Persistently high levels of ozone pollution in Asia are costing China, Japan and South Korea an estimated $63 billion annually in lost rice, wheat and maize crops, a new study says. maize crops in both China and South Korea were also affected at lower levels. The crop is not grown in Japan in significant quantities. The researchers said their findings were limited by several factors, including that ozone monitors are mostly in urban areas and levels in rural areas are often higher.