Relationships between nitrous acid and other nitrogen oxides in urban air

Nitrous acid (HNO2), nitric acid (HNO3), nitric oxide (NO) and nitrogen dioxide (NO2) were measured over a four day period in Clairmont, CA. Concentrations of each nitrogen oxide (NOx) compound varied diurnally during the study period HNO3, NO2, and NO generally reached maxima during daylight hours. Conversely, HNO2 concentrations were highest at night. HNO3 and HNO2 concentrations increased with increasing NO and NO2. HNO3 dependance became limited at high NO2 and NO. HNO2 concentrations declined when high NO and NO2 concentrations were present. The decline in HNO2 is postulated to result from direct photolysis during the time periods of NO and NO2 maxima or from reactions to form HNO3.