FRESNO, Calif. (KSEE/KGPE) – The San Joaquin Valley Air Pollution Control District (APCD) warns that stagnant atmospheric conditions and record-hot weather are leading to deteriorating air quality in the Central Valley. As of Thursday, one-third of counties in the San Joaquin Valley were experiencing unhealthy air quality levels; by Friday, that number is expected to jump to almost 50%. According to the National Weather Service, multiple record-high temperatures have already been surpassed this October. APCD says these temperatures are helping to trap pollutants at ground level. The district adds that poor dispersion conditions and a stable atmosphere overhead have led to an increase in PM10 (particulate matter 10 microns and smaller) and higher ozone concentrations across the Valley. The Happy Fire in Fresno County is also contributing PM2.5 pollution in the area. Exposure to such particulate pollution can trigger asthma attacks, aggravate chronic bronchitis, and increase the risk of heart attack, stroke, and respiratory infections. Anyone experiencing poor air quality is advised to move to a filtered, air-conditioned environment with closed windows. APCD says air quality is expected to continue to deteriorate throughout the weekend and into early next week. An up-to-date daily air quality forecast can be found by visiting San Joaquin Valley APCD online.