Starting this week, the federal government has tightened its air pollution standards for fine particulates.

The federal Environmental Protection Agency has lowered the Air Quality Index threshold for good air quality from 15 to 12 micrograms per cubic meter. The result will likely be that more days will be classified as having moderate air quality, said Aeron Arlin-Genet, spokeswoman for the county Air Pollution Control District.

“It is important to note that the general air quality conditions in the county are expected to remain the same — the AQI scale is changing, not the air quality conditions,” she said.

Moderate air quality is unhealthy for very sensitive people, including infants and people with heart and respiratory diseases. These people are advised to stay indoors on moderate air quality days.

The South County is most prone to having poor particulate air quality because of dust and sand blowing off of the Oceano Dunes. The area with the worst air quality is the portion of Nipomo along Highway 1 from Callender Road to Calle Bendita.

According to the EPA, the new standard is intended to protect against the health effects of associated with long- and short-term exposure to fine particulates including premature death, strokes and heart disease. The old standard had been in place since 1997.

Air quality forecasts for various areas in the county can be found at http://www.slocleanair.org/air/AirForcasting_map3.php.