April 1998 Air Quality Report

Here you will find information about:

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

Air Quality Report - April 1998

Weather during April was typical for a spring month except for below normal rainfall. Dispersion was very good and resulted in good air quality, except for the last 3 days of the month. It appears that a cloud of particulate from dust storms in China reached the Pacific Northwest creating very hazy conditions which degraded visual range across the region.

• Precipitation was below normal with Sea-Tac airport receiving 43% of normal rainfall for April. The airport average monthly temperature of 50.4 degrees F was 1.2 degrees above normal for March with a maximum temperature of 80° F on the 30th and a minimum temperature of 34° F on the 8th.
• Preliminary data shows that none of the air quality measured values exceeded a federal standard (NAAQS) or reached the Unhealthful category on the national Pollutant Standards Index (PSI). The highest pollutant reading was in the moderate category (PSI of 69) and occurred on Wednesday, the 29th caused by particulate (PM10). The last three days of the month were in the moderate category.
• The highest PM10 value of 87 µg/m3 (PSI of 69) was measured on Wednesday the 29th at the 54th Avenue site in northeast Tacoma overlooking the port area.
• The highest 8-hour average for carbon monoxide was 3.4 ppm (PSI of 38) and occurred the early evening of Thursday the 23rd at the University district site in Seattle.
• The highest 8-hour average for ozone was 0.056 ppm and occurred Thursday afternoon the 30th at the Pack Forest site in La Grande.

Puget Sound Air Pollution Control Agency