What are the Air Quality Objectives?

Air Quality Objectives are intended to protect the environment and human health. Through legal instruments such as the Environmental Impact Assessment Ordinance, we should be able to limit new sources of pollution which will degrade air quality and cause harm to sensitive receivers such as children. Air pollution potentially affects everyone in both the short and long term.

The HKSAR government has not revised the existing Hong Kong Air Quality Objectives (HKAQO) since they were established in 1987, despite updates of the WHOAQG in 2000 and 2005. The data in 1987 was based on research which dated back to the early 1980s. So our AQO are really 30 years out of date.

The more recent WHO updates were both based on comprehensive reviews of epidemiologic evidence on air pollution effects to identify the minimum air quality requirements to protect human health and well-being. The outdated 1987 HKAQO are set too high with little relevance to current scientific evidence on limits needed to protect public health. For example, the daily (24 hour average) SO₂ limit of 350μgm^-3 is 17 times above the present WHOAQG for a 24 hour average of 20μgm^-3.

In 2009, the HKSAR government proposed new HKAQO based mainly on the most lax of the WHO air quality limit, the so-called "interim targets". These “interim targets” were designed for low income developing regions to provide a preliminary basis for an air quality improvement strategy. They are not intended as guidelines for a high GDP per capita region like the HKSAR. For example, the government’s proposed new AQOs for SO₂, PM_2.5 and O₃ are based on the “entry level” Interim Target 1 (IT-1). The lax limit for PM₁₀ is based on the second WHO Interim Target 2 (IT-2) with an annual limit of 50μgm^-3, which is only slightly better than the previous Hong Kong AQO of 55μgm^-3, which was introduced more than two decades ago.

The question is why did the government's consultants set such lax limits and ignore the opportunity to set notional standards which would drive meaningful improvement of air quality? The lack of a clear strategy to improve air quality is clearly reflected by the government’s selection of the most lax limits available as the basis for the proposed new HKAQO.

In fact, the proposed HKAQO are even worse than the selected WHO lax limits because these WHO advisories have been further modified by adding additional days of allowable exceedances above the short-term limits, so that the long-term annual limits may actually shift to even higher levels than the original selected WHO limits.

Our latest analyses show that the proposed new HKAQO of 125μgm^-3 for SO₂ could lead to annual SO₂ concentrations even higher than the current mean concentrations (Lai et al 2010). This is a clear and alarming signal that public health impacts were not properly considered when setting the new AQO. The government's strategy lacks any elements of a precautionary approach; this has serious implications for the future health of children and others most vulnerable to air pollution.

Edited by AJH

Reference:

Lai HK, Wong CM, McGhee SM, Hedley AJ. Assessment of the health impacts and economic burden arising from proposed new air quality objectives in a high pollution environment. Open Epidemiology. 2011;4:106-122. http://www.benthamscience.com/open//toepij/articles/V004/SI0001TOEPIJ/106TOEPIJ.pdf