LFU:online

- The course will provide a detailed overview of the chemical transformations that control the abundances of key trace species; no previous knowledge of atmospheric chemistry is required.

- Focus is on the “fast photochemistry”, and the underlying physical chemistry, that controls radical cycles, ozone levels, and pollutant concentrations.

- The course focuses on topics of current scientific/societal interest, related to the effects of human activity on air quality and climate: chemistry of urban air, particulate matter, and chemistry-climate coupling

- Emphasis of the course is on assessing the impact latest findings have on our understanding of important atmospheric trace species (secondary pollutants and greenhouse gases) in the Earth's atmosphere (topics include: new particle and cloud condensation nuclei formation including “isoprene suppression”, implications of viscosity of aerosol, uncertainties in understanding of atmospheric oxidative capacity, auto-oxidation chemistry that drives rapid chemical transformations, role of aqueous aerosol chemistry).

In this course a framework of tropospheric chemistry will be generated that requires no previous knowledge of this topic. The goal is to develop an understanding of chemical and physical processes in the troposphere. Focus is on the main processes transforming emissions into the secondary pollutants that affect the environment, human health, and climate, in particular with respect to the role of anthropogenic influence. This will provide a foundation for the evaluation of the impact the newest scientific studies have on our understanding of processes that are important for the part of the atmosphere we live in.

The first part of the course will generate a framework of tropospheric chemistry. After that three topics will be discussed in more detail:

Topic 1: Impact of recently discovered auto-oxidation/auto-catalysis

Recently discovered atmospheric auto-oxidation reactions of hydrocarbons are changing our understanding of how secondary pollutants, in particular secondary organic aerosol, and new particles are formed. After an initial oxidation reaction molecules undergo a number of internal reactions that rapidly increase the oxygen content of the molecules, which affects their physical and chemical properties, and also has direct implications for our understanding of the oxidative capacity of the atmosphere. The rapid oxidation, compared to a slower, step-wise mechanism represents a fascinating chemical system that is changing our understanding of tropospheric oxidation with direct implications for the environment.

Topic 2: Implications of the physical state of atmospheric aerosol:

In the last years “glassy” atmospheric aerosol (aerosol = fine particulate matter suspended in air) has received intense study. The term refers to aerosol with very high viscosity. It is important to fully understand this phenomenon, which has a strong dependence on humidity and temperature. Diffusion in high viscosity aerosol can be extremely slow, preventing equilibration, e.g., with the gas-phase, and effectively trapping molecules inside the aerosol. The viscosity state of aerosol impacts environmentally important aerosol properties, such as the amount (mass) of aerosol, chemical and, in particular, physical properties, all of which impact the environment ranging from health to climate effects. “Glassy” aerosols represent another fascinating system in which fundamental physical and chemical processes have direct implications for the environment.

Topic 3: The role of aqueous (aerosol) chemistry:

(Secondary) organic aerosol, (organic aerosol formed in the atmosphere and not directly emitted) plays an important role in the environment as it affects climate and human health. However, the physical and chemical processes of OA formation remain poorly understood. Traditional aerosol studies were conducted almost exclusively under dry conditions, largely as this is experimentally much easier. Clearly, reactions in water can follow different pathways than in organic solutions. Furthermore, some molecules will be highly soluble in water but not in organic solutions. In recent years aqueous aerosol - in contrast to dry aerosol only consisting of organic compounds and inorganic salts – has therefore received a lot of attention. However, unambiguous evidence for the importance of aqueous aerosol remains elusive. This topic will explore to which degree evidence for the role of aqueous chemistry in controlling important physical and chemical aerosol properties has been uncovered and discuss what experiments are needed.

Class presentation: Each student will give one 20-minute lecture to the class on a current atmospheric chemistry technique or approach (measurement/modelling). These will be given throughout the semester, with the specific topic related to that day’s lecture. Intended as an overview of the subject, with citations from the recent literature. Topics/schedule determined in the second week of class.

Most readings assigned from current literature.

Useful textbooks:

• Jacob, Introduction to Atmospheric Chemistry, (Princeton, 1999); text available online (http://acmg.seas.harvard.edu/people/faculty/djj/book/index.html)

• Seinfeld and Pandis, Atmospheric Chemistry and Physics, 2^nd ed. (Wiley, 2006) 1^st edition okay also, though page numbers differ – need to cross-reference with 2^nd edition

• Finlayson-Pitts and Pitts, Chemistry of the Upper and Lower Atmosphere (Academic Press, 2000)

Oxidative Chemistry of Volatile Organic Compounds: Reaction Kinetics and Modelling