ENST 403, Environmental Chemistry, Spring 2009, UNC
Room 201 Dey Hall 11 to 12:15pm
Long Homeworks are due one week after completion of the lecture. If for example, lecture 2 was supposed to be finished on Jan 15, but was not till Jan 20, than the HW for Lect 2 would be due Jan 27. You can work with one another, but I want see your thinking.
Lecture 1. Write the general chemical structures for PAHs, chlorinated dioxins, and PCBs. Based on the summary of different studies presented in Lecture 1, are there any implications for us with respect to day to day typical toxic exposures.
Lecture 2. Go through the exercise of estimating the energy yields per mole and per gram of petroleum and coal. Write down all your work.
Explain why hydrogen does not have any green house inputs of CO2
Is ethanol combustion really green house neutral? Why or why not?
List out the sources of available fuels and their amounts in descending order. Explain why you think China is projecting to invest in coal technology for the next 100 years.
Lecture 3. (Review). Calculate Avagrado’s number based on the information in the lecture. Calculate the value for R, the gas constant in atm/(liter mole K)
Lecture 4. (The Atmospheric compartment)
The total atmosphere weights ~5.13x1018 kg. Assume that an average car weighs 1000 kg or one metric tonne. How many cars are equal to the weight of the atmosphere? if you could cover the earth in cars how high would the stack be? Assume the average car has a “foot print” of 4x2 meters and is 2 meters high?
Estimate the air temperature at a height of 5 miles above the surface of the earth assuming a decrease in temperature corresponding to the dry adiabatic lapse rate Gd
and then a water saturated Gs of 5 oK/km. Assume that the temprature at the surface is 25oC.
Lecture 5. (Global Warming) . How do greenhouse gases keep heat in our lower atmosphere? List 6 greenhouse gases. What evidence do we have that global warming is already taking place?
Assume as students that you each use 1000 Watts of power for 12 hours each day (lights, computers, class room air conditioning, etc). Much of this energy in Thailand is generated from coal. Assume that the process is only 50% efficient, and if you use 1000 Watts it really requires 2000 Watts of coal power. Calculate how much CO2 is going into that atmosphere to maintain you at this level of energy consumption for each year and put your answer in metric tones/year CO2. If you use a spreadsheet make sure you document all of your work so that one can follow all of your assumptions.
Lecture 6. Kinetics.
1. derive a ss relationship for O3 as a function of NO2, NO, k1 and k3; assume that dNO2/dt is at ss..
2. Calculate the equilibrium ozone for the following conditions
time 6:00 7:30 9:00 12:00 15:00
NO (ppm) 0.06 0.11 0.08 0.03 0.005
NO2 (ppm) 0.03 0.07 0.14 0.15 0.10
Temp (oC) 25 26 28 35 34
TSR(cal cm-2min-1) 0.05 0.12 0.25 0.5 0.3
*TSR= total solar radiation flux in cal /cm2/min
** k3 = 2.64310+03 exp(-1370/ T)
plot your results for NO, NO2, and O3 vs. time. If this was a real urban atmosphere explain why O3 is being produced. Where do NO and NO2 come from?
Lecture 7. Strat-O3.
Explain the formation of O3 in the stratosphere and use chemical equations to illustrate your answer
How do freons destroy the O3 layer. Use chemical equations where necessary
Explain the involvement of polar stratospheric clouds in O3 destruction
Calculate the minimum wavelength needed to destroy O3 in the atmosphere.
Lecture 8. Particles in the Atmosphere
A. Particle Size: If the particle mass concentration on the main streets infront of CMU (Ta nown Sutep and Huwi Gaow) is ~120 ug/m3, and the average particle size is 0.2 um, what is the average number of particles/cc?? I mm = 10-6 meters and 1 cm = 0.01 meters; assume a density of 1 g/ cm3. In the Kamens lab at UNC-Chapel Hill, USA there is a particle instrument that measures particle numbers from 102 to 107 particles/cc. If it were to measure particles in front of KMUTT (Technical Univeristy outside Bangkok) would the particles be in the range that this instrument can measure?
