Smoke from California's hundreds of wildfires is continuing to affect the Valley's air quality. But things are looking up.

Air quality readings today in Tulare County show pollution levels in the unhealthy range — an improvement from the very unhealthy range on Friday — but initially for a different kind of air pollution than that experienced in recent days.

Smoke from the fires contributed to extremely poor air quality here over the past week. The offending pollutant, however, was consistently ground-level ozone. Today's forecasted air quality was deemed unhealthy earlier in the day for fine particulate matter smaller than 2.5 microns in size — consistent with the soot from smoke.

The change in offending pollutant brings with it an improvement in air quality, one that continued this afternoon as the offending pollutant shifted back to ground-level ozone.

The San Joaquin Valley Air Pollution Control District posted an Air Quality Index reading of 203 on Friday for ground-level ozone in Tulare County, which is considered very unhealthy. Saturday's AQI was 187, again for ground-level ozone, dipping back into the unhealthy range. Today's AQI was forecast at 162, near the middle of the unhealthy range but for PM2.5 rather than ground-level ozone. That forecast shifted at 4:30 p.m. today to an adjusted AQI of 124 for ground-level ozone.

As air pollutants changed and air quality improves in the southern reached of the eight-county San Joaquin Valley air basin, the same was holding true in the northern counties.

Air quality readings in San Joaquin County, the northernmost county in the basin, were unhealthy Friday and moderate Saturday, with a moderate reading expected again today — all for ground-level ozone. A similar trend of improving air quality is shown moving south from San Joaquin in the counties of Stanislaus, Merced, Madera and Fresno, and in neighboring Kings County, although expected air quality readings today are in one of the three unhealthy categories in every county south of Stanislaus.

PM2.5 has consistently been the offending pollutant earlier in the week in the Valley's northern counties, primarily due to smoke from the state's wildfires. Ozone is a more typical pollutant in the Valley during summer months. AQI totals for the entire Valley shifted back to ground-level ozone with the 4:30 p.m. update today.

Starting in the most northern Valley county and moving south, Monday's anticipated air quality is:

--San Joaquin: Moderate (84) for ground-level ozone.

-- Stanislaus: Unhealthy for Sensitive Groups (111) for ground-level ozone.

-- Merced: Unhealthy for Sensitive Groups (101) for ground-level ozone.

-- Madera: Moderate (97) for ground-level ozone.

-- Fresno: Unhealthy for Sensitive Groups (129) for ground-level ozone.

-- Kings: Unhealthy for Sensitive Groups (129) for ground-level ozone.

-- Tulare: UnhealthySensitive Groups (124) for ground-level ozone.

-- Kern (only that portion in the Valley): Unhealthy (161) for ground-level ozone.

-- Contact Glen Faison at 784-5000, Ext. 1040, or gfaison@portervillerecorder.com.