Figure 1: Air Quality Days

Figure 2: Number of Days that Ozone, Particulate Matter and Carbon Monoxide Determined Air Quality

Figure 3: Particulate Matter Concentrations, Seattle Duwamish Site

Figures:  
• Figure 1: Air Quality Days  – 
• Figure 2: Number of Days that Ozone, Particulate Matter and Carbon Monoxide Determined Air Quality  – 
• Figure 3: Particulate Matter Concentrations, Seattle Duwamish Site

Data Discussion

The Indicator Defined

Air quality is measured across the nation using the Air Quality Index (AQI). The AQI measures concentrations of the following six criteria pollutants: carbon monoxide, nitrogen dioxide, sulfur dioxide, ozone and particulate matter. There are four air quality levels that are dependent on concentrations of the pollutants. The levels include: good, moderate, unhealthy for sensitive people and unhealthy. The worst pollutant, or the pollutant with the highest concentration, determines the AQI.

Data Interpretation/Evaluation

The number of good and moderate air quality days has remained steady since 2001. However, overall the number of moderate days has declined. (Figure 1)

More stringent standards for fine particulate matter (P.M.2.5) were developed in 1999. Ozone standards also changed in 1997 to help protect people and the environment from long exposure periods. As a result of these more stringent standards, there was a significant decrease in the number of good days beginning in 1999. The Environmental Protection Agency (EPA) is currently in the process of proposing new fine particulate standards which will likely be more stringent based on new health information.

Concentrations of air pollutants have decreased over the last decade due to better control of air pollution. However, ozone and P.M.2.5 remain a concern in our area and are driving the air quality ratings in King County. Ground-level ozone levels have hovered just below federal standards. (Figure 2) On-road vehicles are the largest contributor to ozone. Stationary sources, such as burning trash and wood in fireplaces and woodstoves, are the largest source of particulate matter. Higher concentrations of ground-level ozone are directly correlated with warm and dry weather.

Due to cleaner vehicles on the road, carbon monoxide concentrations have reduced dramatically in this region. In addition, the number of days in the Air Quality Index determined by carbon monoxide was significantly reduced when P.M.2.5 standards became more stringent.

Since 1999, P.M.2.5 has met federal standards but not the more stringent Puget Sound Clean Air Agency’s (PSCAA) Health Goal, as seen in the chart. (Figure 3)

Data Source and Limitations

The air quality data were contributed by Communities Count (www.communitiescount.org) and originally collected from the Puget Sound Clean Air Agency Air Quality Reports, 2003 as well as personal communications with Kathy Himes and Mary Hoffman from the Puget Sound Clean Air Agency (http://www.pscleanair.org/) and the King County Benchmark Program.

Air quality is defined by the Air Quality Index (AQI), a national standard identified by the United States Environmental Protection Agency. The AQI is reported according to a 500-point scale for each of the major criteria pollutants. Good air quality (0-50) demonstrates that there is little or no risk from pollutants. Moderate air quality (51-100) is denoted when there are health concerns for a small number of people. A more stringent index (101-150) was identified in 1999 and demonstrates when air quality is unhealthy for populations that are sensitive, such as people with health conditions. Unhealthy air quality (151-200) is when the air is considered unhealthy for the entire population.

The federal standard for daily PM2.5 concentrations is currently 65 _g/m3. The Puget Sound Clean Air Agency Board of Directors adopted a more stringent goal based on recommendations of Particulate Matter Health Committee. The Committee conducted a systematic review of health data and determined that a daily average of 25 _g/m3 is protective of human health.

The main limitation with the data is due to the change in the way data were collected for fine particulates in 1999. Due to the stringent standards air quality appears to have declined from 1998 and 1999 though the decline can be attributed to more types of pollutants being measured more frequently.

The Air Quality Index includes data on criteria pollutants, thereby excluding all other types of air pollution such as air toxins and greenhouse gases.

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