Air quality information availability in YRD

A milestone change in the AQ data and information availability in Yangtze River Delta cities and China in general is captured from 2012 to 2013. The highlights of air quality reporting improvements are:

• Hangzhou is one of the first pilots in Asia while Jiangsu is the first province to communicate air quality management with stakeholders by comprehensive and systematic reporting- Jiangsu Clean Air Report was released in 2012 and will be reported annually in future.
• The National Ambient Air Quality Standard was improved in March 2012 (from GB3095-1996 to GB3095-2012), in which PM2.5, CO and O3 are added as indicators for monitoring and reporting. YRD was one of the pioneer regions to conduct PM2.5 monitoring and reporting in China.
• For air quality data at the inception phase of this project and years before that, most air quality data for YRD were in the daily API format (which represents average of all stations, and API level) and actual concentrations data were quite hard to access and rarely available online.
• By March 2013, 74 cities in China including the 25 YRD key cities, have started reporting the Air Quality Index (AQI), releasing concentration value of 6 types of air pollutants (SO2, NO2, CO, O3, PM10 and PM2.5) and the related AQI index, which a more appropriate expression for the purpose of emphasizing the air quality characteristics and public health impact. The 25 YRD cities are: Shanghai, Nanjing, Wuxi, Xuzhou, Changzhou, Suzhou, Nantong, Lianyungang, Huai’an, Yancheng, Yangzhou, Zhenjiang, Taizhou, Suqian, Hangzhou, Ningbo, Wenzhou, Jiaxing, Huzhou, Quzhou, Zhoushan, Taizhou, Lishui, Shaoxing, Jinhua. (
• Pollutant concentration data and the corresponding AQI index of those cities mentioned above could now be found online . YRD was the first region to report real-time monitoring air quality data online synchronously starting from January 2013.

Comparing the AQI and API
a. Definition
In principle, the concept behind the API and AQI are the same; both are designed to inform the public about the status of air pollution level in an easy-to-understand manner. Using a simple calculation formula, the concentration value of several pollutants presented as a simple conceptual numerical form and description of health implications.
AQI is a more appropriate expression for the purpose of emphasizing the air quality characteristics.

b. Pollutants considered and Breakpoints
The pollutants considered in the AQI involve six pollutants (PM2.5, PM10, SO2, NO2, O3 and CO) while the API only evaluated three pollutants (PM10, SO2 and NO2). The breakpoints for each pollutant in the AQI are also stricter compared with the API, as this is based on the revised Ambient Air Quality Standard (GB3095-2012).

The calculation approach remains same only that with AQI, there are additional pollutants and with stricter breakpoints. The calculation can be divided into 3 main steps:
The first step: calculate the Individual Air Quality Index (IAQI) by comparing to the classification of various pollutants concentration limits (concentration limit of AQI, referent to GB3095-2012; concentration limit of the API, referent to GB3095-1996), and actual measured concentration values of PM2.5, PM10, SO2, NO2 , O3, CO and other pollutants;
The second step: choose the maximum value from IAQI and determine it as the AQI, when AQI goes above 50, determine the pollutant that achieves the greatest value of IAQI as the priority pollutant;
The third step: determine the level, category and color signs of air quality index; relating with the health effects and recommended measures according to the AQI grading standards.
To simply put, AQI is the maximum of the IAQI, when AQI goes above 50, the pollutant that achieve the maximum value of IAQI is the priority pollutant. Detailed computational formula could be found in Technical Guideline on Ambient Air Quality Index (Trial) (HJ 633-2012).

c. Reporting Frequency
The API is reported once a day with a period from 12:00 of the former day to 12:00 of the same day. This is different from the concept of natural day which is familiar to the public, which results in potential misunderstanding with the public.
On the other hand, the AQI are reported in two ways – daily and real-time. The daily AQI reported period is 24 hours (which is the last 24-hour before 0:00 of the same day) and considers seven pollutants indicators in total (SO2, NO2, CO, O3 1-hour, O3 8-hour, PM10, PM2.5). Real-time report releases data with an interval of 1 hour, from automatic monitoring stations with no more than 1-hour delay.

Overall, access to air quality monitoring information has significantly improved since last year. Launched in January 2013 ,the ‘Air Quality Data Real-time Release Platform’ of the Ministry of Environmental Protection Data Center provide the concentration value of six air pollutants (SO2, NO2, CO, O3, PM10, PM2.5) and their respective AQI index, with the color representing the corresponding air quality level and health advisory. Pollutant concentration data and their corresponding AQI index of 74 Chinese cities is available at