It is generally assumed that levels of air pollutants that
trigger air quality alerts are below thresholds of human
detection by odor, irritation, or specific symptomatic
responses. However, levels or air pollutants at central
monitors can misrepresent local conditions, especially
during transient, local air pollution episodes that humans
may sense by odor, irritation, or other responses (28). Some
studies have found correlations between perceptions of air
quality and monitoring data (29-32), but other studies have
not (33,34).