<?xml version='1.0' encoding='utf-8'?>
<oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
  <dc:contributor>T.M. Lopez</dc:contributor>
  <dc:contributor>Christoph Kern</dc:contributor>
  <dc:contributor>Santiago Arellano</dc:contributor>
  <dc:contributor>Nemesio M. Perez</dc:contributor>
  <dc:contributor>J Barrancos</dc:contributor>
  <dc:creator>D.S. Kushner</dc:creator>
  <dc:date>2025</dc:date>
  <dc:description>&lt;p&gt;&lt;span&gt;A large source of error in SO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;emission rates derived from mobile Differential Optical Absorption Spectroscopy (DOAS) of volcanic gas plumes is the uncertainty in atmospheric light paths between the sun and the instrument, particularly under non-ideal atmospheric conditions, such as the presence of low clouds. DOAS instruments measure the SO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;column density along the effective light path, so changes to that pathway directly affect the measured SO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;signal. Due to complex radiative transfer mechanisms when a cloud is between the DOAS viewing position and a volcanic plume, measured plumes can appear spatially offset from their true location, a phenomenon informally referred to as “ghost plumes.” In addition to the appearance of ghost plumes, DOAS measurements recorded in non-ideal conditions have poorly characterized errors and are often discarded, limiting the data available to characterize volcanic degassing. In this study we simulate the radiative transfer associated with zenith-facing mobile DOAS traverses using the McArtim radiative transfer model for scenarios when there is a cloud layer between the instrument and the volcanic plume. In total, 217 permutations of atmospheric optical conditions are considered with varying cloud opacities (AOD&amp;nbsp;=&amp;nbsp;0, 1, 2, 4, 8, 20), plume opacities (AOD&amp;nbsp;=&amp;nbsp;0, 1, 2, 4, 8), solar zenith angles (SZA&amp;nbsp;=&amp;nbsp;1°, 30°, 60°), and cloud thicknesses (200, 400, 800&amp;nbsp;m). We first develop objective criteria for selecting SO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;baseline absorption levels and plume spatial extents. The simulated plume traverses are then integrated to obtain the SO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;cross-sectional burdens which, after multiplication with the wind speed, yield SO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;emission rates. We find large modification in the shape of the modeled cross-sectional burdens even under translucent (low AOD) cloud conditions in our modeled scenarios. Despite modification of the plume shape, the presence of a low cloud layer is typically not a large source of error in the SO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;cross-sectional burden or emission rate obtained from zenith-facing DOAS traverses. We find that all measured cross-sectional burdens simulated using an aerosol-free plume in the above conditions and SZA&amp;nbsp;≤&amp;nbsp;30° are within ±25% of the true value.&lt;/span&gt;&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1016/j.jvolgeores.2024.108217</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Elsevier</dc:publisher>
  <dc:title>The ghost plume phenomenon and its impact on zenith-facing remote sensing measurements of volcanic SO2 emission rates</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>