1^st week homework (due 7^th September):

1. write down the electron configurations of P, S, and Br

2. why do halogens (X) form X₂ in the gas phase?

3. why do the alkali metals (Li, Na, ….) do so too?

4. Draw the potential energy diagram of Cl₂, and give the bonding order

5. Same as 4. but for NO; is NO a radical?

6. Same as 4 & 5 but for ClO

7. Same as 4 & 5 but for CO; what molecule does this resemble to?

2^nd week homework (due 16^th September):

1. Light and energy are directly related: List the definitions and relationships between wave length, wave number, frequency, temperature, and photon energy in physical (Electron-Volt) and molar (kJ mol^-1) units

2. Where in the atmosphere is nitrogen (N₂) photolyzed? Why?

3. The fluorescence yield from an electronically exited molecule in the gas phase can be increased by decreasing gas pressure, which lowers the ‘mean free path’ of a molecule in the gas phase …

… but what could be done to a molecule itself to increase its likelihood to fluoresce out of its S₁ state?

4. Name the electronic ground states of the bi-atomic molecules you drew for last week’s homework

5. Consider two molecules that both have a dipole moment: CO₂ is a strong, CO is a weak IR absorber. Suggest possible reasons for that fact.

6. Considering both atmospheric transmission in the IR and molecular properties: What do you think makes the perfect greenhouse gas?

3^rd week homework

1. Consider a generic molecule with an absorption spectrum in the UV-B/A (Excel file). The molecule has a dissociation energy of 352 kJ mol^-1. Calculate its photolysis frequency for a reference solar spectral radiation under 1.5 air masses (aka 1.5 times standard thickness of atmosphere; find that!). Make a reasonable estimate for the spectral distribution of any unknown parameters.

2. Suppose this generic molecule reacts with the ∙OH radical in the atmosphere. As you have access to the molecule, you test its reactivity in the lab by injecting a large amount of it into a flask to make a 10 ppm mixture. Then you added ∙OH and measured its decay, the data are to be found in the Excel file (sheet “OH”). Calculate the reaction rate constant, k, and its error. After repeating the experiment at a temperature 20 K lower than room temperature, you found that k dropped by 20%. Estimate the activation energy of the reaction.

3. Calculate the ·OH radical lifetime (at stp) as a result of reactions with CO and CH₄ (assume [CH₄] = 1.8 ppm, [CO] = 100 ppb). Use the tabulated data for the reaction rate constants.

4^th/5^th weeks homework (due 14^th October):

1. Assess the tropospheric lifetime of ozone. Consider all the processes you learned about. How, and if so why does τ_O3 vary with geographic location and/or elevation? Does it vary in time/diurnally? 3 pts

2. What determines the amplitude of the ozone diurnal variation within the adjusted Null-Cycle (consider a generic “RO₂∙”, not only CH₃O₂∙) ? 2 pts

3. Derive a SS abundance of the HO₂· radical, considering only its dominant reactions in the troposphere, and including CO and CH₄ oxidation sources. Assuming ∙OH abundance is, on average, 1×10⁶ molecules cm^-3, what approximate [HO₂∙]_SS results? (use stp, and reasonable inputs for the remaining ‘unknowns’) 3 pts

4. At a remote station in Africa, the soil emits NO at a rate of 10 µg m^-2 h^-1 throughout the night. Make a reasonable assumption for nighttime boundary layer depth and calculate the possible overnight reduction in ozone concentrations at this site. 2 pts

7^th/8^th weeks homework (due 4^th November):

1. Oxidize the molecule trans-2-hexene. Consider all possible pathways (i.e. options for the alkoxy radical) but limit yourself to several products: Show pathways that produce formaldehyde (methanal) and acetaldehyde (ethanal); show a pathway that produces a dihydroxy carbonyl compound; show a pathway that produces butanal. 3 pts

2. How much ozone would be formed from 10 ppb propane (k_OH = 1.1×10^-12 cm³ molec.^-1 s^-1) as compared to 0.1 ppb 2-butene (k_OH = 6.3×10^-11 cm³ molec.^-1 s^-1) within 4 hours of processing at a daytime [·OH] = 10⁷ molec. cm^-3 (Hint: Calculate the VOC removal rates, then gather from the oxidation mechanism how many ozone molecules are formed per VOC molecule reacted; caveat: make an assumption about the VOC concentrations) 2 pts

3. Realize that the graph from the lecture material that shows ozone production as a function of NO_x at three different VOC reactivities represents cross-sections of the ozone isopleth chart. Where are they located? Why, do you suppose the HO₂· and RO₂· abundance show a very similar functionality with [NO_x] as ozone production rate? (Hint: Refer to the Warneck chapter on CH₄ and CO chemistry) 2 pts

4. Gather information on “biogenic hydrocarbon” or “biogenic VOC” emissions from the literature/online/etc. What are the dominant VOCs emitted from the biosphere? Are some VOC species grouped together? Is the global biosphere believed to be a minor or a dominant source of VOCs to the atmosphere, and what is the approximate source strength? (1-2 paragraphs shall suffice!) 3 pts

11^th week homework (due by 30 November):

1. Calculate the necessary terrestrial sink of OCS from a presumed steady state abundance in the troposphere of 500 ppt, its lifetime against OH reaction, and assuming OCS emissions of 350×10⁹ g S per year. (Hint: volume/mass of the troposphere is needed) 2 pts

2. Particle mass in the marine boundary layer is dominated by sea spray, and sulfate from sea spray cannot be distinguished from sulfur from oxidized DMS. How have scientists overcome this problem and defined and now routinely quantify “non sea-salt sulfate” in particles? 2 pts

3. Aerosol particle number size distributions become more narrow and particle abundances smaller over time spend in the atmosphere. Explain! 2 pts

4. Aerosol surface area is an important parameter for heterogeneous chemistry (here: reactions involving the gas-phase AND aerosol surface). Compare the surface area of a presumed monodisperse and homogeneously distributed urban aerosol (eqv. diameter of 200 nm) with “ground” surface area: Assume that urban impervious area is 50%, of which 20% is covered by buildings, and that average property-size is 1 ha. Plot aerosol surface area as function of number density and boundary layer height; plot ground surface area as a function of building height and average urban vegetation LAI (look up definition). Under which conditions does aerosol surface area exceed (outcompete) total “ground” surface area? 4 pts