APEC blue in China: air pollution data are censored after controversy on PM2.5 data released from US-Embassy in Beijing

The air pollution in Beijing and surrounding areas were supposed to be reduced by one third before the November 2014 APEC meeting, through a series of air pollution control measures.

"China will take action at the highest level to ensure air quality during the APEC meeting," said the vice president of the Chinese Academy of Environmental Sciences."It is expected that the discharge of pollutants in the Beijing-Tianjin-Hebei region will be reduced from 30 to 40 percent, and air quality will hopefully be further improved," he had said.

To prepare this APEC meeting scheduled from 8 to 10 Nov. 2014, Beijing had closed since June 2014  some of its plants, eliminated the old vehicles, used clean energy, and closed more than 300 polluting factories to reduce emissions.The use of car based on an even or odd number depending of the day was also planned to reduced by almost half the number of cars in the meeting.

Vice Premier Zhang Gaoli stated that the guarantee of the quality of the air for the APEC meeting was the "top priority".

Nevertheless the above picture is showing vehicles driving on Beijing's Fourth Ring Road amid heavy smog, on Oct 24, 2014 [Photo/Agencies]. 

The AQI issued on a daily basis by the various AQI data providers on the internet,  including MEP and US Embassy in the run up of APEC meeting were showing that the pollution was not controled and also extremely high. 

Government efforts to control smog ahead of the Nov. 5-11 Asia-Pacific Economic Cooperation events in Beijing had gained so much attention that the clearer skies programme got a nickname, “APEC blue”. 

China government after failing to clean the skies before APEC meeting tried to put the blame on the smog data providers and especially the US Embassy and decided to block all MEP AQI and Air pollution data publications. 

Why censoring the monthly publications of air quality and pollution data of the 190 major Chinese cities released from Jan. 2014?

As a consequence the monthly publications of air quality and pollution data of the 190 major Chinese cities (AQI derived from the concentration of the various pollutants: PM2.5, PM10 etc..) are censored by the China’s Ministry of Environment Pollution (MEP) since November 2014.

No air quality data was provided concerning the last two months of 2014, which will prohibit - if the MEP deadlock is maintained- to assess urban air quality for the 190 cities throughout 2014.

This interruption is very damaging to the complete information of the population on the quality of the air, in order to prevent the risks and prepare the provisions to be taken.

 What was really the situation of Beijing Air Pollution using the available data from MEP and US Embassy?

The air quality index (AQI) and associated pollutants concentration were obtained from the monthly average of the 190 main cities released progressively by MEP since 2013. No detailed data is provided concerning hourly and daily air pollutant apart from the number of days where AQI is above 100 or 50. As the PM2.5 is most of the time the main pollutant AQI is in clause relation with the PM2.5 level with AQI=135 when PM2.5=100 for instance (see my blog dated 11 Dec. 2013).

The air pollution data from US Embassy are obtained from the US Stateair feed . 

They include the hourly PM2.5 only on 5 cities Beijing, Shanghai, Guangzhou, Chengdu and Shenyang.  These cities are among the biggest in PRC with Shanghai N°1 (22Mil), Beijing N°2 (19Mil), Guangzhou N°4 (11Mil), Chengdu N°8 (7Mil) and Shenyang N°14 (6Mil).  These cities are being reported by MEP since Nov. 2013 and we have a 12 months past information comparable to the US Embassy data.  

The following figure 1 is showing monthly PM2.5 concentration in Beijing as issued by MEP or US Embassy on the latest 12 months period available ( Nov. 2013 to Oct. 2014) plus an estimation of Nov. 2013 based on US Embassy.

The missing Nov 2014 PM2.5 of Beijing average is estimated from Nov. 2014 PM2.5 at US_Embassy by applying Nov 2013 correlation number (1.26) between both Nov 2013 concentrations.

Beijing monthly average increased by 19% compared to the value in November 2013. However, this situation is a major effort of the municipality to reduce pollution for the duration of the APEC meeting and this results necessarily more pollution than when the situation is normal!

Figure 1: Monthly PM2.5 concentration in Beijing as issued by MEP or US Embassy on Nov. 2013 to Oct. 2014 plus an estimation of Nov. 2013 based on US Embassy

Altogether, both data are extremely comparable because the US Embassy is a specific location in Beijing while the MEP monthly is averaged on the entire Beijing Municipality area which is around 17000km2 with a great variety of density between urban districts (30000 people/km2) - where is located the US Embassy- and suburbs  4000people/km2.

