Simulating PM2.5 Air Quality when only PM10 is available: case study for South Korea

Share: aqicn.org/sensor/hongkong/midlevels/vn/
Experiment published on Thursday, July 31st, 2014
[updated on Saturday, January 11th, 2020]

When it comes to measuring Air Quality, the golden standard nowdays is to measure PM2.5, also known as small respirable particle matter. That was however not the case few years ago, when the golden standard was still about measuring PM10, also known as standard particle matter, as well as other Volatile Oganic Compounds (aka VOC, which includes Ozone, NO2, SO2 and CO).



PM2.5 forecast from www.tenki.jp
The reason for upgrading from PM10 to PM2.5, explained by Dr Sarath Guttikunda in this explantion about PM10 vs PM2.5 is that there are now new studies presenting evidence that PM2.5 is more harmful than PM10. As Dr Dr Sarath Guttikunda sates in the article, “physically, this makes sense since smaller than particle have a higher probability to go deeper into the lungs and harm people”.

Many countries, like China have done tremendous efforts in modernizing their monitoring equipement to the PM2.5 standard. Howerver, there are still quite a lot of countries not yet providing PM2.5 data, but only PM10. And among those countries with only PM10 data, the most surprising one in South Korea (with the exception of Seoul).

It is surprising since the Air Quality in South Korea is very similar to it's neighboors countries, namely Japan and China - where PM2.5 AQI is quite often peaking above 200, while PM10 AQI is acceptable and below 100. From the picture on the right (taken from tenki.jp), which represent the PM2.5 data flux, there is no doubt that South Korea is suffering from the same PM2.5 high densities as China and Japan.
Note: This article was written in 2014. Since then, all stations in South Korea provide PM2.5 data.

Correlating PM2.5 and PM10

So, the question that we would like to answer is: Can we deduct the PM2.5 AQI when only PM10 data readings are avaialble? The answer is yes, and the main reason is that there is a very strong correlation between the PM10 and PM2.5 mass concentration. The South Korea governement has recently released, for few stations, both PM10 and PM2.5 hourly concentration data, and this will be the basis for this experiment. The graph below shows the last 30 days concentration for the station 경기 탄벌동 (gyeong-gi tanbeoldong) for both PM10 and PM2.5:


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Note that the ordinate axis scale is different for PM10 and PM2.5, so although the graphs overlap, the values are actually different. From the correlation graph, there is just no doubt that there is a very strong linear correlation for the PM10 and PM2.5 concentration. The pearsons cooeficient for the last 30 days is . The resulting linear regression is defined with this formula:


Also, it is worth noticing that there are three periods where PM10 is significantly devaiting from PM2.5, two between October 27th and November 3rd, and one arround November 18th. This usually occurs during sand storms.

Deducting PM2.5 from PM10

So, all we need to convert the PM10 AQI into the PM2.5 AQI, is to stretch the mass scale from PM10 to PM2.5 to determince the corresponding PM2.5 mass value from the PM10 reading, and finally use the PM2.5 AQI scale to deduct the final AQI.

The graph on the right shows the mass to AQI convertion formula. The absissa (x axis) is the mass (in milligrams) and the ordinate (y axis) is the AQI. The two graphs correspond to the PM10 and PM2.5 deducted from PM10 readings. Note that it empirically confirms the hypothesis that PM2.5 AQI is always higher than PM10 when the PM10 mass is not too hight (in this case, lower than 480 milligrams).

PM2.5 deducted map

From the two maps below, the one titled "Interpolated PM2.5 AQI" is using the above formula to show what the "actual" Air Quality could be, if PM2.5 stations would be used. The result is indeed quite scarying, but on the other hand, that's not a surprise: The PM2.5 AQI is much more strict than the PM10 AQI, as explained in the begiging of this article (see explantion about PM10 vs PM2.5).

Actual PM10 AQI
Interpolated PM2.5 AQI
Actual PM2.5 AQI


Important notes

Before concluding, there are few very important points to mention:
  • First, this convertion only applies to the PM10 readings, and in summer, the Ozone tends to be very often the major pollutant. So, if you do the convertion yourself, please, make sure that you are converting the PM10 AQI and not the overall AQI, which is defined as the maximum of all individual AQIs.

  • Second, this is an experiment, and despite having a very good coorelation cooeficient (pearsons factor is 0.96) between PM10 and PM2.5, there are some days where PM10 is much higher than PM2.5 (for instance, check this experiment about PM10 vs PM2.5). Those days, the convertion formula should not be used.

  • Last, the linear regression equation is very specific to the place where you measure the data. This is also known as the "dust type" property, which says that the "typical" dust in South Korea is different from the one in US or Malaysia. This means that this formula should be updated if used outside of South Korea. Duing this summer, we will start a new reasearch where will will study the PM10 / PM2.5 correlation factors accros different countries.

Conclusion

As a conclusion, provided you take all the precautions related to the 3 remarks above, you could use the following convertion table to calculate the actual AQI:
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Note that the data provided is this article follows the Korea Open Government License (kogl.or.kr)


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大気汚染指数の測定方法:

大気汚染レベルについて

指数大気質指数の分類(米国)健康影響 / カテゴリ粒子状物質(PM10,PM2.5)
0 - 50良い - Good通常の活動が可能なし
51 -100並 - Moderate特に敏感な者は、長時間又は激しい屋外活動の減少を検討非常に敏感な人は、長時間または激しい活動を減らすよう検討する必要がある。
101-150敏感なグループにとっては健康に良くない - Unhealthy for Sensitive Groups心臓・肺疾患患者、高齢者及び子供は、長時間又は激しい屋外活動を減少心疾患や肺疾患を持つ人、高齢者、子供は、長時間または激しい活動を減らす必要がある。
151-200健康に良くない - Unhealthy上記の者は、長時間又は激しい屋外活動を中止
すべての者は、長時間又は激しい屋外活動を減少
心疾患や肺疾患を持つ人、高齢者、子供は、長時間または激しい活動を中止する必要がある。それ以外の人でも、長時間または激しい活動を減らす必要がある。
201-300極めて健康に良くない - Very Unhealthy上記の者は、すべての屋外活動を中止
すべての者は、長時間又は激しい屋外活動を中止
心疾患や肺疾患を持つ人、高齢者、子供は、全ての屋外活動を中止する必要がある。それ以外の人でも、長時間または激しい活動を中止する必要がある。
300+危険 - Hazardous上記の者は、屋内に留まり、体力消耗を避ける
すべての者は、屋外活動を中止
全ての人が屋外活動を中止する必要がある。特に、心疾患や肺疾患を持つ人、高齢者、子供は、屋内に留まって激しい活動を避け静かに過ごす必要がある。
(Reference: see wikipedia,and cn.emb-japan.go.jp/)

大気汚染についての更なる詳細をお知りになりたい方は、WikipediaAirNowを参照してください。

北京在住の医師Richard Saint Cyr氏による大変役に立つ健康上のアドバイスは、 www.myhealthbeijing.com をご覧ください。


使用上の注意: すべての大気質データは公開時点では妥当性が担保されていないため、これらのデータは予告なしに修正することがあります。 世界大気質指数プロジェクトは、この情報の内容を編集に最善の注意を尽くしておりますが、いかなる状況においても World Air Quality Index プロジェクトチームまたはそのエージェントは、このデータの供給によって直接的または間接的に生じる損失や損害について責任を負いません。



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