The concentrations of common trace gaseous constituents of the atmosphere have been measured in clean air in rural Illinois and Missouri. Sulfur dioxide (S02), nitrogen dioxide (NO2), ammonia (NH3), and aldehydes (RCHO) were removed from the air by 1 hour of wet scrubbing. Hydrogen sulfide (I-I2S) was collected by passing air through an impregnated filter for I or 2 hours. Background concentrations of SO•, NO2, and RCHO ranged from less than I to 5 ppb. The NI-L concentrations were found to be as high as 10 ppb. The H._,S concentrations varied from less than 0.10 to 0.35 ppb. Comparison with previous measurements and with assumed worldwide values indicates that the concentrations of NO2 and I-LS assumed
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