HYDROXYL RADICAL (OH) IS THE MOST IMPORTANT OXIDIZING AGENT IN THE TROPOSPHERE PROVIDING THE MAIN SINKS OF CO AND CH4 AS WELL AS OTHER SPECIES OF INTEREST TO THE AIR QUALITY CLIMATE AND STRATOSPHERIC OZONE COMMUNITIES. THE CHEMISTRY OF TROPOSPHERIC OH (OHTROP) IS COMPLEX AND WILL RESPOND TO VARIOUS FACTORS SUCH AS FUTURE LEVELS OF CO AND CH4 CHANGES IN ATMOSPHERIC TRANSPORT DRIVEN BY GREENHOUSE GASES AS WELL AS INCREASING ANTHROPOGENIC EMISSIONS OF SHORT-LIVED SPECIES IN SOME GEOGRAPHIC REGIONS AND DECLINING EMISSIONS OF THESE SPECIES IN OTHER REGIONS. ONE RESPONSE OF FUTURE OHTROP POSITED BY IPCC (2001) AND NOW REPRESENTED IN NUMEROUS TEXTBOOKS IS THAT INCREASES IN ATMOSPHERIC CH4 WILL LEAD TO FUTURE DECLINES IN OHTROP. THE ANALYSES THAT LED TO THIS CONCLUSION THOUGH DO NOT ACCOUNT FOR MANY FACTORS THAT WILL AFFECT OHTROP. ONE SUCH FACTOR IS THE EXPANSION OF THE HADLEY CELL SUGGESTED BY A VARIETY OF RECENT OBSERVATIONS. THIS WIDENING OF THE TROPICAL BELT WILL LIKELY CAUSE A POLEWARD EXPANSION OF THE REGIONS OF LOW TROPICAL O3 COLUMN AND HIGH RELATIVE HUMIDITY DRIVING UP FUTURE OHTROP. ADDITIONALLY OH CHEMISTRY DEPENDS ON CONCENTRATIONS OF NITROGEN OXIDE RADICALS VOLATILE ORGANIC COMPOUNDS AND OTHER HYDROCARBONS. EMISSIONS OF THESE SPECIES ARE EXPECTED TO CHANGE THROUGHOUT THIS CENTURY IN WAYS THAT DO NOT UNEQUIVOCALLY INDICATE DECREASING OHTROP. FINALLY FUTURE ABUNDANCES OF CH4 ARE QUITE UNCERTAIN AND AT THE TIME IPCC (2001) WAS WRITTEN DCH4/DT WAS MUCH LARGER THAN DURING THE PAST DECADE.