Halogen activation in the plume of Masaya volcano: field observations and box model investigations
<p>Volcanic emissions are a source of halogens in the atmosphere. Rapid reactions convert the initially emitted hydrogen halides (HCl, HBr, and HI) into reactive species such as BrO, Br<span class="inline-formula"><sub>2</sub></span>, BrCl, ClO, OClO, and IO....
| Main Authors: | , , , , , , , , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-03-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/21/3371/2021/acp-21-3371-2021.pdf |
| Summary: | <p>Volcanic emissions are a source of halogens in the
atmosphere. Rapid reactions convert the initially emitted hydrogen halides
(HCl, HBr, and HI) into reactive species such as BrO, Br<span class="inline-formula"><sub>2</sub></span>, BrCl, ClO, OClO, and
IO. The activation reaction mechanisms in the plume consume ozone (O<span class="inline-formula"><sub>3</sub></span>),
which is entrained by ambient air that is mixed into the plume. In this study, we present
observations of the oxidation of bromine, chlorine, and iodine during the
first 11 min following emission, examining the plume from Santiago crater of the
Masaya volcano in Nicaragua. Two field campaigns were conducted: one in July
2016 and one in September 2016. The sum of the reactive species of each halogen was
determined by gas diffusion denuder sampling followed by gas chromatography–mass spectrometry (GC-MS) analysis,
whereas the total halogens and sulfur concentrations were obtained by
alkaline trap sampling with subsequent ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS) measurements. Both
ground and airborne sampling with an unoccupied aerial vehicle (carrying a
denuder sampler in combination with an electrochemical SO<span class="inline-formula"><sub>2</sub></span> sensor) were
conducted at varying distances from the crater rim. The in situ measurements
were accompanied by remote sensing observations (differential optical absorption spectroscopy; DOAS). The reactive
fraction of bromine increased from 0.20 <span class="inline-formula">±</span> 0.13 at the crater rim to
0.76 <span class="inline-formula">±</span> 0.26 at 2.8 km downwind, whereas chlorine showed an increase in
the reactive fraction from (2.7 <span class="inline-formula">±</span> 0.7) <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>−4</sup></span> to
(11 <span class="inline-formula">±</span> 3) <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>−4</sup></span> in the first 750 m. Additionally, a
reactive iodine fraction of 0.3 at the crater rim and 0.9 at 2.8 km downwind was
measured. No significant change in BrO <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="6bfc4ae3491d603d986b6e1d0e6866cf"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-3371-2021-ie00001.svg" width="8pt" height="14pt" src="acp-21-3371-2021-ie00001.png"/></svg:svg></span></span> SO<span class="inline-formula"><sub>2</sub></span> molar ratios was observed
with the estimated age of the observed plume ranging from 1.4 to 11.1 min. This study presents a large complementary data set of different halogen
compounds at Masaya volcano that allowed for the quantification of reactive
bromine in the plume of Masaya volcano at different plume ages. With the
observed field data, a chemistry box model (Chemistry As A Boxmodel Application
Module Efficiently Calculating the Chemistry of the Atmosphere; CAABA/MECCA) allowed us to
reproduce the observed trend in the ratio of the reactive bromine to total
bromine ratio. An observed contribution of BrO to the reactive bromine
fraction of about 10 % was reproduced in the first few minutes of the
model run.</p> |
|---|---|
| ISSN: | 1680-7316 1680-7324 |