(1º semestre, 4º ano)
2 de Fevereiro de 2017
Chemistry Test (1 hour)
1 (4) – Usually the temperature of a gas depends on the number of collisions between the gas molecules and, therefore, in the number of molecules present. However, in the stratosphere and thermosphere the temperature increases with altitude (despite of fewer molecules when the altitude increases). Explain both these phenomena, and present the chemical equations of the reactions involved in the stratosphere.
2 (4) – Knowing that the molar fraction (%) of oxygen is constant in all atmospheric layers and that the pressure in the tropopause is 100 hPa calculate the number density (molecules m-3) of O2 in that region of the atmosphere (T = 0oC). (Please notice that the Ideal gas law relates physical quantities with the number of moles and not molecules).
Patm(air) = 1.013 x 105 Pa
R = 8.314 J K-1 mol-1
NA = 6.023 x 1023particules mol-1
3 (3.5) In the figure below you will find a representation of the Sulphur Cycle. Number alongside the arrows are estimates of average annual fluxes in Tg(N) per year; numbers in brackets are total amounts of species in the atmosphere; data is from the year 2000.
Calculate the residence time of SO2 based on the average influxes. Based on the value obtained what can be concluded about the global or regional relevance of atmospheric SO2 concentration in acid rain?
4 – CFC’s and Halons (compounds with C-Br bonds) are among the responsible for the destruction of the ozone layer.
a) (3.5) Write the chemical equations of the processes involved in ozone destruction by CFC’s, namely CFC 12. Why is this a catalytic process?
b) (2.5) Explain why the Ozone Depletion Potencial of CFC-11 is 1, that of halons is 15 and that of hydrocarbons is 0.
c) (2.5) CFC’s are being replaced by hydrofluorocarbons (HFC) and hydrocarbons. Despite being harmless in the depletion of ozone these compounds still affect the global climate of the Earth. How and why?
Thermodynamics Test (40 minutes)
Grupo I (5 valores)
/ This picture illustrates the mean global energy budgeta)Make an energy balance to the atmosphere. What is the necessary and sufficient condition for the mean temperature of the surface to be constant?
b)How do clouds change the energy budget of the atmosphere?
Grupo II (3 valores)
/ a)What are the white plane trails composed of?b)Why do white trails occur in some atmospheric conditions and not with others? Illustrate this using a chart with the temperature in the x axis and the equilibrium vapour pressure in the y axis.
Grupo III (12 valores)
/ The graph shows the evolution of the partial pressure (in orange) and the equilibrium partial pressure (in blue) of air mass that ascends adiabatically.Answer the following questions justifying your answers.
a)Why does the temperature decrease as the air parcel ascends?
b)What happens to the mixing ratio and to relative humidity as the parcel ascends?
c)What is the temperature of the air parcel when it reaches the lifting condensation level?
d)What is the height of the lifting condensation level?
e)Do you expect clouds to form by convection if the environmental gradient is -12ºC/km?
Do you expect radiation fog to form if the temperature at the surface decreases to 5ºC during the night?
Physics Test (1 hour)
Group 3.1 (10 marks)
a)In the atmosphere, what is the force that initially sets the air in motion (horizontally)?b)What is a geostrophic wind? Why would you not expect to observe a geostrophic wind at the equator?
c)Since there is always an upward-directed pressure gradient force, why doesn’t the air rush off into space?
Group 3.2 (10 marks)
a)Why is the difference in surface wind speed between morning and afternoon typically greater on a clear, sunny day than on a cloudy, overcast day?b)Why do clouds tend to form over land with a sea breeze and over water with a land breeze?
c)Why is it impossible on the earth for a Hadley cell to extend from the pole to the equator?