Exceedances of WHO Air Quality Guidelines in 2010

Summary of World Health Organization (WHO) Air Quality Guideline (AQG):
PM₁₀ 24-hr mean of 50 μgm^-3 & annual mean of 20 μgm^-3,
NO₂ 1-hr mean of 200 μgm^-3 & annual mean of 40 μgm^-3,
SO₂ 24-hr mean of 20 μgm^-3 & annualized mean of 5 μgm^-3,
O₃ maximum 8-hr mean of 100 μgm^-3 & annualized mean of 23.5 μgm^-3

WHO guidelines do not indicate totally safe air quality, only safer air. Hong Kong's pollutant levels violate the safer WHO limits on most days of the year. This analysis indicates the frequency and magnitude of the problem.

In Year 2010, monthly pollutant concentrations at all urban monitoring stations violated the expected WHO annual limits during cool season (January to March and October to December). This indicates there was no effective protection to public health (Figure). Among all 14 monitoring stations, only the Eastern station in July showed that air quality complied with the annual AQG of PM₁₀ and NO₂ and with the expected annual limit for SO₂ and O₃. All other stations, in all months of the year, showed violations of either single or multiple guidelines for the four criteria pollutants.

Daily or hourly pollutant concentrations at urban monitoring stations also frequently violated the WHO short-term AQG, mostly during the cool season for PM₁₀, NO₂ and O₃ and warm season for SO₂ (Figure). Among all 14 stations, Eastern station has the least number of days exceeding any of the WHO short-term AQG of the four criteria pollutants (128 days), followed by Tai Po (132 days), Kwun Tong (137 days), Yuen Long (152 days), Tung Chung (152 days), Central/Western (157 days), Sha Tin (167 days), Sham Shui Po (169 days), Tsuen Wan (183 days), Mongkok (184 days), Tap Mun (191 days), Central (207 days), Kwai Chung (231 days) and Causeway Bay (256 days).

These large numbers of days on which the air was unsafe to breathe, because of violation of the minimum standard for health protection, show that everyone in Hong Kong has a very high exposure to toxic chemicals which cause diseases of the lungs, heart, and blood vessels. They also cause health problems in diabetics, in pregnant mothers, the sick, elderly and poor.

Edited by AJH

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

Update: Evidence of harmful health effects (Nitrogen Dioxide)

Human population studies in 2010 showed that exposure to NO₂ was associated with several bad health outcomes including increased risk of congenital heart defects (Vrijheid et al 2010), lower infant birth weight (Lepeule et al 2010, Darrow et al 2010), post-menopausal breast cancer in women (Crouse et al 2010), impairments in children’s lungs especially among genetically susceptible persons (Breton et al 2010), increased risks of developing childhood asthma (Clark et al 2010), exacerbated wheezing among asthmatic children (Mann et al 2010), and increased acute childhood leukaemia among those living nearby heavy-traffic road (within 500 meters) or chronically exposed to more than 27.7μgm^-3 of NO₂ (Amigou et al 2010).

Earlier epidemiologic evidence quoted by WHO showed the adverse health effects of NO₂ on daily mortality, children’s hospital admissions for asthma, emergency visits due to ischaemic heart disease, chronic obstructive pulmonary disease and asthma, lung cancer, preterm birth, foetus growth retardation, and sudden infant death (WHO 2006).

Apart from the health effects attributable to exposure to NO₂, other recently reported health effects of exposure to this pollutant include increased infant mortality risks (Son et al 2010), narrowed arteries in the retina (Adar et al 2010), atherosclerosis (Bauer et al 2010), cardiovascular mortality (Guo et al 2010), inflammation of the middle ear in infants (Macintyre et al 2011), damage to DNA (Ren et al 2010), all-causes of mortality and specifically, respiratory and lung cancer deaths (Hales et al 2010), childhood bronchial hyper-reactivity and asthma (Carlsten et al 2010), emergency hospital visits for hypertension (Guo et al 2010), hospital admissions for ischaemic stroke (Andersen et al 2010), daily mortality (Kan et al 2010) and altered cardiac autonomic function (Wu et al 2010).

While we must be cautious about attributing bad health outcomes to a single pollutant in environments where several pollutants are raised, the accumulating weight of evidence suggests that NO₂ levels are an important indicator of health risks. Urgent and effectice action is needed to reduce all emissions including NO₂ and volatile organic compounds. 

Edited by AJH

Reference:

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Lepeule J, Caïni F, Bottagisi S, Galineau J, Hulin A, Marquis N, et al. Maternal exposure to nitrogen dioxide during pregnancy and offspring birth weight: comparison of two exposure models. Environ Health Perspect. 2010;118:1483-9.

Darrow LA, Klein M, Strickland MJ, Mulholland JA, Tolbert PE. Ambient Air Pollution and Birth Weight in Full-Term Infants in Atlanta, 1994-2004. Environ Health Perspect. 2010. [Epub ahead of print].

Crouse DL, Goldberg MS, Ross NA, Chen H, Labrèche F. Postmenopausal Breast Cancer is Associated with Exposure to Traffic-related Air Pollution in Montreal, Canada: A Case-Control Study. Environ Health Perspect. 2010. [Epub ahead of print]

Breton CV, Salam MT, Vora H, Gauderman WJ, Gilliland FD. Genetic Variation in the Glutathione Synthesis Pathway, Air Pollution, and Children's Lung Function Growth. Am J Respir Crit Care Med. 2010. [Epub ahead of print].

Clark NA, Demers PA, Karr CJ, Koehoorn M, Lencar C, Tamburic L, et al. Effect of early life exposure to air pollution on development of childhood asthma. Environ Health Perspect. 2010;118:284-90.

Mann JK, Balmes JR, Bruckner TA, Mortimer KM, Margolis HG, Pratt B, et al. Short-term effects of air pollution on wheeze in asthmatic children in Fresno, California. Environ Health Perspect. 2010;118:1497-502.

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