Decision No. 1459/QD-TCMT dated November 12, 2019 promulgating a guide to calculation and publishing of Vietnam Air Quality Index (VN_AQI)

DECISION

PROMULGATING A GUIDE TO CALCULATION AND PUBLISHING OF VIETNAM AIR QUALITY INDEX (VN_AQI)

DIRECTOR GENERAL OF VIETNAM ENVIRONMENT ADMINISTRATION

Pursuant to the Law on environmental protection dated January 01, 2015;

Pursuant to the Government's Decree No. 19/2015/ND-CP dated February 14, 2015 providing guidelines for the implementation of the Law on environmental protection;

Pursuant to the Government's Decree No. 40/2019/ND-CP dated May 13, 2019 on amendments to Decrees providing guidelines for the implementation of the Law on environmental protection;

Pursuant to the Decision No. 15/2018/QD-TTg dated March 12, 2018 of the Prime Minister defining functions, tasks, powers and organizational structure of Vietnam Environment Administration affiliated to the Ministry of Natural Resources and Environment;

At the request of the Director of Environmental Quality Management Department and the Director of Northern Center for Environmental Monitoring,

HEREBY DECIDES:

Article 1.A Guide to calculation and publishing of Vietnam Air Quality Index(VN_AQI) is promulgated together with this Decision.

Article 2.This Decision comes into force from the day on which it is promulgated and supersedes the Decision No. 878/QD-TCMT dated July 01, 2011 of Director General of Vietnam Environment Administration promulgating the Manual for calculation of air quality index.

Article 3.Chief of Office of Vietnam Environment Administration, Director of Environmental Quality Management Department, Director of Northern Center for Environmental Monitoring, heads of other agencies/units affiliated to Vietnam Environment Administration, and relevant organizations and individuals shall implement this Decision./.

GUIDE

TO CALCULATION AND PUBLISHING OF VIETNAM AIR QUALITY INDEX (VN_AQI)
(Enclosed with Decision No. 1459/QD-TCMT dated November 12, 2019 of Vietnam Environment Administration)

1. General provisions

1.1. Objectives

This document provides instructions on calculation and publishing of Vietnam air quality index (VN_AQI) based on monitoring data obtained from automatic and continuous air quality monitoring stations.

1.2. Recommended application

Environmental agencies, organizations and individuals engaging in the establishment and publishing of environmental quality data and information in Vietnam are recommended to follow instructions in this document.

1.3. Definitions

1.3.1. Vietnam air quality index (VN_AQI) is an index which is calculated based on monitoring data about air pollutants in Vietnam, used to report air quality and helps understand the impact of air quality on human health, and measured on a scale.

1.3.2. Daily AQI (AQId) is the AQI value that represents the air quality in a day.

1.3.3. Hourly AQI (AQIh) is the AQI value that represents the air quality in an hour.

1.3.4. IndividualAQI (AQIx) is the calculated AQI value of each monitoring pollutant. AQIx includes the individual AQI per day (AQIxd) and the individual AQI per hour (AQIxh).

1.3.5. Nowcast value is aweighted average of the most recent 12 hourly averages. Nowcast value is calculated for PM10 and PM2.5.

1.3.6. Air quality monitoring station refers to a fixed-site or mobile motoring station which is used to automatically and continuously measure air quality parameters.

1.4. Assessment ofAQI values

AQI is calculated on a scale (ranges of AQI values) with specific icons and colors indicating the levels of air pollution and health risks. To be specific:

Table 1: AQI values and corresponding air pollution levels

2. Instructions on calculation of AQI

2.1. Requirements to be satisfied when calculating VN_AQI

a. Data used for calculating VN_AQI

- Monitoring equipment must have its quality controlled and calibrated in accordance with law regulations.

- Monitoring data shall be processed before being used for computation of AQI values in order to ensure that all outliers are removed and the used monitoring data shall comply with the process of data quality assurance and control.

b. Methods of using data for calculating VN_AQI

- VN_AQI values to be calculated include hourly AQI and daily AQI. Data used for calculating VN_AQI values shall be average 1-hour, 8-hour and 24-hour monitoring values.

- VN_AQI shall be calculated for ambient air quality based on data obtained from each air quality monitoring station.

- At each monitoring station, AQIx value shall be calculated for each monitoring pollutant. The final AQI value shall be the highest of AQIx values of each pollutant.

- Pollutants used in calculating VN_AQI include SO2, CO, NO2, O3, PM10, and PM2.5.

- The calculation of VN_AQI must have at least one of two mandatory pollutants, PM10 and PM2.5.

2.2. Calculation of VN_AQI values

2.2.1. Calculation of hourly AQI values (AQIh)

Hourly AQI values shall be calculated with average 1-hour monitoring values.

a. Calculation of Nowcast values for PM2.5 and PM10

Let c1, c2, …c12represent 12 average hourly monitoring values (c1 represents the most recent hourly value, and c12 representsthe hourly average for12 hours before present).

