A Smog Watch has been called by the Puget Sound Clean Air Agency in Kitsap, King, Pierce and Snohomish counties.

People sensitive to pollution are advised to limit time outdoors. Even healthy individuals should consider limiting their outdoor exercise, or plan to work out indoors.

The weather pattern from now through Saturday night will result in ozone pollution rising to unhealthy levels. The communities most impacted are south and southeast of the core urban areas of Everett, Seattle and Tacoma where air quality is predicted to decline to “Unhealthy for Sensitive Groups” on Friday and Saturday due to the production of ozone.

Fine particle pollution will also increase resulting in reduced visibility and likely creating moderate air-quality conditions on Friday and Saturday in most areas throughout the Puget Sound region.

Air quality is predicted to improve overnight on Saturday as a push of marine air is expected to scour out the accumulated pollution in the Puget Sound region and return air-quality conditions to “Good” on Sunday. The Smog Watch will be cancelled at noon Sunday unless high temperatures and poor air quality persist.

The Department of Health reminds people with asthma and parents of children with asthma to limit outdoor activities during hazy, sunny, hot weather when ozone levels are high. Adults with lung and cardiovascular diseases (heart disease and stroke) should also be mindful of poor air quality.

This week’s Smog Watch is the second called this month. With a new, more stringent air quality standard for ozone, it is more difficult for the region to stay in compliance with the federal standard.

Ozone comes primarily from automobile tailpipes and “cooks” in heat and sunlight on hot days to produce smog. Exposure to ground-level ozone can reduce lung function, cause respiratory irritation, aggravate asthma symptoms and weaken the immune system. Ozone has environmental impacts as well; studies show that ozone can damage agricultural crops and forests.

To learn more about smog and how to lessen pollution leading up to it, visit www.pscleanair.org/airq/basics/weather/smog.aspx.

Check air-quality forecasts and current conditions at www.pscleanair.org/airq/aqi.aspx#.