 ratio the same in Beijing and Paris? YES. the PM10 indicators can be directly compared. The ratio is around 60% in Paris and Beijing (among all particles PM10, 60% are PM2.5) 2.4/ Why the data are only "Mostly" comparable? Because it depends on many factors that can affect slightly the measures. For example, measurement depends on the distance to roads and industries. A complete comparison would require to go deep in the measurement process. 3.1/ Is there proven evidences that those PM10 have an impact on health? YES. The range of health effects is broad, being predominantly to the respiratory and cardiovascular systems. All population is affected, susceptibility to the pollution may vary with health or age. 3.2/ Is there a level of PM10 that can set a limit for what is "Good" and what is "Bad" for health? NO and YES. Scientific studies show that PM10 have an impact on health, but the impact is progressive and no limit can be identified clearly. However, WHO published in 2005 guidelines for particles. The guideline are: 20µg/m3 on annual-mean and 50µg/m3 on 24h-mean. This level is the lowest value for which an impact on health has been shown. 3.3/ Can we evaluate the impact of particles level on mortality? YES. WHO states that for a PM10 level of 70µg/m3, the long-term mortality is 15% higher than at the guideline level. For reference, the target in Beijing is 150µg/m3. Extra: Is Paris compliant with the guidelines regarding particles? Partly. On main traffic axes, the limits are often exceeded, but on average, the particles are below WHO guidelines. Sources:
Comments
Adrien wrote :
Well that sounds frightening... what can we do against PM10?
hawei wrote :
Great! Thanks Julien.
Here in Shanghai, we try to: - check each day the SEPB API indexes - illustrate the comparizon with the ATMO sub-indexes (I am French & always very concerned with the quality of environment) - alarm the school to avoid outside physical exercices... sure good for the health but not into bad air conditions! But pity to say, we have no much support untill these days... We also asked for more with SEPB concerning O3 et PM2.5 Tuesday 20, May 2008
Hawei wrote :
If we refer to the index ATMO (the one in airparif) the sub-index in PM10 at 65-85 (SEPB in Shanghai gives these values on June 05) means ATMO at 7 or 8 not at 9 so it means poor or bad... not very bad!
Julien wrote :
Re Hawei
Thank you for your comment. It is unfortunately not straightforward to compare indexes, that's why I created this tool.
On June 5th, Shanghai index (API) is 90. Using the calculation method provided by SEPA, we know that the PM10 concentration is 130µg/m³. This is above the highest level of ATMO (Paris) which is at 125µg/m³.
hawei wrote :
Could you give me the calculation method of SEPA or where I can find it.
My background is mathematics. Thanks in advance
hawei wrote :
and more about...
Don't send me... I found it!
Calculations & formulation are easy... and you are right to say that the pollution is higher than it looks like! Next step: try to know more about the reliability and the localisation of the stations in charge of the measures... cos whatever the physics experiment, if the basics are not sure the results could be non relevant... |
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