Smoke from the Northern California wildfires is affecting air quality throughout the entire San Joaquin Valley, prompting local air pollution officials to issue an Air Quality Alert.

The San Joaquin Valley Air Pollution Control District issued the Air Quality Alert on Wednesday due to smoke impacts from wildfires for San Joaquin, Stanislaus, Merced, Madera, Fresno, Kings, Tulare and the Valley portion of Kern counties. The alert is in effect through Saturday.

As of Wednesday, 22 wildfires were burning in Northern California, up from 17 the day before. The blazes killed at least 21 people and destroyed an estimated 3,500 homes and businesses, many of them in California wine country.

The smoke from those wildfires is extending through the Bay area into the Delta and Sacramento Valley, and into the Sierra, according to satellite and observations reported by the National Weather Service.

According to the weather service, a northerly wind is acting to mix and shift the smoke southward.

Dry with temperatures and wind gusts are expected to continue critical fire weather conditions through Thursday in Northern California, with further fire concerns from north winds possible this weekend, according to the National Weather Service.

Smoke from wildfires is a mixture of gases and fine (microscopic) particulates that result from the burning of wood and other organic material. These microscopic particles can get into eyes and the respiratory system, where they can cause health problems such as burning eyes, runny nose and illnesses such as bronchitis. Fine particles can also aggravate chronic heart and lung diseases — and are even linked to premature deaths in people with these conditions. According to the air district, if you see or smell smoke, you are likely being impacted by it.

Residents are advised to use caution as conditions warrant. People with heart or lung diseases should follow their doctor’s advice for dealing with episodes of unhealthy air quality.

Additionally, older adults and children should avoid prolonged exposure, strenuous activities or heavy exertion, as conditions dictate.

Anyone being exposed to poor air quality or wildfire smoke should move inside to an air-conditioned environment.

Residents can check the air district’s wildfire page at www.valleyair.org/wildfires for information about any current wildfires and whether they are impacting the Valley. Residents can also check the nearest air monitor to their location to determine localized air-quality conditions. Visit the Real-time Air Advisory Network page on the District’s website to subscribe for free: www.valleyair.org/RAAN.