Analysing the effects of the 2002 McNally fire on air quality in the San Joaquin Valley and southern Sierra Nevada, California

Smoke from wildfires can expose individuals and populations to elevated levels of particulate matter (PM) and ozone (O3). Between 21 July and 26 August 2002, the McNally Fire burned over 150000 acres (61000 ha). The fire occurred in the Sequoia National Forest, in the southern Sierra Nevada of California. This study evaluated the effects of the McNally Fire on air quality, specifically particles <10 μm in diameter (PM10) and O3. Downwind of the fire on the eastern side of the Sierra Nevada, 24-h concentrations of PM10 more than doubled. The PM10 federal standard was exceeded four times during the fire. Violations of the California PM10 standard increased drastically during the fire. The California PM10 standard was violated six times before the fire and 164 times during the fire. Most of the PM10 exceedances occurred at the Kernville Work Center and sites east of the fire. Compared with the other sites, the highest 2-week average O3 concentrations occurred in the eastern part of the Sierra Nevada and north of the fire, where O3 increased by a factor of two at two locations.