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Interpreting the data

The hourly pollutant values, shown in the graphs, are based on the national Air Quality Index (AQI). The AQI is computed from data collected by a network of air monitoring sites. The AQI converts the pollutant concentrations to a value easily compared to the health standard of each pollutant.

8-hour Ozone and 24-hour Particle Pollution concentrations with an AQI over 100 have exceeded the health standard.

The Regional Summary graph is a visual display of the final AQI value for each day of the last seven days. The final AQI value for a given day is the highest AQI reached by any monitor in that region regardless of which pollutant was involved.

Site-specific graphs display the AQI associated with the current running average. When viewed late in the day one can see how the pollution levels changed over the course of that day.

The color-coding is based on the AQI. Green indicates values in the "good" range; yellow in the "moderate" range; orange in the "unhealthy for sensitive groups" range; red in the "unhealthy" range, and purple in the "very unhealthy" range. An X indicates suspect data.