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Daily Wintertime PM2.5 Speciation at Hawthorne and Smithfield

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For the primary purposes of better validating Utah DAQ’s photochemical modeling, UDAQ will do more frequent speciation of wintertime PM2.5 filters. EPA’s Chemical Speciation Network (CSN) requirements specify either one-in-three or one-in-six day speciation of PM2.5 at three Utah locations (Hawthorne, Bountiful, and Lindon).

The State of Utah is in nonattainment of EPA’s 24-hour PM2.5 standards. Wintertime violations of the National Ambient Air Quality Standard (NAAQS) for 24-hour PM2.5 are due to relatively short lived persistent cold-air pool (PCAP) episodes, driven by prolonged temperature inversions occuring in Salt Lake Valley, Utah Valley, and Cache Valley.

Due to the short-lived nature of these PCAP events (e.g., 1-2 weeks), exceedances of the NAAQS may occur for only 2 or 3 days during an event. For that reason, the relatively infrequent sampling required by CSN protocols could be insufficient for model validation as peak PM2.5 days might not coincide with days when CSN sampling is scheduled.

To address these issues, UDAQ will 1) increase sampling at Hawthorne (located in Salt Lake Valley) to a daily frequency and 2) conduct daily sampling in the Cache Valley during occasional PCAP events.

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