September
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 September. Precipitation was well below
normal with Sea-Tac airport receiving 38% of normal rainfall
for September. The airport average monthly temperature of
63.1 degrees F was 2.5 degrees above normal for September
with a maximum temperature of 86° F on the 1st and a minimum
temperature of 46° F on the 26th.
- 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 1-day period on September 1st. 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 just
over the 8-hour federal standard (0.086 ppm) or reached
the "Unhealthy for Sensitive Groups" category
on the national Pollutant Standards Index (PSI).
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 (0.097
ppm) was in the "Moderate" category (PSI of 81) and
occurred on Tuesday the 1st at the Pack Forest site in La
Grande.
8-Hour Standard: The highest 8-hour average for ozone (0.086
ppm) was in the "Unhealthy for Sensitive Groups"
category (proposed PSI of 104) and also occurred on Tuesday
the 1st at the Pack Forest site.
- The highest PM10
value of 59 µg/m3 (PSI of 55) was measured on Tuesday the
8th at the 54th Ave. NE site in Northeast Tacoma. The
highest PM2.5 value of 20 µg/m3 (proposed PSI of 54) was measured on
Tuesday the 1st at the Kent and Issaquah sites and on the
21st and 23rd at the Duwamish site.
- The highest 8-hour average for
carbon monoxide was 4.1 ppm (PSI of 46) and occurred the
afternoon commute hours of Monday the 21st and 28th at
the Everett site.
- The worst visual range of 12.3
miles occurred the afternoon of Thursday the 3rd during
the hour from 2:00-3:00 pm PDT at the Kent site.
Puget
Sound Air Pollution Control Agency