BOUNDARY-LAYER MEASUREMENTS OF THE OH RADICAL IN THE VICINITY OF AN ISOLATED POWER-PLANT PLUME - SO2 AND NO2 CHEMICAL CONVERSION TIMES

Reported are the first direct measurements of the OH radical in the vicinity of an isolated power plant plume (Four Corners). These measurements were used to estimate the conversion time of SO2 to H2SO4-sulfate aerosol via the initiating step OH + SO2 + M→ HSO3. Using the near high noon measured value of OH (9.5 × 106cm-3), resulted in a 1/e conversion time of 1.4 days. The latter lifetime would correspond to a conversion rate of ~2%h-1. When the lifetime calculation was modified to take into consideration the OH diurnal cycle, the 1/e conversion time for SO2 was found to be 4.4 days, giving an apparent overall rate of conversion of ~ 0.7% h -1. Similar calculations carried out for the conversion of NO2 to HNO3 resulted in 1/e lifetimes for NO2 of 2-3 h for mid-day time periods. © 1979.