Rolf Sander Discusses Models for Atmospheric Chemistry

Scientist Interview: September 2011

Rolf Sander

In a recent analysis of Essential Science IndicatorsSM from Clarivate Analytics, Dr. Rolf Sander was named a Rising Star in the field of Geosciences. His current record in this field includes 43 papers cited a total of 1,013 times between January 1, 2001 and April 30, 2011.

Sander is a member of the Air Chemistry Department of the Max Planck Institute for Chemistry in Mainz, Germany.


SW: Please tell us about your educational background and research experiences.

I have studied chemistry and obtained my Ph.D. in 1994. Today I spend most of my time at the computer to develop code calculating the very complex mechanisms of atmospheric chemistry. However, in order not to lose contact with reality during my theoretical studies, I occasionally also join measurement campaigns which provide results that can be compared to the model results.

SW: What first drew you to atmospheric sciences? Is there a specific area within this field on which you focus, or do you maintain a wide variety of interests?

I had my first contact with atmospheric chemistry while I was a graduate student at Düsseldorf University, Germany. At that time I read a newspaper interview with Paul Crutzen, who has contributed substantially to the explanation of the ozone hole and who later received the Nobel Prize for his work. I decided to start my Ph.D. in this environmentally very important as well as scientifically interesting field of atmospheric chemistry. I moved to the Max-Planck Institute in Mainz and Paul Crutzen became my Ph.D. supervisor. Since then, halogen chemistry has been my favorite research topic. However, there are of course many other areas I'm interested in as well.

SW: One of your most-cited original papers from our database is the 2002 J. Geophys. Res. Atmos. paper you coauthored, "Modeling halogen chemistry in the marine boundary layer—1. Cloud-free MBL," and several other papers of yours deal with halogen chemistry. Why are halogens so important, and what have you found out about them over the years? What would you say is the ultimate goal or benefit of this work?

"To improve our understanding further, we need to couple these separate models into comprehensive Earth System Models."

It is well known now that halogens in the stratosphere create the ozone hole. In addition, halogens also affect the chemistry in the lowest level of the atmosphere, the troposphere. Ozone and highly toxic elemental mercury in near-surface air in polar regions can disappear completely in the spring. This is caused by reactive halogens (mostly bromine compounds but also iodine and chlorine).

We studied how chemical reactions similar to those in polar regions can also affect ozone and organics over the ocean. If we want to be able to understand the ozone hole and to make climate predictions on a global scale, the chemistry of these tropospheric ozone depletion events needs to be understood first.

SW: You've worked on the development of several atmospheric chemistry models, such as MECCA and MESSy. Can you give us a rundown of these models and their uses?

MECCA is a flexible atmospheric chemistry model that contains reactions of many different compounds: ozone, halogens (chlorine, bromine, iodine), production of sulfuric acid ("acid rain"), organic chemistry (e.g. methane, isoprene), and mercury chemistry.

MESSy is an interface with infrastructure to couple individual physical or chemical processes to a global climate model. It contains submodels describing these processes, and it also is a coding standard. In contrast to its self-deprecating name, MESSy is a very modularized and highly-structured system.

A key concept of our model development is that we make the code freely available to the research community. We think this is the best way to improve scientific knowledge and to obtain a large base of colleagues who contribute to developing, maintaining, and using the model.

In addition, we publish most of our results in open-access journals. In interdisciplinary studies, it is important that our publications are also available to colleagues who do not specialize in atmospheric chemistry and who therefore do not have subscriptions to highly specialized journals in our field. Open access allows them to read our papers even though their libraries may not have printed copies of them.

SW: Your 2006 Atmos. Chem. Phys. paper, "Carbonate precipitation in brine—a potential trigger for tropospheric ozone depletion events," resulted in a bit of discussion in the literature (Morin et al., 2008, followed by Sander and Morin 2010). Would you tell us a bit about this aspect of your work?

"If we want to be able to understand the ozone hole and to make climate predictions on a global scale, the chemistry of these tropospheric ozone depletion events needs to be understood first."

You mention an interesting paper here, which could be called an experiment in publication procedure. It started with two conflicting papers in the peer-reviewed literature (Sander et al., 2006 and Morin et al., 2008). Instead of the usual way of scientific discourse with "Comment" and "Reply" papers, Samuel Morin and I decided it would be more productive to discuss the issue directly between us.

In the end, we came up with an explanation that reconciled the results from the previous papers and eventually we described it in the common publication by Sander and Morin (2010). We think this is a good way to achieve scientific progress because in contrast to the traditional "Comment" and "Reply" procedure, the reader is not left with two opposing views.

SW: Are there any projects you have forthcoming that you are free to discuss?

In addition to the ongoing work of halogen chemistry and model code development, I have another research interest: Our air is always in contact with water via rain, clouds, rivers, oceans, and more. Pollutants can be washed out into the aqueous phase, but they may also degas out of the aqueous phase. The distribution between the phases can be described with Henry's law. Unfortunately, publications of the necessary Henry's law constants are spread throughout the literature and often difficult to obtain.

I am working on a comprehensive list that summarizes available data sets. I hope that I can finalize this list and publish it before the end of this year. A preliminary version is available at already.

SW: In what directions do you see your field (or key aspects thereof) going in the next decade?

The scientific knowledge of humankind is vast. So vast that even experts can only know a tiny fraction of it. Universal geniuses may have existed at the time of Leonardo da Vinci but today they are unthinkable. Of course, this also applies to computer modeling. At the moment, we have models of certain aspects of atmospheric chemistry or physics. There are also geoscientific models describing the land, the oceans, and humans.

To improve our understanding further, we need to couple these separate models into comprehensive Earth System Models. This requires that experts in different fields work together. As a necessary first step, legacy code needs to be modularized and updated. This will be a big and important task for the climate research community in the near future. Halogen chemistry (including man-made products like CFCs as well as natural sources from oceans, salt lakes, and volcanoes) will be one of the ingredients necessary for a successful Earth System Model.End

Rolf Sander
Air Chemistry Department
Max Planck Institute for Chemistry
Mainz, Germany


Jockel P, et al., "The atmospheric chemistry general circulation model ECHAM5/MESSY1: Consistent simulation of ozone from the surface to the mesosphere," Atmos. Chem. Phys. 6: 5067-104, 7 November 2006 with 84 cites. Source: Essential Science Indicators from Clarivate Analytics.



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