On the other hand the MEP does not provide information on hourly detailed pollution in specific sites where pollutants are measured. And the method used to determine the average value for the entire city is unknown: is-it an arithmetic mean or is it weighted by the density of the urban population?

What is the relationship between hourly, daily and monthly PM2.5 in Beijing?

The figure 2 below compares for PM2.5 concentration daily data issued by US Embassy with monthly MEP data. We see arge number of high daily values even for the month of November 2014 with 2 days with PM2.5 daily value >300µg/m3.

Figure 2:  Comparison of PM2.5 measurements daily  (US Embassy) or monthly values (MEP)

During the measuring period of 13 months or 395 days, there were all together 121 days or 31% of the total days where PM2.5 > 115µg/m3, which is about AQI> 150. We find comparable figures concerning MEP considering it is over a period of 12 months. However, we see that MEP needs  to specify the values of PM2.5 that are greater than 100, because there are lots of very high values

China's Provinces air pollution ranking from Jan to Jun 2014: Hebei, Hubei, Henan, Beijing, Shaanxi, Tianjin, Xinjiang & Shandong had more than 50-72% of exceedance days

Bubble pie map of provinces and municipalities over the first six months of 2014 

The 8 following regions and municipalities (see Figures 2 & 3) have had the highest population-weighted average urban air pollution (1^st quintile): Hebei, Hubei, Henan, Beijing, Shaanxi, Tianjin, Xinjiang & Shandong. They concern a population of 139 Mil. 

These regions and municipalities have had 90-149 exceedance days (50-72% of total 181 days) above the threshold of 100 (AQI) and 75 µg/m3 (PM2.5).

The best regions and municipalities (5th quintile) were Hainan, Yunnan, Fujian, Tibet and Guangdong with only 4-18% exceedance days. 

Figure 1 :  Air pollution provinces & municipalities urban air pollution ranking over the first 6 months of 2014 (Jan. to Jun. 2014: 181 days)

The 8 most polluted regions or municipalities are: Hebei (13Mil pop); Hubei (12 mil); Henan (12 Mil), Beijing (19 Mil); Shaanxi (17 Mil); Tianjin (11 Mil); Xinjiang (4 Mil)  & Shandong (50 Mil). AQI is around 120-160 and there are more than 55% of days with AQI>100 (90 on 181  days).

As explained in my post dated 22 Sep 2013, AQI is a random variable with a log normal distribution and the repartition of daily AQI above 50 or 100 AQI is more or less correlated with the average AQI value. 

The correlation is good for days with daily AQI>100,  less good for days with AQI>50 and more loose for days with 50< daily AQI <100.

Figure 2 : Correlation between average AQI and daily AQI repartition

Air pollution in China from Jan to Jun 2014 far exceeds all limits put forward by UE or US standards : out of the 190 major cities, the highest 38 air pollution ranked cities have a population of 113 Mil with 125 exceedance days (70% of days), above 100 AQI or 75µg/m3 (PM2.5)

Bubble pie map of cumulated number of daily AQI repartition over the first six month of 2014 (Jan. to Jun. 181 days)

During Q2-2014, there had been only a slight improvement of urban air pollution over Q1, but we still have AQI>100 over 31% of days (29 days over 81 days) for the 190 monitored cities by China’s Ministry of Environmental Protection (see June 2014 MEP Chinese city air quality ranking).

After the first 6 months of 2014: the first 38 air pollution ranked cities out of 190 main Chinese cities (1^st quintile) could be considered as the “core urban polluted area” comprising around forty cities - among them Jinan, Wuhan, Xi'an, Beijing, Chengdu. This core urban area population of 113 Mil, after 6 months, have had in average 125 cumulated exceedance days (70% of total 181 days), above 100 AQI or 75µg/m3 (PM2.5).

This is far exceeding the health exceedance limits put forward by EU and US air pollution standards where the maximum exceedance days permitted is around 35 days in one year!  

It means that the concerned population had been exposed to a harmful air pollution level 7 times more important than the level permitted by health regulations.   

