Particulate matter days (percent)
Maryland - Worcester
Percent of days with maximum 24-hour average PM 2.5 concentration over the National Ambient Air Quality Standard
Number of days during the year that air quality in a county was over the National Ambient Air Quality Standard for fine particulate matter (FPM, < 2.5 µm in diameter).
Total number of days in the year.
2006 - Dimensions
Comparison of 22 Counties
- Air Quality Standard monitoring data were used for counties and days with monitors and hierarchical Bayesian data were used for any county or day without monitors. The spatial resolution of the HB grid cell used is 36 Km. The grid cell values were transferred to counties based on a population weighted approach. The indicators are available for counties/states in the conterminous US (Lower 48 + Washington DC). HB modeled data are not available for AK and HI.
Public Health Air Surveillance Evaluation Project Team (PHASE)
Because of the problems inherent in measuring air quality, particularly the lack of air quality monitors, the Public Health Air Surveillance Evaluation project team developed an innovative strategy to model air quality. Researchers used the model output to estimate peak fine particulate matter and ozone concentrations for each day in the year and, using National Ambient Air Quality Standards, estimate the number of days that the air quality was poor for sensitive populations due to these contaminants.
Data Source Methodology
The Environmental Protection Agency's (EPA) first step to address insufficient data collection sites was the creation of an air quality simulation model, the Community Multi-Scale Air Quality Model (CMAQ). To improve upon CMAQ, the PHASE project uses both CMAQ output and monitor data in a hierarchical spatial-temporal model to estimate daily ozone and fine particulate matter concentrations throughout the year