Can statistics of turbulent tracer dispersion be inferred from camera observations of SO₂ in the ultraviolet? A modelling study

• Main Authors: A. Kylling, H. Ardeshiri, M. Cassiani, A. S. Dinger, S.-Y. Park, I. Pisso, N. Schmidbauer, K. Stebel, A. Stohl
• Format: Article
• Language: English
• Published: Copernicus Publications 2020-06-01
• Series: Atmospheric Measurement Techniques
• Online Access: https://www.atmos-meas-tech.net/13/3303/2020/amt-13-3303-2020.pdf

<p>Atmospheric turbulence and in particular its effect on tracer dispersion may be measured by cameras sensitive to the absorption of ultraviolet (UV) sunlight by sulfur dioxide (<span class="inline-formula">SO₂</span>), a gas that can be considered a passive tracer over short transport distances. We present a method to simulate UV camera measurements of <span class="inline-formula">SO₂</span> with a 3D Monte Carlo radiative transfer model which takes input from a large eddy simulation (LES) of a <span class="inline-formula">SO₂</span> plume released from a point source. From the simulated images the apparent absorbance and various plume density statistics (centre-line position, meandering, absolute and relative dispersion, and skewness) were calculated. These were compared with corresponding quantities obtained directly from the LES. Mean differences of centre-line position, absolute and relative dispersions, and skewness between the simulated images and the LES were generally found to be smaller than or about the voxel resolution of the LES. Furthermore, sensitivity studies were made to quantify how changes in solar azimuth and zenith angles, aerosol loading (background and in plume), and surface albedo impact the UV camera image plume statistics. Changing the values of these parameters within realistic limits has negligible effects on the centre-line position, meandering, absolute and relative dispersions, and skewness of the <span class="inline-formula">SO₂</span> plume. Thus, we demonstrate that UV camera images of <span class="inline-formula">SO₂</span> plumes may be used to derive plume statistics of relevance for the study of atmospheric turbulent dispersion.</p>