Large interannual variations in nonmethane volatile organic compound emissions based on measurements of carbon monoxide

We present source estimates of atmospheric carbon monoxide from nonmethane volatile organic compound (NMVOC) oxidation during a period of 8 years (1997-2004) using a Bayesian inversion analysis. The optimized global NMVOC-derived CO source strength indicates a change of a factor of 2 between the 1997-1998 strong El Niño and subsequent La Niña conditions. For comparison, the average 8 year interannual variability (IAV) is 18%. The variation of NMVOC-derived CO is closely correlated with the Oceanic Niño Index (ONI) and surface temperature. A time-lagged correlation analysis between ONI and NMVOC-derived CO inventory indicated El Niño/Southern Oscillation leads the Northern Hemisphere (NH) NMVOC-derived CO production by about 3 months earlier than the Southern Hemisphere's (SH). The SH NMVOC-derived CO was positively correlated with the lagged-ONI (r = 0.57), while the temperature change barely influenced SH NMVOC-derived CO (r = 0.01). In the NH, temperature was more robustly correlated with NMVOC-derived CO (r = 0.58) than the lagged- ONI (r = 0.35). In particular, the extra-tropical temperature showed a strong correlation (r = 0.90) with the NH NMVOCderived CO and suggested its primary role in controlling the interannual variability of the NH NMVOC-derived CO.