Atmospheric Chemistry and Ozone

The Atmospheric Chemistry and Ozone group investigates chemistry and transport processes with relevance to the stratosphere, with an emphasis on polar ozone depletion and long-term changing ozone.

Our focus is on understanding the processes in the atmosphere by a combination of modelling, measurement campaigns and data analysis.

Background

The ozone layer is an important component of the global environmental system. The absorption of harmful solar UV radiation in the ozone layer protects the biosphere and heats the stratosphere. Thus changes in the atmospheric circulation and in the emission of anthropogenic substances that affect the abundance of ozone in the atmosphere have direct effects on the global climate system. A detailed understanding of the processes that regulate the distribution of ozone in the atmosphere is fundamental for reliable climate predictions and for estimating future UV-levels at the surface - an important parameter for the biosphere.

Modelling

ATLAS - Global Stratospheric Chemistry and Transport Model

ATLAS is a Lagrangian (trajectory-based) model for the global modelling of chemistry and transport in the stratosphere (Wohltmann et al., 2010). It has been used for a wide range of applications, including estimation of ozone loss (Manney et al., 2011) and sensitivity of polar ozone depletion to uncertainties in stratospheric chemistry and microphysics (Wohltmann et al., 2013). Recently, an extension of the model to the troposphere has been started, including a convection scheme and schemes for the chemistry of SO2 and short-lived halogen species.

SWIFT - Fast Ozone Chemistry for Climate Models

The SWIFT model is a fast scheme for simulating the chemistry of stratospheric ozone depletion in polar winter (Wohltmann et al., 2017). It is intended for use in climate models to enable the simulation of interactions between the ozone layer and climate. While the importance of interactions between climate change and the ozone layer has long been recognized, ozone is often prescribed in climate models due to computational constraints. In order to overcome this limitation, SWIFT was developed to enable interactions between the ozone layer and climate in models.

ECHAM6 - SWIFT

SWIFT has also been integrated as an optional submodel into the atmospheric general circulation model ECHAM6 (Stevens et al., 2013). It allows to simulate stratospheric ozone changes interactively in an Earth system model without significant impact on the numerical efficiency. First simulations results show that an interactive stratospheric ozone layer leads to more reasonable interactions between troposphere and stratosphere, and eventually to an improved reproduction of atmospheric circulation patterns.

Pathway analysis of atmospheric chemical reaction systems

An algorithm, that was originally developed for the automatic determination of catalytic ozone destruction cycles from the output of a chemical model (Lehmann, 2004), is now used for a wider range of problems. It was also applied to determine the dominant reaction sequences in Antarctic stratospheric chlorine chemistry, mesospheric ion chemistry and in the atmospheres of Mars and potential extra-solar planets.

 

Campaigns and Measurements

Match - Ozone loss from coordinated ozonesonde measurements

Chemical ozone loss cannot be deduced from isolated measurements of ozone alone, since ozone values at a given location are always determined not only by chemistry, but also by transport.

From the different approaches developed to overcome this problem, the Match approach developed at AWI (Rex et al., 1999) is the most straightforward and reliable solution. In the Match approach, an air mass probed by an ozonesonde is measured for a second time by predicting the trajectory of the air parcel and a coordinated sonde launch at a different station.

Since 1992, more than 15 international measurement campaigns involving a large number of ozonesonde stations have been conducted in the Arctic and Antarctic.

Campaigns and stations

In addition to ozonesonde measurements at the Arctic AWIPEV station and the Antarctic Neumayer station, the group operates a temporary station in Palau, in the region where the majority of tropospheric air enters the stratosphere. The group is and was leading or involved in numerous international measurement campaigns, including

StratoClim
SHIVA
RECONCILE