The Air Quality Index (AQI) is composed of a variety of air pollutant indicators for reporting daily air quality. Every country has its own air quality indices that have similar names but differ in standards for severity, such as the US AQI, South Korea’s CAI (Comprehensive Air Quality Index), Australia’s Daily Air Quality Index (DAQI), China’s AQI, and so on. To improve air quality, the EPA aims to reduce the number of red alert days (PM2.5 ≧ 54 μg/m³) by 20% of 2015 levels by 2017, and 50% by 2019

To help reduce the number of red alert days, the EPA started using the AQI from 1 December 2016. The AQI lowers the threshold for issuing a red alert to the public. Previously, the EPA issued a red alert warning when daily average PM2.5 concentration reached 71μg/m³ (AQI purple level); now it is issued if the level reaches 54μg/m³ (AQI red level). In 2016, there were a total of 143 days on which the daily PM2.5 concentration reached 71μg/m³ and 874 days on which the concentration reached 54μg/ m³. Lowering the threshold for a red alert therefore warns residents of deterioration in the air quality earlier, to alert them to take response measures sooner. The EPA also tightened the air quality control rules to enable it to take swifter reduction measures. The air quality control measures that were originally taken on days when the PM2.5 value reached 71μg/ m³ must now be taken when PM2.5 levels reach 54μg/m³. The EPA also reminds the public to pay more attention to changes in air quality so that they can take precautions further in advance. To this end, the EPA will start releasing warnings once the PM2.5 concentration reaches 35.5μg/m³ (AQI orange level) in an effort to help prevent continuing deterioration of air quality.