Air pollution health standards 

Following our last post dated 21 July 2014, it is necessary to look more thoroughly at Chinese cities’ daily AQI inside the first six month period. This information– numbers of days with daily AQI>50 or AQI>100 - are provided each month by China’s Ministry of Environmental Protection (see June 2014 MEP Chinese city air quality ranking), along with the monthly average of the main pollutants and the resulting AQI

.

Concerning human health issues we know that what really counts is not the average AQI over defined monthly, quarterly or 6 months periods - qualified as moderately polluted (50<AQI<100) or unhealthy for sensitive groups  (100<AQI<150)- but the number of cumulated days where daily AQI has been above a defined dangerous limit. The longer the cumulated effect the more dangerous it is.

There is a cumulative effect especially for fine particulate matter: after some days of exposure above this limit a high number of tiny particulate are entering the lung’s cells. In the coal mining industry the dust contained in the inhaled breath is transforming progressively the lungs in stone after days and years of continuous silicate inhaling (silicosis).

Even if AQI level is classified as lightly polluted following China's standards (or “Unhealthy for sensitive group” as denominated by US standards): maintaining this risk level for a lengthly period could be extremely harmful to health. This is the notion of exceedance days permitted by the air pollution standards:

-     For EU (2008-2010) over a yearly period, there should be less than 36 exceedance days (10% of days) having air pollution above 50 µg/m3 (PM10) or 50 (AQI);

-     For USA (2012) over a period of 3 years, there should be less than 2% exceedance days above 35 µg/m3 (PM2.5) or again 50 (AQI).

As fine particulate matter in China’s city are almost always the main air pollutant as explained in our previous surveys, the number of exceedance days above 50 - 100 (AQI)or 35-75 µg/m3 (PM2.5) thresholds are two risk levels to consider with a target of a maximum exceedance days permitted each year .

In the following survey - due to the extremely air polluted China’s situation- we are considering mainly an interim target of 36 exceedance days in a  year (10%) above 100 (AQI) or 75 µg/m3 (PM2.5).

Situation in China of daily AQI  over Q1 & Q2-2014 or 6 first months of 2014

Over Q1 and Q2- 2014, daily AQI had been above 100 during 40% of days (73.6 days over 181 days).

During Q2 there had been only a slight improvement on Q1, but we still have AQI>100 over 32% of days (29 days over 81 days).

These values are population weighted average over the monthly values of the 190 monitored cities.

Figure 1: Average population-weighted evolution of urban daily AQI over first 6 months 2014

The geographic repartition of urban air pollution is described in zoomed in Figure 2 below: the most polluted urban area or “core polluted area”concerns a urban population of 113 Mil people (2010 census) where 75% of days have been AQI>100!

Figure 2: Bubble pie map of daily urban air pollution in Northern, Middle and Southern China’s regions showing the “core polluted area” (half circle in red) of the 38 worst air polluted cities (first air pollution quintile ranking).

The detail evolution over the 6 first months of 2014 of this “core polluted area” is described in the following Figure 3:

-    38 cities with an overall population of 113 Mil had in average 125 exceedance days (70% of total), above 100 AQI or 75µg/m3 (PM2.5);

-    5 cities in Q1 and 10 cities in Q2 are not in the concerned 6 first months core polluted area;

-    Concerning the biggest cities improving their air quality: Xi’an (Shaanxi) N°12 in Q1 , N°25 on 6 months; Weinan (Shaanxi) N°16 in Q1, N°27 on 6 months; and Chengdu (Sichuan) N°24 in Q1, N°36 on 6 months;

-    The biggest cities reducing their relative ranking air quality: Beijing N°42 in Q1, N°30 on six months; Tangshan (Hebei) N°15 on Q1, N°9 on 6 months; Jinan (Shandong); Wuhan (Hubei) etc…

Figure 3 : First quintile air pollution ranking cities and cumulated days where daily AQI is > 100

Around two thirds of Chinese urban population during the first six months of 2014 have had 40% of days with an unhealthy daily Air Quality Index (AQI> 100)

Q2-2014 bubble map of China’s Air Pollution is showing a concentration of Air Pollution in 8 Northern and middle provinces or municipalities: Hebei, Beijing, Tianjin, Shandong, Jiangsu, Anhui, Henan & Hubei

The China’s urban Air Quality ranking is issued monthly by the Ministry of Environmental Protection (MEP), with Air Quality Index (AQI) and main pollutants concentration of the 190 biggest cities. The last updated data for June 2014 (MEP link ) was released this month.

