On October 18, 2024 and November 6, 2024, strong Santa Ana winds in Southern California caused dust storms in parts of Riverside and San Bernardino Counties. Dust was transported from open lands near Cajon Pass, and in the Jurupa Hills in Jurupa Valley, causing an increase in PM10 concentrations in parts of western San Bernardino and Riverside counties. As a result of the windblown dust, the daily Federal Equivalent Method (FEM) PM10 concentration measured at Mira Loma Van Buren on both October 18 and November 6, 2024, exceeded the 150 μg/m3 24-hour PM10 National Ambient Air Quality Standard (NAAQS).
All human-caused PM10 sources upwind of Mira Loma Van Buren were reasonably controlled. This document provides the analysis that demonstrates that the windblown dust events on both days are exceptional events according to the Federal exceptional event definition in 40 CFR 50.1. If this exceptional events demonstration is concurred upon by U.S. EPA, those PM10 exceedances should not be considered when determining attainment of the 24-hour PM10 standard at Mira Loma Van Buren. The PM10 data affected by these events at the Mira Loma Van Buren measurement station will still be available in the U.S. EPA Air Quality System and on the South Coast AQMD webpage.
This draft exceptional events demonstration is made available for a 30-day public comment period ending October 22nd, 2026. After any feedback from public comment is incorporated into the document, it will be submitted to the U.S. Environmental Protection Agency (EPA) for review.