Hong Kong, Hong Kong Air Quality & Smog

Dominant pollutants, when pollution and smog are worst, a notable historical episode, and the official monitoring agencies for Hong Kong, Hong Kong — plus how to check the current reading. Hong Kong reports air quality on the Hong Kong Air Quality Health Index (AQHI) — our full guide explains how that scale works and how it compares to the US AQI.

Dominant pollutants

Roadside NO₂, PM2.5, ozone.

Seasonal pattern: when smog is worst

Hong Kong's air has two faces: dense roadside pollution in the urban canyons of Kowloon and Causeway Bay, and regional smog driven by emissions transported from the wider Pearl River Delta. Ozone has been rising. Air is generally worst in autumn and winter, when northerly continental flow carries pollution in; summer's southerly maritime air is cleaner.

A notable air-quality episode

Hong Kong adopted its own Air Quality Health Index (AQHI), a 1–10+ health-risk scale, in late 2013 — replacing an older index — to better communicate the combined short-term health risk of roadside and regional pollution.

The local index and who runs it

Hong Kong reports air quality using the Hong Kong Air Quality Health Index (AQHI), not the US AQI — so the same air can read as a different number than you may be used to. The EPD publishes the AQHI for general and roadside stations at aqhi.gov.hk. Note that Hong Kong's AQHI is its own scale, distinct from Canada's AQHI of the same name.

• Hong Kong Environmental Protection Department (EPD)

How to check air quality in Hong Kong

For the official live reading, the agency portals above are the canonical source. To understand what the numbers mean, start with our guide to the Hong Kong Air Quality Health Index (AQHI) and the broader comparison of world air-quality indices. Smog Report puts glanceable air quality on your iPhone — widgets, Live Activities, Siri, and Apple Watch — free and with no account.

Common questions about Hong Kong air quality

Why does Hong Kong have air-quality and smog problems?

Hong Kong's air has two faces: dense roadside pollution in the urban canyons of Kowloon and Causeway Bay, and regional smog driven by emissions transported from the wider Pearl River Delta. Ozone has been rising. Air is generally worst in autumn and winter, when northerly continental flow carries pollution in; summer's southerly maritime air is cleaner.

What are the main air pollutants in Hong Kong?

Hong Kong's dominant pollutants are roadside NO₂, PM2.5, ozone. The reading on any given day is usually driven by whichever of these is highest.

Has Hong Kong had a major air-quality or smog event?

Hong Kong adopted its own Air Quality Health Index (AQHI), a 1–10+ health-risk scale, in late 2013 — replacing an older index — to better communicate the combined short-term health risk of roadside and regional pollution.

What air-quality index does Hong Kong use?

Hong Kong reports air quality on the Hong Kong Air Quality Health Index (AQHI) (AQHI), not the US AQI — so the same air can read as a different number than you may be used to. For live, glanceable readings on your iPhone, the free Smog Report app auto-selects the right local index for wherever you are.

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