NPM AQI Calculator

Foreword

All methods, constraints use in this project follows US EPA AQI Calculation Method (which includes breakpoint table and calculation formulas) . Since each country issues different AQI calculation methods, using this package might be inappropriate, consider your usage.

This project is intended to community target for free use. The author is not associated with USA government, nor United States Environmental Protection Agency (a.k.a US EPA)

Highlights

Calculate AQI from raw concentration
The result from calculation includes Air Quality Index, AQI Category, General Message, Specific Health Effects Statements for the pollutant and the corresponding guidance message
Support various pollutants
Support Nowcast Concentration
The AQI Calculation approach issued by US EPA by far is the most sensible way I've seen after working with various AQI calculation formulas.

Support the following pollutants

Pollutant	Scientific name	Unit of Measurement	Input Code Usage	Regular Calculation Support	Nowcast Support	Health Effects Statements	Guidance Message
PM10	10 μm Particle Pollutant	μg/m3	PM10	✔️	✔️	✔️	✔️
PM2.5	2.5 μm Particle Pollutant	μg/m3	PM2.5	✔️	✔️	✔️	✔️
O3	Ozone	ppb	O3	✔️	✔️	✔️	✔️
CO	Carbon Monoxide	ppb	CO	✔️	❌	✔️	✔️
SO2	Sulfur Dioxide	ppb	SO2	✔️	❌	✔️	✔️
NO2	Nitrogen Dioxide	ppb	NO2	✔️	❌	✔️	✔️

Installation

npm install aqi-bot --save

Extract the aqi-bot to use it

let aqibot = require('aqi-bot');

Quick Usage

For Regular AQI Calculation

2 required parameter is pollutant code and concentration. The unit of measurement for the pollutant code is as defined in the pollutants specification table.

aqibot.AQICalculator.getAQIResult("PM10", 125).then((result) => {
    console.log(result);
  }).catch(err => {
    console.log(err);
  })

Or you might use the pollutant code constants from the aqibot: aqibot.AQICalculator.getAQIResult(aqibot.PollutantType.PM10, concentration)

And the result object there contains all the information that you need

{
    "pollutant": "PM10",
    "concentration": "125",
    "aqi": 86,
    "category": "Moderate",
    "generalMessage": "Unusually sensitive people should consider reducing prolonged or heavy outdoor exertion",
    "healthEffectsStatements": "Respiratory symptoms possible in unusually sensitive individuals; possible aggravation of heart or lung disease in people with cardiopulmonary disease and older adults",
    "guidanceStatement": "Unusually sensitive people should consider reducing prolonged or heavy exertion"
}

For Nowcast AQI Calculation

2 required parameter is pollutant code and an array of average concentration for each hour recorded (more explanation below). The unit of measurement for the pollutant code is as defined in the pollutants specification table.

/* Example Data for Nowcast PM2.5 12h period - 30.5, 12.5, 14.3, 30, 32.4, 31.1, 28.2, 30.7, 32.8, 32.6, 33.1, 28.5 */

let concentrationData = [30.5, 12.5, 14.3, 30, 32.4, 31.1, 28.2, 30.7, 32.8, 32.6, 33.1, 28.5];

AQIBot.AQICalculator.getNowcastAQIResult(PollutantType.PM25, concentrationData).then((result)=>{
  console.log(result);
}).catch(err =>{
  console.log(err);
})

Please note that the concentration in result object here is the Nowcast Concentration

{
    "pollutant": "PM2.5",
    "concentration": 24,
    "aqi": 76,
    "category": "Moderate",
    "generalMessage": "Unusually sensitive people should consider reducing prolonged or heavy outdoor exertion",
    "healthEffectsStatements": "Respiratory symptoms possible in unusually sensitive individuals; possible aggravation of heart or lung disease in people with cardiopulmonary disease and older adults",
    "guidanceStatement": "Unusually sensitive people should consider reducing prolonged or heavy exertion"
}

The first number in the array is the average concentration value of the selected hour, and the upcoming element in the array represent one step of hour before the selected hour.

If the hour doesn't have data, replace missing data in the hour with -1

Example Nowcast Dataset for PM10: (have some missing data in hour)

Hour	Avg Concentration
14	64 ppb
13	63 ppb
12	----
11	77 ppb
10	65 ppb
9	----
8	70 ppb
7	71 ppb
6	----
5	57 ppb
4	58 ppb
3	64 ppb

Presume that you want to calculate Nowcast AQI for PM10 at 14, the data array should be

  let concentrationData = [ 64, 63, -1, 77, 65, -1, 70, 71, -1, 57, 58, 64 ];

  AQIBot.AQICalculator.getNowcastAQIResult(PollutantType.PM10, concentrationData).then((result)=>{
    console.log(result);
  }).catch(err =>{
    console.log(err);
})

{
    "pollutant": "PM10",
    "concentration": 66,
    "aqi": 56,
    "category": "Moderate",
    "generalMessage": "Unusually sensitive people should consider reducing prolonged or heavy outdoor exertion",
    "healthEffectsStatements": "Respiratory symptoms possible in unusually sensitive individuals; possible aggravation of heart or lung disease in people with cardiopulmonary disease and older adults",
    "guidanceStatement": "Unusually sensitive people should consider reducing prolonged or heavy exertion"
}

AQI Calculation Turtorial

US EPA AQI Breakpoint

Image from Wikipedia

Calculation Formula

The AQI is the highest value calculated for each pollutant as follows:

Identify the highest concentration among all of the monitors within each reporting area and truncate as follows:

Using US EPA AQI Breakpoint, find the two breakpoints that contain the concentration.
Using AQI Equation , calculate the index.
Round the index to the nearest integer.

Nowcast for PM and Ozone

The concentration of PM10, PM2.5 is so dynamic since wind can completely clean the air in less than 30 minutes, or a wildfire can raise the concentration with a very fast rate in an hour. So Nowcast is introduced, it mainly focus on detect the average changing of the period hour and perform counter balancing.