| Summary: | A measurement campaign was undertaken April–October 2021 using PM<sub>10</sub> filter samplers to collect 24 h samples downwind of the Oceano Dunes State Vehicular Recreation Area (ODSVRA), an area that allows off-highway driving on its coastal dunes. The PM<sub>10</sub> samples were analyzed and these data were used to identify the sources that contributed to the PM<sub>10</sub> under varying meteorological conditions. Exposed filters were weighed to calculate mass concentration and analyzed using X-ray fluorescence to quantify elemental composition, ion chromatography to quantify water-soluble ions, and thermal/optical reflectance to quantify organic carbon and elemental carbon in the particulate matter. These speciated data were used to attribute the sources of PM<sub>10</sub> for eight days that exceeded the California state 24 h mean PM<sub>10</sub> standard and 39 days that were below the standard. The mean attribution of sources for the eight identified exceedance days was mineral dust (43.1%), followed by sea salt (25.0%) and the unidentified category (20.4%). The simultaneous increase in the mineral dust and unidentified categories with increasing levels of PM<sub>10</sub> arriving from the direction of the ODSVRA suggests that the unidentified components were unmeasured oxides of minerals and carbonate. This increases the attribution of mineral dust for a mean exceedance day to 63.5%. The source of the mineral dust component of the PM<sub>10</sub> is attributable to wind-driven saltation and dust emission processes within the ODSVRA.
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