History of Air quality index in Timeline

By Popular Timelines Editorial Team · Updated: July 15, 2026

The Air Quality Index (AQI) is a standardized tool used by government agencies to communicate the current and forecasted health risks associated with outdoor air pollution. It functions as a yardstick, converting complex air quality data into a simple numerical scale—typically ranging from 0 to 500—and color-coded categories. The index primarily monitors five major air pollutants regulated by the Clean Air Act: ground-level ozone, particulate matter (PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide. As the AQI value increases, the level of air pollution and the associated health concerns rise proportionally. Values are divided into tiers, ranging from 'Good' (green, minimal risk) to 'Hazardous' (maroon, emergency health warnings). By providing timely, accessible information, the AQI allows individuals, particularly sensitive populations such as children, the elderly, and those with respiratory conditions, to make informed decisions about outdoor activities, thereby mitigating exposure to harmful pollutants and protecting public health.

1968: Debut of the Air Quality Index

In 1968, the National Air Pollution Control Administration launched an initiative to establish an air quality index, applying this methodology to Metropolitan Statistical Areas to increase public awareness of pollution and encourage local officials to implement control measures.

1990: Passage of the Clean Air Act

In 1990, the United States enacted the Clean Air Act, which mandated that the Environmental Protection Agency (EPA) must review and update its National Ambient Air Quality Standards (NAAQS) every five years to incorporate the latest scientific data regarding public health effects.

2006: Introduction of the Common Air Quality Index (CAQI)

In 2006, the Common Air Quality Index (CAQI) was established and implemented as a standardized air quality reporting tool within Europe.

2011: Baseline Air Quality Lighting Observation

In 2011, the N Seoul Tower served as a visual indicator for air quality by lighting up in blue for a total of 48 days, establishing a baseline for the subsequent 2012 spring season.

2012: Standardization of CAQI Components

As of 2012, the Common Air Quality Index (CAQI) established specific mandatory components for its reporting metrics, requiring NO2 and PM10 for roadside measurements and adding O3 for background measurements, while also permitting optional pollutants like PM2.5, CO, and SO2.

2012: N Seoul Tower Air Quality Monitoring Initiative

During the spring of 2012, the N Seoul Tower in South Korea was illuminated in blue for 52 days to indicate that the city's air quality index was 45 or lower.

2012: CiteairII Project Evaluation of CAQI

In 2012, the EU-supported project CiteairII published an evaluation of the Common Air Quality Index (CAQI). The project clarified that the index was designed to simplify air quality communication for the public and facilitate cross-European comparisons, rather than serving as a complex health-based warning system. The primary intent of the CAQI in 2012 was to raise awareness about urban air pollution and its correlation with traffic, helping citizens manage their personal exposure.

January 1, 2013: Expansion of Air Quality Monitoring in China

On January 1, 2013, China's Ministry of Environmental Protection began monitoring daily pollution levels in 163 major cities based on a standardized AQI calculated from six atmospheric pollutants, including PM2.5 and ozone.

December 30, 2013: Implementation of the Air Quality Health Index in Hong Kong

On December 30, 2013, Hong Kong officially transitioned from its previous Air Pollution Index to the new Air Quality Health Index (AQHI). This new system, managed by the Environmental Protection Department, utilizes a scale of 1 to 10+ based on the cumulative risk of hospital admissions linked to hourly concentrations of ozone, nitrogen dioxide, sulfur dioxide, and particulate matter (PM10 and PM2.5).

September 2014: Launch of the National Air Quality Index (NAQI)

On 17 September 2014, the National Air Quality Index (NAQI) was officially launched in New Delhi as part of the Swachh Bharat Abhiyan initiative to monitor and improve air quality awareness in India.

2014: Recommendation of the New AQI Scheme

In 2014, an Expert Group and researchers from IIT Kanpur recommended a new Air Quality Index (AQI) scheme for India, which expanded the monitoring framework from three indicators to eight distinct parameters.

November 2017: Launch of the European Air Quality Index (EAQI)

During November 2017, the European Environment Agency introduced the European Air Quality Index (EAQI) and began promoting its adoption across various public information platforms to improve air quality transparency.

November 12, 2019: Promulgation of Vietnam Air Quality Index Technical Guidelines

On November 12, 2019, the Vietnam Environment Administration formally issued Decision No. 1459/QD-TCMT, which established the official technical guidelines required for the calculation and public reporting of the Vietnam Air Quality Index (VN_AQI).