Causality
The principle of, or relationship between, cause and effect (for example, smoking causes lung cancer).
Chemical transport models
Chemical transport models (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.
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.