AQI population weighted average over the 190 monitored cities decreased to AQI= 89 in the second quarter (Q2-2014) after AQI= 119 in Q1-2014.

The urban population concerned is around 435 Mil based mostly on the last 2010 census totaling around 66% of Chinese urban population.

Average days number with their daily AQI>100 decreased to 29.1 days (on 91 calendar days) during Q2 after 44.6 days (on 90) during Q1.

Daily AQI>50 decreased to 79.3 days during Q2 after 82.2 days during Q1.

Altogether on the first 6 months with an urban population of around 435 Mil we had AQI= 104 and on average 41% of the days with AQI>100 (73.7 days on 181) and around 90% of the days with AQI>50 (161.5 days on 181 or 89%).

This is far away from the limit for daily AQI specified by UE and USA:

UE air quality standards for 24-hour exceedance limit applies to the 90.4^th percentile (cf. EU-PM10 limit), which means that AQI may be greater than 50 but less than 35 exceedance days (9.6% of calendar days) over a year, not to mention US exceedance limit (cf. US-PM2.5 limit) which applies to the 98^th percentile over 3 years (see my blog dated 22 Sep 2014).

Here we can see on the first six month of 2014 that we have only 10^th percentile of days under the AQI=50 limit!

Q2-2014 Air Pollution Ranking

The most polluted cities over Q2-2014 are the first quintile of the Air pollution Ranking (see Figure 1 below). They were mostly Northern with few Middle or Western cities :

Korla N°1 (Xinjiang), Xingtai N°2, Shijiasuhuang N°3, Baoding N°9 (Hebei), Jinan N°7 (Shandong), Zaoguang N°8 (Shandong), Tangshan N°10 (Hebei), Linyi N°14 (Shandong), Zibo N°15 (Shandong), Nanjing N°17 (Jiangsu), Beijing N°21 were the most polluted cities with monthly AQI average > 120, almost no day with AQI<50 and about 70 days on 90 calendar days (80%) with AQI>100.

Figure 1 : The first quintile of the Air pollution Ranking of 190 main cities

 Q2-2014 most important pollutants

As during Q1-2014 the leading pollutants for the AQI determination were mostly PM2.5 or sometime PM10.

The O3 pollution had shown an increase of more than 60% in Q2 over Q1: with O3 being the leading pollutant in some cities such as Rongshen, Wendeng & Weihai (Shandong), Lhasa (Tibet), Zhangjiakou (Hunan), Zhoushan (Zeijiang) or Shanwei (Guangdong).

The test made on the various pollutants’ sub indexes is showing some weird discrepancies such as Korla in April 2014 where AQI=245.93 with PM10 leading pollutant concentration value being 621μg/m3 (see MEP updatedin 1 May 2014) or even in May 2014 where AQI=234.06 with PM10 leading pollutant being  386μg/m3 (see MEP updated 1 June 2014 ).

Figure 2 : Pollutants’s population weighted averaged value in Q1 and Q2 – evolution in %

Most polluted urban areas

During Q2-2014  the core area of urban air pollution as compared to Q1-2014 (see my blog dated 26 May 2014) is less extended and more North- Southwest oriented with strong pollution in the following 8 Provinces or Municipalities:

Hebei, Beijing, Tianjin, Shandong, Jiangsu, Anhui, Henan & Hubei.

Figure 3 : Zooming of Q2-2014 bubble map of China’s Air Pollution showing the core area of urban air pollution

Overall situation during the first 6 months of 2014

The Provinces Air Pollution ranking over the combined first 6 months of 2014 is presented in Figure 4 hereafter.

The most remarkable aspect is the steady weight of Hebei, Hubei, Beijing and Tianjin in the Air Pollution ranking of provinces and municipalities throughout  Q1 and Q2.

Shaanxi (strong in Q1), Henan (Q1), Sichuan (Q1), Xinjiang (Q2) and Ganzu (Q2) provinces contributions are more fluctuating over the quarterly periods.  

