Human induced dust in Aruba. An assessment of the transport and spatial deposition dynamics of dust from off-road driving in Aruba and the effect of driving speed and traffic density.

Off-road driving has a range of impacts on the environment and human health. In Aruba, traffic on dirt roads and recreational off-road driving has put nature and environment under high pressure. However, the exact effect and dust cloud dimensions, i.e. dust transport and deposition patterns, have not yet been assessed. Furthermore, the effect of different driving speeds and traffic densities on the dust cloud dimensions have not yet been established. Measurements were done to analyse dust transport and spatial deposition along an off-road track, using Modified Wilson And Cooke (MWAC) catchers and placing Inverted Frisbee Dust Deposition (IFDD) catchers in a transect, up to 300 m from the source. In addition, experiments were set up using a quad to measure the effect on dust transport and spatial dust deposition for increasing the driving speed and traffic density. Dust deposition is shown to decrease rapidly with distance from the source, but remains more or less constant from 200 m onwards. Increasing the traffic density results in a slight decrease in deposition per pass, but shows an exponential increase of dust transport. Increasing the driving speed increased dust transport exponentially: 1.71, 2.72 and 5.07 g m-1 per pass for 10, 25 and 45 kmph respectively. The dust deposition increased more than linear: 3.55, 5.74, 7.74 g m-1 per pass between 15 and 50 m from the source for 10, 20 and 45 kmph respectively. Driving faster on the dirt or off-roads in Aruba thus results in an increase in production of dust per vehicle kilometre travelled (vkt), which is most probably undesirable with regard to the environment and human health. The trade winds blowing predominantly from East can carry the dust far inland, which may have an effect on the health risk of people living downwind from the off-road tracks. 

Keywords: off-road driving; dust transport; dust deposition; Modified Wilson And Cooke (MWAC) catcher; Inverted Frisbee Dust Deposition (IFDD) catcher.