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for example, indicated a risk in older people of about twice that observed in younger persons (see Fig 16); similar findings are reported for hospitalisations. These comparisons are relatively crude ('older', variously categorised, versus 'not older') and probably obscure a stronger effect. The explanation(s) are likely to be several and have not been examined fully, but they will include the higher frequency of pollution-sensitive pulmonary, cardiovascular and metabolic diseases in older populations. Few studies have explicitly compared risks in children with those in adults, but there is evidence of an adverse effect of air pollution on the health of children who spend a higher proportion of their time outdoors and are therefore at greater risk of exposure to ambient pollutants. 4 Moreover, in 2015 nearly 25% of all schoolchildren in London were exposed to levels of air pollution that exceeded legal limits. 5 First author, year Faustini, 2011 Cakmak, 2011 Goldberg, 2000 Katsouyanni, 2009 Wichmann, 2000 Biggeri, 2005 Samoli, 2008 Franklin, 2007 Forastiere, 2008 Samoli, 2011 O'Neill, 2008 Aga, 2003 Zeka, 2006 Wong, 2010 Yang, 2012 Revich, 2010 Chen, 2010 O'Neill, 2008 Samoli, 2008 Samoli, 2008 O'Neill, 2008 Qian, 2010 Katsouyanni, 2009 Garrett, 2011 Katsouyanni, 2009 Ma, 2011 Balakrishnan, 2011 Kan, 2008 Son, 2012 Balakrishnan, 2011 Overall –1 0 1 2 3 4 5 6 Increase (%) in risk of death per 10 µg/m 3 PM 10 Fig 16. Meta-analysis of the association with age of increased risk of death from exposure to PM 10 . Solid squares represent results from younger populations; open squares represent those for older populations. Each square represents a central risk estimate, and each horizontal line its 95% confidence interval. Diamonds represent overall results from the meta-analysis. Adapted from Bell et al, 3 by permission of Oxford University Press. © Royal College of Physicians 2016 71 5 Our vulnerable groups