A simple formulation of the CH&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O photolysis quantum yields

Röth, E. P.; Ehhalt, D. H.

doi:10.5194/acp-15-7195-2015

Cited by 14 publications

(26 citation statements)

References 20 publications

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“…We have employed the recommended setup for both cross sections and quantum yields for 223 K (Sander et al, 2011). Using the photolysis 30 quantum yields suggested by Röth and Ehhalt (2015) yields very similar results to those presented here (Zafar, 2016). Branching ratios of 0 and 100% cannot not occur in reality (Röth and Ehhalt, 2015) but were used here as lower and upper limits.…”

supporting

confidence: 83%

The maintenance of elevated active chlorine levels in the Antarctic lower stratosphere through HCl null-cycles

Müller¹,

Grooß²,

Zafar³

et al. 2017

Preprint

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Abstract. The Antarctic ozone hole arises from ozone destruction driven by elevated levels of ozone destroying ("active") chlorine in Antarctic spring. These elevated levels of active chlorine have to be formed first and then maintained throughout the period of ozone destruction. It is a matter of debate, how this maintenance of active chlorine is brought about in Antarctic spring, when the rate of formation of HCl (considered to be the main chlorine deactivation mechanism in Antarctica) is extremely high. 5Here we show that in the heart of the ozone hole (16-18 km or 100-70 hPa, in the core of the vortex), high levels of active chlorine are maintained by effective chemical cycles (referred to as HCl null-cycles hereafter). In these cycles, the formation of HCl is balanced by immediate reactivation, i.e. by immediate reformation of active chlorine. Under these conditions, polar stratospheric clouds sequester HNO 3 and thereby cause NO 2 concentrations to be low. These HCl null-cycles allow active chlorine levels to be maintained in the Antarctic lower stratosphere and thus rapid ozone destruction to occur. For the observed 10 almost complete activation of stratospheric chlorine in the lower stratosphere, the heterogeneous reaction HCl + HOCl, the production of HOCl via HO 2 + ClO, with the HO 2 resulting from CH 2 O photolysis, is essential. These results are important for assessing the impact of changes of the future stratospheric composition on the recovery of the ozone hole. Our simulations indicate that, in the lower stratosphere, future increased methane concentrations will not lead to enhanced chlorine deactivation (through the reaction CH 4 + Cl −→ HCl + CH 3 ) and that extreme ozone destruction to levels below ≈ 0.1 ppm will occur until 15 mid-century.

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supporting

confidence: 83%

The maintenance of elevated active chlorine levels in the Antarctic lower stratosphere through HCl null-cycles

Müller¹,

Grooß²,

Zafar³

et al. 2017

Preprint

View full text Add to dashboard Cite

show abstract

“…We have employed the recommended setup for both cross sections and quantum yields for 223 K (Sander et al, 2011). Using the photolysis quantum yields suggested by Röth and Ehhalt (2015) produces very similar results to those presented here (Zafar, 2016).…”

Section: Model Descriptionsupporting

confidence: 69%

“…A possible temperature dependence of both the cross sections and the quantum yields of the photolysis of CH 2 O could be important, as it could potentially lead to a different production of HO 2 in the photolysis of CH 2 O for the temperature range below 200 K relevant here. The intensities of the maxima of each absorption band increase with lower temperatures, but an accurate temperature dependence of these kinetic data for temperatures in the polar lower stratosphere cannot be considered here due to a lack of laboratory information (Smith et al, 2006;Röth and Ehhalt, 2015).…”

Section: Model Descriptionmentioning

confidence: 99%

“…The branching ratio between Reactions (R14) and (R22) is uncertain; it is about 30 % for the radical channel (Reaction R14) for the conditions in question here (Röth and Ehhalt, 2015; see also Sect. 2.1).…”

Section: The Path To Full Activation Of Hclmentioning

confidence: 99%

“…1 in Röth and Ehhalt, 2015). In a sensitivity study, we also employ branching ratios of 0 and 100 %, which cannot occur in reality (Röth and Ehhalt, 2015).…”

Section: Model Descriptionmentioning

confidence: 99%

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The maintenance of elevated active chlorine levels in the Antarctic lower stratosphere through HCl null cycles

Müller¹,

Grooß²,

Zafar

et al. 2018

Atmos. Chem. Phys.

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Abstract. The Antarctic ozone hole arises from ozone destruction driven by elevated levels of ozone destroying ("active") chlorine in Antarctic spring. These elevated levels of active chlorine have to be formed first and then maintained throughout the period of ozone destruction. It is a matter of debate how this maintenance of active chlorine is brought about in Antarctic spring, when the rate of formation of HCl (considered to be the main chlorine deactivation mechanism in Antarctica) is extremely high. Here we show that in the heart of the ozone hole (16-18 km or 85-55 hPa, in the core of the vortex), high levels of active chlorine are maintained by effective chemical cycles (referred to as HCl null cycles hereafter). In these cycles, the formation of HCl is balanced by immediate reactivation, i.e. by immediate reformation of active chlorine. Under these conditions, polar stratospheric clouds sequester HNO 3 and thereby cause NO 2 concentrations to be low. These HCl null cycles allow active chlorine levels to be maintained in the Antarctic lower stratosphere and thus rapid ozone destruction to occur. For the observed almost complete activation of stratospheric chlorine in the lower stratosphere, the heterogeneous reaction HCl + HOCl is essential; the production of HOCl occurs via HO 2 + ClO, with the HO 2 resulting from CH 2 O photolysis. These results are important for assessing the impact of changes of the future stratospheric composition on the recovery of the ozone hole. Our simulations indicate that, in the lower stratosphere, future increased methane concentrations will not lead to enhanced chlorine deactivation (through the reaction CH 4 + Cl −→ HCl+CH 3 ) and that extreme ozone destruction to levels below ≈ 0.1 ppm will occur until mid-century.

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Photodegradation of α-Pinene Secondary Organic Aerosol Dominated by Moderately Oxidized Molecules

Pospíšilová

Bell

Lamkaddam

et al. 2021

Environ. Sci. Technol.

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Atmospheric secondary organic aerosol (SOA) undergoes chemical and physical changes when exposed to UV radiation, affecting the atmospheric lifetime of the involved molecules. However, these photolytic processes remain poorly constrained. Here, we present a study aimed at characterizing, at a molecular level and in real time, the chemical composition of α-pinene SOA exposed to UV-A light at 50% relative humidity in an atmospheric simulation chamber. Significant SOA mass loss is observed at high loadings (∼100 μg m–3), whereas the effect is less prevalent at lower loadings (∼20 μg m–3). For the vast majority of molecules measured by the extractive electrospray time-of-flight mass spectrometer, there is a fraction that is photoactive and decays when exposed to UV-A radiation and a fraction that appears photorecalcitrant. The molecules that are most photoactive contain between 4 and 6 oxygen atoms, while the more highly oxygenated compounds and dimers do not exhibit significant decay. Overall, photolysis results in a reduction of the volatility of SOA, which cannot be explained by simple evaporative losses but requires either a change in volatility related to changes in functional groups or a change in physical parameters (i.e., viscosity).

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A simple formulation of the CH<sub>2</sub>O photolysis quantum yields

Cited by 14 publications

References 20 publications

The maintenance of elevated active chlorine levels in the Antarctic lower stratosphere through HCl null-cycles

The maintenance of elevated active chlorine levels in the Antarctic lower stratosphere through HCl null-cycles

The maintenance of elevated active chlorine levels in the Antarctic lower stratosphere through HCl null cycles

Photodegradation of α-Pinene Secondary Organic Aerosol Dominated by Moderately Oxidized Molecules

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