In January 2023, the U.S. Environmental Protection Agency (U.S. EPA) proposed to lower the annual standard for fine particulate matter (PM 2.5) from its current limit of 12 micrograms per cubic meter (µg/m3) to a level between nine and 10 µg/m3. The proposal is the result of an extensive scientific review conducted by U.S. EPA’s Clean Air Scientific Advisory Committee, which found that the current level does not sufficiently protect public health. The proposal also includes changes related to monitoring network design criteria to enhance protection in communities overburdened by air pollution.

PM2.5 is one of six criteria pollutants regulated by U.S. EPA. It is directly emitted from combustion (such as from vehicles, locomotives, and refineries) and non-combustion sources (such as dust from paved and unpaved roads, and dust from tire and brake wear). PM2.5 is also formed in the atmosphere through chemical reactions of other air pollutants such as nitrogen oxides (NOx) and Volatile Organic Compounds (VOCs). Exposure to PM2.5 can worsen pre-existing health conditions and lead to the development of lung and heart disease as well as premature death.

The South Coast Air Basin (Basin) is designated under federal law as a “serious” nonattainment area for the 2006 24-hour and 2012 annual PM2.5 standards. The Coachella Valley attains both PM2.5 standards. PM2.5 levels in the Basin continue to decline and last year had the lowest PM2.5 levels ever recorded due to continued weather and emission reductions. While Coachella Valley is close to meeting the 2006 24-hour standard (35 µg/m3), additional emission reductions of PM2.5 beyond existing regulations will be required to meet the 2012 annual standard of 12 µg/m3. South Coast AQMD is developing a new plan to attain the 2012 annual standard, which will assist with future efforts to meet the more stringent PM2.5 standard now proposed by U.S. EPA. While emissions from combustion sources are declining, non-combustion sources that are challenging to control, such as paved road dust and tire and brake wear, increase with economic growth and population. Complex chemistry involved in the formation of PM2.5 pose additional challenges to improve PM2.5 air quality.

Despite our challenges to meet existing federal air quality standards, South Coast AQMD strongly supports establishing air quality standards based on the best available science, however, given the substantial challenges South Coast AQMD would face in achieving a lower PM2.5 standard, U.S. EPA must take action to reduce emissions from federally regulated mobile sources of air pollution to protect public health. Federal action is also needed for our Basin to meet ozone standards.