The effect of dispersed Petrobaltic oil droplet size on photosynthetically active radiation in marine environment

Abstract

Oil pollution in seawater, primarily visible on sea surface, becomes dispersed as an effect of wave mixing as well as chemical dispersant treatment, and forms spherical oil droplets. In this study, we examined the influence of oil droplet size of highly dispersed Petrobaltic crude on the underwater visible light flux and the inherent optical properties (IOPs) of seawater, including absorption, scattering, backscattering and attenuation coefficients. On the basis of measured data and Mie theory, we calculated the IOPs of dispersed Petrobaltic crude oil in constant concentration, but different log-normal size distributions. We also performed a radiative transfer analysis, in order to evaluate the influence on the downwelling irradiance Ed, remote sensing reflectance Rrs and diffuse reflectance R, using in situ data from the Baltic Sea. We found that during dispersion, there occurs a boundary size distribution characterized by a peak diameter d0 = 0.3 μm causing a maximum E d increase of 40% within 0.5-m depth, and the maximum Ed decrease of 100% at depths below 5 m. Moreover, we showed that the impact of size distribution on the "blue to green" ratios of Rrs and R varies from 24% increase to 27% decrease at the same crude oil concentration.

Remote Sensing of Dispersed Oil Pollution in the Ocean—The Role of Chlorophyll Concentration

“…Radiative transfer simulations were conducted using the Monte Carlo code created and made available by Prof. Jacek Piskozub [ 65 ] and applied also by the authors of [ 66 , 67 , 68 , 69 , 70 ]. We adapted the model for studies of remote sensing of dispersed oil in seawater described previously in [ 39 , 40 , 49 ].…”

“…Oil droplets participate in the process of radiative transfer in seawater as optically significant components [ 37 , 38 ]. They absorb and scatter light; therefore, they affect both the inherent and the apparent optical properties in the area of their occurrence [ 39 ]. The scope of their influence can be estimated using numerical modeling based on the radiative transfer equation, as long as their IOPs are known [ 40 , 41 ].…”

Influence of Dispersed Oil on the Remote Sensing Reflectance—Field Experiment in the Baltic Sea

“…The main conclusion of these studies was that at even as low a concentration as 1 ppm of oil, droplets can cause significant changes to the R rs . This effect was dependent on oil type [65], droplet size distribution [62], and seawater optical properties [61], as well as wind conditions and sensor geometry [66]. In this study, we took a step forward from modeling to in situ experiment in a unique attempt to measure the R rs of dispersed oil pollution in open sea conditions.…”

“…All oil dispersions consisted mostly of micrometer-sized droplets and reached main maxima between 5 and 7 µm. Dispersed BD, EJ, PB, and FL also contained smaller oil particles which contribute very significantly to the backscatter signal [62,63]. Dispersed EJ, QL, and CL (as well as FL and BD in a minor degree) also contained large oil droplets of tens of micrometers.…”

On the role of the seawater absorption-to-attenuation ratio in the radiance polarization above the southern Baltic surface

“…The influence of dispersed oil droplets on the absorption coefficient of seawater was researched by Otremba (2007) as well as Haule and Freda (2016), while their influence on scattering properties has been tested by Freda (2014). The consequences of changes in IOPs for remote detection of dispersed oil pollution have been discussed by Otremba et al (2013), Otremba (2016) and Haule et al (2017) based on radiative transfer modeling. Knowledge and datasets collected in the Baltic throughout the past two decades helped us to perform a unique study on polarized radiation above the southern Baltic sea surface.…”