Hong Kong saw the concentration of ozone rise to the highest level in the past 18 years in 2017, suggesting that the air quality in the city posed a greater health risk for people living here.
According to data released by the Environmental Protection Department (EPD) on Tuesday, the annual average concentration of ozone monitored by general stations increased 30 percent to 51 µg/m³ in 2017 from the previous year. 1µg equals one-millionth of a gram.
It was the highest level since records began in 1999, up 50 percent during the period.
Data collected from roadside stations showed the concentration was 23 µg/m³, up 70 percent from 13µg/m³ in 2011, when these stations began functioning, the Hong Kong Economic Journal reports.
Ozone is known to cause various types of respiratory diseases and one could die of exposure to high concentration of it.
The roadside concentration of nitrogen dioxide rose 5 percent to 86 µg/m³ last year, from 82 µg/m³ in 2016.
As a result of higher concentrations of ozone and nitrogen dioxide, the EPD said a total of 44 days and 55 days when the Air Quality Health Index was “high”, “very high” or “serious”, were recorded last year by general stations and roadside stations, respectively.
By comparison, it was 26 and 31 days respectively in 2016, or an increase of 70 percent for both.
Dave Ho Tak-yin, acting EPD assistant director for air policy, pointed out that although concentrations of most pollutants in Hong Kong – respirable suspended particulates (PM10), fine suspended particulates (PM2.5), sulfur dioxide (SO2), and carbon monoxide (CO) – had shown a downward trend over the past 18 years until 2017, or declines between 13 and 74 percent, those of ozone and nitrogen dioxide had kept rising.
Ho explained that longer spells of sunshine and less rainfall last year facilitated the formation of ozone.
Hong Kong experienced 19 percent more hours of sunshine last year, while total rainfall was down 15 percent, Ho said, adding that northwesterly winds tended to bring ozone that accumulated around the Pearl River estuary to the western part of Hong Kong and affect the local air quality.
He said Hong Kong, to effectively control ozone, needs enhanced regulation of the use of volatile organic compounds and more cooperation with the provincial government of Guangdong, where most of the hazardous pollutants come from.
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