Method for the Automated Measurement of Fine Particle Nitrate in the Atmosphere

An integrated collection and vaporization cell has been developed to provide automated, 10-min resolution monitoring of fine particle nitrate in the atmosphere. Particles are collected by a humidified impaction process and analyzed in place by flash vaporization and chemiluminescent detection of the evolved nitrogen oxides. Particle collection efficiency was measured between 95% and 100% for particles above 0.1 μm. Evaporative losses for ammonium nitrate were 2 ± 4%. Average nitrate values from the automated system were compared to traditional denuder filter measurements in three cities, with correlation coefficients of greater than 0.97 and regression slopes ranging from 0.96 to 1.06. The detection limit is governed by the field blank, which for the Los Angeles area was 0.4 μg/m3. The system operated unattended for days at a time, with data recovery of 97%.