Is the biomass burning source of CO decreasing?

To investigate secular changes in CO and CH4, we examined monthly means of tropospheric measurements made from samples collected at 19 ®xed sites in the National Oceanic and Atmospheric Administration (NOAA) Climate Monitoring and Diagnostics Laboratory (CMDL) global cooperative ̄ask sampling network. The CH4 data are available for the period 1984±1995. A somewhat shorter time series is available for CO (1989±1995). The data were analyzed to extract a consistent pattern of change in time and in latitude. The most important preliminary ®nding is that the patterns of CO and CH4 change appear to resemble that of biomass burning. That is, there is maximum change during local spring in both northern and southern hemispheres. If we attribute a signi®cant part of the change in CH4 trend (3±6 ppb/yr) to biomass burning, the corresponding change in CO is approximately 2±5 ppb/yr. This would explain the bulk of the observed change in CO (4±7 ppb/yr). Ó 1999 Elsevier Science Ltd. All rights reserved.