Measurements of HNO3 and NO3− particulates at a rural site in the Colorado mountains

The concentrations of HNO3 and NO3− particulates have been measured simultaneously with NO and NO2 concentrations at a nonurban field site in the Colorado mountains during a 5‐year period. Seasonal and diurnal trends of these species are presented. Correlations of HNO3 and NO3− levels with each other and with NOx (NO + NO2) levels elucidate atmospheric chemical processes. Generally, the measurements agree with the widely accepted views of odd nitrogen chemical cycles in the atmosphere, with the exception that fast surface deposition of nitric acid replaces rain out as the primary loss mechanism. Local anthropogenic sources of odd nitrogen are primarily responsible for the airborne nitrate in the air samples at this rural mountain site.