Unit 17

sulfur cycle
Schematic view of the sulfur cycle. From: Mölders and Kramm (2014)

Learning goal

Upon finishing this unit students can

  • explain the basics of aerosol formation and growth from precursor gases
  • interpret aerosol size distributions
  • explain atmospheric aerosol removal processes in the framework of thermodynamics, cloud microphysical, and chemical processes
  • biogeochemical cycles of the Earth’s system, and identify linkages

Students’ Tasks

  1. Repeat the sections on sinks and sources of atmospheric constituents (Chap. 1), the gas laws, moisture measure, saturation (Chapt. 2), heterogenous nucleation, diffusion (Chap. 3), absorption and scattering (Chap. 4) as they are central to understanding of the linkages of the biogeochemical cycles.
  2. Watch this video
  3. Read chapter 5.4 and 5.6.3 (included) of Lectures in Meteorology and take notes to be able to present the material in class.
  4. Answer the questionnaire by 1500 AST the day before the next class.

You can find the powerpoint presentation here.


Q: For a given aerosol particle, how can we judge whether it is formed through gas-to-particle conversion or it is formed via direct emission?
A: The size may give hints as new particles are in the Aitken nucleus range. Sulfur, nitrogen, organic and carbonaceous materials are the major chemical species involved in gas-to-particle-conversion. This size range is the nucleation mode. Here, most particles formed by oxidation of sulfur containing precursor gases like SO2, H2S, CS2, COS, CH3SCH3, or CH3SCH3 to sulfate (SO4=), and subsequent condensation, a process called homogenous gas-to-particle conversion. Many of these sulfate aerosols finally end up in the 0.1-1 micrometer size range. Sulfur dioxide, for instance, can form various sulfates in the presence of water and ammonia (NH3) by gas-to-particle conversion.
Q: How do thermophoretic processes look like when at work?
A: Watch this animation

Class work

We will discuss these problems among other things.