August
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 August. Precipitation was well below normal
with Sea-Tac airport receiving 24% of normal rainfall for
August. The airport average monthly temperature of 66.8
degrees F was 1.3 degrees above normal for August with a
maximum temperature of 88° F on the 13th and a minimum
temperature of 52° F on the 19th and 25th.
- 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.
- Elevated ozone levels occurred
during a brief 2-day period from August 3-4. This period
was characterized by stable weather with a nighttime
low-level temperature inversion followed by warm
afternoon temperatures in the lower 80's. Preliminary
data shows that one measured ozone value elevated to
exactly the 8-hour federal standard (0.084 ppm) or
reached the top of the "Moderate" category on
the national Pollutant Standards Index (PSI).
It appears likely that the Puget Sound region avoided
exceeding the 8-hour federal standard for the years
1996-1998. For the years 1996-1998, the 3-year average of
the 4th highest concentration for Enumclaw is 0.082 ppm,
Pack Forest is 0.077 ppm and Lake Sammamish is 0.065 ppm.
1-Hour Standard: The highest 1-hour average for ozone (0.098
ppm) was in the "Moderate" category (PSI of 82) and
occurred on Monday the 3rd at the Pack Forest site in La
Grande.
8-Hour Standard: The highest 8-hour average for ozone (0.098
ppm) was in the "Moderate" category (PSI of 100)
and also occurred on Monday the 3rd at the Pack Forest site
in La Grande.
- The highest PM10
value of 56 µg/m3 (PSI of 53) was measured on Monday the
3rd at the Alexander Avenue site in the Tacoma Tideflats.
The highest PM2.5 value of 24 µg/m3 (proposed PSI of 56) was measured on
Monday the 31st at the Kent and Issaquah sites.
- The highest 8-hour average for
carbon monoxide was 3.1 ppm (PSI of 34) and occurred the
evening of Friday the 28th at the 5th & James site in
Seattle.
- The worst visual range of 7.7 miles
occurred the afternoon of Sunday the 30th during the hour
from 2:00-3:00 pm PDT at the Kent site.
Puget
Sound Air Pollution Control Agency