Number of Clear Days in Hong Kong 2019

The citizens in Hong Kong enjoy more clear days over the past few years. The air pollution problem seems to have slightly improved but the polluted air is still heavily threatening the health of 7 million people in the city.

In 2019, in a total of 196 days were defined as “Polluted Days” which is more than 169 days as “Clear Days” according to the Hedley Environmental Index. This figure shows that more than half a year, the city’s air quality levels exceeded the safety limits set by the World Health Organization Air Quality Guidelines (WHOAQG). There is still a lot of work to be done to tackle the air pollution problem.


“Clear Day” vs “Polluted Day”

Icon of clear days 清新日的定義

The day which all five major air pollutants (Fine suspended particulates, Respirable suspended particulates, Sulphur dioxide, Nitrogen dioxide and Ozone) at all 13 urban rooftop monitoring stations complied with the short-term WHOAQG.

Polluted Day 污染日的定義

The day which the air data in one of the monitoring stations exceeded the safety limit of WHOAQG


What is Hedley Environmental Index (HEI) ?

The HEI aims to enhance health risk communication and to better inform and assist members of the public in the interpretation of air pollution levels. The Index is based on the latest scientific evidence for health risks and referenced to the WHOAQG with a new approach to aggregate air pollutants.

The website of HEI provides lots of real-time information about air pollution in the city:

  • Air Quality Index
  • Pollution map in Hong Kong showing the levels of pollutants
  • Rolling clocks of avoidable harm and economic cost to the community
  • Calendar of high pollution days
  • Historical data


The HEI also develops a mobile app which can be downloaded on Android ( & iOS (


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Story posted on
26th Jan, 2020


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