Figure 4 : Provinces Air Pollution ranking  during 6 first months of 2014

Bubble pie map of daily AQI over main Chinese cities during 1st quarter 2014

China bubble pie map of daily AQI showing pollution over main cities during Q1- 2014

In addition to our previous post, the above chart is showing that in average the days where air quality was good (AQI < 50) have been very limited over main chinese cities during the first quarter. 

This ranking covers the 190 largest cities in China, about 416 Mil people, accounting for about 63% of the urban population.

 Averaged over the urban population and during Q1-2014 period of 90 days, the daily AQI repartition had been the following: 

• 8 days /90 days or only 9% of total days had  AQI<50
• 37 days /90 days or 41% had 50<AQI <100
• 45 days or 50% had AQI>100

The area where the most polluted cities were located is shown in Figure 1 below. In this vast swath of land straddling the Northern and the Middle zones, urban citizens have seen virtually no days with AQI <50 during Q1 2014, apart Chongqing and Beijing.

Figure 1: China bubble pie of daily AQI zooming the Beijing- Wuhan- Chengdu- Xi'an semicircular area where are located the 30 most polluted cities

The  Southern coastal area presented in Figure 2 hereunder had shown over Q1-2014 relatively very few days where AQI was >100, but the good days with AQI<50 were generally very limited and the air was mostly moderately polluted (50<AQI<100).

Figure 2: China bubble pie of daily AQI zooming the Southern Chongqing-Shanghai-Guangzhou triangle of relative moderate pollution

The Southernmost cities of Haikou and Sanya located in Hainan "beautiful island" , were the only main cities with a majority of good air quality days: Haikou and Sanya had respectively 52 and 61 good days (AQI<50) on the 90 days period.

Air Quality Index ranking of China’s main cities during the 1st quarter of 2014

AQI bubble map is showing during Q1-2014 a concentration of very polluted or unhealthy urban pollution  in Hebei (Shijiazhuang, Baoding) , Shandong (Zibo), Hubei (Wuhan), Sichuan (Chengdu) and Shaanxi (Xi’an) cities

The ranking of the Chinese 190 main cities is issued each month by the China’s Ministry of Environmental Protection (see MEP link). It covers an overall population about 416 Mil people in main cities totaling around 63% of Chinese urban population.

Main results from AQI issued by MEP over Q1-2014

Based on the methodology described in my previous posts, the population weighted average AQI overall value over these 190 cities was AQI= 119 during Q1-2014 (90 days).

The  population-weighted average daily AQI repartition over these cities - during the period- was the following :

-    8 days /90 days or 9% where AQI < 50

-    37 days/90 days or 41% where 50< AQI <100

-    45 days/90 days or 50% where AQI >100

If we arrange these 90 population-weighted averages according to their decreasing daily  AQI values, the last day of the first and worst decile- assuming a lognormal distribution is valid - should be close to 150.

We know that EU is requesting a maximum value of 50 for the last day of the first decile. In average over a year an exposure to AQI >5O (or PM2.5>35µg/m3) during more than 36 days a year (10%) is considerated as dangerous, due to the cumulative effect  -even of a small pollution -on human health over a long period.

U.S. appellation to qualify the dangerousness same AQI levels in China and USA are used, these appearing to be more pertinent that the Chine's. 

AQI ranking is addressed in decreasing order unlike the publications from MEP. It is thus rather a "ranking" of Air Pollution urban areas.

We use the same color convention to represent the various AQI levels as in our previous posts. Nevertheless we should bear in mind that averaging tends to reduce daily or monthly average over time and cities. 

The best indicator of Air Pollution health hazards is undoubtedly the daily value in each city.  We know only AQI repartition inside three intervals: AQI <50; 50< AQI<100  and AQI >100 - although a splitting of the last interval in two would be helpful.

A bubble map of air pollution in China is given above. It gives a good feeling of the AQI situation during Q1-2014. It is nevertheless difficult to read as urban grid is very tight in the Beijing-Tianjin-Hebei area and in coastal regions.

Figure 1 : 30 of the most Air polluted cities are located in a semicircular area around Beijing, Tianjin,  Zibo, Wuhan, Chengdu and Xi’an

Zooming on the most polluted area is showing that the 30 most polluted cities were located within an semicircular area (see Figure 1 above) , located between the Yangze and the Huang He rivers, which surface is around 1,200,000 km2  or altogether: France, Germany, Netherlands, Belgium and Italy .

