Question

1 of 2 GEOL 3382/6334 Atmospheric Chemistry Problem Set #2 1. Methane (CH4) is emitted to the atmosphere through natural and anthropogenic processes. The following table shows the most current understanding of the sources and sinks of CH4 a. Calculate the atmospheric burden of CHs in Tg (1 Tg 10g) in the troposphere with a global average mixing ratio of 1.782 ppmv. Tropospheric air has an average density of 0.71 kg m3. The Standard Atmosphere Calculator (http://www.digitaldutch.com/atmoscalc/) may be of some help. Based on your calculate the lifetime of CH4 in the atmosphere. If climate change results in temperature increases in the atmosphere, wetlands could potentially dry out. Assuming all other sources remain the same, determine the average atmospheric mixing ratio of CH4 if the contribution from wetlands decreases by one half. How does the lifetime of CH4 in the atmosphere change if wetlands are no longer a b. and the information provided in the table below c. d. What effect might this have on the budget of CO in the troposphere and what are the implications on the oxidative capacity of the atmosphere with respect to OH? e. Sinks Soils Wetlands Termites Ocean Hydrates Ene Landfills Ruminants Waste treatment Rice Agriculture Biomass Burning 37 20 15 10 109 36 93 14 60 23 heric OH loss 506 40 COMPOSITION, STRUCTURE, AND DYNAMICS OF THE ATMOSPHERE Table 1-6. Air Masses (in kg) Contained in Various Regions of the Lower Atmosphere Total atmosphere Tropical troposphere Extratropical troposphere Total troposphere Lower stratosphere (<30 km) Upper stratosphere (30-s0 km) Total stratosphere Remaining atmosphere 5.13 x 10 2.25 x 10 1.97 x 10 4.22 x 10 8.48 x 10" 5.80x 10'e 9.06 x 10' 4x 10'

Answer 1

a) Volume mixing ratio for CH₄ of 1.782 ppmv

Mass of the troposphere = 4.22 X 10¹⁸

1 ppmv (ml/m³)= 1.782

Total atmospheric burden = concentration of CH₄ / Mass of the troposphere

Total atmospheric burden = 1.782 X 10^-6 X 4.22 X 10¹⁸ X 10^-12

Total atmospheric burden = 7.52 T_g

Lifetime can be calculated by burden / loss rate

		lifetime			lifetime
Wetland	237	3.17 X 10-2	Soil	30	.250
Termites	20	..376	Tropospheric OH	506	1.48 X 10-2
Ocean	15	.501	Stratospheric loss	40	.188
Hydrates	10	.752
Energy	109	6.89 X 10-2
Landfills	36	.208
Ruminants	93	8.08 X 10-2
Waste Treatment	14	.537
Rice Agriculture	60	.125
Biomass Burning	23	.326

Mixing ratio is the amount of water vapour in air when the water vapour in air decreases then the mixing ration also decreases it can be calculated by

Mixing Ratio = w / w_s

w_s = saturation mixing ratio

At 0 degree celsius ws = 3.84 g/kg and at 20 degree celsius ws = 15 g/kg then

Mixing ratio = 1/2 X 3.84/15

Mixing ratio = 0.128

If wetland are not available then the methane present in soil come up and the methane emission reduces and methane emission increases in the plants.