Quantifying the Source Attribution of PM10 Measured Downwind of the Oceano Dunes State Vehicular Recreation Area

Abstract

A measurement campaign was undertaken April–October 2021 using PM10 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 PM10 samples were analyzed and these data were used to identify the sources that contributed to the PM10 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 PM10 for eight days that exceeded the California state 24 h mean PM10 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 PM10 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 PM10 is attributable to wind-driven saltation and dust emission processes within the ODSVRA.