Issue link: https://hi.iaq.net/i/670243
Chapter 2: The air we breathe Our day-to-day world comprises a range of micro-environments through which we, as individuals, uniquely move, live and breathe through the course of a day – and indeed throughout our lifetime. It includes, of course, the outdoor environment, which is affected by a wide range of factors. Outdoor air, in turn, influences the quality of the air in indoor environments. But indoor environments also have their own sources of contaminants, so that consideration of particular exposures in the home, public places, schools/colleges, hospitals, workplaces and transport is very important in assessing impacts of the breathed environment on our health and wellbeing. As will be demonstrated in this chapter, there are often 'unintended consequences' of actions and policies that impact the breathed environment, including problems relating to the design and/or formulation of products and materials, and the health consequences of exposure to their ingredients or components. 2.1 The air outside 2.1.1 What are the main pollutants, where do they come from and what effects do they have? Outdoor air contains a range of pollutants from a variety of sources, both natural and man-made. As outlined in Chapter 1 of this report, the principal anthropogenic pollution sources are transport vehicles (petrol and diesel engine emissions, along with products from tyre and brake wear), power stations and factories. The atmosphere also contains dust from geological sources and compounds that are the product of chemical reactions between individual substances in the air, as well as a wide variety of gases and particles that originate from natural and biological sources, ranging from volcanic activity to natural ecosystems, agriculture and forestry. The key pollutants in outdoor air are generally regarded to be particles (measured as PM 10 and PM 2.5 ), oxides of nitrogen (principally NO 2 ) and ozone (O 3 ), with sulphur dioxide (SO 2 ), carbon monoxide (CO), hydrocarbons (including benzene, 1,3-butadiene and PAHs) and metals also being significant from a health perspective. The health effects of all these substances have been intensively studied, and comprehensive assessments of their individual impacts on health are available elsewhere. 1–3 Chapter 6 shows that their effects are considerable, and that these pollutants are all subject to national and/or international ambient concentration limits. Pollutants with the greatest current impact on public health are considered to be PM 2.5 , O 3 and NO 2 . However, in most cases legislated concentration limits do not represent a 'safe' level for the population as a whole, but are often talked about as levels considered to not pose a 'significant risk' to health. This begs the question of the meaning of 'significant' – given, for example, that impacts of exposure to fine particles have been observed at very low concentrations and that there is no evidence for a threshold for exposure at the population level. The Committee on the Medical Effects of Air Pollutants (COMEAP) estimates 29,000 'equivalent' deaths annually from exposure to PM 2.5 in the UK, 4 with only a small fraction of that figure relating to exposures to concentrations in excess of legal limits. This figure increases to around 40,000 if the recently described effects of NO 2 are taken into account. 5,6 The reality is that agreed standards often incorporate considerations of practicality, ie by how much is it economically reasonable to reduce emissions? For this reason, World Health Organization (WHO) guidelines – based solely on health concerns – are considerably lower in some important cases than national or EU limit values, and even these are not totally protective. 7 18 © Royal College of Physicians 2016