In December 2012, the U. S. Environmental Protection Agency lowered the primary annual PM2.5 standard to 12.0 ug/m3. This action strengthens the nation’s air quality standards for fine particulate pollution to further protect public health. In addition, EPA has modified the AQI scale to incorporate the new PM2.5 standard. The changes to the AQI took effect on March 18, 2013.

The AQI is EPA’s color-coded tool for telling the public how clean or polluted the air is, and steps they can take to reduce their daily exposure to pollution. The AQI focuses on health effects individuals may experience within a few hours or days after breathing polluted air. The AQI converts concentrations for criteria pollutants, including fine particles, to a number on a scale from 0 to 500. The AQI scale is broken down into four categories that best represent local air quality conditions: Good, Moderate, Unhealthy for Sensitive Groups, and Unhealthy. Each category is a 50 unit index value e.g., Good ranges from 1 – 50 on the AQI scale.

With recent changes to the PM2.5 standard, EPA updated the AQI scale to become more conservative and reflect the epidemiology and human health effects that are present at lower PM2.5 concentrations. The upper end of the range for the “Good” AQI category, an index value of 50, has been set at the new annual PM2.5 standard, 12.0 ug/m3. The “Moderate” category upper end of 100 value is set at the 24-hour PM2.5 standard, 35 ug/m3. In addition, EPA is setting the upper end of the “Unhealthy for Sensitive Groups” range, AQI of 150, at 55 ug/m3.

The forecasted air quality index is available here. The forecasted AQI is also available to the public via email.  A recorded message describing San Luis Obispo County air quality conditions is available by calling (805) 781-4390.