Letter to the Editor of SCMP - Response to a letter on air quality

 
Letter to the Editor of SCMP - Response to a letter on air quality

I would like to respond to S.P. Li’s letter (“Question left unanswered”) of June 14.

The air quality in Hong Kong can be affected by the emissions generated locally as well as those generated in the Pearl River Delta Economic Zone. According to studies by the Hong Kong University of Science and Technology, our air quality could be dominated by local sources for around half of the time in a year; and the regional sources could contribute some 60% of the measured pollution level in Hong Kong annually, and the percentage could increase to 70% in winter.

The wind data provided by the Hong Kong Observatory also suggest that it is not rare for Hong Kong to be influenced by regional sources. Despite the fact that the prevailing winds in Hong Kong are easterly, Hong Kong can come under northerly or northwesterly winds for 20% of the time in a year. Even if the wind is easterly, the air mass could at times come from the Mainland before approaching Hong Kong.

We have also observed that in most of the incidents when Tung Chung experienced very high readings in the Air Pollution Index (i.e. exceeding 100), Hong Kong was under northerly/northwesterly winds with the atmosphere relatively stagnant.

However, when Hong Kong is downwind of the economic zone, our air quality is not necessarily bad. Take 24 May 2010, which was mentioned in S.P. Li’s letter of 29 May, as an example. The sky was quite clear even though a northerly wind prevailed. The reason was that the rain in the preceding few days had cleaned up the air mass before it arrived in Hong Kong.

While meteorological factors dominate day-to-day air quality changes, lasting air quality improvement can only be attained through effective actions in reducing air emissions in the whole Pearl River Delta Region including Hong Kong. We will continue our efforts to reduce both local and regional emissions to bring clean air to Hong Kong.

Dave HO
Principal Environmental Protection Officer
Environmental Protection Department