Nitrogen Dioxide and Nitric Oxide in Non-Urban Air

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Abstract
Measurement of NO2 and NO has been carried out in Piedmont, N. C. and in the southern Appalachian Mountains. Average values for the Piedmont were: continuous NO2 measured 30 ft above surface, 0.76 pphm (14.3 μg/m3), 1 20 ft, 0.61 pphm (11.5 μg/m3); simultaneous values (also Piedmont) (2-hr discrete samples) taken at an earlier time at 4 ft, NO2, 0.56 pphm (10.6 μg/m3), NO, 0.19 pphm (2.34 μg/m3). The mountain top values (5120 ft, 1573 m) were: NO2, 0.46 pphm (6.4 μg/m3), NO, 0.26 pphm (2.72 μg/m3). The results of this study furnish further proof that tropospheric NO and NO2 are produced at the surface of the earth. Data obtained are consistent with the belief that a major sink for NOx is reaction with O3 and ultimate conversion to nitrate. Ozone values frequently increased and NOx values decreased ahead of cold fronts, probably as a result of deep vertical mixing. Also, in small scale turbulence the changes in NOx values and in the O3 values tended to be “out of phase,” i.e., as O3 concentration increased, NOx concentration decreased and vice versa. Values of NOx from Green Knob, N. C. (mountain top) also tended to be higher at times when O3 values were lowest. The NO2 hourly average values in Piedmont, N. C, demonstrated a diurnal cycle reminiscent of diurnal urban changes. An early morning peak was followed by a minimum in mid-afternoon. Next, the values rose to a broad evening peak and then decreased slowly during the night. Reported urban concentrations are usually about ten times those found in Piedmont, N. C.

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