July 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 July, however two significant air pollution events occurred that are noteworthy. Precipitation was below normal with Sea-Tac airport receiving 54% of normal rainfall for July. The airport average monthly temperature of 67.6 degrees F was 2.4 degrees above normal for July with a maximum temperature of 97° F on the 28th and a minimum temperature of 53° F on the 13th.

• For the first time in 15 years, the quarterly federal standard (NAAQS) for lead was violated during the period April through June, 1998. The quarterly lead concentration at the Harbor Island site was 2.03 µg/m³. The site is adjacent to an old lead smelting facility which has ceased smelting operations, but still produced some lead products. This facility ceased all production of lead products in May and is currently in the process of closing permanently. The high concentrations occurred over a consecutive 8-week period and stand out as an unusual event looking back over the last decade. As a result of these high readings, the Agency has begun a formal investigation to determine the cause. Additionally, the Agency has increased the frequency of sampling to better document concentrations and to confirm that lead has returned to levels below the NAAQS.
• High ozone levels occurred during a three-day period from July 26 to 28. This period was characterized by stable weather with a nighttime low level temperature inversion followed by hot afternoon temperatures in the mid to upper 90's. Significant ozone levels were measured downwind (east to southeast) of the Everett-Seatte-Tacoma urban area. Preliminary data shows that measured ozone values exceeded a federal standard or reached the "Unhealthful" category on the national Pollutant Standard Index (PSI) on three successive days (July 26-28) for both the 1-hour and new 8-hour standard.

1-Hour Standard: Pack Forest (July 26-27) and Enumclaw (July 27-28) each exceeded the level of the 1-hour standard (0.12 ppm) on two successive days. The highest 1-hour average for ozone (0.140 ppm) was in the "Unhealthful" category (PSI of 117) and occurred on Monday the 27th at the Pack Forest site in La Grande. These exceedances do not currently violate the 1-hour standard since there were no exceedances at these sites during 1996 and 1997.

8-Hour Standard: Three stations -- Pack Forest, Enumclaw, and Lake Sammamish State Park -- exceeded the level of the new 8-hour standard (0.084 ppm) on three successive days (July 26-28). The highest 8-hour average for ozone (0.109 ppm) was in the proposed "Generally Unhealthful" category (proposed PSI of 163) and also occurred on the 27th at the Pack Forest site. For the years 1996-1998, the 3-year average of the 4th highest 8-hour concentration for Enumclaw is 0.082 ppm, Pack Forest is 0.077 ppm and Lake Sammamish is 0.065 ppm. Should another exceedance occur which releases 0.090 ppm at Enumclaw between now and the end of 1998, this location would violate the 8-hour ozone standard for the years 1996-1998.

• The highest PM10 value of 75 µg/m³ (PSI of 50) was measured on Tuesday the 28th at the Alexander Avenue site in the Tacoma Tideflats. The highest PM2.5 value of 26 µg/m³ (proposed PSI of 58) was measured on Monday the 27th at the Kent site.
• The highest 8-hour average for carbon monoxide was 3.4 ppm (PSI of 38) and occurred the afternoon of Tuesday the 14th at the University District site in Seattle.
• The worst visual range of 6 miles occurred the evening of July 4th during the hour from 10:00-11:00 pm PDT at the Kent site.

Puget Sound Air Pollution Control Agency