Figure 2: China Air Quality Index bubble zooming the Southern Chongqing-Shanghai-Guangzhou triangle moderate pollution

Figure 2 above is showing "unhealthy for sensitive groups" urban pollution just South to the Yangze river, becoming only moderatly polluted down to the coastal region. 

AQI main cities ranking over Q1-2014

Both following Figures 3 & 4  give the AQI ranking of the first two "quintiles" presented by MEP  concerning the 76 most polluted cities : 

- 1^st quintile: urban population 74 Mil with 38 cities all their AQI but one being either "very polluted" or "unhealthy”, the largest cities being: Xi'an N°12 (Shaanxi), Chengdu N°24 (Sichuan) and Wuhan N°26 (Hubei) ;

- 2^nd quintile: urban population 81Mil with 38 cities which AQI are all “unhealthy for sensitive groups”, the largest being Beijing N°42 ,Tianjin N°44, Harbin N°52,  Nanjing N°64 (Jiangsu) and Chongqing .

Figure 3: First quintile of AQI ranking of 190 main cities over Q1-2014

Figure 3 : Second quintile of AQI ranking of 190 main cities over Q1-2014

Discussion of AQI values on Q1-2014

In general, the main pollutant was PM25 except for some few exceptions where it was PM10.

The result for Beijing, which exhibits 14 days with AQI < 50 when in average AQI = 147 seems quite unlikely, while similar cities for their AQI level - such as Tianjin- are all showing 0-5 days for this indicator.

Furthermore, comparing the sub-AQI corresponding to the value of the monthly concentration of PM2.5, to the monthly value of the AQI (see my last post) it is possible to highlight some possible errors. 

This test establishes that 99 values out from 570 (190 cities x 3 months) or 17% might be inaccurate with an AQI value underestimated in the following cases:

Ma'anshan- in Mar 2014-(underestimation: 24.1 /AQI=108.4); Zhangqiu-Feb- (19.3/149.2); Langfang- Feb- (14.6/195.3); Ma'anshan-Jan- (12.7/187.78); Beijing- Feb- (12.0/183.7); Handan- Feb- (10.8/210.2);Tangshan-Feb-(9.71/190.3); Xianyang-Jan- (9.58/194.4); Baoji- Jan-(9.21/173.7)…Xi'an-Jan- (8.48/185.8)…Zibo-Jan- (7.09/185.8); Shijiazhuang-Feb (7/266.0)…etc

As the concerned cities are mosly  classified on a monthly basis either "Unhealthy" or "Very Polluted", such AQI underestimation could rock the ranking list and expend the number of "Unhealthy " or"Very Polluted" cities on a quarterly basis, such as Beijing for instance.  

Last Chinese Air Quality Index (AQI) showing persistent Air pollution during Jan & Feb 2014 with high level of Particulate Matter pollution in Northern regions

Shijiazhuang is struggling to contain a dense smog because of its heavy reliance on coal; both Xingtai and Shijiazhuang cities- located in Hebei 300 km South of Beijing- had the worst AQI throughout China during Jan & Feb 2014. From CCTV reporter Ning Hong - 16 Oct 2013

In the first two months of 2014, the 190 most important Chinese cities sample were recorded with an Air Quality Index (AQI) value around 130. Most affected areas were the industrial North region including Harbin, Beijing and Tianjin.

Particulate Matters (PM2.5 and PM10) were almost always the principal pollutants determining the value of Air Quality Index, PM2.5 with 68% of the city-month records being mostly concerned with PM10 only 29%. As a consequence, the PM2.5 inclusion in the new AQI definition has dramatically changed the Air quality perception.  


During Jan. & Feb. 2014, on a 59 days' period: the 76 most polluted cities (40% of 190 sample) had largely exceeded the yearly budget of "exceedance" days (with AQI>50 or PM2.5> 35μg/m3) normally permitted in the WHO, the US or the UE for instance.

This means that based on the first two months and for 40% of major urban areas China is more or less six times more polluted as compared with Western standards! 

The new Air Quality Index publications, concerning China’s major urban areas, are being speeding up gradually by the Ministry of Environmental Protection (MEP).

