Bärbel Vogel

Impact of a possible future global hydrogen economy on Arctic stratospheric ozone loss

The potential role of molecular hydrogen (H2) as a future alternative energy carrier has generated widespread interest. The possible amount of additional hydrogen emission into the atmosphere in a hydrogen-based economy depends on future hydrogen production and leakage rates throughout the complete process chain. However, the expected emissions are highly uncertain. Based on the current literature an upper limit is estimated. Additional hydrogen emissions yield enhanced water vapor concentrations in the stratosphere which will have an impact on stratospheric temperatures and on polar ozone loss. Both stratospheric water vapor and ozone are important drivers of climate change. The potential environmental risks are described and assessed to be low compared to the environmental benefits.

Midlatitude ClO during the maximum atmospheric chlorine burden: in situ balloon measurements and model simulations

Chlorine monoxide (ClO) plays a key role in stratospheric ozone loss processes at midlatitudes. We present two balloon-borne in situ measurements of ClO conducted in northern hemisphere midlatitudes during the period of the maximum of total inorganic chlorine loading in the atmosphere. Both ClO measurements were conducted on board the TRIPLE balloon payload, launched in November 1996 in Léon, Spain, and in May 1999 in Aire sur l’Adour, France. For both flights a ClO daylight and night-time vertical profile was derived over an altitude range of approximately 15–35 km. ClO mixing ratios are compared to model simulations performed with the photochemical box model version of the Chemical Lagrangian Model of the Stratosphere (CLaMS). Simulations along 24-hour backward trajectories were performed to study the diurnal variation of ClO in the midlatitude lower stratosphere. Model simulations for the flight launched in Aire sur l’Adour 1999 show an excellent agreement with the ClO measurements. For the flight launched in Léon 1996, an overall good agreement is found, whereas the flight is characterized by a more complex dynamical situation due to a possible mixture of vortex and non-vortex air. We note that for both flights at solar zenith angles greater than 86 –87 simulated ClO mixing ratios are higher than observed ClO mixing ratios. However, the present findings indicate that no substantial uncertainties exist in midlatitude chlorine chemistry of the stratosphere. Correspondence to: B. Vogel (b.vogel@fz-juelich.de)

Lagrangian simulations of the transport of young air masses to the top of the Asian monsoon anticyclone and into the tropical pipe

We have performed backward trajectory calculations and simulations with the three-dimensional Chemical Lagrangian Model of the Stratosphere (CLaMS) for two succeeding monsoon seasons using artificial tracers of air mass origin. With these tracers we trace back the origin of young air masses (age < 6 months) at the top of the Asian monsoon anticyclone and of air masses within the tropical pipe (6 months< age< 18 months) during summer 2008. The occurrence of young air masses (< 6 months) at the top of the Asian monsoon anticyclone up to ∼ 460 K is in agreement with satellite measurements of chlorodifluoromethane (HCFC-22) by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument. HCFC-22 can be considered as a regional tracer for continental eastern Asia and the Middle East as it is mainly emitted in this region. Our findings show that the transport of air masses from boundary layer sources in the region of the Asian monsoon into the tropical pipe occurs in three distinct steps. First, very fast uplift in “a convective range” transports air masses up to 360 K potential temperature within a few days. Second, air masses are uplifted from about 360 K up to 460 K within “an upward spiralling range” within a few months. The largescale upward spiral extends from northern Africa to the western Pacific. The air masses are transported upwards by diabatic heating with a rate of up to 1–1.5 K per day, implying strong vertical transport above the Asian monsoon anticyclone. Third, transport of air masses occurs within the tropical pipe up to 550 K associated with the large-scale Brewer– Dobson circulation within ∼ 1 year. In the upward spiralling range, air masses are uplifted by diabatic heating across the (lapse rate) tropopause, which does not act as a transport barrier, in contrast to the extratropical tropopause. Further, in the upward spiralling range air masses from inside the Asian monsoon anticyclone are mixed with air masses convectively uplifted outside the core of the Asian monsoon anticyclone in the tropical adjacent regions. Moreover, the vertical transport of air masses from the Asian monsoon anticyclone into the tropical pipe is weak in terms of transported air masses compared to the transport from the monsoon anticyclone into the northern extratropical lower stratosphere. Air masses from the Asian monsoon anticyclone (India/China) contribute a minor fraction to the composition of air within the tropical pipe at 550 K (6 %), and the major fractions are from Southeast Asia (16 %) and the tropical Pacific (15 %).

