Health is defined as homeostasis of the cellular ecology, and a state where there has not been an inordinate loss, reversible or irreversible, of the structural and/or functional reserves of the body. An adverse health effect is defined as the causation, promotion, facilitation and/or exacerbation of a structural and/or functional abnormality, with the implication that the abnormality produced has the potential of lowering the quality of life, contributing to a disabling illness, or leading to a premature death. Experimental animal studies indicate that poor air quality has the potential for serious adverse health effects through perturbations of the cellular ecology over long-term periods. Some of the most important concerns are inordinate depletions of lung reserves (in particular, emphysema), the facilitation of cancer metastasis to the lung, the facilitation of immunologic deficits with the concomitant expression of opportunistic organisms, and amplification of cardiovascular abnormalities (in particular, ischemic heart disease). It is argued that air quality standard setting should more strongly consider adverse health effects that are presently subclinical in nature in order to achieve early prevention instead of late correction.