Prior to the 2015 to 2017 monitoring period, Seattle had met federal attainment levels for the allowable number of “unhealthy” PM2.5 and ozone days. Since 2016, all key measures for PM2.5 and ozone pollution have been on the rise. More concerning is a trend of recently declining air quality in King county, of which Seattle is the county seat. Other days in Seattle tend to achieve “good” to “moderate” US AQI ratings. The frequency of Seattle’s pollution spikes is thereby more than double the targeted allowance.įrom a broader perspective, the 14.2 unhealthy pollution days represent just 4 percent of the year. 1 The US Environmental Protection Agency (EPA) recommends no more than 3.2 unhealthy pollution days each year for each pollutant. On average, Seattle experiences 14.2 unhealthy pollution days a year, with 7 owing to high ozone and 7.2 owing to high PM2.5. Despite “good” US AQI levels over recent years, Seattle failed to meet federal targets for allowable unhealthy ozone days and unhealthy PM2.5 days in 2019.
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