Measurements and modeling of methyl bromide and other trace gases

This dissertation investigates three main topics using a 3-D chemical transport model (CTM). First, the inverse relationship between variability and lifetime of tropospheric trace gases (the Junge relation) is explored using the CTM and observations from PEM Tropics A and B campaigns. The effects of sources, sinks, and location and time of sampling on the Junge relation are discussed. The Junge relation upholds in both the model and the observations, for τ from 0.16 yr to 7.0 yr, but changes with variation of the factors above. The Junge relation is also investigated using a combination of source/sink patterns for a gas similar to methyl bromide (CH₃Br) with τ of ∼1 yr. The estimation of τ using the Junge relation in this case involves an error of ±20%.; Next, observations of CH₃Br over the Pacific Ocean during PEM Tropics A and B campaigns are discussed. The global mean mixing ratio is about 9 pptv with a latitudinal gradient ranging from 1.0–1.3. The distribution and strength of non-industrial sources are investigated using the CTM. With 50 Gg yr−1 industrial emissions predominately in the northern hemisphere and τ of 0.8 yr, a uniform distribution of natural sources totaling 110 Gg yr−1 is needed to reconcile the observed mixing ratios. The estimated range of natural sources is 90–130 Gg yr−1, taking into account variation in τ, source strength, and the range of observations.; Finally, the potential for carbon dioxide (CO₂) sequestration via engineered chemical sinks is developed. The meteorological and chemical constraints are discussed. An example chemical system is calcium hydroxide (Ca(OH)₂). With small energy input (∼30 kcal mole−1 ), CO₂ may be extracted and then recovered at atmospheric pressure. The CTM examines deposition velocity (ν) driven sinks with 4° x 5° latitude/longitude resolution at various locations and ν. A maximum uptake of ∼20 Gton (1015 g) C yr−1 is attainable with ν greater than 5 cm s−1 at a mid-latitude site. The atmospheric increase of CO₂ (3 Gton yr−1 ) can be balanced by an engineered sink with an area of 75,000 km 2 at ν of 1 cm s−1.