Maria Kanakidou. Environmental Chemistry and Processes Laboratory, Chemistry Department, University of Crete, Heraklion, Greece

Transcription

1 Maria Kanakidou Environmental Chemistry and Processes Laboratory, Chemistry Department, University of Crete, Heraklion, Greece

2 Why ocean should care for atmospheric chemistry? Impact on energy/radiation/water cycle (chemistry/climate) Interactions human s/land/ocean emissions air quality issues Atmospheric inputs of nutrients to the ocean (toxic compounds) Chemical processing in the atmosphere + solubility/bioavailability of nutrients

3 Atmospheric composition Lifetimes Photochemical decay in the atmosphere notions of chemical kinetics Atmospheric Chemistry issues relevant to the low atmosphere: stratospheric (driving tropospheric chemistry) tropospheric free radicals (H x,n x,x x ) Aerosols (rganics, sea-salt, natural sulfur, acid displacement reactions)

4 Atmospheric compartments Temperature profile

5 Composition of the remote troposphere 10-6 Surface tropopause Atmospheric chemistry cares for constituents that all together are less than 1 %

6 What determines the environmental impact of an atmospheric constituent? - Its properties - its presence (levels and time it spends) in the atmosphere. It is thus important to know sources/emissions (E), sinks/removal flux (S) and lifetime (τ) Atmospheric lifetime (τ) is related to the atmospheric burden (Q) and removal flux (S) by: τ= Q/S Lifetime τ of a constituent A is the time needed to be reduced to the 1/e of its initial concentration

7 Seinfeld & Pandis, 1998 Lifetime of trace constituents, transport times & spatial scales

8 Lifetime of trace constituent A in the atmosphere To calculate the chemical lifetime of a constituent A in the atmosphere some chemical kinetic notions are needed: Chemical reactions in the atmosphere can be : Homogeneous (reactants in the same phase) Heterogeneous (reactants in different phases) Multiphase chemistry Photochemical (impact of solar radiation)

9 Reaction velocity and reaction order Molecules/(cm s) (unimolecular reactions) Moles per liter

10 Temporal evolution of the concentration - Reaction velocity

11 Lifetime of trace constituents in the atmosphere Lifetime τ of a constituent A is the time needed to be reduced to the 1/e of its initial concentration [A]=[Ao] e -kt when e -kt = e -1 t=τ τ=1/k where k (in s -1 ) is the overall pseudo first order loss rate of A Turnover time τ i can be defined for a species A with respect of the processes i that removes it from the atmosphere The overall lifetime τ of A is related to its turnover times τ i : 1/τ=Σ i (1/τ i )

12 Reaction velocity and reaction order conc

13 N + H HN C + H (+ ) C + H CH 4 + H CH

14 Reaction velocity and reaction order

15 rd order reactions or Termolecular reactions Recombination reactions

16 Photodissociation reactions

17 Photodissociation reactions function

18 What is driving atmospheric chemistry? WM, 1998

19 Human driven changes in profile Surface zone Europe s Environment, 1998; Marenco et al., J. Geograph. R., , 1994; Staehelin et al., Atmos. Environ., 5, , 1991.

20 What is driving atmospheric chemistry? A molecule of resides for s in the atmosphere before photodissociation

21 X X X X Why is not increasing in the stratosphere? WM 1986 Chapman Fractional contribution to stratospheric Ο depletion X / X can be: HX H / H H / H Cl / Cl Br / Br I / I Clx Nx N / N Cl Cl Cl Cl Cl Cl Cl Cl Cl M 400nm hv Cl hv Cl ( destruction of M )

22 Taken from Finlayson-Pitts and Pitts book

23 X X X X H H H H H H H H N N N N Cl Cl Cl Cl ) estruction of ( 400 d hv Cl hv Cl M Cl M Cl Cl Cl Cl nm Fractional contribution to stratospheric Ο depletion HX Nx Clx Chapman Why is not increasing in the stratosphere? WM 1986

24 Can we stop catalytic cycles in the atmosphere? What are reservoir species? Termination reactions reservoir species H Cl N N M M HN ClN M M Important reactions for stratospheric loss of Ο coupling of element cycles HCl + ClN HN + Cl ClN + H HN + HCl HCl + HCl H + Cl N 5 + HCl HN + ClN N 5 + H HN

25 What is driving tropospheric chemistry? Stratosphere from D. Jacob handbook Stratospheric is the driving force for tropospheric production Ο Ο 1 D + H H

26 Atmospheric processes taken into account in models Chemistry transport deposition

27 Tropospheric

28 What is driving tropospheric? 1. Photochemical production and destruction. Exchanges with the stratosphere. Deposition to surfaces WM