However every month already published AQIs ​​are modified retrospectively due to errors found after publication.

But we believe that many errors are still present: from a test performed by computing the highest values ​​of all pollutant sub-indices, we found that at least 181 cities indications already published - or 16% of all published city-month records- should still be corrected, including: Harbin (Oct & Dec), Xi’an (Dec & Jan) and Beijing (Feb).

What are the main information resulting from last AQI data released on the most important Chinese cities?

After 76 cities recorded from May 2013, then 144 cities from Sep 2013, we have now 190 cities- all among the largest urban areas- recorded from Jan 2014 with the new Air Quality Index (AQI) format that incorporates the finest Particulate Matter (PM2.5).

As explained in our previous blog dated 12 Nov 2013, we may establish average per capita pollution over specific region or on an overall national basis only after urban population weighting the results of each city inside the concerned area.

In the first two months Jan. & Feb. 2014, the population weighted average AQI value is 129 for an overall urban population of 408 Mil of the 190 concerned cities.

The most affected areas were the industrial North regions including Harbin, Beijing and Tianjin. The list of the top 76 most polluted cities is given in the following Figures 1 (a) and 1 (b):

Figure 1 (a): 38 most polluted cities or first quintile (1/5 of  the 190 cities) from mean Jan & Feb 2014

Figure 1 (b): 39th to 76th most polluted cities or second  quintile from mean Jan & Feb 2014

The first 40% - or 2 fifths (quintile) - of the ranked 190 Chinese cities are located mostly in the Northern (60%) or in the Middle (37%) regions.

These cities were classified with an Air Quality Index- following US denominations- either "Very polluted" (11 cities including Xi'an), or "Unhealthy" (40 cities including Beijing and Harbin), or "Unhealthy for sensitive groups" (25 cities including Chongqing).

Xi'an (ranking n°11), Harbin (n°40), Beijing (n°45), Chongqing (n°53), Tianjin (n°56) and Nanjing (n°64) are among the greatest Chinese cities but are also those which air is the most heavily polluted by Particulate Matter. 

The G06 Northern region (Beijing, Tianjin, Hebei Provinces & Dalian City) plus being the People's Republic of China capital location were certainly the most polluted during the period.

With 10 cities ranking respectively n°1 (Xingtai), n°2 (Shijiazhuang), n°3 (Baoding), n°5 (Handan), n°7 (Hengshui), n°16 (Langfang), n°25 (Tangshan), n°37 (Cangzhou), n°45 (Beijing) &  n°56 (Tianjin) and a population totaling 48 Mil: the population-weighted AQI value is around 162  with only  4.8 "good days" over the 59 days period. 

Most of the pollution is coming from the surrounding Hebei Province which burned over 300 million tons of coal in 2011, more than all of Germany!

The number of "good " days - where AQI <50 or PM2.5 <35μg/m3- during Jan. & Feb. 2014 where nil for Xi'an, Harbin and Tianjin, 3 for Chongking and Nanjing and -quite unexpectedly- 10 for Beijing with 5 in Jan. and again 5 in Feb.. 

As a result, after over the first two months of the year all these cities have largely exceeded the yearly budget of "exceedance" days such as defined for instance in the UE . This means that based on these first two months China is more of less six times more polluted following normal western standards.

Figure 2 : Most polluted 78 Chinese Cities from mean Jan & Feb 2014

 What are the most important pollutants concerned?

For a specific day the AQI value is the value reached by the highest underlying sub-index of each of the 7 main different pollutants recorded: PM2.5, PM10, CO, NO2, SO2 , O3-1h & O3-8h.

Since the publication of the new monthly AQI values, we have 1102 city-month records of monthly average AQI and associated pollutants over a period of 10 months from May 2013 to Feb 2014.

It is possible to compute monthly sub index values from each monthly recorded pollutant average concentration. In the vast majority of city-month records, PM2.5 or PM10 were almost always the most important pollutants as defined by the value of the various sub-index (see Figures 3 (a) & 3 (b)).

Under this approach we found that PM2.5 was the most important pollutant for 750 city-month records (68%), then PM10 for 325 (29%), NO2 for 17 (1.5%) and O3-8h then SO2 respectively for 6 (0.5%) & 3 (0.25%) city-month records only.

