UNDERSTANDING THE PRODUCTION AND INTERCONVERSION OF THE HYDROXYL RADICAL DURING THE TROPOSPHERIC OH PHOTOCHEMISTRY EXPERIMENT

The hydroxyl radical plays a critical role in the chemistry of the low er atmosphere. Understanding its production, interconversion, and sink s is central to modeling and predicting the chemistry of the troposphe re. The OH measurements made during the 1993 Tropospheric OH Photochem istry Experiment provide a detailed look at these mechanisms since NOx , j(O-3), RO(2), HO2, nonmethane hydrocarbons (NMHC), and many other r elevant species were measured simultaneously. The relationship of OH t o NOx and to primary production is extensively examined. Close agreeme nt with theory is shown in the NOx/OH relation with OH concentrations increasing with increasing NO to a maximum at 1-2 ppbv due to conversi on of HO2 to OH, and then OH decreasing with further increasing NOx du e to conversion of NO2 to HNO3. Close correlations of OH concentration s with primary production (water, ozone, j(O-3)) are also shown both o n average and on rapid timescales.