.EQ delim $$ gsize 12 gfont roman .EN .EQ define O3 'O sub 3' define CH4 'CH sub 4' define CH3 'CH sub 3' define O2 'O sub 2' define H2O 'H sub 2 O' define H2 'H sub 2' define HO2 'HO sub 2' define NO2 'NO sub 2' define cm2 'cm sup 2' define m3 'm sup 3' define cm-2 'cm sup -2' define cm3 'cm sup 3' define cm6 'cm sup 6' define cm-3 'cm sup -3' define s-1 's sup -1' .EN .nj .ps 12 .vs 13.5 .he ///# .ce 5 METO/CHEM 637 FINAL EXAM 50 points possible May 18, 1994 CIRCLE YOUR ANSWERS!! .sp 2 NAME _______________________________________________________ .sp 3 A. BASIC ATMOSPHERIC CHEMISTRY AND PHYSICS (10) .sp 2 A1. (2) The mixing ratio of OCS in the air is 510(+/-10) ppt (parts per $10 sup 12}$ by volume). Express this concentration in $mu g/ m3$ and $molecules/ cm3$ at STP (298 K and 1.00 atm). .sp 15 A2. (2) If mixing ratio of OCS is reasonably constant throughout the troposphere, estimate the OCS concentration in the same three units an altitude of 5.5 km. .bp A3. (6) Derive an expression for the relative concentrations of an atmospheric species in the vapor and aqueous phases. Assume a Henry's Law coefficient of H (M/atm) and a liquid water content of LWC (g/$m3$). .bp B. THERMODYNAMICS AND KINETICS (15) .sp 2 B1. (10) Calculate the RTP equilibrium constant for the following reaction. Repeat the calculation for 200 K. What does this tell you about the importance of thermal decomposition of peroxy nitric acid ($HO2 NO2$) as a function of altitude? What role might $HO2 NO2$ play in global photochemistry? .EQ HO2 ~+~ NO2 ~+~ M~ =~ HO2 NO2 ~+~ M .EN .bp B2. (5) What is the lifetime of the hydroxyl radical, OH, with respect to each of the following reactions for the clean-air concentrations given below? Which mechanism is most important for OH removal, and what is the \fIoverall\fR lifetime of OH in the clean troposphere? Use conditions appropriate to the Earth's surface. .ce [$CH4$] = 1700 ppb; [CO] = 120 ppb; [$O3$] = 25 ppb; [S$O2$] = 100 ppt .EQ (1) CH4~+~OH~->~CH3~+~H2O .EN .EQ (2) CO~+~OH~->~C O2~+~H .EN .EQ (3) O3~+~OH~->~H O2~+~O2 .EN .EQ (4) S O2~+~OH~+~M~->~HO- S O2 ~+~ M .EN .bp C. SPECTROSCOPY AND PHOTOCHEMISTRY (15) .sp 2 C1. (8) Derive an expression for R, the rate at which energy is deposited into the air at a given altitude in terms of the extraterrestrial solar intensity, $I sub inf$, the surface pressure, $P sub 0$, the altitude, Z, the scale height, $H sub 0$, and the zenith angle, $theta$, and the absorption cross-section,$sigma$, of the principal absorber. Assume a constant mixing ratio with altitude, use the Hypsometric Equation, Beer's Law, and the geometry of the atmosphere: .EQ P~=~P sub 0 exp(-Z/H sub {0} ) .EN .EQ I/I sub {inf} ~=~ exp(- sigma P l) .EN .EQ dl~=~-dZ/cos theta .EN Note, you will need to derive an expression for I as a function of the variables given above and then substitute R = - dI/dl. Refer to the diagram given below. .sp 2 .ce \fBTop of Atmosphere .sp 15 .ce Surface\fR .bp B1. Write your derivation here. .bp C2. (7) Derive an expression for the altitude at which the deposition will be a maximum, and show how these equations describe "Chapman Layers." What role do Chapman Layers play in atmospheric chemistry? How is R related to the photolysis rate coefficient? .bp D. BIOGEOCHEMICAL CYCLES (10) .sp 2 D1. (10) In 1977, the National Academy of Sciences released a report stating that methane oxidation is the principal source of atmospheric carbon monoxide (CO), and that anthropogenic emissions contributed but insignificantly. Support or refute this statement using global biogeochemical cycle arguments. Cite relevant field observations, laboratory studies or model simulations from your readings. .bp .ce POTENTIALLY USEFUL INFORMATION .sp 2 Molecular Weights .sp 2 H = 1 O = 16 N = 14 C = 12 S = 32 K = 39 Cl= 35.5 F = 19 R = 2 cal/mole K = 8.31 J/mole K N = $6.023x10 sup 23$ molecules/mole 1 mole air = 22.4 l at STP There are $1.8x10 sup 20$ moles of air in the Earth's atmos. The globally averaged OH number density is $5~x~10 sup 5~cm-3$ in the troposphere. .ls 2 $k sub 1 ~=~ 2.3~x~10 sup -12~exp(-1700/T)~cm3~s-1$ $k sub 2 ~=~ 1.5~x~10 sup -13 (1+0.6P sub atm)~cm3~s-1$ $k sub 3 ~=~ 1.6~x~10 sup -12~exp(-940/T)~cm3~s-1$ $k sub 4 ~=~ 3.0~x~10 sup {-31} (T/300) sup {-3.3} ~cm6~s-1$ $k sub {4 inf} ~=~ 1.5~x~10 sup -12 ~cm3~s-1$ (high pressure limit) .ta 2i 4i SUBSTANCE $DELTA Hf~sup o~kcal~mole sup -1$ $DELTA Gf~sup o~kcal~mole sup -1$ $O2~&~N2$ 0 0 $H2O$ -57.8 -54.6 $H2O sub (l)$ -68.3 -56.7 ${HNO3} sub (g)$ -32.1 -17.9 ${HNO3} sub (aq)$ -49.6 -26.6 $NO2$ 7.9 12.4 $HO2$ 3 5 $HO2 NO2$ -11.2 5.6 NO 21.6 20.7 ${H sup +} sub (aq)$ 0 0 ${OH sup -} sub (aq)$ -55.0 -37.6