The UK measures the effects of daily air pollution, like sunburn risk, on a one to 10 index. As the air quality index increases, official advice tells vulnerable people to avoid outdoor exercise and reminds asthmatics to use their inhalers more often. This index is used in national forecasts and alert systems in southern England and Scotland and in the warnings that appear at London bus stops when high air pollution is forecast.

Scientists at King’s College London tested different types of messages with volunteers who used the CityAir app. Rather than telling people to make changes only when air pollution was bad, the scientists focused on helping people to know how to prepare and protect themselves, and overcome perceived barriers stopping them from changing how they travel. For instance, a message targeting asthmatics encouraged them to take their preventative medication, rather than simply warning them to carry their inhalers. Other messages included pollution maps to help people to find clean places to exercise and to find routes away from the worst roads. Anticipating that people might be reluctant to change, the messages pointed out that low pollution routes need not make their journeys any longer.