The weight factor is calculated as follows:

Where Cmin represents the lowest value of 12 average hourly monitoring values; and

Cmax represents the highest value of 12 average hourly monitoring values.

If Let

If Let w=w*

Where the Nowcast value is given by:

Where the Nowcast value is given by:

Notes:

- Nowcast value is only calculated when at least 2 of 3 values c1, c2, c3 are available. Conversely, it is considered as “missing data” (Nowcast value cannot be calculated).

- If civalue is not available, wi-1 = 0.

b. Calculation of AQIh for each individual pollutant (AQIx)

AQIh values for the following pollutants SO2, CO, NO2, O3, shall be calculating by adopting the following formula 1, and AQIh values for PM10, PM2.5 shall be calculating by adopting the following formula 2:

Where:

AQIx: The AQI value for pollutant x

BPi: The lower concentration limit of the value of monitored pollutant as prescribed in Table 2, corresponding to level i

BPi+1: The upper concentration limit of the value of monitored pollutant as prescribed in Table 2, corresponding to level i+1

Ii: The AQI value at level i as given in the table below corresponding to BPi

Ii+1: The AQI value at level i+1 as given in the table below corresponding to BPi+1

Cx: The average hourly monitoring value of pollutant x. Nowcastx: Nowcast value calculated in section a.

Table 2: BPi values for pollutants

Notes:

- AQIh for O3 shall be calculated with 1-hour BPi value for O3

- AQId for O3 shall be calculated with 1-hour and 8-hour BPi values for O3

c. Overall hourly AQI

After having calculated AQIx for each pollutant, the highest AQI value among all of values of monitored pollutants shall be the overall hourly AQI.

AQIh = max(AQIx)

Note: The AQI shall be rounded to the nearest integer.

2.2.2. Calculation of daily AQI values (AQId)

The daily AQI shall be calculated with the following values:

- Values for PM2.5 andPM10: 24-hour averages.

- O3 value: The daily maximum 1-hour average and the daily maximum 8-hour average.

- Values for SO2, NO2 and CO: daily maximum 1-hour averages.

a. Determining daily maximum 1-hour average,daily maximum 8-hour average and 24-hour average

- The daily maximum 1-hour average is the highest of 1-hour average values.

- The daily maximum 8-hour average is the highest of 8-hour average values.The 8-hour average value is the arithmetic mean of 1-hour average values continuously measured during 8 hours.

E.g. Calculating the daily maximum 8-hour average with the following table of 1-hour average values for O3:

The daily 8-hour averages are calculated and specified in the following table (there are 24 8-hour averages every day).

The daily maximum 8-hour average is 74,4.

- The 24-hour averageis the arithmetic mean of 1-hour average values continuously measured within a day (from 01:00 to 00:00 of the following day).

b. Calculation of AQId for each individual pollutant (AQIx)

The daily AQI for SO2, CO, NO2, O3, PM10, PM2.5 are calculated by adopting the following formula 1:

Where:

BPi and Ii values shall follow table 2.

AQIx: The AQId value for the pollutant x

BPi: The lower concentration limit of the value of monitored pollutant as prescribed in Table 2, corresponding to level i

BPi+1: The upper concentration limit of the value of monitored pollutant as prescribed in Table 2, corresponding to level i+1

Ii: The AQI value at level i as given in the table below corresponding to BPi

Ii+1: The AQI value at level i+1 as given in the table below corresponding to BPi+1

Cxshall be provided for as follows:

- For PM2.5 and PM10: Cx valuesare 24-hour average values.

- For O3: Cx values are daily maximum 1-hour and 8-hour averages.

Notes:The AQI for O3 shall not be calculated if the daily maximum 8-hour average is higher than 400 µg/m3 (In this case, the AQI shall be calculated with the daily maximum 1-hour average).

- For SO2, NO2 and CO: Cx value is the daily maximum 1-hour average.

c. Overall daily AQI

After having calculated daily AQIx for each pollutant, the highest AQI value among all of values of monitored pollutants shall be the overalldaily AQI.

AQId = max(AQIx)

Note: The daily AQI shall be rounded to the nearest integer.

2.3. Example calculation

a. Calculation of Nowcast value

With PM2.5 monitoring data given in the following table:

Because w*=0,61 > 0,5, w=w*=0,61

b. Calculation of hourly AQI

With hourly monitoring averages given in the following table:

Define AQI values for pollutants:

Thus, AQIh = 60.

c. Calculation of daily AQI

With monitoring data given in the following table:

Define AQI values for pollutants:

Thus, AQId = 110.

3. Instructions on publishing of AQI

Information relating to VN_AQI shall be published when data and calculations comply with provisions in Section 2 hereof.

Information relating to VN_AQI shall be made available to the public by means of mass media such as press, radio, television, electronic display boards, websites and mobile applications.

Table 3: Requirements for VN_AQI-related information

Notes: (x): compulsory; (-):optional

Table 4: VN_AQI levels and health implications

Table 5: VN_AQI levels and recommended activities