The Influence of Energetic Particles on the Chemistry of the Middle Atmosphere

Energetic particle precipitation (EPP) during solar and geomagnetic active periods causes chemical disturbances in the lower thermosphere and in the middle atmosphere. Additional HOx (H, OH, HO2) and NOx (N, NO, NO2) are produced in the middle atmosphere, and enhancements of NOx produced in these events can be transported to the winter stratosphere. These trace species take part in ozone chemistry and, by chemical-radiative coupling, the dynamical state in the middle atmosphere can be altered. There is evidence both from observations and from chemistry-climate models that the EPP induced signal in the middle atmosphere may then propagate into the troposphere. Thus particle precipitation could connect to possible climate effects. The first step in this functional chain is the impact of EPP on the chemical composition in the middle atmosphere and lower thermosphere, and the downward transport in the polar winter middle atmosphere. The general objective of this project was to assess quantitatively the chemical composition change in the middle atmosphere by combining model simulations and observations. The study relays mainly on the observations of the MIPAS instrument on the ENVISAT satellite, whose data set has been expanded in the context of this project by a newly developed retrieval of the gas H2O2, a reservoir for the members of the HOx family. Simulations have been carried out with the two chemical transport models CLaMS and KASIMA, which cover chemistry and transport effects in the stratosphere up to the mesosphere/lower thermosphere region. The impact on the global NOy budget and (the resulting) total ozone change are assessed in these studies. In addition, the ion reaction mechanism for the conversion of N2O5 to HNO3 based on positive ion chemistry was refined. The detailed comparison of model results and observation for the SPE 2003 showed that models can simulate the impact of EPP on ozone chemistry but deficiencies exist for some minor species.

The relevance of reactions of the methyl peroxy radical (CH3O2) and methylhypochlorite (CH3OCl) for Antarctic chlorine activation and ozone loss

Abstract The maintenance of large concentrations of active chlorine in Antarctic spring allows strong chemical ozone destruction to occur. In the lower stratosphere (approximately 16–18 km, 85–55 hPa, 390–430 K) in the core of the polar vortex, high levels of active chlorine are maintained, although rapid gas-phase production of HCl occurs. The maintenance is achieved through HCl null cycles in which the HCl production is balanced by immediate reactivation. The chemistry of the methyl peroxy radical (CH3O2) is essential for these HCl null cycles and thus for Antarctic chlorine and ozone loss chemistry in the lower stratosphere in the core of the polar vortex. The key reaction here is the reaction ; this reaction should not be neglected in simulations of polar ozone loss. Here we investigate the full chemistry of CH3O2 in box-model simulations representative for the conditions in the core of the polar vortex in the lower stratosphere. These simulations include the reaction CH3O2 + Cl, the product methylhypochlorite (CH3OCl) of the reaction CH3O2 + ClO, and the subsequent chemical decomposition of CH3OCl. We find that when the formation of CH3OCl is taken into account, it is important that also the main loss channels for CH3OCl, namely photolysis and reaction with Cl are considered. Provided that this is the case, there is only a moderate impact of the formation of CH3OCl in the reaction CH3O2 + ClO on polar chlorine chemistry in our simulations. Simulated peak mixing ratios of CH3OCl ( ppb) occur at the time of the lowest ozone mixing ratios. Further, our model simulations indicate that the reaction CH3O2 + Cl does not have a strong impact on polar chlorine chemistry. During the period of the lowest ozone concentrations in late September, enhanced values of CH3O2 are simulated and, as a consequence, also enhanced values of formaldehyde (about 100 ppt) and methanol (about 5 ppt).