Plant scientist Felicity Hayes checks on her crops inside one of eight tiny domed greenhouses set against the Welsh hills. The potted pigeon pea and papaya planted in spring are leafy and green, soon to bear fruit.
In a neighboring greenhouse, those same plants look sickly and stunted. The pigeon pea is an aged yellow with pockmarked leaves, while the papaya trees reach only half as tall.
The only difference between the two greenhouse atmospheres: ozone pollution.