Background trace gas concentrations in the central United States

The concentrations of common trace gaseous constituents of the atmosphere have been measured in clean air in rural Illinois and Missouri. Sulfur dioxide (SO2), nitrogen dioxide (NO2), ammonia (NH3), and aldehydes (RCHO) were removed from the air by 1 hour of wet scrubbing. Hydrogen sulfide (H2S) was collected by passing air through an impregnated filter for 1 or 2 hours. Background concentrations of SO2, NO2, and RCHO ranged from less than 1 to 5 ppb. The NH3 concentrations were found to be as high as 10 ppb. The H2S 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 H2S assumed to exist over land at temperate latitudes may be too high.