The second year results involved air monitoring at five urban and nonurban stations with the help of an instrumented environmental mobile laboratory. The monitoring stations included urban, remote marine, remote continental, high altitude and intermediate locations. In situ analysis was performed for a total of 31 chemical species and six meteorological parameters. Of the 31 chemical species sought, 19 were halogenated compounds, five were nitrogen containing species, and the remaining seven included hydrocarbons, CO, and O3. Data suggest that the troposphere (northern hemisphere) contains 2906 ppt of chlorine atoms. The chlorine contribution of fluorocarbons is 33% of the total while that due exclusively to chlorocarbons is 77%. The natural chlorine contribution due solely to CH3Cl is 25% of the total organic chlorine burden. The burden of halocarbons in the troposphere is increasing when compared to background data collected exactly a year ago. Based on the budget and distribution of methyl chloroform and its emissions inventory, a two-box model was used to develop the conclusion that average tropospheric hydroxyl radical (OH) concentration was about 400,000 HO/ml. This is significantly lower than the hitherto accepted OH concentrations in the troposphere. It was further found that there may be significant gradients in the northern and southern hemispheric HO concentrations.

"EPA-600/3-78-017." "January 1978." "Project Officer: John Spence." "Environmental Monitoring and Support Laboratory"--Cover. PB 278 198--NTIS. Includes bibliographical references (p. 54-55).