Hong Kong's air quality to worsen as pollutant PM2.5 hits 'unhealthy' levels

The air quality in Hong Kong is expected to worsen later today after pollution readings hit "very high" and "high" in various areas, the Environmental Protection Department (EPD) warned on Wednesday.

The air quality health index (AQHI) – which measures the risk of hospital admissions due to air pollutants – hit "very high" levels in Central, Yuen Long in the New Territories and Tap Mun Island off northeastern Sai Kung.

The remaining 12 monitoring stations across the city recorded "high" readings.

The highest warning on the index is "serious" – and the last time Hong Kong hit that reading was on June 8 and again on September 19, two of the smoggiest days of the year.

The EPD said abundant sunshine heightens photochemical smog formation, a chemical process in which nitrogen oxides (emitted from combustion sources such as car exhaust) combine with volatile organic compounds to form ground-level ozone.