Some Characteristics and Applications of Nitrogen Dioxide Passive Samplers

Ion chromatography has been used to measure nitrite (NO2 −) and nitrate (NO3 −) concentrations in the aqueous extracts from exposed and blank (unopened) passive samplers designed for the measurement of atmospheric nitrogen dioxide (NO2). Concentrations of NO2 − increased on storage of both opened and unopened samplers, however NO3 − concentrations were dependent on sampler cleaning and preparation. Only extract NO2 − concentrations were needed to calculate atmospheric NO2 levels when using the samplers for monitoring. Analytical methods for passive samplers extracts have been compared in the laboratory with good agreement being found. Calculations of possible background contamination levels suggest that sampler results may be influenced by the solubility of NO2 in the plastic construction materials but not by permeation of NO2 through the sampler walls. Passive samplers have been used to measure NO2 in a variety of locations. Outdoor urban sites in Auckland city and rural locations the Waikato Valley, New Zealand, were compared, with the seasonal variations of concentration showing a dependence on location. Samplers were also used to measure concentrations over vegetated surfaces, water and on the outside of a tall building. Vertical concentration gradients of NO2 over grassed surfaces were detected, indicating deposition, however a similar phenomenon was not observed over water. Calculation of the deposition velocity of NO2 from these data gave an unrealistic value which was most likely caused by windspeed effects or chemical reactions.