PRESENT OH MEASUREMENT LIMITS AND ASSOCIATED UNCERTAINTIES

The first ion-assisted OH measurement instrument was developed and fie ld tested in 1989. Since that time both instrument and technique have evolved substantially and several potential measurement interferences have been investigated. Included among these are reactions that could compete with the H2O/SO3 reaction, the effect of H2O on the NO3-.HNO3/ H2SO4 reaction, and potential wall losses. These investigations have a lso provided data of relevance to atmospheric ion and neutral chemistr y for the two reactions listed above, as well as for the OH measuremen t itself. Measurements made at Mauna Loa Observatory in Hawaii show fo r the first time a diurnal variation in tropospheric OH which spans mo re than 2 orders of magnitude. Nighttime measurements revealed hydroxy l radicals in the 10(4) molecules cm(-3) concentration range well afte r dark.