B. What does PM2.5 and PM 10 mean?
C. Particles and Mortality: Assume that there are 300 million people in the US and the average particle concentration is 17 um/m3. Assume that at 10 mm/m3 there is no increased risk. Since many of have not yet been able to get the book, let’s use the following graphs: From Figure 1(slide#86 in the new notes) estimate the number of excess deaths/year due to fine particle exposures in the US. Assume that a mortality ratio of 1 means a death rate of 700 deaths/year per 100000 people.
How would this differ if you used Figure 2-21 in you book (which is a more up to date figure and shown below as Figure 2) where there seems be a 4% linear increase in the death rate for a 30 ug/m3 increase in particulate matter. Use this graph to estimate the excess deaths in Thailand. Assume an average PM2.5 concentration year round of 60 mg/m3.
D. Partitioning: A number of years ago we conducted two wood smoke experiments in our Teflon film chambers to evaluate the stability of oxy-PAH. The average chamber temperature for one experiment was 20oC and the other was 38oC. A third experiment was conducted at 30oC, but only filters were analyzed. Data from these experiments are given below. Three years later it became very important to know the XAD-2 (gas phase) and particle phase distribution of the compounds in the 30oC experiment. It costs, however, 10,000 USD to re-run experiments. Can you make a crude estimate of the gas and particle phase concentrations in the 30oC experiment for 9,10 anthraquinone and 7-benzanthrone? Kp = [part. phase]/ [gas phase x TSP] and lnKp = a 1/T + const.
Experiment Compound XAD-2 Filter TSP
ng/m3 ng/m3 mg/m3
38oC 9,10-anthraquinone 228 105 0.512
30oC 9,10-anthraquinone ? 440 0.832
20oC 9,10-anthraquinone 38 381 0.366
38oC 7-benzanthrone 36 211 0.512
30oC 7-benzanthrone ? 426 0.832
20oC 7-benzanthrone 2 179 0.366
Lecture 9-11. (It will be less painfull to attempt this after I have derived the relevant equations in class). The attached chromatographic data we taken from a uv irradiated Teflon bag at UNC, which contained primarily benzene, and ethane and generated OH radicals. The purpose of the experiment was to determine the rate consent for ethane with OH based on its disappearance, from the simultaneous disappearance of benzene with OH. It is called the relative rate technique. From the enclosed chromatographic data you should be able to do this. Use benzene as a reference (i.e. you know its rate constant). It has a second order rate constant of 1.1 x10-12 cm3 molecule-1 sec-1.
You will first have to derive a rate relationship for benzene and ethane from
Benzene =B; and ethane = E
B+ OH --> products with a rate const of k1
E + OH --> products with a rate const of k2
to derive this relationship set up second order rate law expressions for B with OH and E with OH; i.e. d[B]/dt = k[OH] [B]. Assume that neither benzene or ethane photolyze. For each equation, solve for [OH] and the rest should be obvious. A reasonable literature value for the rate constant for OH and ethane in the gas phase (Pitts and Pitts, 1999) is 0.23x x10-12 cm3 molecule-1 sec-1 . How close do you come to the published value using the UNC data?
Lecture 11. Ozipw: In small groups of 2s or 3s, use Ozipw to illustrate the impact of temperature on O3 formation. Show the the impact of using CB4 and the Carter mechanism on the same set of emissions, mixing height, temperature, etc. How well do the mechanisms compare? What is the impact of reducing initial hydrocarbons by a factor of 2, but keeping VOC emissions constant. What is the impact of keeping intial hydrocarbons unchanged, but reducing VOC emissions by 75%? Do the same fo NOx. What happens if you reduce temperatue by 10oC, or increase it by 10oC?. What happens if you change the initial and final mixing height? Explore anathing else you want with the model.
Lecture 12. Visit to Smog Chamber. What is the aerosol chamber volume? What are the chamber walls made of? How is the chamber air temperature measured? Exactly how are gases such as NO or NO2 added to the chamber. How do we calculate how much to add say if we want 0.5 ppm of NO in the chamber, and the backgourd chamber O3 was 0.05 ppm, and background NO was 0.008 ppm? How much NO2 should appear in the chamber. How do the automated instruments sample air from the chamber. How long does air spend in the sampling lines from the chamber to the instruments? What gas do we use as a dilution tracer? How is it measured? Typically what kind of sampling lines are used; does this matter? How are aerosol sizes and number measured for particles under 1000nm.? How is total solar radiation (TSR) measured inside the chamber measured? We will try to analyze a known air sample on a gas chromatograph. Then you will analyze an unknown; calculate the concentration of all of the unknown compounds and identify as many as you can.
