The role of off-highway vehicle activity in augmenting dust emissions at the Oceano Dunes State Vehicular Recreation Area, Oceano, CA

Abstract

The Oceano Dunes State Vehicular Recreation Area (ODSVRA) allows off-highway vehicle (OHV) activity on this coastal dune system. Three sources of data were examined to determine if OHV activity increased wind-blown dust emissions originating from the ODSVRA. Measurements of emissivity (mg m −2 s −1 ) of particulate matter (PM) from dune sands were made using the PI-SWERL® instrument from 2013 through to 2020 in the area with OHV activity and in areas where OHV access is not permitted. These measurements indicated that the mean emissivity of the riding area was two to three times higher than the mean of the non-riding areas, for wind shear velocity ( u ∗ , m s −1 ) conditions well-above threshold ( u ∗ > 0.5 m s −1 ). Measurements of Wind Power Density (WPD, W m −2 ) and suspended particulate matter (PM, μg m −3 ) at monitoring stations in the riding areas and downwind of the riding areas made between May and September 2019 indicate that PM concentrations increased 12% per month for similar WPD conditions. In 2020, OHV activity was prohibited beginning in March due to the SARS-CoV-2 pandemic. Network measurements of PM and WPD, April to August 2020 indicated a 12% decrease in PM concentrations per month for similar WPD conditions, suggesting the cessation of OHV activity resulted in the dunes becoming less emissive through time. Measurements of wind speed and suspended PM at a monitoring station downwind of a dune preserve area (no OHV activity allowed) for 2019 and 2020 indicate that PM and WPD measurements do not follow the same temporal trends for the in-Park and downwind of riding area influenced area stations, further suggesting that OHV activity influences dune emissivity. • Measurements of emissivity on areas without riding have significantly lower emissivity than areas with riding. • PM 10 decreased by 12% per month during COVID19 closure for similar values of wind power density. • These environmental measurements provide compelling evidence that OHV activity augments the amount of PM 10 mineral dust.