Air quality in PRD region worsened in 2021, indicators show

Air quality in the group of cities comprising the Pearl River Delta (PRD) region have been mixed during 2021, with some indicators showing improvements while others worsen, the annual report of the Guangdong-Hong Kong-Macau PRD Regional Air Quality Monitoring Network shows.

According to the 2021 report, all but one pollutant in the analysis showed worse results compared to the previous year. The only exception from the group of six major pollutants in the analysis was carbon monoxide (CO) which showed an average yearly concentration of 0.600 mg/m3, 0.011 mg/m3 fewer when compared to 2020 and making 2021 the best result recorded since 2015, the first year in which the pollutant was measured.

The other five major pollutants including sulfur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3), respirable suspended particulates (PM10) and fine suspended particulates (PM2.5) all recorded year-on-year increases in 2021.

Although the 2021 results show a general worsening of air quality in the region, and consequently in Macau, analysis from over the last 15 years since the monitoring network was first implemented, shows a significant improvement in three of the pollutants: SO2 (- 83.7%), NO2 (-40.5%) and PM10 (-44.8%).

Outside of this improvement, ozone concentrations have been growing almost yearly for the past 15 years, with the 2021 figure the second-highest concentration ever recorded (59µg/m3, a 34.1% increase). The highest concentration of this pollutant was recorded in 2019, with a figure of 60µg/m3.

According to the report, the annual ozone average in 2021 shows that the photochemical smog problem in the region has not been addressed, but in fact has been worsening.

The report does not point to any solutions or suggest any measures to address the issue, noting only that “Guangdong, Hong Kong and Macau governments will continue to implement emission reduction measures to further improve the air quality in the region and tackle the photochemical pollution problem.”

Ozone is not directly emitted by polluters, instead it is formed by the photochemical reaction of oxygen, nitrogen oxides (NOx), and volatile organic compounds (VOCs) in the air under sunlight. It is one of the main components of photochemical smog. 

Ozone can irritate the eyes, nose and throat and, at high levels, it can increase susceptibility to respiratory diseases and aggravate pre-existing respiratory conditions such as asthma. The precursors of ozone (NOx and VOCs) mainly originate from pollution sources in urban areas.