Lecture 16 Themodynamics. Write expressions for the 1st , 2nd and 3rd laws of thermodynamics and define each of the terms.
Describe the difference between internal energy and enthalpy.
What is heat capacity expression ? Is it difference for constant volume vs. constant pressure.
What is entropy? Write an expression for entropy as a function of heat capacity.
Write the defining expression for the Gibbs free energy as a function of enthalpy and entropy.
Define chemical potential.
Define in words and with mathematical expressions fugacity, mole fraction activity, activity coefficients, and molar volume.
Define liquid concentration in terms of mole fraction and total molar volume. What is the molar volume of water and of hexane?
Write an expression for the equilibrium constant as a function of free energy.
An organic liquid is equilibrated with pure water in a stoppered flask:
Assuming that the organic liquid consists of pure toluene (molecular weight 92.13, density 0.8669, aqueous solubility 515 mg/L at 25°C), what is:
(i) the concentration of toluene in the aqueous phase in mol/L and in mole fraction units;
(ii) the aqueous activity coefficient and the activity of toluene in the aqueous phase (neglect any dissolution of water in the organic phase).
Lecture 17 Vapor Pressure:
Convert 1 atm to mm Hg, torr, pascals, and psi.
What is the supercooled vapor pressure of a compound?
Are heats of vaporization affected by polarity?
What is Trouton’s rule?
Write an expression for estimating vapor pressure at a given temperature as a function of boiling point.
Write an expression to convert from a solid to a liquid vapor pressure.
Calculate the vapor pressure at 25oC of naphthalene, phenanthrene, anthracene, pyrene and benz(a)anthracene from its boiling point by assuming 1., a constant entropy of vaporization (88 kJ/mole/K, eq 1) and 2, by 1st calculating its entropy of vaporization from DSvap= Kf (36.6 +8.31 ln Tb) with eq with a Kf =1 and then using eq 2. How well do the two equations agree?
eq 1.
eq 2.
Lecture 18 (Henry’s Law)
What is the relative importance of the heat of vaporization on the Henry’s law values
Do Henry’s law values increase or decrease in going from fresh water to sea water?
Compute a dimensionless Henry’s law valve for for phenol.
A Fugacity problem (first some additional theory )
In a compartment, Ci, the rate of decay in moles m-3 year-1 for a given process, j, is
rateCi = kj[Ci]
where kj = bio degradation
photolysis
hydrolysis
oxidation
advection
etc.
rateSCi= kB[Ci]+ kP[Ci]+ kH[Ci]+ kOX[Ci]+ kA[Ci]
rateSCi = [Ci] Skj = [Ci] kT
in moles per year the total rate in a compartment of volume Vi is:
rateSTi = [Ci] kT Vi
if the system is at steady state in each compartment, the total input rate for all the compartments in moles/ year will equal the amount reacted in moles/year
I = S([Ci]kT Vi) = SZi fi kT Vi) and
I = fi S Zi kT Vi); why?
so
fi= I / S(Zi kT Vi)
Assume three compartments air, water and sediment (sed) in equilibrium with one another and a total input rate of 1000 moles/year goes into the entire system. From the following rate constant data (years-1), calculate for each compartment the fugacity, the resulting concentration (moles/m3), the total decay rate (moles/year) and the total #moles in each compartment. Use Z values and volumes from the class example. From the total decay rate, where does most of the degradation take place? where does most of the mass end up?
Rate constants (years-1)
Biodeg. Photolysis hydrolysis oxidation advection kT
Air 0 130 0 0 50 180
water 100 100 100 0 200
Sed. 0.1 0 0 0 0
Lecture 19 Octanol Water.
Hint: First plot all of the data and then divide it into two reasonable groups based groups based on similar chemical structures. Then redo the regression analysis.