Along with greenhouse gases goes a deterioration in air quality. I suspect that many of you have traveled to some of the world’s megacities and be appalled by what passes for ambient air. Ten years ago I flew to Santiago, Chile for a conference and was amazed when the pilot had to make an instrument landing – at noon on what was supposed to be a clear day. Once on the ground it was clear what the problem was – the air was as much a liquid as a gas, and breathing was a challenge. More and more of our cities suffer from this condition. Is it surprising that asthma is epidemic?