Uncertain road to ozone recovery

Influence of NOX, Cl, and Br on the upper core of the ozone valley over the Tibetan Plateau during summer: Simulations with a box model

The ozone valley (OV) in the upper troposphere-lower stratosphere (UTLS) over the Tibetan Plateau (TP) has been identified since the 1990s during boreal summer. Recent studies have shown that another upper core of the OV appeared in the middle and upper stratosphere (10-2 hPa); however, the formation mechanism of the OV in the upper stratosphere remains unclear. In this paper, Microwave Limb Sounder (MLS) data from the Aura satellite and the stratospheric heterogeneous chemical reaction box model are used to investigate the impact of chemical substances, including NO, NO₂, Cl and Br, on the ozone valley in the middle and upper stratosphere over the TP. The results show that the formation mechanism of the diurnal and nighttime variation in the upper core of the OV over the TP in the summer may be related to the different daytime and nighttime distributions of NO₂ and the difference in daytime and nighttime average temperatures between the TP and the same latitude regions.

Impact of ozone mini-holes on the heterogeneous destruction of stratospheric ozone

A comprehensive study of ozone mini-holes over the mid-latitudes of both hemispheres is presented, based on model simulations with the coupled climate-chemistry model ECHAM4.L39(DLR)/CHEM representing atmospheric conditions in 1960, 1980, 1990 and 2015. Ozone mini-holes are synoptic-scale regions of strongly reduced total ozone, directly associated with tropospheric weather systems. Mini-holes are supposed to have chemical and dynamical impacts on ozone levels. Since ozone levels over northern mid-latitudes show a negative trend of approximately -4%/decade and since it exists a negative correlation between total column ozone and erythemally active solar UV-radiation reaching the surface it is important to understand and assess the processes leading to the observed ozone decline. The simulated mini-hole events are validated with a mini-hole climatology based on daily ozone measurements with the TOMS (total ozone mapping spectrometer) instrument on the satellite Nimbus-7 between 1979 and 1993. Furthermore, possible trends in the event frequency and intensity over the simulation period are assessed. In the northern hemisphere the number of mini-hole events in early winter decreases between 1960 and 1990 and increases towards 2015. In the southern hemisphere a positive trend in mini-hole event frequency is detected between 1960 and 2015 in spring associated with the increasing Antarctic Ozone Hole. Finally, the impact of mini-holes on the stratospheric heterogeneous ozone chemistry is investigated. For this purpose, a computer-based detection routine for mini-holes was developed for the use in ECHAM4.L39(DLR)/CHEM. This method prevents polar stratospheric cloud formation and therefore heterogeneous ozone depletion inside mini-holes. Heterogeneous processes inside mini-holes amount to one third of heterogeneous ozone destruction in general over northern mid- and high-latitudes during winter (January-April) in the simulation.

Global warming in the twenty-first century: an alternative scenario

A common view is that the current global warming rate will continue or accelerate. But we argue that rapid warming in recent decades has been driven mainly by non-CO(2) greenhouse gases (GHGs), such as chlorofluorocarbons, CH(4), and N(2)O, not by the products of fossil fuel burning, CO(2) and aerosols, the positive and negative climate forcings of which are partially offsetting. The growth rate of non-CO(2) GHGs has declined in the past decade. If sources of CH(4) and O(3) precursors were reduced in the future, the change in climate forcing by non-CO(2) GHGs in the next 50 years could be near zero. Combined with a reduction of black carbon emissions and plausible success in slowing CO(2) emissions, this reduction of non-CO(2) GHGs could lead to a decline in the rate of global warming, reducing the danger of dramatic climate change. Such a focus on air pollution has practical benefits that unite the interests of developed and developing countries. However, assessment of ongoing and future climate change requires composition-specific long-term global monitoring of aerosol properties.

Biological UV dosimeters in the assessment of the biological hazard from environmental radiation

To determine the impact of environmental UV radiation, biological dosimeters that weight directly the incident UV components of sunlight have been developed, improved and evaluated in the frame of the BIODOS project. Four DNA-based biological dosimeters ((i) phage T7, (ii) uracil thin layer, (iii) spore dosimeter and (iv) DLR-biofilm) have been assessed from the viewpoint of their biological relevance, spectral response and quantification of their biological effectiveness. The biological dosimeters have been validated by comparing their readings with weighted spectroradiometer data, by comparison with other biological doses, as well as with the determined amounts of DNA UV photoproducts. The data presented here demonstrate that the biological dosimeters are potentially reliable field dosimeters for measuring the integrated biologically effective irradiance for DNA damage.