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EHA : Yearkbook 2009
EHA YEARBOOK 2009 Lidia Morawska International Laboratory for Air Quality and Health, Queensland University of Technology Inadequate air quality and the inhalation of airborne pollutants pose many risks to human health and wellbeing, and are listed among the top environmental risks worldwide. The importance of outdoor air quality was recognised in the 1950s and indoor air quality emerged as an issue some time later and was soon recognised as having an equal, if not greater importance than outdoor air quality. Identification of ambient air pollution as a health hazard was followed by steps, undertaken by a broad range of national and international professional and government organisations, aimed at reduction or elimination of the hazard. However, the process of achieving better air quality is still in progress. The last 10 years or so have seen an unprecedented increase in the interest in, and attention to, airborne particles, with a special focus on their finer size fractions, including ultrafine (< 0.1um) and their subset, nano particles (< 0.05 um). This paper discusses the current status of scientific knowledge on the links between air quality and health, with a particular focus on airborne particulate matter, and the directions taken by national and international bodies to improve air quality. Air Quality and Health It has been well known for centuries that certain natural processes, as well as human activities, result in air pollution. For example, air pollution in Rome in the first century AD has been described as: “... a noisome brown haze would be hanging low over the city’s streets, capable of dulling their majestic polish and sparkle. Charcoal smoke from household kitchens, baker’s ovens, blacksmiths’ furnaces, funeral pyres and clouds of dust kicked up by shuffling pedestrians...” (Perrottet 2002). Nowadays the air which we breathe contains a complex cocktail of pollutants including: particulate matter; gaseous pollutants such as nitrogen oxides (NOx); carbon monoxide (CO); sulphur dioxide (SO2); ozone (O3) and carbon dioxide (CO2); volatile and semivolatile organic compounds; and inorganic trace elements (Pb, V, Br). Airborne particulate matter is a complex mixture of particles, ranging in size over five orders of magnitude, from molecular dimensions to the sizes that are distinguishable with the naked eye. For many decades, ambient particulate matter has been monitored in terms of mass concentration, currently defined as PM10 and PM2.5 (mass concentration of particles with aerodynamic diameters of < 10um and < 2.5um, respectively). The health effects of airborne pollutants range from irritative effects on skin and mucous membranes of the eyes, nose and throat, to other effects on respiratory, reproductive, cardiovascular, cardiopulmonary, immune and sensory nervous systems, as well as causing allergic reactions, cancer and even death. Some pollutants cause specific health effects. For example, the effects of exposure to carbon monoxide range from fatigue to death (CO combines with haemoglobin and reduces transport of oxygen to the tissues); nitrogen oxide is a trigger for asthma attacks and long term effects on the respiratory system; lead leads to mental retardation; ozone can cause eye irritation, damage to sensitive tissue and the exacerbation of asthmatic symptoms; and radon has been linked to increased risk of lung cancer (World Health Organization [WHO] 2000). It has been common knowledge for a long time that the inhalation of certain pollutants leads to a deterioration in health, however, it was only in the 195 0 s that a full appreciation of the hazards related to air pollution emerged, following serious episodes of air pollution in London and in several industrial cities of the US, which were retrospectively linked to significant increases in mortality (WHO 2000). Regulations were then put in place, as the first step on the way towards the process of modern air pollution prevention and control. While there have been significant improvements in air quality, with respect to some pollutants and countries, there are still for example two million premature deaths per year which are attributable to urban outdoor air pollution, as well as indoor pollution from the burning of solid fuels (WHO 2002), and the number of deaths attributed to vehicle generated air pollution is actually higher than those that can be attributed to road accidents (Seethaler et al. 2003). Indoor Versus Outdoor Air Quality It is outdoor air quality which has predominantly been linked to human ill health. Large databases on outdoor pollutants have been used for prospective and retrospective epidemiological studies, which showed a clear link between outdoor pollution and health, despite the fact that most people spend the majority of their time indoors. In relation to particulate matter, it was established that there is a linear relationship between outdoor mass concentration – PM2.5 and PM10 – and health (Pope & Dockery 2006), again despite the fact that we are generally inside 90% of time or more. This leads to the question: is the 10 % of time spent outside so important? The answer is in outdoor particulate matter which penetrates indoors, providing continuous indoor background pollution. Some of the particles will deposit on indoor surfaces, and as a result, the ratio of indoor to outdoor concentration will be below one, however, for naturally ventilated buildings the ratio would usually be above 0.5 (Morawska & He 2003). In other words, in the absence Air Quality and its impact on Health: Focus on particulate matter
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EHA Yearbook 2010