A first set of interventions to mitigate the health impacts of pollution involves reducing levels of exposure to it. Exposure reduction requires a good understanding and measurement of the spread of pollution in the relevant media (e.g. air, water, ground), as well as effective communication to the public. Therefore, exposure reduction often starts with an appropriate
monitoring system, the design of which will depend on the source of pollution and specificity of the pollutant (e.g. water pollution from fertilisers used in agriculture is often assessed fortnightly or monthly only45). The sampling process to monitor pollutants is normally designed to optimise costs and benefits, as measurements can be expensive (e.g. in the case of milk dioxin monitoring46) and need to be justified by their benefits.
Air quality monitoring is the most common. Air quality monitoring technology has improved significantly over the last decade; it has become cheaper, smaller and more reliable. Portable and affordable devices are now available to the public, although their precision varies greatly. Furthermore, air quality networks with continuous monitoring such as the London Air Quality Network (LAQN)xxvii are now accessible to all free-of-charge and increase people’s awareness of air quality in their local area. The information from these networks can also be combined with mobile phones’ geographical information47 to estimate people’s exposure to pollution without carrying monitoring devices. Although monitoring is a key element to evaluate the air quality, identify problems, and support changes with factual information, the Royal Borough of Kensington and Chelsea has closed or removed from the LAQN seven out of its nine monitoring stations in October 2017. Monitoring is a cornerstone in air quality improvement, and this decision goes against the evidence reviewed in this chapter.
However, in order to be beneficial, monitoring needs to be complemented by additional information such as overall indicators that are meaningful to the user (e.g. a colour scheme that translates pollution metrics for non-expert into recommendations), alerts of high pollution levels, or practical suggestions to avoid or reduce exposure (e.g. alternative commuting routes). Alerts are effective in informing the public about peaks of pollution48,49 but had no clear impact on hospital admissions in a study based in Southampton.50 In the case of smog alerts in California, individuals responded to the information, although the effect was mostly limited to the first day of the alerts when there were
xxvii Website of the London Air Quality Network (LAQN).
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consecutive days of high pollution. As the cost of substituting activities between days increases over time51, alerts would not be effective in case of numerous and repeated peaks. Walking or cycling along a street with low traffic can reduce exposure to some pollutants.52 Mobile phone apps that propose alternative routes to individuals using active transport are becoming increasingly popular.xxviii However, the success of these alternatives could be limited by the existing infrastructure in some cities where walkable routes are limited.53. In the future, we should see a more dynamic and personal use of alerts by combining individual exposure and needs (e.g. information on when to take or increase respiratory drugs on the way to school.54).
When the source of emissions cannot be modified, retrofitting air filters to the source of emissions can be an effective solution. The Washington State clean school bus program provided $5 million in annual funding for 2003–2008 for retrofitting old diesel buses, and a conservative benefit–cost ratio was estimated between 7:1 and 16:1, equivalent to a net present value of
children’s health benefits between 424,000 and 989,000 dollars per adopter school district55 (this study is further detailed in Box 1). Stevens et al.
considered retrofitting old cars in Mexico City with either type of diesel particulate filter or an oxidation catalyst, and find positive net benefits. At current prices (2010), retrofit with an oxidation catalyst provided greatest net benefits. However, the authors suggest “as capital costs decrease, retrofit with diesel particulate filters is expected to provide greater net benefits”.56 Some authors have modelled building ventilation and retrofitting homes according to certain standards to reduce indoor exposure to outdoor PM2.5 using enhanced filtration among others leads to positive net health benefits 57,58 but empirical evidence is lacking. Others have modelled the optimal ventilation rates to radon, while accounting for the increase in heating cost and have concluded that periodic ventilation in this context should be preferred over a continuous one, but no health impacts have been assessed.59
Many more alternatives have been suggested to reduce existing pollution levels, such as planting trees and shrubs60, optimal ventilation routines to address various sorts of pollutants but formal economic impact assessments accounting for the health impacts are not available.
xxviii
The World Health Organization has developed a Health Economic Assessment Tool
(HEAT) to measure the benefits of walking and cycling (World Health Organization, “Health economic assessment tools (HEAT) for walking and for cycling - Methods and user guide, 2014 update,” 2014.). For example in Brighton and Hove, the tool
estimated that 30% increase in the number of cyclists during 2007-2010 was associated with a mean annual benefit averaged across 10 years of £220,115, but these estimates to do not take into account exposure to pollution.
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Indoor air pollution is also a health hazard, but cost-benefit analyses of interventions to improve health outcomes in this context are limited. A study from the Department for Communities and Local Government published in 2009 finds that carbon monoxide caused the poisoning of about 80 individuals in a year in England and Wales, but based on a cost-benefit analysis, the authors found that the installation of CO detectors alongside new gas
appliances (already incorporating secondary safety systems) comes at a very favourable cost-benefit ratio (except in the case of solid fuel).61 A model of indoor air ventilation and filtration has been developed by the EU-funded HEALTHVENT project. Their analysis shows a potential for a significant health risk reduction, but the benefits have not been compared to the interventions’ costs.62
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