16 February 2019
The overall air quality in Hong Kong may be improving, but the concentration of ozone continues to rise. Photo:
The overall air quality in Hong Kong may be improving, but the concentration of ozone continues to rise. Photo:

HK air quality improving, but ozone concentration rising

Hong Kong’s general air quality has been improving, but the concentration of ozone, a major constituent of smog, has been building up over the past years.

Levels of sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), repairable suspended particulates and fine suspended particulates all declined last year, compared with 2013, according to preliminary data from the government’s monitoring network. (See tables below)

However, the concentration of ozone continues to show a rising trend, increasing 7 percent last year from 2013 and by 35 percent since 1999, data from the Environmental Protection Department (EPD) showed.

At a media briefing Tuesday, EPD assistant director Mok Wai-chuen noted that the increase in ozone concentration is partly due to meteorological factors—more hours of bright sunshine and less rainfall in 2014 accelerated chemical reactions that resulted in higher concentrations of ozone.

Ozone is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of heat and sunlight.

Mok said efforts by authorities to cut vehicle and industrial emissions have shown notable effects in 2014.

For example, given the increased ozone level in the city last year, NO2 levels should have increased as chemical reactions between NOx and ozone normally produce NO2.

However, air quality monitoring showed that NO2 levels actually dropped about 10 percent in 2014 from the previous year, he said.

Since March 2014, when the government launched an incentive-cum-regulatory scheme to phase out pre-Euro IV diesel engines, about 20 percent of such vehicles have been eliminated, Mok said.

The goal is to phase out about 82,000 such vehicles by the end of 2019.

Mok also stressed the importance of regional cooperation in reducing ozone and particulate levels while efforts are pursued to cut emissions from the transport sector.

For example, a new regulation requiring ocean-going vessels to switch to cleaner fuel may be enacted this year.

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EJ Insight reporter

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