Figure 3 (a) : Beijing, Canton and Chongqing 10 month records from May 2013 to Feb 2014 

Figure 3 (b) : Beijing, Canton and Chongqing 10 month sub indexes as derived from May 2013 to Feb 2014 detailed AQI and associated pollutant records

As explained above, each new AQI monthly issue from China’s MEP might is bringing corrections to several of the preceding issued city-month records.

And nevertheless lots of mistakes are still uncorrected! We found that for 181 city-month records, the value of the month was less than the value of the sub highest index computed from the monthly average of the corresponding pollution (See Harbin in Oct. and Dec., in Beijing in Feb in following Figure 4).

These are certainly errors since the highest sub index including the daily volatility during the specific month is certainly higher than the sub index without volatility!  

181 errors on 1102 values is a level of mistakes around 16% with lots of errors still concerning Oct., Nov. and Dec..

Figure 4 : 40 among 181 errors found in the last AQI issues where the sub index is higher than the recorded AQI

These values ​​are average monthly which might hide severe daily pollution

As we have not for each city the detailed daily value of each of 7 main pollutants we can only assess the most severe daily pollution from the monthly average issued each month.    

Figure 5: Existing correlation between monthly  AQI or PM2.5 sub-index and PM2.5 monthly average PM2.5 for all 1102 city-month records; a large number of PM2.5 sub-index higher than that recorded AQI necessarily corresponds to an error

Figure 6: Correlation between overall AQI and calculated monthly Sub Index PM10 for all monthly-cities 1102 records

But in each of the 1102 city-month records we have the number of days during the month period where AQI was "good" (AQI<50) which permits an estimation of the size of population exposed over long periods to unhealthy air quality.

Figure 7: Number of days where AQIcity is "good" or <50

The Figure 7 above is showing that "good air quality" had only 22-29 "good" days during each last month; when "moderate air quality" had only 5-10 "good days"; and "unhealthy air quality" only 1-5 "good days"!   

These performances are more than extremely exceeding the health limitations put forward by WHO, EU or US regulations which are -in the EU-  90.4 percentiles with PM10 < 50μg/m3  or less than 35 exceedance days (9.6%) over one year and - in the US- 98 percentiles  for PM2.5 < 35 μg/m3 or less than 7 exceedance days (2%) over one year (see my last blog dated 22 Sep 2013). 

During Jan & Feb 2014 the population-weighted "good days" (AQI<50 or PM2.5<35μg/m3) were around 5.5 days for all the 190 cities. 

This mean as exposed above that on the overall 190 cities during Jan. to Feb. 2014 there were 53 (=59-5.5) unhealthy days (with AQI>50 or PM2.5>35μg/m3)  or 1.5 times the 35 days exceedance yearly period accepted by WHO, the US or the UE!

Finally is it possible to know whether air pollution is on an upward or downward trend during the last years?

As we did in our last post dated  10 Nov. 2013, we may use the benchmark of air pollution introduced by W. J. Qu et al. in their 2010 study "Spatial distribution and inter-annual variation of PM10 concentrations over 86 Chinese cities" as established  from Jun. 2000 to Feb. 2007 daily API data available.

As during that period the finest particulate matter were not recorded, we might only compare PM10 pollution using this 86 cities bench mark which are the biggest cities inside the 190 cities recorded by MEP.

On the overall 86 cities the total population weighted PM10 is +2.17% higher than the 2000-2007 bench-mark (see Figure 8 and 9 below):

Figure 8: Monotonous curve comparison with the bench-mark

Figure 9 : Comparison for 2000-2007 86 cities benchmark ; in blue the 2000-2007 population weighted 10 months PM10 value ; in red the last 10 month values from same 86 cities recorded completed progressively with small missing cities deducted from previous seasonal factors; for each cluster the number of cities and the overall population are given

On the 16 city’s clusters (see Figure 9 & 10):

There are reduction for Northern G01 (-21.76%); Northern G03 (-23.35%); Northern G05 (-17.87%); Southern G12 (-13%) & West GX1 (-10.14%). 

But also we note a huge increase for Northern G07 (37%); Northern G08 (34%); Southern G13 (30%); Northern G02 (11%) & Middle G11   (8.8%).      

Figure 10 : The 16 clusters of correlated cities used as a bench-mark