Any substance that can cause cancer.
The principle of, or relationship between, cause and effect (for example, smoking causes lung cancer).
Chemical Transport Models
Chemical transport model (CTMs) consist of mathematical representations of the relevant physical and chemical atmospheric processes, which are solved using numerical algorithms to obtain pollutant concentrations as a function of space and time for a given set of pollutant emissions and meteorological conditions. More here.
Chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease (COPD), including chronic bronchitis and emphysema, is a lung disease characterized by chronic obstruction of lung airflow that interferes with normal breathing and is not fully reversible.