Air pollution<span> is a major environmental </span>risk<span> to </span>health<span>. By reducing </span>air pollution<span> levels, countries can reduce the burden of disease from stroke, heart disease, lung cancer, and both chronic and acute respiratory diseases, including asthma.</span>
It means that you consider the elements as a list organized by atomic number, the property is seen to repeat over and over as you move through that list.
