HR: 09:45h
AN: A41G-07    [Abstracts]
TI: Chlorocarbon Fluxes in Coastal and Upland Ecosystems of California
AU: * Rhew, R C
EM: rrhew@atmos.berkeley.edu
AF: Univ. California, Berkeley, Department of Geography 507 McCone Hall #4740, Berkeley, CA 94720-4740, United States
AU: Mazéas, O
EM: omazeas@berkeley.edu
AF: Univ. California, Berkeley, Department of Geography 507 McCone Hall #4740, Berkeley, CA 94720-4740, United States
AU: Miller, B R
EM: brmiller@ucsd.edu
AF: Univ. California, San Diego, Scripps Inst. Oceanography, 9500 Gilman Drive, MC #0244, La Jolla, CA 92093-0244, United States
AU: Pingatore, C
EM: missclaudia@berkeley.edu
AF: Univ. California, Berkeley, Department of Geography 507 McCone Hall #4740, Berkeley, CA 94720-4740, United States
AU: Weiss, R F
EM: rfweiss@ucsd.edu
AF: Univ. California, San Diego, Scripps Inst. Oceanography, 9500 Gilman Drive, MC #0244, La Jolla, CA 92093-0244, United States
AB: Anthropogenic chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) account for ~ 70% of the organic chlorine in the global atmosphere, with CH₃Cl (methyl chloride), CHCl₃ (chloroform), CCl₄ (carbon tetrachloride) and CH₃CCl₃ (methyl chloroform) supplying most of the balance. Since 1994, the total atmospheric chlorine burden has been decreasing, owing in large part to the declining concentrations of CH₃CCl₃ and CCl₄, two chlorocarbons regulated by the Montreal Protocol. The primary sink of all four compounds is attributed to destruction processes in the atmosphere (oxidation or photodissociation). However, several recent studies have reported a potentially significant terrestrial sink for CH₃Cl, CCl₄ and CH₃CCl₃. Particularly surprising is the report that coastal salt marshes in China appear to be net sinks for all four of these chlorocarbons. If these sinks are indeed significant relative to atmospheric destruction processes, then their estimated lifetimes would need to be reduced and their source and sink budgets reassessed. In this study, we report net fluxes of CHCl₃, CCl₄, and CH₃CCl₃ from a variety of southern California ecosystems, including coast sagebrush, chamise chaparral, creosote bush scrub, shoreline, and coastal salt marsh. 75 flux chamber measurements were conducted between 1997 and 2000. We find no evidence of a significant soil sink in these ecosystems but rather a small net source of CHCl₃ and CCl₄. Meanwhile, previously reported CH₃Cl fluxes from these ecosystems show that coastal salt marshes are large sources of this compound while shrublands act as either a net source or sink, depending on predominant vegetation, soil conditions and season. To address the possibility of simultaneous production and consumption of CH₃Cl in salt marshes, we employed a stable isotope tracer technique at a northern California salt marsh during the spring of 2007. We measured gross consumption rates of CH₃Cl, but gross production rates were much greater at all sites, resulting in large net emissions overall. We suggest that salt marshes are typically net sources of CH₃Cl and CHCl₃ but may become net sinks if ambient concentrations of these compounds are unusually high, as reported from the salt marshes in China.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0322 Constituent sources and sinks
DE: 0490 Trace gases
DE: 0497 Wetlands (1890)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting