October 1998 Air Quality Report

• Weather patterns affecting air quality
• Highest monitored levels of air pollution
• Highest levels of particulate matter (PM10 & PM2.5), carbon monoxide (CO), and ozone (O3)

Good pollutant dispersion generally prevailed during October except for a brief stagnation during the period of the 21st through 24th. Fine particulate pollution levels during this period are depicted graphically. Precipitation was generally normal with Sea-Tac airport receiving 107% of normal rainfall for October. The airport average monthly temperature of 52.6 degrees F was 0.2 degrees below normal for October with a maximum temperature of 72° F on the 7th and a minimum temperature of 36° F on the 30th.

• In last month's report we informed you of a violation of the federal standard (NAAQS) for lead during the period April through June 1998 at the Harbor Island monitoring site. Our investigation is progressing and we hope to complete that part of the enforcement process soon. This report includes updated lead averages through mid-August. Please note that lead concentrations have returned to their normally low levels.
• Thr highest 1-hour average for ozone (0.061 ppm) was in the "Moderate" category (PSI of 51) and occurred on Wednesday the 7th at the Pack Forest site in La Grande. The highest 8-hour average for ozone (0.056 ppm) was in the "Good" category (proposed PSI of 44) and occurred on Saturday the 24th at the Enumclaw site.
• The highest PM10 value of 76 µg/m³ was in the "Moderate" category (PSI of 63) and was measured on Thursday the 22nd at the Duwamish site in Seattle. The highest PM2.5 value of 42 µg/m³ was in the "Moderate" category (proposed PSI of 69) and was also measured on Thursday the 22nd at the Duwamish site.
• The highest 8-hour average for carbon monoxide was 6.9 ppm, in the "Moderate" category (PSI of 46), and occurred during the evening hours of Wednesday the 21st at the NE 8th site in Bellevue.
• The worst visual range of 8.1 miles occurred the evening of Friday the 23rd from 11:00-12:00 pm PST at the Lake Forest site during the stagnation period.

Puget Sound Air Pollution Control Agency