Highlights from the UC-Irvine Global Monitoring Program (1978-2010)
I.J. Simpson1, S. Meinardi1, M.P.S. Andersen1, L. Bruhwiler2, F.S. Rowland1 and D.R. Blake1
1University of California at Irvine, Irvine, CA 92697; 403-529-6089, E-mail: isimpson@uci.edu
2NOAA Earth System Research Laboratory, Boulder, CO 80305
The University of California, Irvine (UC-Irvine) has monitored global atmospheric trace gas mixing ratios continuously since 1978 using ground-based measurements in the Pacific Basin (71°N to 47°S). The measured gases include methane (CH4), C2-C4 alkanes, ethyne, C1-C3 alkyl nitrates, chlorofluorocarbons (CFCs), CH3CCl3, CCl4 and H-1211. Long-term records of several of these gases are unique to the UC-Irvine global monitoring network, and here we present our program’s research highlights. The global growth rate of CH4 has slowed considerably in the past three decades, from 19 ± 2 ppbv yr-1 in 1985 to 5.3 ± 0.9 ppbv yr-1 in 2010. Over the same time, the global mixing ratio of ethane (C2H6) has declined by approximately 170 pptv (21%), from 791 ± 19 pptv in 1986 to 625 ± 12 pptv in 2010. The global trends of CH4 and ethane have shown remarkably good agreement in the past 25 years, both in terms of their long-term declines (most of which occurred prior to 2000) and short-term anomalies. Whereas the global CH4 and ethane trends dissociated from each other for the first time in 2008, CH4 and ethane increased together again in 2010, and the ethane growth rate in 2010 was 31 ± 11 pptv yr-1. The long-term global ethane decline has been accompanied by simultaneous decreases in global levels of propane and the butanes since 1996, as well as an 11% decline in global levels of the combustion tracer ethyne between 1996 and 2008. The anthropogenic tracer tetrachloroethene (C2Cl4) has shown a 60% decline in its global mixing ratio since 1989 and is currently approaching 2 pptv. Global mixing ratios of CFCs, CH3CCl3 and CCl4 have also continued to decrease, and our measurements show generally good agreement with other global monitoring networks. In contrast to many halocarbons, global levels of the industrial solvent chloroform (CHCl3) have increased by almost 20% since the late 1990s, from 9.0 ± 0.3 pptv in 1997 to 10.7 ± 0.4 pptv in 2008.
Figure 1. Global atmospheric mixing ratios and growth rates of selected gases measured by the UC-Irvine global monitoring network. (a) Global methane (CH4) growth rate and ethane mixing ratio; (b) global ethyne mixing ratio; (c) global tetrachloroethene (C2Cl4) and chloroform (CHCl3) mixing ratios. The data are plotted as running annual averages.